JPH10271893A - Motor drive - Google Patents

Abstract

(57) [Problem] To provide a motor drive device that reduces the number of power elements and performs efficient operation of the motor. SOLUTION: A motor SR1 that connects windings in a star shape and outputs a neutral point as a terminal, an inverter unit 1 that performs energization control and drives the motor SR1, and a regenerative current of the windings of the motor. A booster unit 2 for boosting the voltage and a step-down unit 3 for discharging the energy charged in the booster unit 2 constitute a drive circuit with a small number of power elements, boost the voltage with the regenerative current of the motor, and stop the current of the winding quickly. By doing so, efficient driving is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an electric motor used for, for example, a compressor or a blower.

[0002]

2. Description of the Related Art FIG. 20 is a block diagram of a conventional driving device for a switched reluctance motor. In the figure, M2
Is a switched reluctance motor (hereinafter abbreviated as SR motor) including windings U, V, and W, and MC1 is a microcomputer that calculates a control content and outputs a predetermined control signal in a control device. DB1 is a diode bridge that uses two-phase AC commercial power supplies R and S as a power supply, performs full-wave rectification, and supplies a DC current to a capacitor C1, and these constitute a power amplification unit. In the SR motor M2, both terminals of the three-phase windings U, V, and W are connected to the SR motor M2.
2, the number of terminals of the SR motor M2 is six.

[0003] TRup, TRun, TRvp, TRv
n, TRwp, and TRwn are switching elements that constitute an inverter unit, and are connected to and controlled by the microcomputer MC1, respectively. Among them, the switching element TR
up, TRvp, TRwp are the respective voltages VH and S
The terminals are connected to the terminals of the windings U, V, W of the R motor M2. Also, the switching elements TRun, TRv
n and TRwn are windings U and SR of the SR motor M2, respectively.
The other terminals of V and W are connected to the voltage VL.

[0004] Switching elements TRup, TRvp, T
The cathodes of diodes Dup, Dvp, and Dwp are connected to the connection points of Rwp with the output terminal of SR motor M2, respectively, and the anodes of these diodes are connected to voltage VL.
Connected to Also, switching elements TRun, TR
The anodes of diodes Dun, Dvn, Dwn are connected to the connection points between vn, TRwn and SR motor M2, respectively, and the cathodes of these diodes are connected to voltage VH.

[0005] Each switching element is composed of TRup and TRu.
n, TRvp and TRvn, TRwp and TRwn are respectively set and turned on and off at the same time.
The operation of sequentially energizing V and W is repeated to drive the SR motor M2.

FIG. 21 shows the structure and operation of an SR motor having, for example, a six-slot stator and a four-pole rotor. When there is a positional relationship between the stator and the rotor as shown in FIG.
When Trun is turned on, the rotor is moved to U by magnetic attraction.
Attracted by the phase and rotated in the direction of the arrow. Next, when the rotor enters the state shown in FIG.
p, TRUn are turned off, and the switching elements TRvp, T
When Rvn is turned on, the rotor is similarly attracted to the V phase and rotates in the direction of the arrow, as shown in FIG. At this time, when the switching elements TRvp and TRvn are further turned off and the switching elements TRwp and TRwn are turned on, the rotor is attracted to the W phase and shifts to the state of (a). By repeating this, the SR motor is driven.

[0007] Alternatively, FIG.
It is a figure which shows the structure of the drive device of the conventional motor described in 05584 gazette. In the figure, M is a winding U1, V
1, an electric motor including W1, and a microcomputer MC1 which calculates and processes control contents and outputs a predetermined control signal.

The power amplifying section uses two-phase AC commercial power supplies R and S as power supplies, and uses a diode bridge DB1 to
Full-wave rectification is performed, and a direct current is supplied to the capacitor C3 to form a first power supply (VG). The capacitor C
2, a DC current is supplied from a charging circuit including a transformer TR1 and a diode bridge DB2, and a second power supply (VR
G) is configured. M is an SR motor having three-phase windings, one of terminals of each of windings U1, V1, and W1 is connected to a neutral point to form a star connection, and an output terminal of the SR motor M Is composed of four wires, the other end of each winding and the neutral point. The terminal at the neutral point is connected to the first power supply (VG). Further, the other end of each winding U1, V1, W1 is connected to a switching element TR for flowing a current through each winding.
u, TRv, and TRw are connected.

TRu, TRv, TRw are drive switching elements, which are connected to a reference potential (VCOM), and whose base is connected to the microcomputer MC1. And
According to a predetermined control signal supplied from the microcomputer MC1,
The switching elements TRu, TRv, TRw operate,
A configuration is adopted in which a predetermined drive current flows through each of the windings U1, V1, and W1.

A predetermined switching element is turned on depending on the position of the rotor of the electric motor M, and a current flows through each of the windings U1, V1, and W1.
An operation of repeatedly turning on and off in a short cycle (hereinafter, referred to as chopping) is performed, an equivalent applied voltage is controlled, and a variable speed control of the electric motor M is performed. When the switching elements TRu, TRv, TRw are turned off at the time of switching or energizing windings performed when the motor M is driven, the current flowing through the windings U1, V1, W1 of the motor M passes through the diodes Du, Dv, Dw. Through the second power supply VRG. This regenerated current is applied to the switching element TRd
Is transferred to the first power supply VG. Thereby, the fluctuation of the first power supply VG due to the regeneration of the energy of the winding of the electric motor M is suppressed, and the stable rotation of the electric motor M is obtained.

[0011]

According to the structure of the conventional motor driving device shown in FIG. 20, the operation can be performed without any particular problem in terms of function, but the cost of the motor and the driving circuit and the operation time are reduced. There are challenges in terms of efficiency. That is, in the case of the motor as shown in FIG. 20, two output terminals are required for each winding of the motor, and the number of terminals is larger than that of a star-connection or ring-connection motor. Disadvantageous. Further, for each winding, two switching elements and two diodes are required in the inverter section, and the utilization efficiency is poor as a configuration of an inverter that allows current to flow in only one direction.

Another problem is that the current in the winding when the current supply to the winding is stopped is regenerated to the capacitor, so that the bus voltage fluctuates and affects the rotation of the motor.
On the other hand, in the case of the configuration of the motor driving device as shown in FIG. 22, the motor has a star connection with one terminal of each winding being common, and the output terminal of the motor is shown in FIG.
0 motors have been reduced. The switching element of the inverter unit is also configured with one for the winding,
The number of elements is also reduced compared to the drive circuit of FIG. In addition, the current of the winding when the current supply to the winding is stopped is regenerated to the second power supply VRG via the diode, and thus does not affect the bus voltage. However, the second power supply VRG
Power circuit required to generate the
This is disadvantageous in cost.

Further, when the switching element is turned off during chopping of the switching element of the inverter unit for performing variable speed control in the motor and the drive circuit of FIG. 22, the current flowing through the winding of the motor is a diode. Through the second power supply VRG. This regenerated energy is transferred to the first power supply VG via the power conversion means, and thus a loss occurs in this conversion. In addition, since the current is regenerated to the second power supply VRG having a higher potential than the first power supply VG, the discharge of the motor winding energy when the switching element of the inverter unit is turned off is accelerated. For this reason,
It does not matter that the current stops earlier when the energized phase is switched, but when chopping for variable speed control, the first
The fluctuation of the current of the winding becomes larger than that of regenerating the current to the power supply, which increases iron loss and lowers efficiency.

As described above, the conventional motor driving device as shown in FIG. 20 has many problems especially in terms of cost, and the motor driving device as shown in FIG.
Although the electric motor driving device described in (1) is improved in cost, there is still a problem in efficiency in operation. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to provide a lower cost and more efficient motor drive device.

[0015]

According to the present invention, there is provided an electric motor driving apparatus including a stator having a plurality of windings connected in a star shape,
A motor having a terminal of each winding and a connection neutral point as an output terminal; and an inverter unit having one switching element corresponding to each winding of the motor, and driving the motor by switching and energization of energization. And a booster for charging and boosting with a current generated in the winding when power supply from the inverter to the motor is stopped, and one switching for each. A step-down unit comprising an element, a diode, and a reactor, for discharging the voltage of the step-up unit, and performing a step-down operation.During energization of the winding, the step-down unit pressurizes the voltage of the step-up unit. When the current supply to the winding is stopped, the booster is boosted by the current generated in the winding.

Further, a motor having a stator in which a plurality of windings are star-connected, having a terminal of each winding and a neutral point of the connection as an output terminal, and one switching device corresponding to each winding of the motor. An inverter unit for driving the electric motor by switching and chopping of current, and one switching element corresponding to each winding of the electric motor,
An inverter for driving the electric motor by switching and chopping of electric current, and one switching element and one diode and one capacitor provided for each winding of the electric motor, and the electric current is supplied from the inverter to the electric motor. When the operation is stopped, a boosting unit that performs charging and boosting by the current generated in the winding, and a step-down unit that includes one switching element, a diode, and a reactor and discharges and reduces the voltage of the boosting unit. When the current is supplied to the winding, the voltage of the boosting unit is reduced by the step-down unit. When the current supply to the winding is stopped, the voltage of the boosting unit is increased by the current generated in the winding. It is to let.

Further, a voltage sensor unit for monitoring the voltage of the boosting unit is provided, and when the voltage becomes higher than a predetermined value, the switching element of the step-down unit is turned on to suppress the rise of the voltage. .

A voltage sensor for monitoring a voltage of the booster is provided. When the voltage becomes higher than a predetermined value during driving of the motor, a switching element of the booster is turned on. This is to suppress the rise of the voltage.

Further, during energization of the motor, chopping is performed in the switching element of the step-down unit, so that the step-down is performed gently.

Further, chopping is performed in the switching element of the step-down unit while the motor is energized, and the chopping is stopped when the voltage of the step-up unit detected by the voltage sensor unit reaches a predetermined value.

Further, when the maximum value of the voltage of the step-up unit detected by the voltage sensor unit becomes larger than a predetermined value, when the energization of the winding of the motor is stopped, the switching element of the step-down unit is chopped. To prevent the voltage from greatly exceeding a predetermined value.

When the maximum value of the voltage of the boosting section detected by the voltage sensor section becomes larger than a predetermined value, when the current supply to the winding of the motor is stopped, the switching element of the boosting section is chopped. To prevent the voltage from greatly exceeding a predetermined value.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a motor driving device according to a first embodiment of the present invention. In the figure, SR1 is an electric motor, and as the electric motor SR1, for example, various electric motors such as an induction motor, a synchronous motor, and a reluctance motor can be used. Although the three-phase winding is represented, the same applies to other various multi-phase windings by increasing the number of phases. 1 is an inverter for switching the current supply to each winding and performing variable speed control by chopping. 2 is a booster for charging and boosting by a motor winding current generated at the same time as the current supply is stopped.
A step-down unit for lowering the voltage, MC1, is a microcomputer that controls the operation of switching elements included in these units. The inverter 1, the booster 2, the step-down unit 3, and the microcomputer MC1 constitute a drive circuit of the electric motor.

The electric motor SR1 has windings U1, V1, and W1, and one of the terminals is connected to the inverter unit 1 as an output terminal of the electric motor, and the other terminal is all connected to the terminal of the electric motor. Connected to the bus voltage. This bus voltage is connected to a diode bridge D
It is obtained by full-wave rectification using B1. Inverter unit 1
Are switching elements TRu, TRv, TRw that perform energization control on windings U1, V1, W1 of electric motor SR1.
And diodes Du and D that regenerate the energy of the winding
v, Dw.

The boosting unit 2 is connected to the inverter unit 1 via diodes Du, Dv, Dw. The switching unit TRu, TRv, TRw controls the motor SR1.
For regenerating the current of the windings U1, V1, W1 to the bus voltage at the time of chopping of the capacitor C4, which is charged and boosted when the current supply to the windings U1, V1, W1 is stopped, and chopping of the switching element of the inverter unit. Element TR
a, a diode D2 for preventing energy charged in the capacitor C4 from flowing into TRa when the switching element TRa is on.

The step-down unit 3 includes a switching element TRb for controlling the transfer of the energy charged in the capacitor C4 of the step-up unit 2 to the bus voltage, and a reactor L for preventing a sudden current from flowing when the switching element TRb is turned on.
1. It comprises a diode D3 for supplying a current to the reactor L1 during the off time when chopping the switching element TRb.

FIG. 2 shows the operation of the switching element in the drive circuit and the change in the potential of the booster. FIG.
It is a flowchart which shows the operation. Hereinafter, the operation of the embodiment of the present invention will be described with reference to FIG. First, when the electric motor SR1 is driven, U-phase energization is performed according to the rotational position of the rotor. In step a1, the switching elements TRu, TRa, TRb are turned on. By turning on TRu, a current flows through the winding U1. By turning on TRa, the current of winding U1 is regenerated to the bus voltage when TRu is chopped. When TRb is turned on, the energy charged in the capacitor C4 is discharged and transferred to the bus voltage. In step a2, the state of a1 is maintained until an energized phase switching command is input. In the case of a synchronous motor or a reluctance motor, for example, a signal from a position detection circuit or the like for detecting the rotational position of the rotor corresponds to this energized phase switching command.

When a switching command of the energized phase is detected, in step a3, the switching elements TRu, TRa, TR
Turn off b. By turning off TRu, the current supply to the winding U1 is stopped. However, since the current of the winding U1 does not stop suddenly, the current of the winding U1 when the TRu is turned off flows to the boosting unit via the diode Du. TR
a is turned off, the current of the winding U1 passes through the capacitor C4.
Flows into Since TRb is off, there is no discharge from the capacitor C4, and the current of the winding U1 raises the potential of the capacitor C4. Since the potential of the capacitor C4 increases, the current stop of the winding U1 is accelerated, and the current stops in a short time. This is the power (energy) of the winding
If a high voltage is applied to release the current, the current will decrease,
As a result, the time until the current stops is shortened. Therefore, the higher the voltage of the booster, the faster the stopping of the winding current is accelerated. Therefore, it is better to make the capacity of the capacitor C4 as small as possible without exceeding the boosted voltage.

In step a4, it waits until the time Tx has elapsed after the operation in a3. During this time Tx, a time sufficient for stopping the winding U1 current is set, and the motor S
No power is supplied to R1. Even before the current of the winding U1 stops, even if the energization of the winding V1 of the next energized phase is started,
Although there is no problem in operation, the current of the winding V1 flows into the capacitor C4 via the diode Dv due to chopping of the switching element TRv. As mentioned earlier,
When the current is regenerated to the boosted capacitor C4, the winding V1
Is not effective in terms of efficiency because there is a case where a continuous current does not flow due to a rapid decrease. For this reason, during this time Tx, the motor SR1 is energized. Since the motor SR1 does not output torque, it is desirable to set the value of Tx as small as possible.

After the elapse of the time Tx, next, the V-phase winding V1 is energized, and from step a5 to a12, step a
Next, similarly to 1 to a4, the energization and operation of the W-phase winding W1 are repeated.

As described above, the configuration is made up of a small number of power elements, and the regenerative current of the winding is not directly applied to the bus voltage, so that the bus voltage has little fluctuation and the rotation of the motor is stabilized. Since the stop of the current is accelerated when the energized phase is switched, the current that does not contribute to the torque is reduced, and efficient operation becomes possible.

Embodiment 2 FIG. FIG. 4 is a configuration diagram of a motor driving device according to a second embodiment of the present invention. The configuration of the booster is different from that of the first embodiment of the present invention. In the figure, the same or corresponding parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The boosting unit 2 includes switching elements TRau and TR for switching the regeneration destination of the winding to one of the bus voltage and the capacitor C4 for each of the windings U1, V1, and W1 of the electric motor SR1.
av, TRaw and diodes D2u, D2v, D2w for preventing backflow from the capacitor C4.

FIG. 5 shows the operation of the switching element in the drive circuit and the change in the potential of the capacitor C4, and FIG. 6 is a flowchart showing the operation at that time. Hereinafter, the operation of the drive circuit will be described with reference to FIG. First, at the time of driving the electric motor SR1, U
Energize the phases. In step b1, the switching elements TRw, TRaw, TRb are turned off. At the same time, TRu and TRau are turned on. Switching element TR
By turning off w, the current supply to the W-phase winding W1 is stopped. By turning off TRaw and TRb, the current flowing through the winding W1 flows into the capacitor C4 via the diodes Dw and D2w, and is boosted. Accordingly, the stopping of the current of the winding W1 is accelerated. When the switching element TRu is turned on at the same time, energization of the U-phase winding U1 is started. At this time, if the chopping operation for the variable speed control is performed at the same time, a part of the current of the winding U1 flows to the booster via the diode Du, but the switching element TR
Since au is on, it does not flow to the capacitor C4,
Regenerated to bus voltage. For this reason, the current of the winding U1 can flow continuously without suddenly stopping, and a torque with little fluctuation can be obtained.

Next, in step b2, the process waits until the time Tx has elapsed. This time sets a time sufficient for the current of the winding W1 to stop, but within this time,
Since the torque is output by energizing the U-phase, it is not necessary to set the time particularly short. After the elapse of Tx in step b2, the switching circuit TRb is turned on in step b3, and the discharge of the energy of the capacitor C4 to the bus voltage is started.

In step b4, a command to switch the energized phase is awaited. When a phase switching command is detected, the energization of the U phase is stopped in step b5, and the same operation as steps b1 to b4 is repeated for the V phase in steps b5 to b8, and then in step b9 for the W phase.
The same operation is performed from to b12.

As described above, the operation of the electric motor SR1 is enabled, and there is no time during which power is not supplied to the windings during operation, so that efficient operation can be performed. Further, since there is no break in torque, vibration and noise during operation of the motor can be reduced.

Embodiment 3 FIG. 7 is a configuration diagram of a motor driving device according to a third embodiment of the present invention. Booster 2
This embodiment is different from the first embodiment in having a voltage sensor unit 4 for monitoring the voltage of the first embodiment. In the figure, the first embodiment
The same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. The voltage obtained by the voltage sensor unit 4 is, for example, directly monitored as an analog value by the microcomputer MC1 via a voltage dividing resistor, or is compared with a predetermined voltage value by a comparator, and is set as a threshold value. For example, a method of giving the value data to the microcomputer MC1 is used.

In the embodiment of the present invention, the protection operation of the drive circuit of the electric motor SR1 is performed based on the information obtained from the voltage sensor section. FIG. 8 shows the operation of the switching element in the drive circuit and the change in the potential of the capacitor C4 of the booster when the protection operation is performed when the U-phase is energized, and FIG. 9 shows the operation at that time. It is a flowchart shown. The operation will be described below with reference to FIG. First, U-phase energization is performed according to the rotation position of the rotor of the electric motor SR1. In step c1, the switching element TRu,
Turn on TRa and TRb. By turning on the switching element TRu, energization of the U-phase winding U1 is started. By turning on switching element TRa, when switching element TRu is chopped for variable speed operation of electric motor SR1, part of the current flowing through winding U1 is regenerated to bus voltage. By turning off the switching element TRb, the capacitor C4 is stepped down and discharged.

Next, in step c2, the state of c1 is maintained until a command to switch the energized phase is received. After receiving the energized phase switching command, step c3 is executed. In step c3, the switching elements TRu, TRa,
Turn off TRb. The energization is terminated by turning off the switching element TRu. By turning off the switching element TRa, the current of the winding U1 when the power supply is stopped flows through the diode Du to the capacitor C4 of the booster, and by turning off the switching element TRb, the discharge of the capacitor C4 is performed. Is stopped, and as a result, the voltage of the capacitor C4 increases, and the stop of the current of the winding U1 is accelerated.

Next, in step c4, the voltage of the capacitor C4 is monitored from the time of step c3 to determine whether or not the voltage is larger than the set value. If the voltage of the booster has become larger than the set value, step c5 is executed next, and if it is smaller, the process proceeds to step c7. In step c5, the switching element TRb is turned on to discharge the energy of the capacitor C4 to the bus voltage, thereby suppressing an increase in the voltage of the capacitor C4.

In this case, since the winding current flows into the high potential capacitor C4, the winding current stops early. However, since the current flowing out of the capacitor C4 passes through L1, the beginning of the current flow is delayed. Therefore, the set value is determined in consideration of the voltage of the capacitor C4 being boosted during the delay time.
Must be set lower.

Further, as shown in FIG. 8, the voltage waveform of the boosting section turns on the switching element TRb, so that the energy of the capacitor C4 is discharged.
The voltage of 4 drops. In step c6, the state of c5 is maintained until the time Tx elapses from the stop of energization of the winding U1 of c3.

Here, the set value of the voltage sensor section is set in accordance with the specifications of the microcomputer, the motor and the like so that the voltage of the capacitor C4 does not exceed the withstand voltage.
1 detects that the voltage of the step-up unit has exceeded the set position, and determines the withstand voltage of the capacitor C4 in consideration of the time until the protection operation of step c5 is performed and the time constant of the step-down unit during the protection operation. Choose a value that does not exceed. Note that this set value is not changed during operation.

Step c7 is a process when the set value is not exceeded in step c4. If the elapsed time from step c3 exceeds Tx, the process proceeds to the energization process of the next phase. If Tx has not elapsed, step c4 is repeated again to check the potential of the booster.

As described above, it is possible to prevent the potential of the booster from becoming too high, and to reliably protect the booster capacitor C4.

Also, during the protection operation of the capacitor C4,
Since the current of the winding is regenerated to the booster which is higher than the bus voltage, it is possible to maintain a state where the stopping of the current is accelerated.

Embodiment 4 The configuration diagram of the motor driving device according to the fourth embodiment of the present invention is the same as the motor driving device according to the third embodiment of the present invention. The protection operation of the drive circuit of the electric motor SR1 based on the information obtained from the voltage sensor unit 4 is also performed in the same manner as in the third embodiment of the invention, but the protection operation is different.

FIG. 10 shows the operation of the switching element in the drive circuit when the protection operation is performed when the U-phase is energized, for example.
FIG. 11 is a flowchart showing a change in the potential of the capacitor C4 of the booster, and FIG. 11 is a flowchart showing the operation at that time. Hereinafter, the operation will be described with reference to FIG. First, U-phase energization is performed according to the rotation position of the rotor of the electric motor SR1. In step cc1, switching element TR
u, TRa and TRb are turned on. Switching element TR
By turning on u, energization of the U-phase winding U1 is started. By turning on switching element TRa, switching element TRu for variable speed operation of electric motor SR1 is provided.
Regenerates a part of the current flowing through the winding U1 to the bus voltage. By turning off the switching element TRb, the capacitor C4 is stepped down and discharged.

Next, in step cc2, the state of step cc1 is maintained until a command to switch the energized phase is received. After receiving the energized phase switching command, step cc3 is executed. In step cc3, the switching elements TRu, TRa, TRb are turned off. The energization is terminated by turning off the switching element TRu. By turning off the switching element TRa, the current of the winding U1 at the time when the power supply is stopped flows through the diode Du to the capacitor C4 of the booster, and the switching element TRb
Is turned off, the discharge of the capacitor C4 is stopped,
As a result, the voltage of the capacitor C4 increases.

Next, in step cc4, step cc
From the time of 3, the voltage of the capacitor C4 is monitored to determine whether or not the voltage is larger than the set value. If the voltage of the booster has become larger than the set value, then step cc5
Is executed, and if it is smaller, the process proceeds to step cc7. In step cc5, the switching element TRa is turned on to stop the current from flowing into the capacitor C4, thereby suppressing the boosting of the capacitor C4. Therefore, the set value can be set to a high voltage near the withstand voltage of the capacitor C4. However, the winding current during protection flows to the bus voltage, so that the time until the current stops is long. Further, as shown in FIG. 10, the voltage waveform of the booster turns on the switching element TRa, so that the current flowing into the capacitor C4 is stopped, and the voltage is maintained. In step cc6, it is checked whether or not the time Tx has elapsed since the energization of the winding U1 was stopped in step cc3.

Here, the set value of the voltage sensor section is set so that the voltage of the capacitor C4 does not exceed the withstand voltage. The microcomputer MC1 detects that the booster section voltage has exceeded the set position, and proceeds to step cc5. The value is selected so that the voltage of the capacitor C4 does not exceed the withstand voltage in consideration of the time until the protection operation is performed. In this case, the switching element TRa
Is turned on, no current flows to the capacitor C4, and the capacitor C4 does not step up any further. Therefore, the set value may be set to a high value within the range of the withstand voltage of the capacitor C4.

Step cc7 is processing when the set value is not exceeded in step cc4.
If the elapsed time from Tx exceeds Tx, the process proceeds to the energization process of the next phase. If Tx has not elapsed, step c is repeated.
Step c4 is repeated to check the potential of the booster.

As described above, boosting beyond the withstand voltage of the capacitor C4 of the boosting section can be suppressed, and the protection of the capacitor C4 can be ensured. Further, since the set value can be set to a high value, the protection operation of the capacitor can be prevented from being wasted.

Embodiment 5 FIG. FIG. 12 shows the operation of the electric motor drive device according to the fifth embodiment of the present invention. The discharge time is adjusted by chopping the switching element TRb of the step-down unit 3 that discharges the energy of the capacitor C4 of the step-up unit 2 to the bus voltage. FIG. 13 is a flowchart showing the operation at this time. Hereinafter, the operation will be described with reference to FIG. First, when the electric motor SR1 is driven, power is supplied to a predetermined phase winding according to the rotational position of the rotor. For example, when energizing the U-phase winding U1, step d in FIG.
In step 1, TRu and TRa are turned on. By turning on TRu, energization of U1 is started. By turning on TRa, when the switching element TRu is chopped for variable speed operation of the electric motor SR1, the winding U
A part of the current flowing through 1 is regenerated to the bus voltage.

Next, in step d2, the switching element TRb is turned on. As a result, discharging of the capacitor C4 of the boosting section is started. This switching element TR
The timing for turning on b may be the same as d1. In step d3, the process waits until the ON time Ton of chopping of the switching element TRb elapses. After the elapse of the time Ton, the process is shifted to d4. At step d4, TRb is turned off. As a result, there is no path for the current to flow from the capacitor C4, and the discharge of the booster is temporarily stopped.
At this time, a current flows from the diode D3 into the reactor L1 of the step-down unit. In step d5, the process waits for the elapse of the chopping off time Toff of the switching element TRb, and after the elapse of the time Toff, proceeds to d6.

Next, at step d6, the microcomputer MC1 monitors and checks whether a signal from the position detection circuit or the like of the electric motor SR1 has been monitored by the microcomputer MC1 to determine whether or not a command to switch the energization of the electric motor SR1 to a predetermined phase has been issued. If there is no phase switching command, the processing from step d2 is repeated. If a phase switching command has been issued, the process proceeds to step d7.
If the phase switching command has not been issued, the process proceeds to step d2.
Then, the switching element TRb is chopped again.

Next, at step d7, the switching elements TRu and TRa are turned off. Switching element TRu
Is turned off, the energization to the U-phase winding U1 is stopped.
By turning off the switching element TRa, the current of the winding U1 is led to the capacitor C4, and the voltage of the booster is boosted. At the same time, the chopping operation of the switching element TRb also stops.

Next, in step d8, after waiting for a lapse of time Tx corresponding to the discharge time of the winding U1, the process of d1 is performed to start energization of the next V-phase winding V1.
At the same time, chopping of the switching element TRb is started.

In this example, the values of Ton and Toff are treated as fixed, but need not be fixed.
For example, initially, the value of Ton is set to a small value, and each time the number of times of chopping is repeated, or by increasing the value of Ton with the passage of time, the initial sudden current is suppressed, and the current is gradually supplied. May be set.

As described above, by performing chopping at the time of the step-down operation in the switching element TRb of the step-down unit, the current discharged to the bus voltage can be moderated. Therefore, the current flowing through the switching element TRb can be controlled, and the switching element can be protected. Further, since the value of reactor L1 can be reduced, the size of reactor L1 can be reduced. Furthermore, in order to suppress a rapid current from flowing into the bus voltage, voltage fluctuation is small, and stable operation of the electric motor SR1 is enabled.

Embodiment 6 FIG. In the sixth embodiment, as shown in the relationship diagram between the operation of the switching element of the drive circuit and the potential of the boosting unit in FIG. However, when the voltage of the booster reaches a predetermined value, chopping of the switching element of the booster is stopped. The circuit diagram of the driving device for the electric motor is the same as that of FIGS. Is the same. FIG. 15 is a flowchart showing the operation at this time.

The operation will be described below with reference to FIG. First, at the time of driving the electric motor SR1, current is supplied to the winding of a predetermined phase according to the rotational position of the rotor. For example, when energizing the U-phase winding U1, in step e1, the switching elements TRu and TRa are turned on. When the switching element TRu is turned on, energization of the winding U1 is started. Also, by turning on the switching element TRa, a part of the current at the time of chopping of the switching element TRu is regenerated to the bus voltage.

Next, in step e2, the switching element TRb is turned on. As a result, discharging of the capacitor C4 of the boosting section is started. This timing may be the same as e1. In step e3, after a lapse of time Ton from the turning on of the switching element TRb,
Then, the process proceeds to the process No. 4.

Next, at step e4, the switching element TRb is turned off. Thus, the discharging of the capacitor C4 is temporarily stopped. At this time, a current is supplied to reactor L1 from diode D3. Step e
At 5, the potential of the booster is compared with the set value, and if the potential of the booster is smaller, the process proceeds to step e9. On the other hand, if the potential of the booster is higher, the process proceeds to step e6.

In step e6, the state of step e4 is maintained until a command to switch the energized phase is detected. When the energized phase switching command is detected, the process proceeds to step e7. Next, in step e7, the switching elements TRu, TR
Turn off a. By turning off the switching element TRu, the energization of the U-phase winding U1 is stopped, and by turning off the switching element TRa, the winding U1 when the energization is stopped.
To the capacitor C4 to boost the voltage of the capacitor C4 and accelerate the stopping of the current of the winding U1.

In step e8, the flow waits for the elapse of time Tx from step e7, that is, after the switching elements TRu and TRa are turned off. The time Tx is set to a time sufficient for stopping the current after the energization of the winding U1 is stopped. After the elapse of the time Tx, the process is moved to the step e1 again to start energization of the winding V1 of the next phase.
Next, in step e9, the switching command of the energized phase is checked, and if no command is issued, the process proceeds to step e2 to repeat the chopping of the switching element TRb.

By the above processing, the capacitor C of the booster is
In discharging the energy of No. 4, in addition to protecting the switching element TRb of the step-down unit, miniaturizing the reactor L1 and preventing a sudden change in the bus voltage, the discharging of the capacitor C4 has a predetermined set value. By stopping the operation until the voltage is stopped, the potential is maintained higher than the bus voltage. This further accelerates the stopping of the current as the winding current begins to flow for higher voltages. Therefore, since the stop of the winding current is hastened, the current that does not contribute to the torque of the motor is reduced, and higher efficiency can be achieved.

Embodiment 7 In the seventh embodiment, as shown in the relationship diagram between the operation of the switching element of the drive circuit and the potential of the booster 2 in FIG. , The switching element TRb of the booster is chopped and the capacitor C
A part of the current flowing into the bus 4 flows into the bus. The configuration diagram of the driving device for the electric motor is the same as FIGS. 1, 4, and 7 showing the first to fourth embodiments. FIG. 17 is a flowchart showing the operation at this time. Note that the waveform shown by the dotted line in FIG. 16 is a voltage waveform of the booster when the switching element TRb is not chopped.

Hereinafter, the operation will be described with reference to FIG. First, when the electric motor SR1 is driven, power is supplied to a predetermined phase according to the rotational position of the rotor. Normally, when the voltage of the booster does not exceed the set value, chopping of the switching element TRb is not performed at the time of boosting. When the voltage sensor unit detects that the voltage of the boosting unit becomes higher than the set value, the switching element TRb
Start chopping.

For example, during normal operation, when energizing the U-phase winding U1, the switching elements Tru, TRa, TRb are first turned on in step f1. Turning on the switching element TRu starts energization of the U-phase winding U1, and simultaneously turning on the switching element TRa, sets the switching element TRu for variable speed operation.
A part of the current of the winding U1 at the time of chopping is regenerated to the bus voltage. Further, by turning on the switching element TRb, the charged energy of the capacitor C4 of the booster is discharged to the bus voltage.

Next, in step f2, a switching command for the energized phase is waited for, and when the switching command is detected, the process proceeds to step f3. During this time, although not shown in the flowchart, the switching element TRu performs a chopping operation for variable speed operation. Step f3 is to switch the switching element T in accordance with the detection of the energized phase switching command at f2.
Turn off Ru, TRa and TRb. Switching element T
By turning off Ru, the energization of the U-phase winding U1 is stopped, and by turning off the switching element TRa, the current of the winding U1 when the energization is stopped is guided to the capacitor C4. By turning off the switching element TRb, the discharging of the capacitor C4 is stopped, and the charging of the winding U1 with the current is started.

Next, in step f4, the voltage of the booster is monitored from the time of the processing in step f3, and if the voltage of the booster does not exceed the set value, the process proceeds to step f5. If the voltage of the booster has exceeded the set value, the process proceeds to step f6. In step yf5, it is determined whether or not the elapsed time from the end of energization to the winding U1 has reached Tx. If the time Tx has elapsed, the processing is performed in step f1 to energize the next V phase. Move to If the time Tx has not elapsed, the process proceeds to step f4 again, and the voltage of the booster is monitored. The time Tx sets a sufficient time until the current of the winding U1 when the current supply to the U-phase is stopped.

Next, from step f6, step f4
Performs the processing when the voltage of the booster becomes larger than the set value. In step f6, the process waits until the time Tx elapses from the stop of energization. After the elapse of the time Tx, the process proceeds to step f
Move to 7. From step f7, for example, energization of the next V phase is performed. In step f7, the switching element T
Turn on Rv, TRa and TRb. Switching element T
By turning on Rv, energization of the V-phase winding V1 is started, and by turning on the switching element TRa, part of the current of the winding V1 during chopping for variable speed operation of the switching element TRv is reduced. Regenerates to bus voltage. By turning on the switching element TRb, the discharge of the energy charged in the capacitor of the booster to the bus voltage is started.

Next, in step f8, the flow waits for a command to switch the energized phase. During this time, the switching element TRv performs chopping for variable speed operation. After detecting the energized phase switching command, the process proceeds to step f9. In step f9, the switching elements TRv, TR
a, Turn off TRb. By turning off the switching element TRv, the energization of the V-phase winding V1 is stopped, and by turning off the switching element TRa, the current of the winding V1 when the energization is stopped is guided to the capacitor C4.

Next, the process of chopping the switching element TRb will be described from step f10. Step f
At 10, the switching element TRb is turned on. As a result, a part of the current charged in the capacitor C2 is discharged, and the rate of voltage rise of the capacitor C4 is suppressed. In this process, when the process shifts from f9, since the switching element TRb has already been turned on, step f10
Then, no processing is performed. In step f11, the process waits until the elapsed time from step f10 reaches time Ton.
After the elapse of the time Ton, the process is shifted to f12.

Next, in step f12, the switching element TRb is turned off. As a result, the discharge of the capacitor C4 is temporarily stopped. Switching element T
While Rb is off, a current is supplied to reactor L1 from diode D3. In step f13, the process waits until the time elapsed from step f12 reaches time Toff. After the elapse of the time Toff, the process is shifted to f14. In step f14, it is determined whether or not the elapsed time from step f9 is the time Tx. If the time Tx has elapsed, the process proceeds to f7, where the energization of the next W phase is performed. If the time Tx has not elapsed, the process proceeds to step f10, and the chopping of the switching element TRb is continued.

In this case, the values of Ton and Toff are treated as fixed, but they are changed according to the value monitored by the sensor unit, and are set so as to increase the voltage as high as possible within the range of the withstand voltage of the capacitor C4. The stop time of the winding current can be shortened.

As described above, the boosting of the capacitor C4 of the boosting unit when the energization of the predetermined phase is stopped and the chopping of the switching element TRb suppress the boosting of the capacitor C4 and protect the capacitor C4. At this time, since the current of the winding always flows into the capacitor C4, the stopping of the current is accelerated, and the current stops in a short time. When chopping the switching element TRb,
Due to the presence of the reactor L1, a current flows even when the switching element TRb is off, and the current flowing to the bus voltage is not interrupted, so that the influence on the fluctuation of the bus voltage can be reduced.

Embodiment 8 FIG. FIG. 18 shows the operation of the motor drive circuit according to the eighth embodiment of the present invention. In order to prevent the potential of the capacitor C4 of the booster 2 from rising to a predetermined value or more, the switching element TRa is chopped to flow a part of the current to the bus without passing through the capacitor C4. FIG. 19 is a flowchart showing the operation at this time. Hereinafter, the operation will be described with reference to FIG. First, when the electric motor SR1 is driven, power is supplied to a predetermined phase according to the rotational position of the rotor. Normally, when the voltage of the booster does not exceed the set value, chopping of the switching element TRa is not performed at the time of boosting.
When the voltage sensor unit detects that the voltage of the boosting unit becomes larger than the set value, chopping of the switching element TRa starts from the next boosting.

For example, during normal operation, when energizing the U-phase winding U1, the switching elements TRu, TRa, TRb are first turned on in step g1. Turning on the switching element TRu starts energization of the U-phase winding U1, and simultaneously turning on the switching element TRa, sets the switching element TRu for variable speed operation.
The current of the winding U1 during the off time during chopping is regenerated to the bus voltage. Further, by turning on the switching element TRb, the charged energy of the capacitor C4 of the booster is discharged to the bus voltage.

Next, at step g2, a switching command for the energized phase is waited for, and when the switching command is detected, the process proceeds to step g3. During this time, although not shown in the flowchart, the switching element TRu performs a chopping operation for variable speed operation. Step g3 is step g2
, The switching elements TRu, TRa, TRb are turned off. By turning off the switching element TRu, the energization of the U-phase winding U1 is stopped, and by turning off the switching element TRa, the current of the winding U1 when the energization is stopped is guided to the capacitor C4. By turning off the switching element TRb, the discharging of the capacitor C4 is stopped, and charging and boosting by the current of the winding U1 are started.

Next, at step g4, the voltage of the boosting section is monitored from the time of the processing of step g3, and if the voltage of the boosting section does not exceed the set value, the process proceeds to step g5. If the voltage of the booster has exceeded the set value, the process proceeds to step g6.

Next, in step g5, it is determined whether or not the elapsed time from the end of energization to the winding U1 has reached Tx, and if the time Tx has elapsed, the energization of the next V phase is started. To this end, the process is shifted to step g1. If the time Tx has not elapsed, the process returns to step g4 to monitor the voltage of the booster. The time Tx sets a sufficient time until the current of the winding U1 when the current supply to the U-phase is stopped. From step g6, processing is performed when the voltage of the booster 2 has become larger than the set value in step g4. In step g6, the process waits until the time Tx elapses from the stop of energization. After the elapse of the time Tx, the process moves to step g7.

Next, from step g7, for example, energization of the next V phase is performed. At step g7, the switching elements TRv, TRa, TRb are turned on. When the switching element TRv is turned on, energization of the V-phase winding V1 is started, and when the switching element TRa is turned on, the switching element TRv is turned off during chopping for variable speed operation of the switching element TRv. Of the winding V1 is regenerated to the bus voltage. By turning on the switching element TRb, the discharge of the energy charged in the capacitor of the booster to the bus voltage is started.

Next, at step g8, a command to switch the energized phase is awaited. During this time, the switching element TRv performs chopping for variable speed operation. After detecting the energized phase switching command, the process proceeds to step g9.
In step g9, the switching elements TRv, TRa,
Turn off TRb. By turning off the switching element TRv, the energization of the V-phase winding V1 is stopped, and by turning off the switching element TRa, the capacitor C4 is charged by the current of the winding V1 when the V-phase energization is stopped. Be started. By turning off the switching element TRb, the discharging of the capacitor C4 is stopped.

Next, the process of chopping the switching element TRa will be described from step g10. Step g
At 10, the switching element TRa is turned off. Thus, charging of the capacitor C2 is started. When the process has shifted from step g9, the switching element TRa has already been turned off, so that the process is not performed in step g10. In step g11,
It waits until the elapsed time from step g10 reaches time Toff. After a lapse of time Toff, the process moves to step g12.

Next, in step g12, the switching element TRa is turned on. As a result, charging of the capacitor C4 is temporarily stopped. While the switching element TRa is off, the current of the winding V1 regenerates to the bus voltage. At step g13, the process waits until the elapsed time from g12 reaches time Ton. After a lapse of time Ton, the process moves to step g14. At Step g14, it is determined whether or not the elapsed time from Step g9 is the time Tx. If the time Tx has elapsed, step g7
The process is shifted to and the energization of the next W phase is performed. If the time Tx has not elapsed, the process proceeds to step g10, and the chopping of the switching element TRa is continued.

As described above, when the energization of the predetermined phase is stopped, the boosting of the capacitor C4 in the boosting section is suppressed by chopping the switching element TRa to suppress the boosting of the capacitor C4 and protect the capacitor C4. When chopping the switching element TRa, the capacitor C4 is not charged when TRa is on, so that the boosting is not performed, and the effect of suppressing the boosting can be increased.

[0089]

Since the present invention is configured as described above, it has the following effects.

A stator having a plurality of windings connected in a star shape;
A motor having a terminal of each winding and a connection neutral point as an output terminal; and an inverter unit having one switching element corresponding to each winding of the motor, and driving the motor by switching and energization of energization. And a booster for charging and boosting with a current generated in the winding when power supply from the inverter to the motor is stopped, and one switching for each. A step-down unit comprising a device, a diode, and a reactor, for discharging and stepping down the voltage of the step-up unit, and while energizing the winding, the step-down unit drops the voltage of the step-up unit, When the power supply to the winding is stopped, the boosting section is boosted by the current generated in the winding. By regenerating ghee to up unit, to stop the current early in order to prevent the flow of current which does not contribute to torque, it is possible to make efficient driving.

Further, a motor having a stator in which a plurality of windings are connected in a star shape, having a terminal of each winding and a neutral point of the connection as an output terminal, and one switching corresponding to each winding of the motor An inverter for driving the motor by switching and chopping of current, and one switching element and one diode and one capacitor provided for each winding of the motor. When the power supply to the motor is stopped, the boosting unit performs charging and boosting by the current generated in the winding, and includes a switching element, a diode, and a reactor, and discharges and reduces the voltage of the boosting unit. And a step-down unit for performing, when the winding is energized, the step-down unit reduces the voltage of the boosting unit, and when the energization to the winding is stopped, By boosting the boosting section by the current generated in the winding, by providing a switching element and a diode of the boosting section for each phase of the electric motor, it is possible to eliminate a break in an energized section and perform driving without vibration and noise. Can be.

Also, a voltage sensor unit for monitoring the voltage of the boosting unit is provided. When the voltage becomes higher than a predetermined value, the switching element of the step-down unit is turned on to suppress the rise of the voltage. The protection of the capacitor of the section can be performed, and the stop of the current of the winding can be accelerated.

Further, a voltage sensor for monitoring the voltage of the booster is provided. When the voltage becomes higher than a predetermined value while the motor is being driven, the switching element of the booster is turned on. Since the rise in the voltage is suppressed, the protection of the capacitor of the booster can be reliably performed.

Also, since the chopping is performed at the switching element of the step-down unit and the step-down is performed gently while the motor is energized, the discharging of the step-up unit capacitor is performed gently by chopping the switching element of the step-down unit during operation. Thereby, the influence on the fluctuation of the bus voltage can be suppressed, the rotation of the electric motor can be stabilized, and the discharge current can be controlled to reduce the size of the reactor in the step-down unit. In addition, it is possible to reduce the capacity of the current of the switching element in the step-down unit.
Heat generation can also be suppressed.

In addition, chopping is performed in the switching element of the step-down unit during energization of the motor, and when the voltage of the step-up unit detected by the voltage sensor unit reaches a predetermined value, the chopping is stopped. The switching element is chopped, and the chopping is stopped when a predetermined voltage value is detected by the sensor unit, thereby maintaining the voltage of the boosting unit at a predetermined voltage equal to or higher than the bus voltage and stopping the current of the winding. It is possible to further shorten the time until the drive is performed, and to drive more efficiently.

Further, when the maximum value of the voltage of the step-up unit detected by the voltage sensor unit becomes larger than a predetermined value, when the energization of the winding of the motor is stopped, the switching element of the step-down unit is chopped. To prevent the voltage from greatly exceeding a predetermined value, so that when the voltage value obtained from the voltage sensor unit becomes larger than a predetermined value, By chopping the switching elements, the voltage rise in the booster section is suppressed and the capacitor is protected.
At the same time, the winding current can be stopped earlier.

Further, when the maximum value of the voltage of the boosting section detected by the voltage sensor section becomes larger than a predetermined value, when the current supply to the winding of the motor is stopped, the switching element of the boosting section is chopped. To suppress the voltage from greatly exceeding a predetermined value, so that when a voltage of a predetermined value is detected by the voltage sensor unit, the voltage of the boosting unit is increased when the voltage to the winding of the motor is stopped. By chopping the switching element, a voltage increase in the booster can be suppressed, and the capacitor can be protected reliably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a motor driving device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an operation of each switching element of the motor driving device according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the electric motor drive device according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram of a motor driving device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an operation of each switching element of a motor driving device according to a second embodiment of the present invention.

FIG. 6 is a flowchart showing an operation of the electric motor drive device according to the second embodiment of the present invention.

FIG. 7 is a configuration diagram of a motor driving device according to Embodiments 3 and 4 of the present invention.

FIG. 8 is a diagram showing an operation of each switching element of a motor driving device according to a fourth embodiment of the present invention.

FIG. 9 is a flowchart showing the operation of the electric motor drive device according to Embodiment 3 of the present invention.

FIG. 10 is a diagram showing an operation of each switching element of a motor driving device according to a third embodiment of the present invention.

FIG. 11 is a flowchart showing an operation of the electric motor drive device according to the fourth embodiment of the present invention.

FIG. 12 is a diagram showing an operation of each switching element of the motor driving device according to the fifth embodiment of the present invention.

FIG. 13 is a flowchart showing an operation of the electric motor driving device according to the fifth embodiment of the present invention.

FIG. 14 is a diagram showing an operation of each switching element of a motor driving device according to a sixth embodiment of the present invention.

FIG. 15 is a flowchart showing the operation of the electric motor drive device according to Embodiment 6 of the present invention.

FIG. 16 is a diagram showing an operation of each switching element of the motor driving device according to the seventh embodiment of the present invention.

FIG. 17 is a flowchart showing an operation of the electric motor driving device according to the seventh embodiment of the present invention.

FIG. 18 is a diagram showing an operation of each switching element of the motor driving device according to the eighth embodiment of the present invention.

FIG. 19 is a flowchart showing the operation of the electric motor drive device according to the eighth embodiment of the present invention.

FIG. 20 is a configuration diagram of a driving device for a conventional switched reluctance motor.

FIG. 21 is a diagram showing the structure and operation of a switched reluctance motor.

FIG. 22 is a configuration diagram of a conventional electric motor driving device.

[Explanation of symbols]

1 Inverter section, 2 step-up section, 3 step-down section, 4 voltage sensor section.

Claims (8)

[Claims] 1. A motor having a stator in which a plurality of windings are connected in a star shape, having a terminal of each winding and a neutral point of the connection as an output terminal, and one switching corresponding to each winding of the motor. An inverter unit for driving the electric motor by switching and chopping of energization, each of which comprises one switching element, a capacitor, and a diode. When the energization from the inverter unit to the electric motor is stopped, Charged by the current generated in the winding,
A step-up unit configured to boost the voltage; and a step-down unit configured to discharge and step down the voltage of the step-up unit, the step-up unit being configured of a switching element, a diode, and a reactor. A drive device for a motor, wherein when a voltage of a booster is reduced and current supply to the winding is stopped, the booster is boosted by a current generated in the winding. 2. A motor having a stator in which a plurality of windings are star-connected, having a terminal of each winding and a neutral point of the connection as an output terminal, and one switching corresponding to each winding of the motor. An inverter unit having an element and driving the electric motor by switching and chopping of electricity; and a switching element and a diode provided for each winding of the electric motor, and a diode and a capacitor. When the power supply to the motor is stopped, the boosting unit performs charging and boosting by the current generated in the winding, and each of the boosting unit includes one switching element, a diode, and a reactor, and discharges and reduces the voltage of the boosting unit. A step-down unit for performing, when energizing the winding, the step-down unit reduces the voltage of the boosting unit, and when the energization to the winding is stopped, The current generated in Kimaki line, the motor of the drive unit, characterized in that for boosting the boosting unit. 3. A voltage sensor unit for monitoring a voltage of a boosting unit, wherein when the voltage becomes higher than a predetermined value, a rise of the voltage is suppressed by turning on a switching element of a step-down unit. The driving device for an electric motor according to claim 1 or 2, wherein 4. A voltage sensor unit for monitoring a voltage of a boosting unit, wherein when the voltage becomes higher than a predetermined value during driving of the electric motor, a switching element of the boosting unit is turned on. 3. The motor driving device according to claim 1, wherein the increase in the voltage is suppressed. 5. The motor driving device according to claim 1, wherein chopping is performed in the switching element of the step-down unit during the energization of the motor to gradually reduce the voltage. 6. The method according to claim 6, wherein chopping is performed in the switching element of the step-down unit during energization of the motor, and the chopping is stopped when the voltage of the step-up unit detected by the voltage sensor unit reaches a predetermined value. The electric motor driving device according to claim 3 or 4, wherein 7. When chopping of the switching element of the step-down unit is stopped when the current supply to the winding of the motor is stopped when the maximum value of the voltage of the step-up unit detected by the voltage sensor unit becomes larger than a predetermined value. 5. The driving device for an electric motor according to claim 3, wherein the driving is performed so that the voltage does not greatly exceed a predetermined value. 8. When the current to the winding of the motor is stopped when the maximum value of the voltage of the booster detected by the voltage sensor becomes larger than a predetermined value, chopping of the switching element of the booster is performed. 5. The driving device for an electric motor according to claim 3, wherein the driving is performed so that the voltage does not greatly exceed a predetermined value.