JPH07274530A - Controller of ac motor - Google Patents

Abstract

PURPOSE:To continue operation unless there is a problem in a main circuit even if a dc short occurs, when an ac motor is driven by a voltage-type inverter. CONSTITUTION:This equipment is provided with a shorting means 43 and a recovery voltage detecting means 27. The shorting means 43 stops the control operation of a converter section 12 and an inverter section 14 and shorts the dc voltage through a reactor 42 and then causes half-wave resonance current to flow in the capacitor 15 and reverses the polarity of the voltage of the capacitor when the discharging current of a capacitor 15 exceeds a specified level. Due to the reverse voltage of the capacitor, half-wave resonance current flows in a free-wheel diode 14c and an anode reactor 14a of the inverter section and the voltage of the capacitor gets back to the normal polarity. It is the recovery voltage detecting means 27 which outputs a recovery signal when a specified period of time has passed after the normal polarity of the voltage of the capacitor is recovered. Then, when the recovery signal is output, the converter section and the inverter section starts control operation again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor control apparatus equipped with a voltage source inverter for converting a DC voltage into an AC voltage to drive an AC motor, and in particular, an excessive current flows due to a short circuit or the like. At times, the present invention relates to a control device for an AC electric motor, which protects the device and continues the operation.

[0002]

2. Description of the Related Art A control device for an AC motor used in a public utility facility, such as a cooling pump for a power generation plant and a water supply / sewerage water supply pump, is required to operate with high reliability. FIGS. 4A and 4B show a conventional device in which a control unit of this type is duplicated.

In FIG. 4 (a), a main circuit section 10 includes a circuit breaker 11, a converter section 12, a reactor 13, and an inverter section.
A current source inverter consisting of 14 is constructed to drive the AC motor 30. The control unit 20 is composed of a speed commander 21, control units 22 and 23, switching operation units 24 and 25, and a switching unit 26, and operation is performed by one of the control units and the other control unit is kept in a standby state. . When a failure occurs in the control unit during operation, the switching operation units 24 and 25 operate to switch to the other control unit and continue the operation. In the case of this conventional example, current control can be performed so that an excessive current does not flow when a DC short circuit fault occurs.

However, as shown in FIG. 4B, the main circuit portion 10
When configuring a voltage source inverter having a capacitor 15, the DC short circuit current cannot be suppressed. in this case,
A short-circuiting device 16 for shunting the short-circuit current flowing through the inverter unit 14 is provided to protect the switch element of the inverter unit.

In this way, when the control section is duplicated, generally, when a failure occurs, the control section in operation is stopped, and after resetting the failure detection, the control section is switched to the waiting control section to restart the operation. To be taken.

There are various kinds of faults and detection means, but for example, an overcurrent fault is detected within the withstand capacity (turn-off capability in the case of GTO) of the main circuit element and the protection is stopped in order to stop the protection. It is possible to switch to the control unit of the standby system and restart without checking the soundness. However, in the case of a DC short-circuit fault in the voltage source inverter, a current exceeding the withstand capacity (turn-off capability in GTO) of the main circuit element flows, so the method of providing the short-circuiter 16 is adopted as described above. . Even when the short circuiter is provided, the main circuit element is not always sound in the case of a DC short circuit failure caused by the control signal. Therefore, when a DC short-circuit failure occurs, there is a concern that the failure of the main circuit device such as an element may spread, so it is common practice not to restart the standby control unit.

[0007]

As described above, in a device which is required to have high reliability and which is used in a public utility facility, a DC short circuit failure occurs even if the control section is duplicated and the operation is continued as much as possible. It was sometimes difficult to continue operating the system, which was a problem in constructing a highly reliable system.

The present invention has been made in view of the above points. When the AC motor is driven by the voltage type inverter, the main circuit condition is monitored and restarted even when a DC short circuit failure occurs, and the operation is restarted. It is an object of the present invention to provide a highly reliable control device for an AC electric motor that continues the above.

[0009]

In order to achieve the above object, the present invention provides a converter for converting an alternating current into a direct current and outputting a direct current voltage smoothed by a capacitor, and an alternating voltage having a variable frequency. The following means is provided in the device provided with the inverter part for converting into AC drive and driving the AC electric motor.

According to a first aspect of the present invention, when the discharge current of the capacitor exceeds a predetermined value, the control operation of the converter section and the inverter section is stopped, and the positive and negative sides of the DC voltage are passed through a reactor. A short-circuiting means for inverting the polarity of the voltage of the capacitor by short-circuiting a half-wave resonance current, and the voltage of the inverted capacitor via the freewheel diode and anodic reactor in the inverter section. A recovery voltage detecting means is provided for outputting a recovery signal when a half-wave resonance current flows to recover a voltage of a normal polarity and a predetermined time has passed, and when the recovery signal is output, the converter section is provided. And restart the control operation of the inverter section.

According to a second aspect of the present invention, when the discharge current of the capacitor exceeds a predetermined value, the control operation of the converter section and the inverter section is stopped, and all the switch elements in the inverter section are turned off. Inverted with a short-circuit means for conducting and short-circuiting between the positive and negative of the DC voltage through an anodic reactor connected in series with the switching element, and causing a half-wave resonance current to flow to invert the polarity of the voltage of the capacitor. Due to the voltage of the capacitor, a half-wave resonance current flows through the freewheel diode and anodic reactor in the inverter section, recovers the voltage of the normal polarity, and recovers when a predetermined time has elapsed. Providing recovery voltage detection means for outputting a signal,
When the recovery signal is output, the control operation of the converter unit and the inverter unit is restarted.

According to a third aspect of the present invention, further, at least two control units for controlling the converter unit and the inverter unit are provided.
One of the control units controls the converter unit and the inverter unit, and when the recovery signal is output, the other control unit is switched to.
Restart the control operation of the inverter section and inverter section.

[0013]

According to the first aspect of the present invention, when a direct current short circuit occurs via the switch element in the inverter section and the discharge current of the capacitor exceeds a predetermined value, the short circuit means operates and the short circuit from the capacitor is performed via the reactor. A half-wave resonance current flows, the polarity of the voltage of the capacitor is reversed, and when the maximum voltage is reached, the half-wave of the half wave is reversed in the reverse direction via the freewheel diode and anodic reactor in the inverter section. A resonance current flows and the polarity of the voltage of the capacitor returns to the original polarity.

At this time, if the switch element in the inverter section has recovered the insulation, the current of the capacitor becomes zero and the voltage becomes constant. The recovery voltage detecting means determines that the inverter section is normal when this state has passed for a predetermined time, outputs a recovery signal, and restarts the operation of the apparatus.

According to a second aspect of the present invention, when a DC short circuit occurs in an arbitrary phase via the switch element in the inverter section and the discharge current of the capacitor exceeds a predetermined value, the short circuit means operates to cause the inverter. A half-wave resonant current flows from the capacitor through the anodic reactors of all phases in the inverter section, the polarity of the capacitor voltage reverses, and the freewheel diode in the inverter section starts when the maximum voltage is reached. -Do and Ano-
Half-wave resonance current flows in the opposite direction through the reactor,
The polarity of the capacitor voltage returns to the original polarity.

At this point, if the switch element in the inverter section has recovered the insulation, the current of the capacitor becomes zero and the voltage becomes constant. The recovery voltage detecting means determines that the inverter section is normal when this state has passed for a predetermined time, outputs a recovery signal, and restarts the operation of the apparatus.

According to a third aspect of the present invention, at least two sets of control units of the apparatus are further provided, and one of the control sections operates the apparatus, and when a DC short circuit occurs and a recovery signal is output, a standby state occurs. The operation of the device is restarted by the other control unit in the state.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment corresponding to claim 1 and claim 3 of a control device for an AC motor according to the present invention. In FIG. 1, a main circuit section 10 is a converter 12 that converts an alternating current into a direct current through a circuit breaker 11 and outputs a direct current voltage smoothed by a reactor 13 and a capacitor 15. This direct current voltage is an alternating voltage of a variable frequency. To an inverter 14 for driving the AC motor 30 and a current detector 41 for detecting the current of the capacitor 15,
When the output signal of the short circuiter 16 and the current detector 41, which is composed of a thyristor or the like for shorting the positive and negative sides of the DC voltage via the reactor 42, exceeds a predetermined value, the short circuiter 16 is operated and a fault signal s ₁ is output. A detector 43 and a level detector 44 that outputs a determination signal a when the DC voltage is equal to or higher than a predetermined positive value are provided.

The control circuit 20 includes a speed commander 21 for giving a target speed of the AC motor 30, control units 22, 23 for controlling the main circuit unit 10, and an operation unit for instructing the operation and stop of the control units 22, 23. 24, 25, a switching unit 26 for selectively outputting one of the control outputs of the control units 22, 23, and a recovery voltage detecting means 27 for outputting a recovery signal s ₂ in response to the failure signal s ₁ and the judgment signal a. Composed.

In the above structure, the converter 12 and the inverter 14 are controlled by either one of the control units 22 and 23 via the switching unit 26, and the other control unit is in a standby state. For example, the operation command b is output from the operation unit 24, the converter 12 and the inverter 14 are controlled by the control unit 22, and the AC motor is controlled.
The current ic flowing in the capacitor 15 when driving 30
Is a ripple current due to the reactive current component of the inverter output, as shown in FIG.

Here, due to an abnormality of the control unit 22 or the like,
When a DC short circuit occurs via the switch 14, the discharge current of the capacitor 15 increases rapidly and the short circuit detector 43 operates to close the short circuit 16 at the time t ₀ when the current exceeds a predetermined current.
₁ is output to stop the output of the operation command b of the operation unit 24.
As a result, the supply of electric power from the converter 12 is stopped, and the discharge current ic due to the charge charged in the capacitor 15 is parallel to the current flowing through the switch element in the short-circuited phase and the reactor 42.
And the resonance current flows through the
Rapidly decreases and becomes a negative voltage with the polarity reversed, and at time t
_{At 1} , the output signal a of the level detector 44 becomes 0. The resonance current is that in the reactor 42 flows diverted becomes a resonance current of a half-wave as shown between t ₀ -t ₂ of FIG. 2 by the rectifier action of the short circuit 16, at time t ₂ the voltage Vd of the capacitor of the negative Maximum voltage. From this time t _{2, the} anodic reactor 14a and the freewheel diode 14a in the inverter 14 are
The resonance current ic flows due to the inverted charge of the capacitor 15 via c and the voltage of the capacitor is restored to the positive voltage again, and the output signal a of the level detector 44 becomes 1 at the time t ₃ . Inverter during the negative period of the voltage Vd at the time t ₂ after the capacitor - if the forward voltage isolation of the switching element 14b of the motor 14 is restored, the time t ₄ when the resonance current of the negative half-wave is finished flows
After that, the capacitor current ic becomes zero and becomes constant at the recovered positive voltage. A certain period of time T this state from the time t ₃
At the time point t ₅ when d has elapsed, the recovery signal s ₂ is output from the recovery voltage detection means 27, the operation command c is output via the operation section 25, the control section 23 in the standby state starts the control operation, and the control section 23 is started via the switching section 26. Restart the operation of the converter 12 and the inverter 14.

When a thyristor is used as the short circuiter 16, the inductance of the anodic reactor is such that the period t ₂ -t ₄ of the half-wave resonance current due to the capacitor 15 is twice the turn-off time of the thyristor. It should be set to be sufficiently large so that it is surely turned off during the negative voltage period of Vd after t ₂ .

A second embodiment of the present invention is shown in FIG. In the second embodiment, all the ignition means 45 for conducting all the switch elements of the inverter 14 according to the command are provided, and the short circuit detector is provided.
Reference numeral 43 is an example in which the short circuiter 16 and the reactor 42 are omitted by giving a command to all the ignition means 45. In this configuration, when positive and negative switching elements of any phase of the inverter 14 are simultaneously turned on to cause a DC short circuit, and the discharge current of the capacitor 15 exceeds a predetermined current, the short circuit detector 43 operates and all points The arc command is output and the inverter is output via all ignition means 45.
All the switching elements of 14 are turned on to stop the operation of the converter 12 and the inverter 14. As a result, the current of the short-circuited phase is shunted to the normal phase, a half-wave resonance current flows through the anodic reactor 14a of each phase, and the voltage of the capacitor 15 is inverted. Further, a negative half-wave resonance current flows through the freewheel diode 14c to restore the voltage of the capacitor 15 to the normal polarity. In this case, if all the switching elements of the inverter 14 have recovered forward voltage insulation, capacitors
The voltage of 15 becomes constant as it is, and the recovery signal s ₂ is output from the recovery voltage detecting means 27 when a predetermined time has elapsed, and the operation of the converter 12 and the inverter 14 is restarted in the same manner as described above.

In the above description, the example in which the control unit is duplicated has been shown, but the present invention can be applied to the one for performing normal control having only one control unit. In this case, it goes without saying that only the DC short circuit caused by factors other than control is protected.

[0025]

According to the present invention, when a DC short circuit occurs in any phase of the voltage source inverter, the device is stopped for a short time to protect the switch element of the short circuit phase from overcurrent. , When the forward voltage insulation of the switch element is restored,
The operation of the device can be restarted, and a control device for an AC motor with high operational reliability can be obtained.

Further, when the control section is duplicated and the operation of the apparatus is restarted, it is possible to switch to another control section, and it is possible to provide a control apparatus for an AC motor with high control reliability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claim 1 and claim 3 of the present invention.

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

FIG. 3 is a configuration diagram of a second embodiment corresponding to claims 2 and 3 of the present invention.

FIG. 4 is a configuration diagram of a conventional device, in which (a) is a current source inverter.
(B) uses a voltage source inverter

[Explanation of symbols]

10 ... Main circuit section 11 ... Breaker 12 ... Converter 13 ... DC reactor 14 ... Inverter 15 ... Capacitor 16 ... Short circuiter 20 ... Control circuit 21 ... Speed commander 22, 23 ... Control section 24, 25 ... Operation Part 26 ... Switching part 27 ... Recovery voltage detecting means 41 ... Current detector 42 ... Short-circuiting reactor 43 ... Short-circuiting detector 44 ... Level detector 45 ... All ignition means

Claims (3)

[Claims] 1. A converter section for converting AC into DC and outputting a DC voltage smoothed by a capacitor, and an inverter section for converting the DC voltage into an AC voltage of a variable frequency to drive an AC motor. In the device, when the discharge current of the capacitor exceeds a predetermined value, the control operation of the converter unit and the inverter unit is stopped, the positive and negative of the DC voltage are short-circuited via a reactor, and a half-wave resonance occurs. A half-wave resonant current flows through the freewheel diode and the anodic reactor in the inverter section by the short-circuiting means for applying a current to reverse the polarity of the voltage of the capacitor and the inverted voltage of the capacitor. A recovery voltage detecting means for outputting a recovery signal when a predetermined time elapses after the voltage is recovered to a normal polarity, and when the recovery signal is output, the converter unit and the inverter are Controller for an AC motor, characterized in that to resume the control operation of the motor unit. 2. A converter section for converting AC into DC and outputting a DC voltage smoothed by a capacitor, and an inverter section for converting the DC voltage into an AC voltage having a variable frequency and driving an AC motor. In the device, when the discharge current of the capacitor exceeds a predetermined value, the control operation of the converter section and the inverter section is stopped, all the switch elements of the inverter section are made conductive, and the switch element and Short-circuit means for short-circuiting between the positive and negative sides of the DC voltage through an anodic reactor connected in series, and flowing a half-wave resonance current to reverse the polarity of the voltage of the capacitor,
Due to the inverted voltage of the capacitor, a half-wave resonance current flows through the freewheel diode and the anodic reactor in the inverter section, and is restored to the normal polarity voltage.
An alternating current characterized by providing recovery voltage detection means for outputting a recovery signal when a predetermined time has elapsed, and restarting the control operation of the converter part and the inverter part when the recovery signal is output. Electric motor controller. 3. The control device for an AC electric motor according to claim 1, further comprising at least two sets of control units for controlling the converter unit and the inverter unit,
One of the control units controls the converter unit and the inverter unit, and when the recovery signal is output, the control unit switches to the other control unit to convert the converter unit and the inverter unit. A control device for an AC electric motor, which restarts the control operation of 1.