JP4591949B2 - Control device for multiphase induction motor - Google Patents

Description

The present invention relates to an induction motor control apparatus having a function of detecting the frequency of an induction motor in order to start or restart a multiphase induction motor (hereinafter simply referred to as an induction motor) without using a speed detector.

  When an induction motor that is rotating without being driven by an inverter is started or restarted by an inverter (hereinafter simply referred to as startup), the frequency, phase, and amplitude of the supplied inverter output voltage are set to a free-run state. It is necessary to match the rotation frequency, the residual voltage phase and the amplitude. If there is a difference in voltage phase and amplitude, an excessive current flows through the inverter, and if there is a difference in frequency, an impact torque is applied to the induction motor, or an excessive regenerative current flows from the induction motor to the inverter. Arise.

  Conventionally, as a method for calculating the rotation frequency, voltage phase and amplitude of an induction motor, there is a method of detecting the rotation frequency and residual voltage phase from the residual induced voltage of the induction motor. Since the induction motor generates an AC voltage having a rotation frequency by rotating the magnetic flux remaining in the iron core even when the power is cut off, the rotation speed can be detected by using this residual voltage (see, for example, Patent Document 1). ).

Further, according to Patent Document 2, after an idling induction motor is operated at a predetermined voltage and a predetermined frequency for a certain period of time, the frequency is detected by a residual voltage when the circuit is shut off again, and a soft start is performed.
JP 54-50812 (page 4, Fig. 3) JP-A-8-336296 (5th page, FIG. 4)

  In the conventional apparatus described in Patent Document 1, the residual voltage is detected for starting and the voltage phase frequency is detected. However, when the residual magnetic flux is small or the rotational speed is low, the residual voltage is detected. Since it becomes small, there was a problem that it could not be detected.

  Further, in the device of Patent Document 2, the induction motor that has been idling is operated for a certain time at a predetermined voltage and a predetermined frequency and then soft-started by detecting the frequency based on the residual voltage when the motor is shut off again. If a predetermined voltage is applied at a frequency close to the frequency, the residual voltage can be detected after a certain time. However, in the apparatus of Patent Document 2, it is not clearly shown how to determine the predetermined frequency, and therefore the rotational speed of the induction motor is not known, so it is difficult to determine the predetermined frequency appropriately. For example, if there is an excessive frequency difference, not only a voltage of a level that can be detected unless a considerably large current is supplied will be excited, but also demagnetization may occur. Further, since the magnetic flux is not established in the reverse phase excitation, there is a problem that it takes time because the above operation needs to be performed twice when the rotational direction is unknown.

  The present invention has been made to solve the above-described problems, and is capable of detecting the rotation speed and starting the induction motor in a short time regardless of the rotation speed and rotation direction of the induction motor. An object of the present invention is to provide a control device for an electric motor.

In order to achieve the above object, a control device for a multiphase induction motor according to the present invention includes a power converter that drives an induction motor, a gate drive circuit of an inverter unit of the power converter, and an output voltage of the power converter. Voltage detection means for detecting and supplying a gate signal for supplying a signal to the gate drive circuit to apply a single-phase power that generates an alternating magnetic field in the stator winding of the multiphase induction motor when the induction motor is started Means, frequency setting means for changing the frequency of the single-phase power within a predetermined range, and gate block means for generating a gate block signal for a predetermined period of one period of the frequency, during the gate block period In addition, the residual voltage of the induction motor is detected by the voltage detection means, and if the residual voltage is less than a predetermined value, the frequency of the single-phase power is determined by the frequency setting means. Performed again the gate block and the residual voltage detected by changing the residual voltage is equal to or greater than a predetermined value, and to complete the start preparation from the residual voltage by detecting the rotational frequency of the polyphase induction motor It is characterized by that.

  According to the present invention, since the electric power applied to the induction motor to detect the residual voltage is configured as a single phase, the rotation speed is detected in a short time regardless of the rotation speed and the rotation direction of the induction motor. It is possible to provide an induction motor control device capable of starting an electric motor.

  Embodiments of the present invention will be described below with reference to the drawings.

  A first embodiment of the control apparatus for an induction motor according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a control device for an induction motor according to the present invention.

  In FIG. 1, a power converter 1 that has received an AC input converts it into an AC of an arbitrary voltage / frequency and drives an induction motor 2. Although not shown in the figure, the power converter 1 is usually composed of a converter unit that converts alternating current into direct current and an inverter unit that converts the obtained direct current into alternating current. The power device constituting the inverter unit of the power converter 1 is controlled by a gate signal from the gate drive circuit 4. The gate drive circuit 4 is supplied with the output signal of the PWM modulation circuit 5, and a normal voltage reference (not shown) is given to the PWM modulation circuit 5 during normal operation. Hereinafter, the configuration for starting the induction motor 2 during idling will be mainly described.

  When the AC input of the power converter 1 is restored after a power failure, the terminal voltage of the induction motor 2 is detected by the voltage detector 5, and when a command signal is given from the gate block signal generator 12, which will be described in detail later, It is determined whether or not the voltage can be detected by the level determiner 6. If the voltage cannot be detected, the frequency setter 7 sets the frequency of the voltage applied to the induction motor 1. In accordance with the set frequency, the pulse width is set by the pulse width setting unit 8, the signals from the pulse amplitude setting unit 9 are synthesized, and the pulse for excitation is created by the pulse generator 10. After the generated pulse is inverted by the inverter 11 and the signal is converted into three phases, a gate command for the power converter 1 is generated by the PWM modulation circuit 4, and the power of the power converter 1 via the gate drive circuit 4 is generated. Control the device. Here, since the output of the inverter 11 is given to two of the three phases simultaneously, the output of the power converter 1 is equivalent to a single phase.

  In response to the signals from the frequency setting circuit 7 and the pulse amplitude setting device 8, the gate block signal generator 12 creates a gate block signal. That is, the signal generated by the PWM modulation circuit 5 is blocked by the gate drive circuit 4 during the period when the gate block signal is supplied to the gate drive circuit 4.

  If the level determination unit 6 determines that the voltage can be detected, the gate block signal generator 12 generates a gate block signal and the frequency detector 14 detects the frequency and phase to start the operation. Complete preparation.

  Next, the operation of the frequency setting unit 7 will be described with reference to FIG. FIG. 2 is a characteristic diagram of the frequency setter of the control device for the induction motor according to the first embodiment of the present invention.

  When the AC input of the power converter 1 is restored, the frequency setting unit 7 first outputs a pulse at a predetermined frequency f1. In this state, the gate block signal generator 12 performs gate block. If the residual voltage in the gate block cannot be detected, the frequency setting unit 7 increases the frequency up to a predetermined frequency f2 at a predetermined rate while repeating the above operation. Here, the predetermined rate is a predetermined rate that matches the secondary time constant of the induction motor 2 in consideration of the time for establishing the magnetic flux of the induction motor 2. The frequencies f1 and f2 are values between the operating frequencies f0 and ftop of the induction motor.

  Next, the relationship among the frequency setting device 7, the pulse width setting device 8, the pulse generator 10, and the gate block signal generator 12 will be described with reference to the timing chart shown in FIG. Based on the frequency command set by the frequency setter 7, the pulse width setter 8 determines the period T, and divides that period into periods A, B, C, D, and E. The pulse generator 10 generates a pulse X in accordance with each of the divided periods. As shown in the figure, for example, the pulse X is 1 in the period B, minus 1 in the period D, and zero in other periods. Similarly, the gate block signal generator 12 generates the gate block signal Y according to the period T set by the pulse width setting unit 8. For example, as shown in the figure, the gate block signal Y is zero in the periods B and D, and is 1 in the other periods.

  Next, a detailed operation in the above configuration will be described. FIG. 4 is a flowchart showing the operation of the control apparatus for the induction motor according to the present invention.

  When power is restored after the occurrence of a power failure (ST1), voltage detection is performed by the voltage detection circuit 3 (ST2). It is determined whether or not the residual voltage detected by the voltage detection circuit 3 is at a level that can be detected by the level determination unit 6 (ST3). If the residual voltage cannot be detected, a single-phase voltage for excitation is applied, so The frequency of the voltage is set (ST4). It is determined whether or not the frequency is within a predetermined frequency range (ST5). If the frequency is within the predetermined range, pulse conditions such as a pulse width and a pulse amplitude are set (ST6), and a single-phase power pulse is transmitted to the induction motor 2 (ST7). Next, when the gate block signal from the gate block signal generator 12 becomes 1 (ST8), the voltage is detected by the voltage detector 3 in the same period as in step ST2 (ST9). Then, similarly to step ST3, it is determined whether or not the residual voltage can be detected by the level determiner 6 (ST10). If not detected, the process returns to step ST4, and the frequency is set by the frequency setter 7 according to a predetermined rate. In step ST5, it is determined whether the frequency is within a predetermined frequency.

  The above operation is repeated until the residual voltage can be detected in step ST10 or until the frequency exceeds a predetermined frequency in step ST5. If the residual voltage can be detected in step ST3 or step ST10, the frequency detector 13 detects the frequency and phase based on the residual voltage (ST11), and start-up preparation is completed in this state (ST12). If the frequency exceeds a predetermined frequency range in step ST5 without detecting the residual voltage, it is determined that the induction motor 2 is stopped.

  In the first embodiment, since the single-phase voltage is applied in the form of pulses, the magnetic field generated in the stator winding is an alternating magnetic field, not a rotating magnetic field, and can be detected in any rotational direction. There is.

  Further, since the frequency is variable, it is possible to generate a residual voltage by giving a frequency close to the rotational speed of the rotor. Furthermore, the variable frequency makes sense that it starts from a lower frequency. This is because the residual voltage decreases when the rotor speed is low, so that the rotational speed of the induction motor 2 decreases during the operation of repeating the frequency setting shown in FIG. 4, and the residual voltage cannot be detected. This is to prevent it.

  FIG. 5 is a characteristic diagram of the frequency setter of the control device for the induction motor according to the first embodiment of the present invention.

In the second embodiment, the operation of the frequency setter 7 is different from that in the first embodiment shown in FIG. A predetermined frequency f2 is first selected as the pulse frequency, and if a residual voltage in the gate block cannot be detected, the pulse frequency is lowered to a frequency f1 at a predetermined rate. Here, the predetermined rate is a predetermined rate corresponding to the secondary time constant of the induction motor 2 as in the case of the first embodiment. The frequencies f1 and f2 are values between the operating frequencies f0 and ftop of the induction motor.

  In the case where the power converter 1 has no regenerative function, according to the method of increasing the frequency from f1 as shown in FIG. 2 of the first embodiment, f1 is lower than the rotational frequency of the free-running rotor. In some cases, the regeneration mode is set, and the power converter 1 may become overvoltage. Therefore, if the frequency is decreased from f2 as in the second embodiment, the above problem can be prevented.

  FIG. 6 is a circuit diagram showing a third embodiment of the control apparatus for an induction motor according to the present invention. The same parts of the third embodiment as those of the control device for the induction motor according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The third embodiment is different from the first embodiment in that a current controller 20 is provided at the output of the pulse generation circuit 10 and PWM modulation is performed using the output of the current controller 20 as a voltage command. The current detector 21 is provided, and the current controller 20 is controlled so that the detected current becomes constant.

  If the output current of the power converter 1 is controlled as in the third embodiment, a current limiter is provided inside the current controller 20 so as to prevent the current from flowing beyond a predetermined current, It is possible to detect the frequency while protecting it. As the frequency setting method of the frequency setting unit 7 in the third embodiment, the acceleration method of the first embodiment and the deceleration method of the second embodiment may be selected according to circumstances.

  A fourth embodiment of the induction motor control apparatus according to the present invention will be described below with reference to FIGS. FIG. 7 is a circuit diagram showing Embodiment 4 of the induction motor control apparatus according to the present invention.

  The same parts of the fourth embodiment as those of the control unit for the induction motor according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The fourth embodiment is different from the first embodiment in that a sine wave generation circuit 30 is provided instead of the pulse generation circuit 10 and the output of the frequency setting circuit 7 is directly input to the sine wave generation circuit 30. The point is that an amplitude setting unit 9A is provided instead of the pulse amplitude setting unit 9, and the output of the sine wave generation circuit 30 is given to the gate block signal generation circuit 12.

  The induction motor control device according to the fourth embodiment is characterized in that the single-phase power supplied to the induction motor 2 is not a pulse but a sine wave. Based on the frequency set by the frequency setter 7 and the amplitude set by the amplitude setter 9A, the sine wave generator 30 creates a sine wave command. Then, the gate block signal generator 12 generates a gate block signal according to the timing of the sine wave. As the frequency setting method of the frequency setting unit 7 in the fourth embodiment, the acceleration method of the first embodiment and the deceleration method of the second embodiment may be selected according to circumstances.

  FIG. 8 shows an example of a mechanism for creating a gate block signal from a sine wave in the fourth embodiment. Since the period T of the sine wave Z created by the sine wave generator 30 is known by the frequency setter 7, one period is divided into predetermined periods F, G, H, I and J, and excitation is performed as shown. A gate block signal Y is generated during periods F, H, and J that are considered to have ended.

  FIG. 9 shows another example of creating a gate block signal from a sine wave in the fourth embodiment. In the case of FIG. 9, if the sine wave Z created by the sine wave generator 30 is in a range smaller than the predetermined amplitude ± K, the gate block signal Y is generated for that period.

  If excitation with a sine wave is performed as described above, the induction motor 2 can be excited smoothly with a sine wave magnetic flux.

  A fifth embodiment of the induction motor control apparatus according to the present invention will be described below with reference to FIGS. FIG. 10 is a circuit configuration diagram showing Embodiment 5 of the induction motor control apparatus according to the present invention.

  The same parts of the fifth embodiment as those of the control device for the induction motor according to the first embodiment of FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The fifth embodiment is different from the first embodiment in that the PWM modulation circuit 5 and the pulse amplitude setting circuit 9 are omitted, and the average voltage control by PWM modulation is performed by the converter voltage control circuit 40 newly provided. In addition, the gate block signal generation circuit 12 is omitted.

  As described above, the converter voltage control circuit 40 controls the converter unit of the power converter 1 </ b> A, so that the frequency set by the frequency setter 7 or the magnitude of the DC voltage according to the pulse width set by the pulse width setter 8. It is possible to directly control the inverter in the power converter 1 without modulating the pulse signal for giving the single-phase power created by the pulse generator 10 via the pulse width setting device 8. Become.

  The above operation will be described with reference to a timing chart shown in FIG. As shown in FIG. 11, one cycle T is obtained by the output of the frequency setting circuit 7, and this one cycle is divided into periods A, B, C, D, and E. As in the case of the first embodiment, the pulse generation circuit 10 generates the pulse X so as to be 1 in the period B, minus 1 in the period D, and zero in other periods.

  In the case of the fifth embodiment, since PWM modulation is not performed, the power device of the inverter unit of the power converter 1 is ON during the period B or D, but the power converter 1 is used during the periods A, C, and E. Since all the power devices in the inverter section are OFF, this is equivalent to performing the gate block, and it is possible to detect the residual voltage. Therefore, in this embodiment, the converter voltage control circuit 40 is required, but the gate block signal generator 12 can be omitted. In addition, what is necessary is just to select the acceleration method of Example 1, and the deceleration method of Example 2 according to the case as the frequency setting method of the frequency setting device 7 in this Example 5. FIG.

The block block diagram of the control apparatus of the induction motor which concerns on Example 1 of this invention. The characteristic diagram of the frequency setter of the control apparatus of the induction motor which concerns on Example 1 of this invention. The timing chart which shows operation | movement of the frequency setting device of the control apparatus of the induction motor which concerns on Example 1 of this invention. The operation | movement flowchart of the control apparatus of the induction motor which concerns on Example 1 of this invention. The characteristic diagram of the frequency setter of the control apparatus of the induction motor which concerns on Example 2 of this invention. The block block diagram of the control apparatus of the induction motor which concerns on Example 3 of this invention. The block block diagram of the control apparatus of the induction motor which concerns on Example 4 of this invention. The timing chart which shows an example of operation | movement of the frequency setting device of the control apparatus of the induction motor which concerns on Example 4 of this invention. The timing chart which shows another example of operation | movement of the frequency setting device of the control apparatus of the induction motor which concerns on Example 4 of this invention. The block block diagram of the control apparatus of the induction motor which concerns on Example 5 of this invention. The timing chart which shows operation | movement of the frequency setting device of the control apparatus of the induction motor which concerns on Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A Power converter 2 Induction motor 3 Voltage detector 4 Gate drive circuit 5 PWM modulation circuit 6 Level judgment circuit 7 Frequency setting device 8 Pulse width setting device 9 Pulse amplitude setting device 9A Amplitude setting device 10 Pulse generator 11 Inverter 12 Gate Block Signal Generator 13 Frequency Detector 20 Current Controller 21 Current Detector 30 Sine Wave Generator 40 Converter Voltage Control Circuit

Claims (9)

A power converter for driving a multiphase induction motor;
A gate drive circuit of an inverter part of the power converter;
Voltage detection means for detecting the output voltage of the power converter;
At the start of the multi-phase induction motor, for applying a single-phase power, such as to cause an alternating magnetic field in the stator windings of the polyphase induction motor, and the gate signal supply means for providing a signal to said gate drive circuit,
Frequency setting means for changing the frequency of the single-phase power in a predetermined range;
Gate block means for generating a gate block signal for a predetermined period of one period of the frequency,
During the gate block period, the voltage detection means detects the residual voltage of the multiphase induction motor,
If this residual voltage is less than a predetermined value, the frequency setting means changes the frequency of the single-phase power and performs the gate block and the residual voltage detection again,
A control device for a multi-phase induction motor, wherein if the residual voltage is equal to or greater than a predetermined value, the rotational frequency of the multi-phase induction motor is detected from the residual voltage and the start-up preparation is completed. 2. The control device for a multi-phase induction motor according to claim 1, wherein the gate signal supply means PWM-modulates the pulse signal to obtain a gate signal. 2. The control apparatus for a multiphase induction motor according to claim 1, wherein the gate signal supply means PWM-modulates a sinusoidal signal to obtain a gate signal. The said gate signal supply means makes a pulse-form signal a direct gate signal, and controls the voltage of the converter part of the said power converter according to the pulse width of the said single phase electric power, The Claim 1 characterized by the above-mentioned. Control device for multiphase induction motor. 5. The control device for a multi-phase induction motor according to claim 2, wherein the gate signal supply means supplies the single-phase power command as a voltage command. 4. The multiphase induction motor according to claim 2, wherein the gate signal supply means supplies the single-phase power command as a current command, and a current limit is provided as necessary. Control device. 2. The control apparatus for a multi-phase induction motor according to claim 1, wherein the frequency setting means performs the residual voltage detection while increasing a frequency rate of the single-phase power. 2. The multi-function according to claim 1, wherein when the power converter does not have a regenerative function, the frequency setting means performs the residual voltage detection while reducing a frequency rate of the single-phase power. Control device for phase induction motor. If the residual voltage is less than a predetermined value in the entire frequency range set by the frequency setting means,
2. The control apparatus for a multi-phase induction motor according to claim 1, wherein the multi-phase induction motor is determined to be stopped.

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