JPH08266059A - Power converter - Google Patents

Abstract

PURPOSE: To reduce switching loss and also feed back the regenerated current with one current control by keeping one of the transistor of a phase, where the absolute value becomes maximum out of three-phase AC voltage, on, and PWM-controlling the transistor of the other phase, according to the DC current held as a sample. CONSTITUTION: In the case of converting AC into DC, it is converted into DC by the diodes d1 -d6 of a converter 1. On the other hand, in the case of regenerating the regenerative power from an inverter circuit to the side of AC power source, block data are made from three-phase AC voltage by a comparator 8, and the selection of transistor T21 -T26 corresponding to the block and the setting of switches 9 and 10 are performed, and ON/OFF control is performed by a PWM control circuit 5. Here, one transistor of the phase where the phase voltage becomes maximum out of the transistors T21 -T26 is kept on, and also Tr of the other phase is controlled, according to the DC current value obtained through a sample and hold circuit 2, so as to perform feedback control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device,
In particular, the present invention relates to a power conversion device including a converter that generates a DC power supply for an inverter that drives a motor and regenerates electric power.

[0002]

2. Description of the Related Art A DC power supply generated by a power converter equipped with a converter capable of reversible conversion using a transistor is used as a DC power supply of an inverter for variable speed operation of a motor used as a drive source of a machine tool. To be done. In this type of power converter, the operating energy of the motor can be regenerated to the AC power source when the motor is decelerated. However, in recent years
It has become a problem that when a regenerative current with a large amount of distortion is regenerated to an AC power source, it adversely affects other machines such as malfunction. Therefore, in order to solve such problems,
Conventionally, the power converter shown in FIG. 5 has been used, and it has been put into practical use to regenerate a sinusoidal current with little distortion. In the power converter shown in FIG. 5, the DC voltage Vdc generated by the converter 1 is converted into AC by the inverter circuit. A variable speed operation of the AC motor is performed by the converted AC. The three-phase alternating current input to and output from the converter 1 is insulated and detected via the current detector 14. The AC current input / output based on this detected value is feedback-controlled so as to be a sine wave.

The operation of the control circuit within the dotted line shown in FIG. 5 will be described. A target voltage of the DC voltage Vdc charged in the smoothing capacitor 2 is set in the reference voltage source 21, and the target voltage and the DC voltage Vdc are set in the subtractor 19.
Is subtracted from the detected value to obtain a voltage deviation signal. The voltage deviation signal is amplified by the amplifier 18, and the amplified voltage deviation signal is input to the vector rotator 15.
The vector rotator 15 generates a sine wave current command having the same phase as the three-phase AC power supply voltage. That is, the isolator 3
The line voltage waveform of the three-phase AC voltage detected via the converter is converted into a phase voltage waveform by the converter 22, and then the phase voltage waveform is multiplied by the output of the amplifier 18, and a sine wave current command is output. . This current command is subtracted from the value detected through the current detector 14 in the subtractor 17, and the subtracted value is amplified by the amplifier 23 and then input to the PWM control circuit 20. In the PWM control circuit 20, the command signal is pulse-width modulated by the carrier signal, and an ON / OFF control signal for the transistor is created. This P
The operation of the WM control circuit 20 is generally used for the control circuit of the inverter circuit, and detailed description thereof will be omitted. By the operation of these circuits, the current flowing through the converter 1 is feedback-controlled according to the sine wave current command output from the vector rotator 15, and the current flowing through each phase is shaped into a sine wave. Further, the choke coil 7 inserted between the AC power supply and the converter 1 smoothes the ripple of the AC current input / output by the switching of the converter 1, and the shaping closer to a sine wave is performed.

[0004]

In the above-described conventional power converter, the alternating current of each phase input to and output from the converter 1 is detected, and the feedback control is performed based on this detection. Therefore, a plurality of current detection means are required, and as a result, the power conversion device becomes expensive. Also,
In order to perform the sine wave regeneration, the transistor of the converter 1 needs to be constantly switched at high speed, so that the transistor generates heat due to switching loss. The present invention has been made to solve the above problems, and the present invention is
It is an object of the present invention to provide an inexpensive power conversion device that can minimize loss and realize regenerative current with less distortion by feedback control of one current detector.

[0005]

In order to solve the above problems, according to the present invention, a plurality of combinations of a transistor and a diode connected in antiparallel to the transistor are configured, and a converter for PWM-controlling the plurality of transistors is input. In a power converter that reversibly converts a three-phase AC voltage into a DC voltage according to the AC voltage command, a unit for detecting a DC current output from the converter, and a DC current depending on the DC voltage output from the converter. A means for generating a command; a means for detecting a magnitude relationship between the three-phase AC voltages connected to the converter; and a first switch for selecting a phase having a maximum absolute value in the three-phase AC voltage based on the detection of the magnitude relationship. And a second switch for selecting two phases other than the first switch, and an AC voltage detection for the phase selected by the first switch. Means for generating an alternating current command from the value and the direct current command, means for sampling / holding the direct current detection value at the timing when the triangular wave of the triangular wave carrier signal is at the apex, and the sampled / holded direct current detection Current error amplifying means for outputting an AC voltage command according to a value and the AC current command, and one transistor of the converter in the phase selected by the first switch is always kept in the ON state, and the second switch A transistor connected to the two phases selected by means of means is PWM-controlled by the AC voltage command and the triangular wave carrier signal to perform ON / OFF control.

[0006]

In the power converter according to the present invention, the magnitude relationship of the three-phase AC voltage connected to the converter is detected, and one transistor of the converter is in the ON state for a certain period of time, so that the number of times of switching can be reduced and the switching loss is reduced. Can be suppressed. In the power conversion device according to the present invention, the DC current output from the converter is further sampled / held at the timing when the triangular wave of the carrier signal reaches the apex, and a current equal to the current flowing through the transistor held in the ON state is detected. An AC current command is generated from the DC current command corresponding to the DC voltage and the AC voltage detection value of the phase held in the ON state. That is, the current command corresponding to the current desired to flow to the transistor held in the ON state is compared with the sampled / held current value, and the transistors connected to two phases other than the phase connected to the transistor held in the ON state are turned ON. Control can be performed while correcting the / OFF signal. Therefore, feedback control can be realized with one current detector.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, elements given the same reference numerals as the elements shown in FIG. 5 have the same functions, and the description will be duplicated, so the description thereof will be omitted. FIG. 1 is a block circuit diagram of an example of a power conversion device according to the present invention.
First, in the case of converting electric power from alternating current to direct current (during power running), the diodes d1 to d constituting the converter 1 are formed.
By the action of 6, the AC voltage is converted without control, the smoothing capacitor 2 is charged, and the DC voltage Vdc is generated. Current flowing in each phase of the AC power supply at this time (iR, iS, iT)
Has the waveform shown in FIG. Further, when the AC motor is decelerated, the DC voltage Vdc rises due to the electric power regenerated from the inverter circuit side, but at this time, the diodes d1 to d6 are in the reverse blocking state and the electric power is not regenerated to the AC power source side.

Therefore, the transistors Tr1 to Tr6 are controlled to regenerate the AC power supply. The operation of the control circuit within the dotted line shown in FIG. 1 will be described below. The control circuit in the dotted line is realized by using a microprocessor,
The operation of this control circuit can be easily realized by software. First, the line voltage of the three-phase power supply voltage is detected via the isolator 3. The comparator 8 determines the magnitude relationship of the voltages, and one cycle of the power supply voltage is 6 as shown in FIG.
It is divided into two sections. Based on this section data, the transistors and switches 9 and 10 corresponding to the section are selected, and the PWM control circuit 5 performs ON / OFF control. Further, the converter 6 performs a process of converting the line voltage into a phase voltage, and outputs a voltage command for each phase. The voltage regenerated from the AC side of the converter 1 only by this voltage command is equal to the power supply voltage.

The reference voltage 21 sets a target value of the DC voltage Vdc, and an allowable value is set for the breakdown voltage of the element used in the converter 1 or the breakdown voltage of the inverter. The subtractor 19 calculates the deviation between the target value and the actual detected value of the DC voltage Vdc. This calculated value is input to the PWM control circuit 5, and outputs a control signal to the transistor to start regeneration when the value is positive, and outputs an OFF signal to the transistor to start regeneration when the value is zero or negative. Is stopped. Further, the calculated value is amplified by the error amplifier 18. This amplified value can be multiplied by the voltage command selected by the switch 9 to create an alternating current command. The sample / hold circuit 24 holds the current value detected by the current detector 4 at the detection timing described later. The current command is subtracted from the current value held by the subtracter 13, the subtracted deviation is amplified by the amplifier 11, and the amplified value is multiplied by the voltage command of each phase to be corrected. The output of the amplifier 11 is (1 + A) where e is the deviation value from the subtractor 13 and A is the amplification factor.
Xe), and even if the output from the subtractor 13 is zero, it is 1
Is output. In this corrected phase voltage command value, the switch 10 disconnects the command signal of the phase that holds the data for each section in the ON state, and becomes the command of the waveform shown in FIG.

Next, with reference to FIG. 4, the operation of the PWM control circuit 5 as an example for the section 1 will be described. FIG. 4 shows an ON / OFF signal of the transistor Tr, and this signal is created by pulse-width modulating the command of each phase with a carrier signal. In the PWM control circuit 5, based on the section data sent from the comparator 8 shown in FIG. 2, the base signal is output to hold the S-phase transistor Tr 3 in the off state and the transistor Tr 4 in the on state. The S-phase AC voltage command is disconnected by the switch 10 shown in FIG. 1 and is not used. Transistor Tr connected to R phase and T phase respectively
The AC voltage command for switching 1, Tr 2, Tr 5, and Tr 6 is the AC current command output from the multiplier 16 to the voltage value calculated by the converter 6 from the line voltage detected by the isolator 3. A value obtained by multiplying the difference between the current detection value output from the sample / hold circuit 24 and the value amplified by the amplifier 11 is used. In other words, by multiplying, a correction proportional to the magnitude of the voltage value is performed, and a large correction is applied to a large voltage value and a large amount of current flows, but a small correction is applied to a small voltage value and a small amount of current It will flow. Next, based on the R-phase AC voltage command and the T-phase AC voltage command obtained by the correction, the carrier signal is turned ON / O of the transistor Tr shown in FIG.
An FF signal pulse is created. The detected value of the current detector 4 fed back to the subtractor 13 is a value detected by the sample / hold circuit 24 using the negative peak value of the carrier signal as a trigger.

The detection timing of the sample / hold circuit 24 is the transistor Tr held in the ON state in section 1.
It must be a timing at which the current flowing in 4 can be accurately measured. That is, when there is no influence of the current flowing through the diode d, the transistors Tr 1 and Tr 5 are turned on.
The timing is good. Therefore, when the carrier signal has a negative peak value, the transistor Tr must be used.
1 and Tr 5 turn on at the same time. Similarly for other sections, when the transistor Tr connected to the plus side of the DC voltage output is held in the ON state, detection is performed by using the plus peak value of the carrier signal as a trigger. When the transistor Tr connected to the negative side of is held in the ON state, the negative peak value of the carrier signal is used as a trigger for detection. Therefore, in the sample / hold circuit 24, the detection timing is determined by the carrier signal from the PWM control circuit 5 and the signal from the comparator 8.

Other sections can be performed in the same manner as section 1. When the converter 1 is controlled by the ON / OFF signal of the transistor Tr thus created, the regeneration of the current having the same phase as the power supply voltage shown in FIG. 3 can be realized.

[0013]

As described above, according to the present invention,
Feedback control is performed by one current detector, a regenerative current of a sine wave can be generated, and an inexpensive power converter can be realized. In addition, since the current is charged by the diode during power running and the transistor through which the largest current flows is held in the ON state during regeneration, it is possible to realize a power conversion device in which loss is minimized.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a motor control power conversion device that can perform power regeneration according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a power supply voltage of the power conversion device shown in FIG. 1 and a command.

FIG. 3 is a diagram showing a relationship between a power supply voltage and a current of the power conversion device shown in FIG.

FIG. 4 is a diagram showing a relationship between a command signal of the power conversion device shown in FIG. 1 and a control signal to each transistor.

FIG. 5 is a system configuration diagram of a power conversion device according to a conventional technique.

[Explanation of symbols]

1 converter, 2 smoothing capacitor, 3 isolator, 4,14 current detector, 5,20 PWM control circuit, 6,22 converter, 7 choke coil, 8 comparator, 9,10 switch, 11,18,23 amplifier,
12, 16 Multiplier, 13, 17, 19 Subtractor, 15
Vector rotator, 21 reference voltage, 24 sample / hold circuit.

Claims (1)

[Claims] 1. A plurality of combinations of a transistor and a diode connected in antiparallel to the transistor are configured, and a three-phase AC voltage is converted into a DC voltage in accordance with an AC voltage command input by a converter that PWM-controls the plurality of transistors. In a power conversion device that performs reversible conversion, a unit that detects a DC current output from the converter, a unit that generates a DC current command according to a DC voltage output from the converter, and a three-phase AC voltage connected to the converter. And a second switch for selecting two phases other than the first switch for selecting a phase having a maximum absolute value in the three-phase AC voltage based on the detection of the size relationship. An alternating current command is generated from the switch and the alternating current voltage detection value of the phase selected by the first switch and the direct current command. Means for sampling / holding the DC current detection value at the timing when the triangular wave of the triangular wave carrier signal is at the apex, and an AC voltage command according to the sampled / held DC current detection value and the AC current command. And a transistor connected to the two phases selected by the second switch that keeps one transistor of the converter in the phase selected by the first switch always on. A power conversion device comprising: means for performing ON / OFF control which is PWM-controlled by a voltage command and the triangular wave carrier signal.