JPH06245565A - Regenerative controller for voltage-type inverter - Google Patents

Abstract

PURPOSE:To make it possible to protect an inverter from an overcurrent in a DC circuit during regenerative operation. CONSTITUTION:In a regenerative controller, the change rate of a regenerative current command (IREF) or a limit of regenerative current is restricted only at the time in which the thylistor converter 2 is changed from forward conversion to backward conversion in order to decelerate an induction motor 5. By this means, a rise in charging voltage can be restricted by controlling a charging current for a DC smoothing capacitor 7, and consequently, a failure of overvoltage in a DC circuit can be prevented during the regenerative operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regenerative control device for a voltage source inverter which controls an induction motor at a variable speed.

[0002]

2. Description of the Related Art As a control device for a voltage source inverter, a first converter that operates as a forward converter during power running and outputs a DC voltage of a constant value, and a second converter that operates as an inverse converter during regenerative operation. A thyristor converter, a DC smoothing capacitor connected in parallel to the DC side of the thyristor converter, and a voltage type for converting the DC power from the first converter into AC power to control the induction motor at a variable speed. An inverter circuit, a speed control means for calculating a current command to make the deviation between the motor speed and the speed command zero, and a means for controlling the output voltage and frequency of the voltage source inverter circuit based on the current command. A control device for a voltage source inverter device is known.

FIG. 4 shows an inverter main circuit of this type and a conventional control device for controlling it.

The main circuit of the apparatus shown in FIG. 4 comprises an AC power source 1 arranged in order from the power source side to the load side, a thyristor converter 2 consisting of a pair of unit thyristors connected in anti-parallel on the DC side, and a DC smoothing capacitor 3. , Voltage source inverter circuit 4,
And an induction motor (IM) 5. A current detector 6 is provided to detect the motor current, a voltage detector 7 is provided to detect the DC circuit voltage, and a speed detector (SS) 8 is provided to detect the motor speed. .

A voltage control circuit (AVR) 31 is provided to keep the DC circuit voltage detected by the voltage detector 7 at a constant value.
The thyristor converter 2 is phase-controlled by the regenerative discharge control circuit 41 via the regenerative discharge resistor 42 between the DC terminals of the inverter circuit 4 for the regenerative control performed in cooperation with the inverter circuit 4. There is.

The speed control of the induction motor 5 is performed through the frequency control of the inverter circuit 4. The motor speed detected by the speed detector 8, that is, the speed feedback amount N _FBK is compared with the speed command N _REF given from the speed setter 11, and it is made zero based on the deviation, that is, the speed deviation (= N _REF −N _FBK ). The speed control circuit (ASR) 14 calculates a current command I _REF for _{changing the} speed. This current command I
_{Based on REF} and the velocity feedback amount N _FBK , the vector control circuit (VEQ) 15 causes the magnetizing current command I on the polar coordinate axis.
_{Calculate DREF} and current command I _QREF . The motor current detected by the current detector 6 is the current detection circuit (CD) 1
8 is decomposed into a magnetizing current component and a torque current component, and the respective current components are current control circuits 16D and 16Q.
The voltage commands V _D and V _Q for reducing the respective deviations (current deviations) to zero are obtained via. PWM control of the output voltage and output frequency of the inverter circuit 4 is performed via the PWM circuit 17 based on the voltage commands V _D and V _Q.

Variable speed control of the induction motor 5 in the apparatus of FIG. 4 is performed according to a well-known method. Here, in the context of the present invention, the operation when the inverter circuit 4 is in the regenerative operation state will be described.

When the induction motor 5 is decelerated, the regenerative current of the inverter circuit 4 is accumulated in the DC smoothing capacitor 3 and its terminal voltage, that is, the DC circuit voltage rises. On the other hand, since the thyristor converter 2 provided for converting the AC power of the AC power supply 1 into the DC power has the ability to control the DC circuit voltage at a constant level via the voltage control circuit 31, the DC circuit voltage rises. In this case, the power regeneration operation is performed to suppress the voltage rise. The thyristor converter 2 becomes uncontrollable due to the switching operation when switching from the forward conversion for supplying electric power to the inverter circuit 4 to the reverse conversion for regenerating the regenerative current from the inverter circuit 4 to the power supply circuit 1. During this time, the DC circuit voltage continues to rise, which may eventually lead to an overvoltage failure.

Conventional measures for preventing device failure due to overvoltage will be described with reference to FIGS. 4 and 5.

(1) First, in FIG. 4, when the voltage type inverter device for variable speed control of the induction motor 5 is in the regenerative operation state, the regenerative energy is accumulated in the DC smoothing capacitor 3 and the DC circuit voltage rises. Keep doing The DC circuit voltage is monitored by the regenerative discharge control circuit 41, and when the voltage exceeds a certain specified voltage, the regenerative discharge resistor 42 is connected in parallel to the DC smoothing capacitor 3 to charge the DC smoothing capacitor 3 with regenerative discharge resistance. The consumption by the device 42 prevents an inverter device failure due to overvoltage during regenerative operation.

(2) Secondly, as shown in FIG. 5, the capacitance of the DC smoothing capacitor 3 is adjusted instead of the regenerative discharge resistor. The apparatus of FIG. 5 includes a regenerative discharge control circuit 4
1 and the regenerative discharge resistor 42 are not provided. Also in this device, the phenomenon that the DC circuit voltage rises is the same as in the device of FIG. The speed at which the DC circuit voltage rises in the regenerative operation state is inversely proportional to the capacity of the smoothing capacitor 3 provided in the DC circuit. Therefore, the maximum value of the regenerative power regenerated from the induction motor 5 is obtained and the thyristor conversion is performed. The DC smoothing capacitor 3 has a sufficiently large capacity so that the overvoltage failure does not occur during the time until the device 2 completes the forward / reverse switching, thereby preventing the inverter device failure due to the overvoltage during regeneration.

[0012]

The above-mentioned measures for preventing overvoltage during regenerative operation have the following drawbacks, respectively.

The disadvantage of the device of FIG. 4 is that the regenerative discharge control circuit 4
1 and the regenerative discharge resistor 42 are provided, the cost is high, and the regenerative discharge resistor 42 having a sufficiently large capacity is required in consideration of the frequency of the regenerative operation. In addition, the drawbacks of the countermeasure described with reference to FIG. 5 are that the capacity of the DC smoothing capacitor becomes extremely large and uneconomical, and if the regenerative power becomes larger than the originally designed value, The need arises to add capacitors.

An object of the present invention is to prevent a DC circuit overvoltage during regenerative operation of a voltage source inverter device without special circuit design, provision of a regenerative discharge resistor, or increase of capacitor capacity as described above. To provide a means of protection against

[0015]

SUMMARY OF THE INVENTION A regenerative controller for a voltage type inverter device according to the present invention makes a determination based on a speed command and a current command when switching from a power running operation to a regenerative operation due to deceleration of an induction motor. Regenerative judgment means,
According to the judgment output of the regeneration judging means, a suppressing means for suppressing the current command is provided only during the time when the thyristor converter switches from the first converter to the second converter. is there.

The above-mentioned suppressing means can be configured to suppress the time change rate or the limit value of the current command.

[0017]

When the induction motor is decelerated, the rate of change of the regenerative current command of the inverter control circuit or the regenerative current limit value is suppressed only during the time when the thyristor converter switches from the forward conversion to the reverse conversion. It is possible to suppress the charging current and the charging voltage, thereby preventing a DC circuit overvoltage failure during regeneration.

[0018]

Embodiments of the present invention include a first method of limiting the rate of change of a current command for a certain period of time during regenerative operation and a second method of reducing the regenerative current limit value for a certain period of time during regenerative operation. Therefore, each embodiment will be described below in order.

First, the first embodiment will be described.

The main circuit of FIG. 1 is the same as that of FIG.
The feature of this embodiment resides in the front part of the vector control circuit 15 in the control device part. That is, the current change rate limiting circuit 21 is interposed between the speed control circuit 14 and the vector control circuit 15, and the current change rate limiting circuit 21 is further provided.
The device of FIG. 1 is characterized in that a regenerative judging device 12 and a delay circuit 13 are provided for controlling the above. The operation mode of this device during the power running operation (non-regenerative operation) is the same as that shown in FIG. 3 or 4.

The speed feedback amount N _FBK detected by the speed detector 8 is the speed command N given from the speed setter 11.
_It is compared with _REF and the deviation (speed deviation) is input to the speed control circuit 14. Based on this speed deviation, the speed control circuit 14 forms a current command I _REF for making it zero. The current command I _REF passes through the current change rate limiting circuit 21 and is decomposed by the vector control circuit 15 into an exciting current command I _DREF and a current command I _QREF on the polar coordinate axis.
On the other hand, the current feedback amount on the rotating shaft detected by the current detector 6 is decomposed by the current detection circuit 18 into the exciting current feedback amount I _DFBK and the torque current feedback I _QFBK on the polar coordinate axis, and compared with each current command. After that, the deviation (current deviation) of each current control circuit 16D, 16Q
Entered in. The current deviations of the respective current control circuits 16D,
The magnetic flux axis voltage command V _D and the torque axis voltage command V _Q are generated by 16Q, converted from the voltage command on the polar coordinates to the voltage command on the rotating coordinates via the PWM circuit 17, and converted into a pulse for driving the inverter circuit 4. , Control the inverter circuit 4.

[0022] Now, lowering the speed command N _REF to provide the speed setter 11, to the speed command N _REF speed feedback amount _{N FBK, | N REF | <} | N FBK | ... becomes a relationship (1), induced The electric motor 5 shifts from the electric motor operation until then to the generator operation, and the energy of the mechanical system charges the DC smoothing capacitor 3 through the inverter circuit 4 and is regenerated as electric energy. This regenerative energy is proportional to the load moment of inertia and the rate of change of speed. If the regenerative energy continues to charge the DC smoothing capacitor 3, an overvoltage is generated, which causes a failure of the inverter device.

Therefore, according to the present invention, the speed setter 11
Paying attention to the time change rate Δ | N _REF | / Δt of the absolute value of the speed command N _REF when the setting of is decreased, this is negative, or the current command I _REF that is the output of the speed control circuit 14 is The regenerative judging device 12 judges whether the power-switching mode is switched to the regenerative mode and is increasing, and the delay circuit 13 is used for a fixed time until the thyristor converter 2 completes the forward / reverse switching and becomes the regenerative operation. 21 regenerative current change rate (di /
dt) to lower the rate of increase of the current command. By doing so, the charging current of the smoothing capacitor 3 can be suppressed and the increase of the charging voltage can be suppressed. When the thyristor converter 2 finishes switching to regenerative operation,
The DC circuit voltage is lowered to a predetermined voltage value by the voltage control circuit 31 to prevent overvoltage failure.

Next, a second embodiment will be described with reference to FIG.

The features of the control device of FIG. 2 are the same. A feature of this embodiment is that a current limiting circuit 22 is provided between the speed control circuit 14 and the vector control circuit 15 to suppress the regenerative current itself, thereby preventing an overvoltage fault. Also in this embodiment, attention is paid to the rate of change Δ | N _REF | / Δt of the absolute value of the speed command N _REF when the speed command N _REF given from the speed setter 11 is lowered, and whether this is negative, Alternatively, whether the current command I _REF, which is the output of the speed control circuit 14, switches from powering to regeneration and is increasing is determined by the regeneration determining device 12, and the delay circuit 1
3 is used to reduce the regenerative current limit value by the current limiting circuit 22 for a certain period of time until the thyristor converter 2 completes the forward / reverse switching and becomes the regenerative operation, and the regenerative current command is suppressed. By doing so, the charging current of the smoothing capacitor 3 can be suppressed and the increase of the charging voltage can be suppressed. Also,
When the thyristor converter 2 finishes switching to the regenerative operation, the DC circuit voltage is lowered to a predetermined voltage value by the voltage control circuit 31 to prevent overvoltage failure.

The present invention has been described above with respect to two embodiments, but it is also possible to employ only one of the two embodiments, and the thyristor converter 2 completes the forward / reverse switching and becomes the regenerative operation operation. In the first half of the constant time until, the regenerative current change rate (di / dt) is lowered by using the current change rate limiting circuit 21 of the first embodiment (FIG. 1), and the remaining time is set to the second It is also possible to use both embodiments together by a method of switching depending on the time zone, such as lowering the regenerative current limit value using the current limiting circuit 22 of the embodiment (FIG. 2).

In the above embodiment, the case where one inverter circuit is provided for one thyristor converter has been described, but as shown in FIG. 3, a plurality of inverter circuits 4A are provided in a common DC circuit. , 4B, 4C are also connected, by providing the same circuit element as that shown in FIG. 1 or FIG. 2 in each inverter device, the same action and effect as described above in each inverter device, that is, regenerative operation It is possible to achieve the action and effect that the regenerative energy can be temporarily suppressed at the time of switching and the overvoltage failure that occurs when the regenerative current is accumulated in the smoothing capacitor of the DC circuit at the time of deceleration can be prevented. In the embodiment of FIG. 3, a plurality of inverter circuits are divided by adding A, B and C to the basic code 4, and the control devices for controlling the respective inverter circuits 4A, 4B and 4C are respectively coded 20A and 20B. , 20C. Similarly, other circuit elements are also represented by adding the reference symbols A, B, and C corresponding to the inverter circuit to the same reference symbols as in FIG.

[0028]

As described above, according to the present invention, in the voltage type inverter device for variable speed control of the induction motor, the thyristor converter switches from the forward conversion operation to the reverse conversion operation during deceleration of the induction motor. By reducing the rate of change (di / dt) of the regenerative current command of the inverter control circuit or reducing the regenerative current limit value only for the time to perform, the regenerative energy is temporarily suppressed, and the regenerative current during deceleration is It is possible to prevent an overvoltage failure caused by being accumulated in the smoothing capacitor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a control device according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the control device according to the present invention.

FIG. 3 is a connection diagram showing a modified example to which the present invention is applied.

FIG. 4 is a block diagram showing an example of a conventional voltage source inverter device and its control device.

FIG. 5 is a block diagram showing another configuration example of a conventional voltage source inverter device.

[Explanation of symbols]

 1 AC power supply 2 Thyristor converter 3 DC smoothing capacitor 4 Inverter circuit 5 Induction motor 6 Current detector 7 Voltage detector 8 Speed detector 11 Speed setting device 12 Regenerative judgment device 13 Delay circuit 14 Speed control circuit 16 Current control circuit 17 PWM Circuit 18 Current control circuit 21 Current change rate limiting circuit 22 Current limiting circuit 31 Voltage control circuit

Claims (3)

[Claims] 1. A thyristor converter comprising a first converter that operates as a forward converter during power running and outputs a constant DC voltage, and a second converter that operates as a reverse converter during regenerative operation, and A DC smoothing capacitor connected in parallel to the DC side of the thyristor converter, a voltage source inverter circuit for converting the DC power from the first converter into AC power to control the induction motor at a variable speed, the motor speed and A voltage-type inverter device comprising speed control means for calculating a current command for making a deviation between speed commands zero, and means for controlling an output voltage and a frequency of the voltage-type inverter circuit based on the current command. Of the regenerative control device, the judgment is made based on the speed command and the current command when the power running mode is switched to the regenerative mode by deceleration of the induction motor. And a suppressing means for suppressing the current command only during the time when the thyristor converter switches from the first converter to the second converter according to the judgment output of the regeneration judging means. A regenerative control device for a voltage type inverter device characterized by the above. 2. The regeneration control device for a voltage source inverter device according to claim 1, wherein the suppressing means suppresses a time change rate of the current command. 3. The apparatus according to claim 1, wherein the suppressing unit suppresses a limit value of the current command.
Regenerative controller for voltage source inverter.