JPS63268499A - Speed controlling device of induction motor - Google Patents

Abstract

PURPOSE:To prevent an inverter from raising input voltage, by detecting that a slip frequency command comes to have a negative value as the result of that a decelerating command is issued, and by switching ON a dummy resistance without delay. CONSTITUTION:When a decelerating command is given from outside, the deceleration command is added to a divider 16 from the secondary flux command PHI2 and the speed command omegar, so that the slip frequency command omegas as the output of this divider 16 gats negative. As soon as the slip frequency command omegas gets negative, an inverter buffer 21 will detect it. By turning ON a transistor 3 and inserting a dummy resistance 2 into a DC circuit, an inverter 104 is controlled so as not to raise its DC input voltage.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a speed control device for an induction motor, and more specifically, to a speed control device for an induction motor, which has the same motor characteristics during regenerative operation as when running, and particularly prevents the generation of magnetic noise. The present invention relates to a speed control device for an induction motor.

[Conventional technology]

Conventional induction motors (hereinafter referred to as 1M) are small.

As a robust and inexpensive constant speed motor, it has been used in applications ranging from household vacuum cleaners to various factory machines.

Here, the rotational speed N of the IM changes depending on the power supply frequency f applied to the primary side of the IM, and the relationship between this N and ``is expressed by the following equation.

r : Power supply frequency ω, : IM execution angular velocity ω, : IM's sliding angular velocity N : Rotation speed P : Maximum On the other hand, variable frequency power supplies have been put into practical use due to recent improvements in semiconductor technology and software technology, and the above frequency f can be changed. Inverter control, which can control the rotational speed N of the IM by controlling the rotation speed, has come to be used.

Furthermore, recently, it has become more than just inverter control.
IM is based on vector control theory that separately controls the torque current component and excitation current component of the current applied to the primary side of M.
Vector control devices that can withstand rapid acceleration and deceleration have also appeared.

Here, an example of a conventional IM speed control device using an inverter will be explained with reference to FIG.

As shown in the figure, the speed control device 100 of the IM includes a rectifier 103.
．． Inverter 104. It is composed of a drive circuit 109 and the like.

That is, one tot of three-phase commercial type fuses 102a and 10
2b and 102c, respectively, and the DC voltage rectified by the rectifier 103 is applied to the input side of the inverter 104.

Appropriate frequency conversion is performed in this inverter 104, and primary currents are applied to IMI O5 at various frequencies, and as a result, IMI O5 is
The rotation speed is controlled according to the frequency output from 4.

With the circuit configuration shown in Fig. 4, acceleration commands, constant speed commands, etc. can be given to the 1M105 from the outside, and deceleration commands can also be applied, and the 1M105 can perform various controls according to these commands. will be done.

When this deceleration command is applied, it is necessary to apply an electric brake, so when the primary frequency of the 1M105 is lowered, the 1M105 operates as a generator and enters the well-known regenerative operation.

Then, the power regenerated from 1M105 is transferred to inverter 1.
04 to the output side of the rectifier 103, and the DC voltage of the DC input circuit of the inverter 104 increases.

If the input DC voltage of the inverter 104 increases in this way, the terminal voltage of the 1M105 will increase,
As a result, the motor characteristics of the IM 105 will deteriorate, and in particular, the magnetic noise will increase.

This increase in magnetic noise is not a big problem in places where the surrounding area is noisy, such as a factory, but for example, if an IM is used in an air conditioner that is often used in a quiet office, even a small amount of this magnetic noise can be It is desirable to lower the

Conventionally, as a means for this purpose, as shown in FIG.
A series circuit consisting of a dummy resistor 106 and a transistor 107 is provided on the output side of the rectifier 103 (that is, on the input side of the inverter 104), and when the output voltage of the rectifier 103 exceeds a predetermined voltage, a voltage regulator diode 108 By detecting this and turning on the transistor 107, a shunt circuit is configured to lower the input voltage, and a predetermined control signal is sent from the drive circuit 109 to the inverter 10.
In addition to 4, the output voltage of the rectifier 103 is prevented from increasing.

[Problem to be solved]

Incidentally, the steps up to the generation of the above-mentioned magnetic sound are illustrated in FIG. 5.

In other words, if a deceleration command is issued during acceleration or constant speed operation, the IM slip becomes negative, and as a result, the IM
acts as a generator and enters regenerative operation.

Then, since DC is regenerated through the inverter, the inverter input DC voltage increases, and this increased DC voltage causes the magnetic noise of the motor to become louder.

This increase in DC voltage is detected by a constant voltage diode, and a dummy resistor is turned on based on the detected result to prevent the DC voltage from increasing.

However, if this is detected after the inverter's DC input voltage has increased, the motor characteristics will deteriorate.
In particular, the magnetic noise became louder, which was not very desirable.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a speed control device for an induction motor that uses an inverter to control the rotation speed by changing the frequency of the primary current. This is detected and switched to regenerative operation to prevent the DC voltage of the inverter DC input circuit from rising.

[Effect]

According to the present invention, if a deceleration command is applied to the IM, the lagging becomes negative, but this negative value is immediately detected and the dummy resistor is immediately turned on (see Figure 2). ).

Therefore, even if the motor becomes a generator due to regenerative operation, the voltage regenerated from the generator is consumed by the dummy resistor turned on as described above, so the DC voltage of the inverter does not increase. Therefore, the IM can maintain the same motor characteristics as during regeneration, and in particular can prevent magnetic noise from increasing.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A speed control device for an induction motor according to the present invention will be explained below based on illustrated embodiments.

FIG. 1 is an electrical circuit diagram when the speed control device for an induction motor of the present invention is used in a device controlled by vector control theory.

As shown in the figure, a three-phase commercial power source 101 is connected to the rectifier 1 through fuses 102a, 102b, and 102c, respectively.

The rectifier 1 includes a thyristor 1a, and as described later, the DC output voltage is controlled by controlling the firing angle of the thyristor 1a.

The output end of the rectifier 1 is connected to the input side of an inverter 104, and a series circuit of a dummy resistor 2 and an NPN transistor 3 is connected in parallel.

A 1M 105 is connected to the output side of the inverter 104, and the actual rotational speed of the 1M 105 is detected by a speed detector 19 and applied to adders 22 and 23 as the execution speed ω.

On the other hand, a secondary magnetic flux command Φ2 is externally applied to the vector analyzer 11 and the divider 12.16, which combine the torque current component and the excitation current component.

Further, a speed command ω is applied from the outside to the adder 22, and the execution speed ω and the speed command ω added by the adder 22 are applied to the divider 12.
is applied to the vector analyzer 11 and constant setter 15.

Then, the output of the constant setter 15 is applied to the divider 16, and the result is added to the adder 23 as the slipping frequency command ω1.

This slipping frequency command ω is applied to the base of the transistor 3 and the input terminal of the buffer 9 via an inverter buffer 21.

The above-mentioned slipping frequency command ω is applied from the buffer 9 to the gate of the thyristor 1a constituting the rectifier 1 to control the firing angle of the thyristor 1a and control the DC output voltage.

When the above-mentioned slipping frequency command ω3 is negative, it is inverted by the inverter buffer 21 and turns on the transistor 3, so that the voltage generated on the output side of the rectifier 1 is consumed via the dummy resistor 2 and the transistor 3.

The output end of the adder 23 is connected to a vector oscillator 14 that determines the speed of the rotating magnetic field applied to the IM, and is also connected to the vector analyzer 11.

Then, the output of the vector oscillator 14 and the output of the vector analyzer 11 are input to a multiplier 13, where they are vector-combined, and the output of the multiplier 13 is further passed through a converter 17 that converts it into a three-phase current signal. It is applied to a current control amplifier 18, and the output of this current control amplifier 18 is applied to an inverter 104 to perform vector control.

Next, the operation of the IM speed control device configured as described above will be explained based on the flowchart shown in FIG.

The commercial type 5tot is rectified by a rectifier 1 and a predetermined DC voltage is supplied to an inverter 104.

Then, 1M105 is commanded Φ2 by vector control theory.
and speed command ω are both positive, so
The hopping frequency command ω is a positive signal.

In this case, since a positive signal is applied to the inverter buffer 21, its output becomes negative, and the transistor 3 is not turned on, so that no current flows through the dummy resistor 2.

Since it is added to the divider 16, the stagger frequency command ω, which is the output of the divider 16, becomes negative.

This negative voltage turns on the transistor 3 via the inverter buffer 21, so this transistor 3
Current is consumed through the dummy resistor 2.

In this state, when 1M105 performs regenerative operation, 1M1
05 serves as a generator, and the voltage increased in this way is consumed via the dummy resistor 2 and transistor 3, so the voltage on the output side of the rectifier 1 (i.e., the inverter 10
4) will not rise.

Therefore, since the DC voltage of the inverter does not increase, magnetic noise is not generated, and the motor characteristics can be maintained as good as when running in regenerative mode.

Next, a modification of the above embodiment will be explained with reference to FIG.

It should be noted that the members that have already been explained in FIG.

In the embodiment shown in FIG. 1, when the slipping frequency command ω becomes negative, this is immediately detected, and a bypass circuit consisting of a dummy resistor 2 and a transistor 3 is used to prevent the DC input voltage of the inverter 104 from rising. I'm suppressing it.

However, in this case, the DC input voltage of the inverter 104 is extremely reduced, and as a result, the inverter 104
There is a risk that it may not operate properly.

In such a case, the modification shown in FIG. 3 may be applied.

The speed control device of the IM shown in FIG.
0 is added.

That is, a series circuit consisting of dividing resistors 4a and 4b is connected in parallel to the input side of the inverter 104.

The connection point between the divided resistors 4a and 4b is connected to the positive terminal of the comparator 6, the negative terminal is connected to the positive terminal of a battery 7 that generates a reference voltage, and the negative terminal of the battery 7 is grounded. .

The output terminal of the comparator 6 is connected to one input terminal of an AND gate 8, and the output terminal of the AND gate 8 is connected to the base of the transistor 3. The other input terminal of the AND gate 8 is connected to the inverter buffer 21.
The output terminal of the buffer 9 is connected to the connection point between the output terminal of the buffer 9 and the input terminal of the buffer 9.

With this configuration, current is not caused to flow through the dummy resistor 2 immediately when the slipping frequency command ω1 becomes negative, and the DC voltage at the input end of the inverter 104 is kept at a predetermined value (determined by the dividing resistors 4a and 4b). ), a positive voltage is generated from the output terminal of the comparator 6 for the first time. Then, only when both the output of the comparator 6 becomes positive and the slipping frequency command ω1 becomes negative are met, current is passed through the dummy resistor 2, etc., and the input voltage of the inverter 104 is changed. I'm trying to prevent it from rising. Even in this case, it is possible to prevent the generation of magnetic noise, and at the same time, it is possible to prevent the input voltage of the inverter 104 from dropping excessively.

In this embodiment, the case of the IM whose rotation is controlled by the vector control theory has been described, but it is of course applicable to the case where the rotation is controlled by a normal inverter.

〔effect〕

According to the present invention, when a deceleration command is issued to the IM and the slippage becomes negative, this is immediately detected and a dummy resistor is turned on to prevent the input voltage of the inverter from increasing.

Therefore, the motor characteristics of the IM are the same as those when the motor is moving, and it is possible to particularly prevent the generation of magnetic noise.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a speed control device for an induction motor according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the speed control device for an induction motor according to the present invention, and FIG. 3 is a diagram of an induction motor according to the present invention. An electrical circuit diagram showing a modification of the speed control device of
FIG. 4 is an electric circuit diagram showing an example of a conventional speed control device for an induction motor, and FIG. 5 is a flowchart showing the operation of the conventional speed control device for an induction motor. DESCRIPTION OF SYMBOLS 1... Rectifier, 1a... Thyristor, 2... Dummy resistor, 3... Transistor, 4a, 4b... Dividing resistor, 6... Comparator, 7... Reference power supply, 101...・Three-phase commercial power supply, 105...Induction motor (IM).

Claims (1)

[Claims] 1. In a speed control device for an induction motor that uses an inverter to control the rotation speed by changing the frequency of the primary current, if the sliding speed becomes negative during operation, this is detected. A speed control device for an induction motor, characterized in that the DC voltage of the inverter DC input circuit does not increase by switching to regenerative operation. 2. If the sliding speed becomes negative during operation, this is detected and the system switches to regenerative operation, turning on a dummy resistor inserted in parallel to the inverter DC input circuit. speed control device for induction motors.