JP5452333B2 - Induction motor control device and induction motor control method - Google Patents

Description

  The present invention relates to an induction motor control device and an induction motor control method.

  In a control device for controlling an induction motor, when restarting (driving again) an induction motor that is not driven, the output voltage to be output from the power converter to the induction motor, the residual voltage of the induction motor, and If there is a difference in frequency between the two, an abrupt torque is generated in the induction motor.

  Therefore, the control device detects the rotation frequency of the induction motor in the free-run state (performs a frequency search). Specifically, the control device dq-axis converts the output current (vector quantity) to be output from the power converter to the induction motor (in the fixed coordinate system), and the current in the rotating coordinate system (dq coordinate system). (Vector quantity) is obtained. The control device performs current control using the current in the rotating coordinate system, and uses the output voltage command, d-axis current (d-axis component of the current vector), and q-axis current (q-axis component of the current vector) at that time. To determine the rotation frequency of the induction motor. The control device determines the frequency of the output voltage so as to match the calculated rotation frequency, and outputs the output voltage to the induction motor.

  At this time, a residual voltage of a predetermined value or more remains in the induction motor immediately after the free run, and when the output voltage is output from the power converter to the induction motor in that state, the phase between the residual voltage and the output voltage If the amplitude difference is large, a large current (overcurrent) flows through the power converter. As a result, the control device suddenly changes the d-axis current and the q-axis current, and the current control of the frequency search is not successful, and the wrong rotation frequency is obtained. Therefore, it is necessary to sufficiently attenuate the residual voltage of the induction motor.

  In Patent Literature 1, when it is detected that a short-time power failure (instantaneous power failure) has occurred in the inverter instantaneous power failure restart device, the current flowing between the output of the inverse converter and the induction motor is detected. It is described that a reference current value given from the outside is compared with a detected current value. Thus, according to Patent Document 1, the output of the PWM signal for simultaneously turning on when all the switching elements of the lower arm in the inverter are turned on at the same time and the short-circuit current passed through the induction motor becomes larger than the reference current value. Is stopped, and when the short-circuit current becomes zero, the output of the PWM signal for simultaneously turning them on again is started, so that the residual voltage can be sufficiently attenuated.

  In Patent Document 2, when a power failure is detected in an inverter device, a short-circuit current flowing between the inverter unit and the induction motor is detected and detected with all the transistors of the upper arm in the inverter unit turned on at the same time. It is described that the direction of the short-circuit current is determined. Thus, according to Patent Document 2, it can be seen that the direction where the direction of the detected short-circuit current is reversed is the zero-cross point of the residual voltage in the induction motor, so the zero-cross point (phase) of the residual voltage can be detected with high accuracy. It is said that.

  Patent Document 3 discloses a frequency of a short-circuit current that flows through an induction motor while maintaining a state where all switches on one side of an inverter circuit are simultaneously turned on when it is detected that the power supply is cut off in the control and drive device for the induction motor. Is described. Thus, according to Patent Document 3, it is supposed that the rotation speed detection without the influence of noise based on ON / OFF of the switch in the inverter circuit can be performed.

JP-A-10-66386 JP-A-5-268794 JP-A-8-331894

  On the other hand, Patent Documents 1 to 3 do not describe how to improve the accuracy of operation when suppressing an overcurrent flowing through the power converter (power conversion unit).

  The present invention has been made in view of the above, and it is an object of the present invention to obtain an induction motor control device and an induction motor control method capable of improving the accuracy of operation when suppressing an overcurrent flowing in a power converter. And

In order to solve the above-described problems and achieve the object, a control device for an induction motor according to one aspect of the present invention converts a supplied DC power into an AC power and outputs it to the induction motor. A power conversion unit that performs the operation, a first detection unit that detects a current vector flowing in a node between the power conversion unit and the induction motor, and a magnitude and a threshold value of the current vector detected by the first detection unit And the comparison unit, and when the comparison result by the comparison unit determines that the magnitude of the current vector is greater than or equal to the threshold value, the first operation by the power conversion unit is stopped, and the comparison unit If the magnitude of the current vector from the comparison result of the is determined to be smaller than the threshold value, so as to resume the first operation by the power conversion unit, and a control unit for controlling the power conversion unit, Comprising a second detector for detecting a supply stop of the serial the DC power to the power converter, wherein the control unit, when the supply stop of the direct current power is detected by the second detection unit, wherein A second operation by the power converter for attenuating the residual voltage of the induction motor is started, and the threshold to be used by the comparator is a second value lower than the first value from the first value. change, if the magnitude of the current vector from the comparison result by the comparison unit is determined to be smaller than the threshold value, and wherein the benzalkonium stops the second operation by the power converting unit.

  According to the present invention, when the supply stop of the DC power is detected by the second detection unit, the threshold for comparing the magnitudes of the current vectors is set to a level lower than that at the time of supplying the DC power. It can be determined that the residual voltage of the induction motor is attenuated at the timing when the residual voltage of the induction motor is attenuated to a level sufficient to suppress the noise. Thereby, the precision of the operation | movement at the time of suppressing the overcurrent which flows into a power converter part can be improved.

FIG. 1 is a diagram illustrating a configuration of a control device 100 according to the embodiment. FIG. 2 is a diagram illustrating an internal configuration of the inverter circuit 2 according to the embodiment. FIG. 3 is a waveform diagram illustrating an operation of the control device 100 according to the embodiment. FIG. 4 is a flowchart illustrating the operation of the control device 100 according to the embodiment.

  Embodiments of a control device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
A schematic configuration of the control device 100 according to the embodiment will be described with reference to FIGS. 1 and 2.

  A control device 100 shown in FIG. 1 is a device for controlling a motor (induction motor) M. The control device 100 includes an inverter circuit (power conversion unit) 2, a current detector (first detection unit) 3, a three-phase full-wave circuit 6, a current comparison circuit (comparison unit) 5, a microcomputer 1, and a detector (first 2 detection units) 7.

DC power Ec (see FIG. 2) is supplied to the inverter circuit 2 from the outside via the power supply node N1. The inverter circuit 2 converts the supplied DC power into AC power (for example, three-phase AC power) and outputs it to the motor M (first operation). The inverter circuit 2 generates, for example, three-phase currents i _u , i _v , i _w, that is, current vectors (i _u , i _v , i _w ) and outputs them to the motor M.

Specifically, the inverter circuit 2 includes an upper arm 2a and a lower arm 2b as shown in FIG. The upper arm 2a has a plurality of switches Q _R , Q _S , and Q _T. The lower arm 2b has a plurality of switches Q _U , Q _V , and Q _W. Each switch Q _R , Q _S , Q _T , Q _U , Q _V , Q _W includes, for example, a bipolar transistor.

The current detector 3 shown in FIG. 1 detects the amplitudes of the three-phase currents i _u , i _v and i _w output from the inverter circuit 2 to the motor M. That is, the current detector 3 detects a current vector (i _u , i _v , i _w ) flowing through the nodes N2 to N4 between the inverter circuit 2 and the motor M. The current detector 3 supplies the detection result to the three-phase full wave circuit 6.

The three-phase full-wave circuit 6 performs full-wave rectification on the three-phase currents i _u , i _v , i _w detected by the current detector 3, and uses the full-wave rectified current value as a current vector (i _u , i _v , I _w ) is output to the current comparison circuit 5.

  The current comparison circuit 5 receives a full-wave rectified current value from the three-phase full-wave circuit 6 and receives a current limit level (threshold) from the microcomputer 1. The current comparison circuit 5 compares the full-wave rectified current value with the current limit level and outputs the comparison result to the microcomputer 1. For example, the current comparison circuit 5 outputs a comparison result “1” when the full-wave rectified current value is equal to or higher than the current limit level, and the full-wave rectified current value is smaller than the current limit level. The comparison result “0” is output.

  The microcomputer 1 receives a comparison result between the current value subjected to full-wave rectification and the current limit level from the current comparison circuit 5. The microcomputer 1 controls the inverter circuit 2 according to the comparison result by the current comparison circuit 5.

Specifically, when the microcomputer 1 determines from the comparison result by the current comparison circuit 5 that the magnitude of the current vector (i _u , i _v , i _w ) is greater than or equal to the current limit level, the microcomputer 1 outputs the AC power. A PWM command CM1 for stopping (first output) (PWM output cutoff) is supplied to the inverter circuit 2. Thereby, the inverter circuit 2 stops the operation of outputting AC power to the motor M.

Alternatively, when it is determined from the comparison result by the current comparison circuit 5 that the magnitude of the current vector (i _u , i _v , i _w ) is smaller than the current limit level, the microcomputer 1 outputs the AC power (first operation). ) Is resumed (PWM output cutoff release) is supplied to the inverter circuit 2. Thereby, the inverter circuit 2 restarts the operation of outputting AC power (for example, three-phase AC power) to the motor M. For example, each switch Q _R , Q _S , Q _T , Q _U , Q _V , Q _W in the inverter circuit 2 is converted from the three-phase currents i _u , i _v , i _w shown by solid line arrows in FIG. To turn on / off at a predetermined timing.

  That is, when the microcomputer 1 shown in FIG. 1 detects that the output current from the inverter circuit 2 to the motor M constantly exceeds the three-phase full-wave rectified current value and exceeds the current limit level, the microcomputer 1 The output of AC power to the motor M is cut off to prevent overcurrent. This function is called an H / W current limiting function.

  The detector 7 detects the voltage (or current) at the node N5 between the power supply node N1 and the inverter circuit 2 to stop the supply of DC power to the inverter circuit 2 (occurrence of a power failure) and to the inverter circuit 2. DC power supply return (end of power failure) is detected. The detector 7 supplies the detection result to the microcomputer 1. In response to this, the microcomputer 1 recognizes the stop of supply of DC power to the inverter circuit 2.

  Next, the operation of the control device 100 when the supply of DC power to the inverter circuit 2 is stopped, that is, when a power failure occurs will be described with reference to FIG.

  At timing t1, when the microcomputer 1 receives the detection result of the occurrence of a power failure from the detector 7, the microcomputer 1 performs control associated with the occurrence of the power failure. That is, when the occurrence of a power failure is detected by the detector 7, the microcomputer 1 supplies the inverter circuit 2 with a PWM command CM2 for starting an operation (second operation) for attenuating the residual voltage of the motor M. To do. Thereby, the inverter circuit 2 starts an operation for attenuating the residual voltage of the motor M.

Specifically, the inverter circuit 2 turns on a plurality of switches in either one of the upper arm and the lower arm at the same time. For example, the switches Q _U , Q _V , and Q _W in the lower arm 2 b in the inverter circuit 2 are simultaneously turned on so that a short-circuit current indicated by a dashed arrow in FIG.

  Further, when the occurrence of a power failure is detected by the detector 7, the microcomputer 1 changes the current limit level to be used for the comparison operation by the current comparison circuit 5 from Ith1 (first value) to Ith2 (second value). change. Ith2 is lower than Ith1 and higher than zero. Thereby, the current comparison circuit 5 compares whether or not the full-wave rectified current value is equal to or greater than Ith1 immediately before the occurrence of the power failure (immediately before the timing t1), and after the occurrence of the power failure (timing t1 to t1). (period t2), it is compared whether or not the full-wave rectified current value is equal to or greater than Ith2.

If the microcomputer 1 determines that the magnitude of the current vector (i _u , i _v , i _w ) is greater than or equal to the current limit level Ith2 from the comparison result by the current comparison circuit 5 after the occurrence of the power failure, In the same manner as before the generation, a PWM command CM1 for stopping the output operation (first operation) of AC power is supplied to the inverter circuit 2. Thereby, the inverter circuit 2 stops the operation of outputting AC power to the motor M.

  At this time, the motor M is in a free-running state, but has a residual voltage, so that a short-circuit current indicated by a broken-line arrow in FIG. 2 flows through the nodes N2 to N4. The current detector 3 shown in FIG. 1 detects this short-circuit current (current vector) flowing through the nodes N 2 to N 4 and supplies the detection result to the current comparison circuit 5 via the three-phase full-wave circuit 6. The current comparison circuit 5 compares the short circuit current (the magnitude of the current vector) with the current limit level Ith2, and supplies the comparison result to the microcomputer 1.

  When it is determined from the comparison result by the current comparison circuit 5 that the short-circuit current (the magnitude of the current vector) is equal to or higher than the current limit level Ith2, the microcomputer 1 stops the AC power output operation (first operation) ( The PWM command CM1 for interrupting the PWM output is continuously supplied to the inverter circuit 2. As a result, the inverter circuit 2 continues to stop the operation of outputting AC power to the motor M. At this time, the short circuit current flowing through the nodes N2 to N4 is reduced due to the loss in the motor M, and the residual voltage of the motor M is also attenuated.

  At timing t2, when the microcomputer 1 determines from the comparison result by the current comparison circuit 5 that the short-circuit current (the magnitude of the current vector) is smaller than the current limit level Ith2, the microcomputer 1 resumes output of AC power (first operation). It enters a standby state for generating a PWM command CM1 for causing (PWM output cutoff release). That is, the microcomputer 1 prepares for outputting the PWM command CM1 for resuming the output of the AC power to the motor M (preparation for releasing the PWM output cutoff).

  On the other hand, when it is determined from the comparison result by the current comparison circuit 5 that the short circuit current (the magnitude of the current vector) is smaller than the current limit level Ith2, the microcomputer 1 operates to attenuate the residual voltage of the motor M (second PWM command CM2 for stopping the operation is supplied to the inverter circuit 2. Thereby, the inverter circuit 2 stops the operation for attenuating the residual voltage of the motor M.

Specifically, the inverter circuit 2 turns off any of the plurality of switches that were turned on in either the upper arm or the lower arm. For example, all the switches Q _U , Q _V , and Q _W that have been turned on in the lower arm 2 b in the inverter circuit 2 are turned off.

  Furthermore, when the microcomputer 1 receives the detection result of the end of the power failure from the detector 7, the microcomputer 1 performs control associated with the end of the power failure.

  At timing t3, the microcomputer 1 determines that the short-circuit current (the magnitude of the current vector) is smaller than the current limit level Ith2 from the comparison result by the current comparison circuit 5, and detects the end of the power failure by the detector 7. The short-circuit current detected by the current detector 3 (the frequency of the residual voltage of the motor M is obtained from the current vector (frequency search is executed). At the same time, the microcomputer 1 uses the current limit level to be used by the current comparison circuit 5. Is returned from Ith2 (second value) to Ith1 (first value), so that the current comparison circuit 5 returns to a state of comparing whether or not the full-wave rectified current value is equal to or greater than Ith1.

Then, the microcomputer 1 restarts the output of AC power (first operation) so that the frequency of the AC power to be output to the motor M matches the frequency of the residual voltage of the motor M obtained as described above (PWM output). PWM command CM1 is generated for releasing the cutoff. The microcomputer 1 supplies the generated PWM command CM1 to the inverter circuit 2 (execution of PWM output cutoff cancellation). Thereby, the inverter circuit 2 restarts the operation of outputting AC power (for example, three-phase AC power) to the motor M. For example, each switch Q _R , Q _S , Q _T , Q _U , Q _V , Q _W in the inverter circuit 2 is converted from the three-phase currents i _u , i _v , i _w shown by solid line arrows in FIG. Is turned on / off at a predetermined timing (PWM switching is performed).

  Next, an operation flow in the control device 100 will be described with reference to FIG.

  In step ST1, the microcomputer 1 determines whether there is a restart setting for an instantaneous power failure and whether an instantaneous power failure has occurred. When the microcomputer 1 receives the detection result of the occurrence of the power failure from the detector 7, the microcomputer 1 determines that an instantaneous power failure has occurred. When the microcomputer 1 does not receive the detection result of the occurrence of the power failure from the detector 7, the instantaneous power failure has occurred. Judge that there is no. If there is a restart setting and a power failure occurs (YES in ST1), the microcomputer 1 proceeds to ST2, and if there is no restart setting or a power failure does not occur (NO in ST1), the processing proceeds to ST4. Proceed.

  In step ST2, the microcomputer 1 supplies the inverter circuit 2 with a PWM command CM2 for starting an operation (second operation) for attenuating the residual voltage of the motor M. Thereby, the inverter circuit 2 starts an operation for attenuating the residual voltage of the motor M.

Specifically, the inverter circuit 2 turns on a plurality of switches in either one of the upper arm and the lower arm at the same time. For example, the switches Q _U , Q _V , and Q _W in the lower arm 2 b in the inverter circuit 2 are simultaneously turned on so that a short-circuit current indicated by a dashed arrow in FIG.

  Here, as described above, the purpose of simultaneously turning on the lower arm (or upper arm) three phases of the inverter circuit 2 is to form a closed circuit as shown in FIG. It is to make it.

  In step ST3, the microcomputer 1 changes the current limit level to be used for the comparison operation by the current comparison circuit 5 from Ith1 (first value) to Ith2 (second value). Ith2 is lower than Ith1 and higher than zero. As a result, the current comparison circuit 5 compares whether or not the full-wave rectified current value is equal to or greater than Ith2.

In step ST4, the current comparison circuit 5 receives the full-wave rectified current value from the three-phase full-wave circuit 6, and receives the current limit level (threshold) from the microcomputer 1. The current comparison circuit 5 compares the full-wave rectified current value with the current limit level and outputs the comparison result to the microcomputer 1. The microcomputer 1 receives a comparison result between the current value subjected to full-wave rectification and the current limit level from the current comparison circuit 5. The microcomputer 1 determines whether or not the magnitude of the current vector (i _u , i _v , i _w ) detected from the comparison result by the current comparison circuit 5 is equal to or greater than the current limit level.

  Here, if NO in ST1, the current limit level is Ith1 (first value). If YES in ST1, the current limit level is Ith2 (second value) smaller than Ith1. Yes.

If the magnitude of the detected current vector (i _u , i _v , i _w ) is equal to or greater than the current limit level (YES in ST4), the microcomputer 1 proceeds to ST5 and detects the detected current vector (i _u , I _v , i _w ) is smaller than the current limit level (NO in ST4), the process proceeds to ST6.

  In step ST5, the microcomputer 1 supplies the inverter circuit 2 with a PWM command CM1 for stopping the output operation (first operation) of AC power (PWM output cutoff). Thereby, the inverter circuit 2 stops the operation of outputting AC power to the motor M.

In step ST <b> 6, if NO in ST <b> 1, the microcomputer 1 supplies the inverter circuit 2 with a PWM command CM <b> 1 for resuming output (first operation) of AC power (PWM output cutoff release). Thereby, the inverter circuit 2 restarts the operation of outputting AC power (for example, three-phase AC power) to the motor M. For example, each switch Q _R , Q _S , Q _T , Q _U , Q _V , Q _W in the inverter circuit 2 is converted from the three-phase currents i _u , i _v , i _w shown by solid line arrows in FIG. To turn on / off at a predetermined timing.

  Alternatively, if YES in ST1, the microcomputer 1 enters a standby state for generating a PWM command CM1 for resuming output of AC power (first operation) (PWM output cutoff release). That is, the microcomputer 1 prepares for outputting the PWM command CM1 for resuming the output of the AC power to the motor M (preparation for releasing the PWM output cutoff).

  In step ST7, if the microcomputer 1 is NO in ST1, the process proceeds to ST8.

  Alternatively, the microcomputer 1 supplies the inverter circuit 2 with a PWM command CM2 for stopping the operation (second operation) for attenuating the residual voltage of the motor M when YES is determined in ST1. Thereby, the inverter circuit 2 stops the operation for attenuating the residual voltage of the motor M.

Specifically, the inverter circuit 2 turns off any of the plurality of switches that were turned on in either the upper arm or the lower arm. For example, all the switches Q _U , Q _V , and Q _W that have been turned on in the lower arm 2 b in the inverter circuit 2 are turned off.

  In step ST8, the microcomputer 1 determines whether there is a restart setting for an instantaneous power failure and whether an instantaneous power failure has occurred. If there is a restart setting and a power failure has occurred (YES in ST8), the microcomputer 1 proceeds to ST9, and if there is no restart setting or no power failure has occurred (NO in ST8), the processing ends. .

  In step ST9, when the microcomputer 1 determines from the comparison result by the current comparison circuit 5 that the short circuit current (the magnitude of the current vector) is smaller than the current limit level Ith2, and the end of the power failure is detected by the detector 7. The short-circuit current detected by the current detector 3 (the frequency of the residual voltage of the motor M is obtained from the current vector (frequency search is executed).

  In step ST10, the microcomputer 1 returns the current limit level to be used by the current comparison circuit 5 from Ith2 (second value) to Ith1 (first value). As a result, the current comparison circuit 5 returns to a state of comparing whether or not the full-wave rectified current value is equal to or greater than Ith1.

In step ST11, the microcomputer 1 restarts the output of the AC power (first operation) so that the frequency of the AC power to be output to the motor M matches the frequency of the residual voltage of the motor M obtained as described above ( PWM command CM1 is generated for PWM output cutoff cancellation). The microcomputer 1 supplies the generated PWM command CM1 to the inverter circuit 2 (execution of PWM output cutoff cancellation). Thereby, the inverter circuit 2 restarts the operation of outputting AC power (for example, three-phase AC power) to the motor M. For example, each switch Q _R , Q _S , Q _T , Q _U , Q _V , Q _W in the inverter circuit 2 is converted from the three-phase currents i _u , i _v , i _w shown by solid line arrows in FIG. Is turned on / off at a predetermined timing (PWM switching is performed).

  Here, suppose that the current limit level is maintained at a value Ith101 equivalent to Ith1 even if the occurrence of a power failure is detected by the detector 7, as indicated by a one-dot chain line in FIG. In this case, it is determined that the residual voltage of the motor M is attenuated at timing t102 when the residual voltage of the motor M is not attenuated to a level sufficient to suppress the overcurrent. In this state, when an output voltage is output from the inverter circuit 2 to the motor M, a large current (overcurrent) flows through the inverter circuit 2 if there is a large difference in phase and amplitude between the residual voltage and the output voltage. As a result, the control device 100 suddenly changes the d-axis current and the q-axis current, so that the current control of the frequency search is not successful, and the wrong rotation frequency is obtained.

  On the other hand, in the embodiment, as indicated by a broken line in FIG. 3, the H / W current limiting function is supplied when power is supplied by lowering the current limiting level during detection of the residual voltage from Ith1 to Ith2 after an instantaneous power failure. Operate at a lower level and detect short circuit current decay (residual voltage decay) without excessive current flow. In other words, the full-wave rectified current of the three-phase current is compared with the current limit level, and if the current limit level is exceeded, the H / W current limit function is used to shut down the output voltage. Simultaneously turn on the three phases of the arm (or upper arm). When it is determined that the residual voltage of the motor is attenuated, the output cut-off is canceled and the frequency search is started. Accordingly, it can be determined that the residual voltage of the motor M has attenuated at the timing t2 when the residual voltage of the motor M has attenuated to a level sufficient to suppress the overcurrent. Therefore, it is possible to improve the accuracy when suppressing the overcurrent flowing through the inverter circuit after the occurrence of a power failure. As a result, since the frequency search is performed in a state where the residual voltage is attenuated, it is possible to obtain an accurate rotational frequency for the residual voltage of the motor, and an alternating current having a frequency determined to match the accurate rotational frequency. Electric power can be output to the motor to smoothly restart the motor. That is, it is possible to provide a motor control device that can safely restart and continue operation.

  Alternatively, suppose that the current limit level is maintained at a value Ith102 equivalent to Ith2 even before the occurrence of a power failure or after returning to the power supply state, as indicated by a two-dot chain line in FIG. In this case, in spite of no overcurrent flowing through the inverter circuit 2, the inverter circuit 2 always outputs excessive power to the inverter circuit in a state where the inverter circuit 2 outputs AC power for driving the motor M to a predetermined condition. It is determined that current is flowing. As a result, an accurate overcurrent suppressing operation cannot be performed before the occurrence of a power failure or after returning to the power supply state.

  In contrast, in the embodiment, as indicated by a broken line in FIG. 3, the current limit level is set to Ith1 before the occurrence of a power failure, and the current limit level is returned from Ith2 to Ith1 after returning to the power supply state. ing. Thereby, the H / W current limiting function is operated at a level suitable for the power supply state, and the motor M can be driven in a state where no excessive current flows in the inverter circuit 2. As a result, an accurate overcurrent suppression operation can be performed before the occurrence of a power failure or after returning to normal operation. That is, it is possible to improve the accuracy when suppressing the overcurrent flowing through the inverter circuit before the occurrence of a power failure or after returning to the power supply state.

Alternatively, suppose that the current vector (i _u , i _v , i _w ) flowing in the nodes N2 to N4 between the inverter circuit 2 and the motor M is not detected after the occurrence of a power failure is detected. In this case, a time obtained by adding a margin to the expected time required for the residual voltage of the motor M to naturally decay to zero is set as a waiting time until the frequency search is started. In this case, since a waiting time longer than necessary is set, the free-run speed of the motor M drops to near zero during that time, and it takes time until the motor M restarts and returns to the original frequency.

On the other hand, in the embodiment, after the occurrence of a power failure is detected, a current vector (i _u , i _v , i _w ) flowing in the nodes N2 to N4 between the inverter circuit 2 and the motor M is detected, The detected current vector (i _u , i _v , i _w ) is compared with the current limit level Ith2. Then, it can be determined that the residual voltage of the motor M is attenuated at timing t2 when the residual voltage of the motor M is greater than zero and the residual voltage of the motor M is attenuated to a level sufficient to suppress overcurrent. Therefore, the waiting time until the start of the frequency search can be shortened within a range sufficient to suppress the overcurrent, and the motor M can be restarted before the free run speed of the motor M drops to near zero.

  As described above, the induction motor control device according to the present invention is useful for control when restarting an induction motor in a free-run state.

1 microcomputer 2 inverter circuit 2a on the arm 2b lower arm 3 a current detector 5 current comparator circuit 6 3-phase full-wave circuit 7 detector 100 controller M motor _{Q R, Q S, Q T} , Q U, Q V, Q W switch

Claims (4)

A power converter that performs a first operation of converting supplied DC power into AC power and outputting the AC power to the induction motor;
A first detection unit for detecting a current vector flowing in a node between the power conversion unit and the induction motor;
A comparison unit that compares the magnitude of the current vector detected by the first detection unit with a threshold;
When it is determined from the comparison result by the comparison unit that the magnitude of the current vector is greater than or equal to the threshold value, the first operation by the power conversion unit is stopped, and the current vector is calculated based on the comparison result by the comparison unit. When it is determined that the size is smaller than the threshold value, a control unit that controls the power conversion unit to resume the first operation by the power conversion unit;
A second detection unit that detects a supply stop of the DC power to the power conversion unit;
With
The control unit starts a second operation by the power conversion unit for attenuating the residual voltage of the induction motor when the supply stop of the DC power is detected by the second detection unit, and The threshold value to be used by the comparison unit is changed from a first value to a second value lower than the first value, and the magnitude of the current vector is determined to be smaller than the threshold value from the comparison result by the comparison unit. In the case, the induction motor control device is characterized in that the second operation by the power converter is stopped. The power conversion unit includes an upper arm and a lower arm each having a plurality of switches,
The induction motor control device according to claim 1 , wherein the second operation is an operation of simultaneously turning on the plurality of switches in one of the upper arm and the lower arm. The second detection unit detects supply return of the DC power to the power conversion unit,
The control unit determines from the comparison result by the comparison unit that the magnitude of the current vector is smaller than the threshold value, and the second detection unit detects the return of supply of the DC power to the power conversion unit. If so, the frequency of the residual voltage of the induction motor is obtained from the current vector detected by the first detection unit, and the threshold value to be used by the comparison unit is determined from the second value to the first value. the return, the control apparatus for an induction motor according to claim 1 or 2, characterized in that to resume the first operation by the power converting unit. In the power conversion unit, performing a first operation of converting the supplied DC power into AC power and outputting the AC power to the induction motor;
Detecting a current vector flowing in a node between the power converter and the induction motor;
Comparing the magnitude of the current vector detected by the first detector with a threshold;
When it is determined from the comparison result by the comparison unit that the magnitude of the current vector is greater than or equal to the threshold value, the first operation by the power conversion unit is stopped, and the current vector is calculated based on the comparison result by the comparison unit. If the magnitude is determined to be smaller than the threshold, controlling the power converter to resume the first operation by the power converter;
Detecting the supply stop of the DC power to the power converter;
With
The controlling step includes
If the DC power supply stop is detected in the step of detecting the DC power supply stop, starting the second operation by the power converter for attenuating the residual voltage of the induction motor;
Changing the threshold to be used in the comparing step from a first value to a second value lower than the first value;
A step of stopping the second operation by the power converter when it is determined from the comparison result in the comparing step that the magnitude of the current vector is smaller than the threshold;
An induction motor control method characterized by comprising:

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