JP3473177B2 - Apparatus and method for picking up electric motor in case of momentary power failure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor pick-up device and method which uses a forward / reverse conversion device to cause a momentary power failure during operation of an AC electric motor, and then restarts the electric motor after power recovery.

[0002]

2. Description of the Related Art The AC power of an AC power supply is once converted into DC power by a forward converter, and this DC power is converted again into AC power of variable frequency, variable voltage, etc. by an inverse converter (hereinafter referred to as an inverter). It has been widely practiced to perform variable speed operation of an AC electric motor (hereinafter abbreviated as an electric motor) such as a three-phase induction motor or a synchronous motor.

When the power source side of the inverter is momentarily interrupted during the operation of the electric motor, the inverter temporarily cuts off the gate signal, and after the power is restored, the inverter is operated again by the gate signal to continue the operation of the electric motor, but the operation is restarted. In doing so, the frequency and phase are detected from the residual voltage of the motor, the detected frequency and phase are matched, and the inverter is operated,
When it fits, restart the motor.

Conventionally, the method of detecting the phase from the residual voltage is performed by the method shown in FIG. FIG. 6 is a schematic circuit diagram of a conventional motor pick-up device during an instantaneous power failure. Reference numeral 1 is a forward converter which converts a three-phase AC voltage into a DC voltage. Reference numeral 2 denotes an inverter, which converts the DC output of the forward conversion device 1 into three-phase AC power and supplies it to the electric motor 3. Reference numeral 4 is a gate drive circuit for the inverter 2, 5 is a control operation unit, 6 is a zero-cross comparator, 7 is a phase / frequency measuring circuit, and the zero-cross comparator 6 is a negative N on the DC side of the inverter 2 and an output side of the inverter 2. The phase voltages of the U, V, and W phases are input, the comparator level is set to 0, a pulse signal that rises at 0 level and drops at the next 0 level is output, and this output signal is input to the phase and frequency measuring circuit 7.

The phase / frequency measuring circuit 7 measures the frequency (rotational speed) of the electric motor 3 and the phase and effective value of the residual voltage from the phase voltage of the output signal of the zero-cross comparator 6,
Input to the control calculation unit 5. The control calculation unit 5 presets this and restarts the inverter 2 via the gate drive circuit 4 after power recovery.

[0006]

In FIG. 6, for example, the phase voltage waveform when the phase voltage of U-V is taken is as shown in FIG. 7 (a). Since the zero-cross comparator 3 forms a 0-level comparison circuit, its output signal is as shown in FIG.
It becomes a square wave in the plus direction by capturing the 0 level as shown in. Therefore, the systemisis can be applied only to the positive side, which makes it difficult to accurately detect the phase of the residual voltage.

Further, since the comparator is started up from the 0 level, it is vulnerable to disturbance and noise and cannot be accurately detected.

As described above, when the phase of the residual voltage cannot be accurately detected, when the inverter is restarted,
The phase of the residual voltage of the electric motor and the phase of the output voltage of the inverter are different, and an overcurrent flows, which causes a problem such as tripping due to the operation of a protection relay or the like.

Further, the residual voltage after the gate is cut off by the inverter due to a momentary power failure or the like varies in various ways depending on the GD ² (moment of inertia) of the electric motor and the operating frequency. For example, if the load is large GD ² , the rotational speed of the electric motor hardly changes even during an instantaneous power failure, and there is almost no attenuation of the residual voltage.

On the contrary, in the electric motor for driving the load via the gear, the residual voltage is instantaneously attenuated, and it is difficult to accurately detect the residual voltage by the method of FIG.

In view of the above points, it is an object of the present invention to provide an apparatus and method that enable accurate residual voltage and phase detection.

[0012]

Means and Actions for Solving the Problems In the Present Invention
Therefore, the means and actions for solving the above problems are
The motor driven by the output power of the inverter
When an instantaneous power failure occurs on the power supply side of the inverter,
The output of the motor is stopped and the level of the residual voltage of the motor is
Phase / frequency measurement for detecting and presetting phase and frequency
Circuit and output voltage of the inverter when the power failure is restored
The phase and frequency of the
Motor pick-up that supplies the output voltage of the motor to the motor.
In the lifting device, the phase and frequency of the residual voltage of the motor
The number detection of the inverter line Voltage is detected and compared
Input to the comparator and the comparator's comparator level
Is the midpoint of the line voltage and its output is the phase and frequency.
Input to the measurement circuit.

By setting the comparator comparator level at the midpoint of the line voltage, it is possible to prevent the influence of noise and to provide hysteresis in the plus and minus directions.

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According to the second aspect of the present invention, the output of the inverter is stopped when an instantaneous power failure occurs on the electric motor driven by the output power of the inverter and the power supply side of the inverter, and the phase of the residual voltage of the electric motor, A phase and frequency measuring circuit for detecting a frequency, and a motor pick-up method for supplying the output voltage of the inverter to the motor by matching the phase and frequency of the output voltage of the inverter with that of the residual voltage when the power failure is restored. , Said phase,
The residual voltage is estimated from the frequency measured by the frequency measurement circuit and the F / V constant coefficient, and the estimated residual voltage is multiplied by a coefficient according to the load condition to obtain the voltage at restart and the voltage is restored. The voltage at the time of restart after electricity, and the residual voltage effective value,
Reduce the error with the restart voltage output from the inverter,
Prevents overcurrent etc. at restart.

In the third aspect of the invention, two modes are set corresponding to the case where the residual voltage of the electric motor can be detected and the case where it cannot be detected.
When the residual voltage level is low and cannot be detected by the detecting means as shown in FIG. 5, the inverter output frequency when the gate of the inverter is cut off is stored, and when power is restored, the voltage 0 to V / F is constant at this frequency. It will be started gradually by increasing until it becomes, and it is possible to restart even when there is no residual voltage (low).

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 is a connection diagram of one embodiment of the first invention of the present invention, which is the same as the conventional circuit of FIG. The same reference numerals are given to the parts and the description thereof will be omitted.

Therefore, in the first aspect of the present invention, the line voltage of the output of the inverter 2 is detected and input to the comparator 6 ', instead of detecting the phase voltage as in the prior art. It is characterized in that the comparator level of the comparator 6'is set at the midpoint thereof.

By detecting in this way, it is possible to provide hysteresis in the plus and minus directions.

FIG. 2 shows a connection diagram of essential parts in which the inverter 2 in FIG. 1 and one comparator 6 "for detecting the line voltage are extracted.

In FIG. 2, the positive side P of the DC power source and the phase voltages of the outputs U, V and W of the inverter 2 are input to the input side of the comparator 6 ", and the comparator 6" is input.
The comparator level is set to 0 to detect the phase voltage.

Since the positive side is common as described above, the rising from 0 is detected by the falling from the maximum voltage as compared with the case where the negative side is common, so that it is not affected by noise. Highly accurate detection is possible.

In FIG. 3, as in FIG. 6, the phase voltage of the output of the inverter is input to the comparator with the negative side being the common, and the voltage e in the recessed portion of the detected waveform is detected without setting the comparator level to 0 level. It is the one.
By doing so, since the comparison is performed in a state where a high voltage is applied, it is less likely to be affected by noise.

FIG. 4 is an explanatory diagram of an embodiment of the second invention and relates to a method of detecting the residual voltage effective value.

In FIG. 4, reference numeral 7 denotes a phase / frequency measuring circuit, which inputs the measured frequency measured by the measuring circuit 7 to a matching circuit 8 and adds the constant coefficient of the V / F constant coefficient circuit 9 at the matching circuit 8. Then, the effective value of the residual voltage is estimated.
Reference numeral 10 is a correction circuit, which has a circuit for setting a coefficient α according to the GD ² of the electric motor, a coefficient β according to the operating frequency, and a coefficient γ according to the type of the electric motor, which are input to the adding circuit 11 via the changeover switches A, B, and C, respectively. Then, the changeover switches A, B and C are selected according to the load condition, and the adder circuit 11 corrects the estimated residual voltage.

Numeral 12 is a voltage setting circuit at the time of restarting after power recovery, which calculates and presets the restart voltage output from the inverter. These circuits are provided in the control calculation unit 5.

In the present invention, the measured frequency and V /
The voltage can be obtained by a constant F coefficient, but the actual residual voltage is lower than the calculated value. In this embodiment, a correction coefficient is further applied according to the load condition to obtain the voltage at restart, and the error between the residual voltage effective value and the restart voltage output from the inverter is reduced to reduce the excess at restart. Preventing current.

FIG. 5 shows a flow chart of an embodiment of the third invention, and relates to picking up when the residual voltage level of the electric motor is low and cannot be detected.

In the present invention, two modes are provided: one with a residual voltage and one without (low). When an instantaneous power failure pick-up command is issued in step S1, first, it is determined in step S2 whether there is a residual voltage, and if there is a residual voltage, frequency measurement is performed by residual voltage detection (S3), and then
Estimate the preset voltage by V / F constant coefficient (S
4) Set the preset frequency and voltage at restart (S
5) Then restart.

If there is no residual voltage or it is difficult to detect it in step S2, the operation (output) frequency when the gate of the inverter is cut off during a power failure is measured and preset (S6), and the output voltage is changed from 0 volt level. Gradually increase until V / F becomes constant (S7).

In this way, even if the residual voltage cannot be detected, it is possible to prevent the restart without restarting.

[0035]

As described above, the present invention has the following effects.

According to the first aspect of the present invention, since the line voltage is detected to detect the phase at the time of zero crossing, it is less susceptible to the noise at the 0 level as compared with the phase voltage detection.

Further, in the conventional method of detecting the phase voltage, only the hysteresis from 0 to the positive direction is provided, but in the present invention, the hysteresis is provided also in the negative direction.

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[Delete]

According to the second aspect of the invention, the voltage can be obtained from the measured frequency by a constant V / F coefficient, and further,
Since the voltage at restart is calculated by multiplying the preset coefficient according to the load condition, the error between the residual voltage effective value and the restart voltage output from the inverter is reduced, and overcurrent at restart is prevented. be able to.

In the invention of claim 3, due to the power failure,
The final output frequency when shutting off is stored in the memory,
When there is no (low) residual voltage, a mode is provided in which only the voltage is gradually increased from 0 at that frequency, so restarting is possible even when the residual voltage cannot be detected.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a main part in the case of detecting a line voltage with the plus side being a common.

FIG. 3 is an explanatory waveform diagram when a comparator level is set with the negative side as a common.

FIG. 4 is an explanatory diagram of a second invention according to the present invention.

FIG. 5 is a flowchart of the third invention of the present invention.

FIG. 6 is a circuit diagram of a conventional motor pick-up device during an instantaneous power failure.

FIG. 7 is a waveform diagram for explaining a conventional residual voltage detection method.

[Explanation of symbols]

1 ... Forward converter 2 ... Inverter 3 ... electric motor 4 ... Gate drive circuit 5 ... Control calculation unit 6,6 ', 6 "... Comparator 7. Phase / frequency measurement circuit 8 ... Matching circuit 9 ... V / F constant coefficient 10 ... Correction circuit 11 ... Adder circuit 12 ... Voltage setting circuit at restart after power recovery

Claims (3)

(57) [Claims] 1. A motor driven by output power of an inverter, and when a momentary power failure occurs on the power supply side of the inverter, the output of the inverter is stopped and the phase / frequency of the residual voltage of the motor is detected and preset. A phase / frequency measuring circuit for adjusting the phase / frequency of the output voltage of the inverter to that of the residual voltage when the power failure is restored, and supplying the output voltage of the inverter to the motor. The phase / frequency of the residual voltage is detected by detecting the line voltage of the inverter and input to the comparator, and the output is input to the phase / frequency measuring circuit with the comparator level of the comparator as an intermediate point of the line voltage. An electric motor pick-up device in the event of a momentary power failure. 2. A motor operated by the output power of an inverter, and a phase for detecting the phase and frequency of the residual voltage of the motor while stopping the output of the inverter when a momentary power failure occurs on the power supply side of the inverter. , A frequency measuring circuit and a motor pick-up method for supplying the output voltage of the inverter to the motor by matching the phase / frequency of the output voltage of the inverter with that of the residual voltage when the power failure is restored. The frequency obtained by measuring with the measuring circuit,
The residual voltage is estimated by a constant F / V coefficient, the estimated residual voltage is multiplied by a coefficient according to the load situation to obtain the voltage at restart, and the voltage is set as the voltage at restart after power recovery. A method of picking up an electric motor during a momentary power failure. 3. An electric motor driven by the output power of the inverter, and when the momentary power failure occurs on the power supply side of the inverter, the gate of the inverter is shut off to stop the output, and the phase of the residual voltage of the electric motor. , A phase / frequency measuring circuit for detecting a frequency, and a motor pick-up method for supplying the output voltage of the inverter to the motor by matching the phase / frequency of the output voltage of the inverter with that of the residual voltage when the power failure is restored. At the moment, the presence of residual voltage of the motor
When there is no residual voltage (low), the output frequency of the inverter when the gate is cut off is stored, and when the power is restored, only the voltage is gradually changed from 0 to V / F constant at this frequency. When there is a residual voltage, the frequency measured by the phase and frequency measurement circuit and the F
/ V constant coefficient is used to estimate the residual voltage, the estimated residual voltage is multiplied by a coefficient according to the load condition to obtain the voltage at restart, and this voltage is used as the voltage at restart after power recovery. A method for picking up an electric motor during an instantaneous power failure.