JPH1042590A - Voltage-type inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide complete restart, even after stopping as a result of capacitor voltage reaching an overvoltage condition. SOLUTION: When a running signal RUN is turned on by a restart command and restart by current limit control begins through a current limit command S1 outputted from a comparator 28, a signal S2 is outputted from an off delay timer 31. A one-shot timer 33 is operated at a fixed time after a timer counter 32 starts counting, so that a converter 10 and an inverter 13 are stopped for a short time to conduct such control as a phase reference θr is synchronized again with the phase of the voltage Vm of an AC motor 14. The running signal RUN is turned on again to repeat the restarting operation by current limit control. After a prescribed time of a one-shot timer 29 started by a restart command has passed, current limit control is released to restore it to ordinary operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-source inverter for driving an AC motor, and more particularly to an improvement of a voltage-source inverter having a restart function for restarting the operation promptly when stopped for some reason during operation. .

[0002]

2. Description of the Related Art As a voltage source inverter for driving an AC motor, an inverter shown in FIG. 5 is used. This voltage type inverter converts a commercial voltage into a DC voltage by a converter 10, smoothes the DC voltage with a reactor 11 and a capacitor 12, and converts the smoothed DC voltage into an AC voltage of a variable frequency variable voltage by an inverter 13. The AC motor 14 is driven at a variable speed.

[0003] The control operation of this voltage source inverter will be briefly described below. The speed reference Sr set by the setting unit 15 is input to the rate-of-change limiting circuit 16, and the frequency reference Fr corresponding to the speed reference Sr is output. This frequency reference Fr is converted to a voltage reference by the function generation circuit 17 and is converted as a voltage reference Vr via the primary delay circuit 30 to the voltage control circuit 1.
8 is input. The voltage control circuit 18 compares the voltage reference Vr with the voltage Vc of the capacitor 12 detected by the voltage detector 19, outputs a phase reference, controls the ignition phase of the converter 10 via the phase control circuit 20, Capacitor 12
Is controlled to a value corresponding to the voltage reference Vr.

On the other hand, the frequency reference Fr is converted into a phase reference θr for controlling the phase of the output voltage of the inverter 13 by the integrator 21, and the pulse distribution circuit 22 controls the inverter 13 based on the output voltage phase reference θr. Output a gate signal. The inverter 13 is constituted by a self-turn-off type switch element such as a gate turn-off thyristor or a transistor, and is controlled by the gate signal to change the DC voltage of the capacitor 12 at a frequency corresponding to the frequency reference Fr and a phase corresponding to the phase reference θr. And output. By controlling in this way,
The AC motor 14 is supplied with an AC voltage having an amplitude corresponding to the voltage reference Vr and a frequency corresponding to the frequency reference Fr, and is controlled at a variable speed. Such a control method is also called a PAM control method.

[0005] Inverters used in important facilities such as power plants are restarted by instantaneous power failure, transient overcurrent, overvoltage, etc., and restarted by instantaneous power failure recovery, automatic reset of failure, etc. to operate. Is required to be continued. FIG.
Has a restart function proposed in consideration of such a case (Japanese Patent Application No. Hei 6-118818), and its operation will be described below with reference to FIG.

When an instantaneous stop or a failure is detected at time t1, the operation signal RUN is turned off, and the converter 10 and the inverter 1 are turned off.
The control of Step 3 is stopped, and the AC motor 14 is brought into a free-run state. When the operation signal RUN is turned off, the input signal of the rate-of-change limiting circuit 16 changes from the speed reference Sr to the PLL circuit 24.
, And the input signal of the primary delay circuit 30 is changed from the output signal of the function generation circuit 17 to the voltage detector 23,
It is switched to the motor voltage Vm detected via the rectifier circuit 26. The PLL circuit 24 compares the output voltage phase reference θr with the phase of the motor voltage Vm detected by the voltage detector 23, controls the frequency reference Fr so that the phase difference becomes zero, and sets the frequency reference Fr in a free-run state. And synchronizes with the rotation speed Nm. In this case, the change rate limiting circuit 16 operates as a proportional amplifier.

When the operation signal RUN is turned on at time t2 due to recovery from a momentary power failure or automatic reset of a failure, the rate-of-change limiting circuit 1
6 and the input signal of the primary delay circuit 30 are switched to the original state, and the control of the converter 10 and the inverter 13 is restarted. Converter 10 is the AC motor 1 at this time.
The control is resumed at the voltage reference Vr corresponding to the rotation speed Nm (frequency reference Fr) of the fourth motor.
Since the voltage Vc is maintained at the charging voltage immediately before the stop, the voltage Vc is higher than the voltage reference Vr. The control of the inverter 13 is restarted in a state where the output voltage phase is synchronized with the induced voltage phase of the AC motor 14 with the frequency reference Fr corresponding to the rotation speed Nm of the AC motor 14 at this time. Further, when the operation signal RUN is turned on by the restart, the one-shot timer 29 operates and the predetermined time T
When the output of the comparator 28 is input to the pulse distribution circuit 22 by 0, and the motor current Im detected by the current detector 25 exceeds the current limit value IL set by the setting unit 27, the current limit command from the comparator 28 is issued. S1 is output, and the output current of the inverter 13 is limited. In this manner, the capacitor 12 is controlled while the current limiting control is being performed for a certain time T0 so that an excessive discharge current does not flow from the capacitor 12 to the AC motor 14.
And the capacitor voltage Vc is changed to the frequency reference Fr.
After returning to the value corresponding to (voltage reference Vr), the current limiting control was canceled and restarted.

[0008]

However, in the above-mentioned conventional device, when the voltage Vc of the capacitor 12 becomes excessively high and stops due to some reason, it may not be possible to restart the capacitor.
This will be described below.

Now, when the frequency reference Fr, the motor voltage Vm, and the capacitor voltage Vc are both operating at 100%, the voltage Vc of the capacitor 12 is changed to the voltage Vc of the capacitor 12 at time t1 for some reason such as control abnormality of the converter 10 or the like. It is assumed that an overvoltage occurs as shown in the figure, the abnormality is detected, and the operation signal RUN is turned off. In this case, as described above, control of converter 10 and inverter 13 is stopped, AC motor 14 is in a free-run state, rotation speed Nm is reduced, PLL circuit 24 operates, and frequency reference Fr follows rotation speed Nm. And drop. The motor voltage Vm also decreases from the overvoltage state in accordance with the rotation speed Nm, but since the exciting magnetic flux gradually decreases, the motor voltage Vm rapidly decreases at a reduction rate larger than the rotation speed Nm. During this time, the capacitor voltage Vc is maintained in an overvoltage state. Then, at time t2, when the operation signal RUN is turned on and restarted, the one-shot timer 29 operates as described above to perform the current limiting control for a fixed time T0, and the inverter 28 receives the current limiting command S1 output from the comparator 28. 13 while limiting the output current of capacitor 13 to frequency reference Fr (voltage reference V
r), the control of the current limit is released and the restart is performed. In this case, since the charge of the capacitor 12 is released from the overvoltage state, the capacitor voltage Vc is reduced within the predetermined time T0. Frequency reference Fr (voltage reference Vr
), And during this time, the output voltage phase of the inverter 13 gradually deviates from the synchronous speed of the AC motor 14, the reactive current component increases, the predetermined torque cannot be secured, and the AC motor 14 is in a stall state. There is a problem that it may not be possible to restart.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has as its object to provide a voltage-source inverter that can be reliably restarted even when the capacitor voltage Vc is stopped due to an overvoltage state.

[0011]

In order to achieve the above object, a voltage type inverter according to the present invention comprises a converter for converting an AC voltage of a constant frequency into a DC voltage, a capacitor for smoothing the DC voltage, and a capacitor. An inverter that converts the DC voltage into a desired AC voltage and drives an AC motor; a voltage control unit that controls the converter by comparing a voltage reference and a voltage detection value of the capacitor; and a phase reference based on a frequency reference. Frequency control means for controlling the inverter based on the phase reference, and when the converter and the inverter are stopped during operation, the phase reference is synchronized with the voltage phase of the AC motor. Means, and voltage reference control means for causing the voltage reference to follow the voltage of the AC motor, and restarting the converter and the inverter. Then, after performing current limiting control for limiting the output current of the inverter to a predetermined current for a predetermined time, stopping the converter and the inverter for a short time and performing control for synchronizing the phase reference with the voltage phase of the AC motor. And then restart control means for canceling the current limit control and returning to the normal operation. Further, the restart control means starts counting when the converter and the inverter are restarted by a command, operates a one-shot timer after a predetermined time, and stops the converter and the inverter for a short time. A timer counter for performing control to synchronize the phase reference with the voltage phase of the AC motor. (Claim 2) Further, the restart control means cancels the current limiting control a predetermined time after the restart and returns to the normal operation. (Claim 3) Further, when the voltage of the capacitor falls below a predetermined value with respect to the voltage reference, the restart control means releases the current limiting control and returns to the normal operation. (Claim 4) The restart control unit further includes a voltage determination unit that determines whether a difference between a voltage detection value of the capacitor and the voltage reference is equal to or less than a predetermined value. When the difference between the voltage detection value of the capacitor and the voltage reference is equal to or greater than a predetermined value, counting is started, and after a certain period of time, the one-shot timer is operated, and the converter and the inverter are stopped for a short period of time. A timer counter for synchronizing a reference with a voltage phase of the AC motor. (Claim 5)

[0012]

FIG. 1 shows an embodiment of a voltage source inverter according to claims 1 to 3 of the present invention. In FIG. 1, reference numeral 31 denotes an off-delay timer which outputs a signal S2 when a current limit command S1 is input, 32 denotes a timer counter which outputs a signal S3 after a lapse of a predetermined time T1 from the time when the signal S2 is input, and 33 denotes a signal S3 Is a one-shot timer that outputs a signal for turning off the operation signal RUN for a fixed time T2 from the point in time when is input. The other components are the same as those of the related art (FIG. 3), and are denoted by the same reference numerals.

The operation of this embodiment will be described below with reference to FIG. Now, for some reason, an abnormality occurs in the control on the converter side, and the capacitor voltage Vc becomes an overvoltage.
When the operation signal RUN is turned off at
Then, the control of the inverter 13 is stopped, the motor current Im supplied to the AC motor 14 becomes zero, and a free-run state is established, and the rotation speed Nm decreases at a deceleration rate determined by the torque and inertia of the load. When the operation signal RUN turns off,
The PLL circuit 24 operates, and the frequency reference Fr follows the phase of the induced voltage of the AC motor 14, and as a result, the frequency reference Fr follows the rotation speed Nm of the AC motor 14. Further, the input of the primary delay circuit 30 is switched from the output signal of the function generating circuit 17 to the detected voltage Vm of the AC motor 14, and the voltage reference Vr input to the voltage control circuit 18 follows the induced voltage Vm of the AC motor 14. I do. AC motor 14
Is gradually attenuated in the free-run state, so that the motor voltage Vm (induced voltage) rapidly decreases at a decreasing rate higher than the rotation speed. Therefore, the voltage reference Vr is much lower than the frequency reference Fr. Since there is no circuit for discharging the capacitor voltage Vc, the overvoltage state is maintained.

Thereafter, when the operation signal RUN is turned on at time t2 due to automatic reset of the failure, etc., the rate-of-change limiting circuit 1
6 and the input signal of the primary delay circuit 30 are switched to the original state, and the control of the converter 10 and the inverter 13 is restarted. Converter 10 is the AC motor 1 at this time.
The control is resumed at the voltage reference Vr corresponding to the rotation speed Nm (frequency reference Fr) of FIG.
2, the voltage Vc is much higher than the voltage reference Vr. Further, the inverter 13 has a frequency reference Fr corresponding to the rotation speed Nm of the AC motor 14 at this time.
Then, the control is resumed in a state where the output voltage phase is synchronized with the induced voltage phase of the AC motor 14, and the discharge current starts flowing from the capacitor 12 to the AC motor 14 due to the difference voltage between the capacitor voltage Vc and the induced voltage Vm of the AC motor 14. The electric charge of the capacitor 12 is released as driving energy of the AC motor 14, and the capacitor voltage Vc starts to decrease.

When the operation signal RUN is turned on by the restart, the one-shot timer 29 is operated, and the output of the comparator 28 is input to the pulse distribution circuit 22 for a predetermined time T0, and is detected by the current detector 25. When the set motor current Im exceeds the current limit value IL set by the setter 27, a current limit command S1 is output from the comparator 28 and the inverter 13
Is temporarily stopped, and the motor current Im becomes the current limit value I
When the value decreases to L or less, the output of the current limit command S1 disappears and the control is started again, the current limit control of pulse width modulation based on the instantaneous current comparison is performed, and the restart is started with the inrush current reduced.

In this case, the current limit command S1 is repeatedly turned on and off in a pulse shape. The off-delay timer 31 is set to be turned off with a delay time longer than the on-off cycle. A signal S2 in a continuous state is output. When the signal S2 is output,
The timer counter 32 starts counting clock pulses of a fixed period, and after a lapse of a certain time T1, outputs a signal S3 to operate the one-shot timer 33, and the time T2
Only the operation signal RUN is turned off. Therefore, as shown in FIG. 2, when the restart is started, after the operation is performed while performing the current limiting control for a certain time T1, the control for stopping the operation for a certain time T2 is repeatedly performed.

In this case, the fixed time T1 is within a range in which the output voltage phase of the inverter 13 gradually deviates from the synchronous speed of the AC motor 14 during the restart due to the current limitation, and the torque decreases. The constant time T2 is set to a time required for the PLL circuit 24 to synchronize the output voltage phase reference θr with the voltage phase of the AC motor 14. By making the control response time of the phase synchronization control fast, the fixed time T2 can be shortened.

By performing such control, the ineffective component of the output current of the inverter 13 is reduced, and the electric charge of the capacitor 12 is quickly released as the driving energy of the AC motor 14, and the capacitor voltage Vc within a certain time T0.
Can be reduced to the voltage reference Vr corresponding to the rotation speed Nm of the AC motor 14 (frequency reference Fr). Therefore, when the one-shot timer 29 releases the current limiting control after a predetermined time T0, it is possible to reliably generate a predetermined torque and restart the vehicle without stalling.
FIG. 2 shows an example in which a predetermined time T0 is reached during the second current limit control.

FIG. 3 shows an embodiment of a voltage source inverter according to the fourth and fifth aspects of the present invention. In FIG. 3, reference numeral 34 denotes a comparator which compares the voltage reference Vr with the capacitor voltage Vc and outputs a non-active signal S4 when the voltage difference (Vc-Vr) becomes smaller than a predetermined value. Others are the same as those in FIG. 1 and are indicated by the same reference numerals. However, the current limit command S1 output from the comparator 28 is an operation signal when the signal S4 is in the ON (active) state and the restart is performed.
RUN is input to the pulse distribution circuit on condition that it is in the ON state, and the timer counter 32 determines that the signal S4 is in the ON (active) state and that the operation signal
The clock pulse count is started on condition that the signal is in the ON state, and the signal S5 is output after a predetermined time T1.

The operation of this embodiment will be described below with reference to FIG. In this embodiment, when the capacitor voltage Vc is higher than the voltage reference Vr by a predetermined voltage or more, the output signal S4 of the comparator 34 is turned on (active). S6
Becomes 1 and the current limit command S1 output from the comparator 28
Is input to the pulse distribution circuit 22, the current limiting control described above is performed, and restart is started. At the same time, the timer counter 32 starts counting clock pulses, and for a certain time T
After one, the signal S5 is output. The one-shot timer 33 turns off the operation signal RUN for a predetermined time T2 from the time when the signal S5 is output, during which the control of the converter 10 and the inverter 13 is stopped, the PLL circuit 24 is operated, and the synchronous control of the frequency reference Fr is performed. Is performed. In addition, the output signal S5 of the one-shot timer 33 causes the timer counter 32
Is cleared, and the comparator 3
If the output signal S4 is ON, clock pulse counting is started again and the same operation is repeated. Thus, every time the starting operation is performed by the current limiting control, the capacitor 1
2 is released, the capacitor voltage Vc decreases, and when the voltage difference between the capacitor voltage Vc and the voltage reference Vr becomes equal to or less than a predetermined value, the output signal S4 of the comparator 34 is turned off (non-active) and the signal S6 Becomes 0, the current limit command S1 input to the pulse distribution circuit 22 is stopped, the current limit is released, and the operation returns to the normal operation. FIG. 4 shows the relationship between the capacitor voltage Vc and the voltage reference V during the second current limit control.
An example is shown where the voltage difference of r drops below a predetermined value. According to this embodiment, it is possible to restart in the shortest time according to the value of the capacitor voltage at the time of stopping during operation.

[0021]

According to the present invention, when the operation is stopped and restarted for some reason during driving of the AC motor, it is possible to surely restart the motor in a short time without stalling even if the capacitor voltage is high. It is possible to provide a voltage-source inverter capable of performing such operations.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a voltage source inverter according to claims 1 to 3 of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a configuration diagram of an embodiment of a voltage source inverter according to claims 4 and 5 of the present invention.

FIG. 4 is a waveform chart for explaining the operation of the embodiment.

FIG. 5 is a configuration diagram of a conventional voltage source inverter.

FIG. 6 is a waveform chart for explaining a problem of the conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Converter 11 ... Reactor 12 ... Capacitor 13 ... Inverter 14 ... AC motor 15 ... Setting device (Sr setting) 16 ... Change rate limiting circuit 17 ... Function generation circuit 18 ... Voltage control circuit 19 ... Voltage detector (Vc detection) 20 ... Phase control circuit 21 ... Integrator 22 ... Pulse distribution circuit 23 ... Voltage detector (Vm detection) 24 ... PLL circuit 25 ... Current detector (Im detection) 26 ... Rectifier circuit 27 ... Setter (IL setting) 28 ... Comparison Unit (Im, Ic comparison) 29 One-shot timer (T0) 30 Primary delay circuit 31 Off-delay timer 32 Timer counter (T1) 33 One-shot timer (T2) 34 Comparator (Vc, Vr comparison)

Claims (5)

[Claims] 1. A converter for converting an AC voltage having a constant frequency into a DC voltage, a capacitor for smoothing the DC voltage,
An inverter that converts the smoothed DC voltage to a desired AC voltage and drives the AC motor, a voltage control unit that controls the converter by comparing a voltage reference and a voltage detection value of the capacitor, and based on a frequency reference. Frequency control means for generating a phase reference and controlling the inverter based on the phase reference, wherein the phase reference is synchronized with the voltage phase of the AC motor when the converter and the inverter are stopped during operation. Current limiting control comprising: synchronous control means; and voltage reference control means for causing the voltage reference to follow the voltage of the AC motor, and when the converter and the inverter are restarted, the output current of the inverter is limited to a predetermined current. After a predetermined time, the converter and the inverter are stopped for a short time, and the phase reference is set to the voltage of the AC motor. Performs control to synchronize the phase, then the voltage inverter, characterized in that it includes a restart control means to release the current limit control to return to normal operation. 2. The voltage-source inverter according to claim 1, wherein said restart control means starts counting when said converter and said inverter are restarted, activates a one-shot timer after a lapse of a predetermined time, and only operates for a short time. A voltage type inverter comprising: a timer counter for stopping the converter and the inverter and performing control for synchronizing the phase reference with the voltage phase of the AC motor. 3. The voltage-source inverter according to claim 1, wherein said restart control means releases the current limiting control after a predetermined time from the restart and returns to a normal operation. . 4. The voltage-source inverter according to claim 1, wherein said restart control means cancels current limiting control when the voltage of said capacitor falls below a predetermined value with respect to said voltage reference. A voltage-source inverter characterized by returning to normal operation. 5. The voltage type inverter according to claim 4, wherein said restart control means determines whether a difference between a detected voltage value of said capacitor and said voltage reference is equal to or less than a predetermined value. Means, restarting the converter and the inverter, when the difference between the voltage detection value of the capacitor and the voltage reference is greater than or equal to a predetermined value, start counting, operate a one-shot timer after a certain time, and A voltage type inverter comprising a timer counter for stopping a converter and an inverter and synchronizing the phase reference with a voltage phase of the AC motor.