JPH08331860A - Power converting apparatus - Google Patents

Abstract

PURPOSE: To provide a power converting apparatus which can generate a recovery current with less distortion even if the power source voltage is distorted. CONSTITUTION: An oscillator 18 generates three AC signals s1, s2, s3 having the phases with difference of 120 deg.. An isolator 8 detects line-to-line voltages ers, est, etr of the 3-phase AC power supply 1. In a multiplier 14 and an adder 15, a phase error difference signal A is generated from the AC signal and line- to-line voltage. Moreover, the phase error signal A is proportionally integrated with pi arithmetic unit 16 to obtain a frequency instruction. The oscillator 18 feedback-controls the frequencies of three AC signals so that the phase error signal A becomes zero, based on this frequency instruction. Thereby, since pi arithmetic unit 16 eliminates harmonic components, if the AC power source is distorted, the AC signal and the QC current instruction based on this AC signal can be freed from the influence of the power source distortion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter equipped with a converter capable of converting an AC power supply into a DC power and regenerating DC power into an AC power supply.

[0002]

2. Description of the Related Art As a direct current power source for an inverter that drives a motor used as a drive source for a machine tool at a variable speed, a plurality of transistors and a plurality of transistors are used to regenerate the operating energy of the motor to an alternating current power source when the motor is decelerated. A power conversion device including a plurality of diodes each connected in antiparallel and having a converter capable of reversible conversion using this transistor has been put into practical use. However, in recent years, it has become a problem that adverse effects such as malfunction of other machines are caused by regenerating a regenerative current having a large amount of distortion to an AC power supply.

In order to solve this problem, conventionally, it has been realized to regenerate a sinusoidal current with little distortion to a power source using the power converter shown in FIG. In this conventional power converter, the three-phase AC power supply 1 is connected to the converter 4 via the choke coil 7. The choke coil 7 has a role of smoothing a current ripple due to switching of the converter 4 of the alternating current input to and output from the converter 4. The converter 4 converts the three-phase AC voltage,
DC voltage Vdc is generated. A smoothing capacitor 5 that normally smoothes the DC output voltage of the converter 4 is connected to the DC voltage Vdc. The DC voltage Vdc is converted into AC by the inverter circuit 2, and the AC motor 3 is operated at a variable speed. The alternating current input / output to / from the converter 4 is insulated and detected via the current detector 6, and feedback control is performed so that the alternating current input / output becomes a sine wave based on the detected value. A current detection resistor is used as another means for detecting the current.

Now, the operation of the control circuit C within the dotted line in FIG. 4 will be described. The reference power supply 11 in the figure is a DC voltage Vdc.
The target voltage is set and the subtracter 12 subtracts the target voltage from the detected value of the DC voltage Vdc to obtain a voltage deviation signal. This voltage deviation signal is amplified by the error amplifier 13 to create a direct current command. Further, the line voltage waveform of the three-phase AC voltage detected via the isolator 8 is converted into a phase voltage waveform by the converter 21, and an AC signal having the same phase and frequency as the three-phase AC power supply voltage is generated.
The AC signal and the DC current command are multiplied by the multiplier 19 to create AC current commands iR *, iS *, and iT *.
This AC current command is sent to the current detector 6 by the subtractor 20.
It is subtracted from the detected current value detected in step A1, further amplified by the error amplifier 10 to create an AC voltage command, and input to the PWM control circuit 9. Based on this AC voltage command, the PWM control circuit 9 pulse-width modulates the input signal with a carrier signal to turn ON / OFF the transistors Tr1 to Tr6.
An F control signal is created. The operation of the PWM control circuit 9 is generally used in the control circuit of the inverter, and detailed description thereof will be omitted. By the operation of these circuits, the current flowing through the converter 4 is feedback-controlled according to a sine wave current command generated from the power supply voltage and the DC voltage detection value. Therefore, during acceleration (powering) and deceleration (regeneration) of the AC motor 3, the currents iR, iS, and iT flowing in the respective phases of the converter 4 have the same phase and frequency as the power supply voltage waveform as shown in FIG. Becomes a sine wave of.

[0005]

In the above-mentioned conventional power converter, the line voltage of the three-phase AC power supply voltage is converted into the phase voltage to generate the current command. Therefore, when the power supply voltage is distorted, the current command is also generated. It will be distorted. As a result, there is a problem that the distorted current command is feedback-controlled and the distorted current is regenerated to the power supply. The present invention has been made to solve the above problems, and an object of the present invention is to provide a power conversion device that can realize a regenerative current with little distortion without affecting the distortion of the power supply voltage.

[0006]

In order to solve the above-mentioned problems, a plurality of transistors and a plurality of diodes connected in anti-parallel to the plurality of transistors are used to respond to an input AC voltage command. 3 by a converter that controls these multiple transistors by PWM
A power conversion device for reversibly converting a phase AC voltage into a DC voltage is
Means for detecting an AC current input to and output from the converter and outputting an AC current detection value; means for generating a DC current command based on a DC voltage output by the converter; and a line of a three-phase AC power supply for the converter. Inter-voltage ers, est, e
The means for detecting tr and outputting the detected value of the line voltage, the oscillating means for generating three AC signals s1, s2, s3 whose phases are different by 120 °, the detected value of the line voltage and the AC signal A = ers.times.s1 + est.times.s2 + etr.times.3 for performing a sum-of-products operation and outputting a phase error signal A; and a calculated value obtained by performing a proportional / integral operation on the phase error signal A as a frequency command and outputting it to the oscillation means Means, means for multiplying the alternating current signal and the direct current command to generate an alternating current command, and means for feedback controlling the alternating current based on an error between the detected alternating current value and the alternating current command. The oscillating means is provided with AC signals s1 and s2.
, S3 are frequencies based on the frequency command.

[0007]

The AC current command for feedback controlling the current input / output to / from the converter is created by multiplying three AC signals each having a phase difference of 120 ° and the DC current command corresponding to the DC voltage of the converter. The AC signal is a phase error signal pi (proportional / integral), which is the result of multiply-accumulate operation of the line voltage detection value of the three-phase AC power source and the AC signal
It is output from the oscillator based on the calculated frequency command. That is, the phase error signal becomes zero, and the frequency command is corrected to be stable. Therefore, the AC signal always has the same phase and frequency as each phase voltage of the three-phase AC power supply. Also, pi
The calculator 16 plays a role of a low-pass filter when pi-calculating the phase error signal. Therefore, the frequency command that is the pi calculation result has little influence on the high-frequency power source distortion.
Therefore, the AC current command obtained by multiplying the AC signal proportional to the frequency command by the DC current command becomes a sine wave that is not affected even when the power supply voltage is distorted. Therefore, since the AC current input to and output from the converter is feedback-controlled based on the AC current command that does not affect the distortion of the power supply voltage, the current flowing through the converter is always a sinusoidal AC current without distortion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an example of a power conversion device according to the present invention in correspondence with FIG. 4, and the same components are designated by the same reference numerals and their description is omitted. The operation of the control circuit D within the dotted line will be described below. This circuit is realized by using a microprocessor or the like, and its operation is realized by software. First, the reference power supply 11 in the figure is a DC voltage Vdc.
The target voltage is set and the subtracter 12 subtracts the target voltage from the detected value of the DC voltage Vdc to obtain a voltage deviation signal. This voltage deviation signal is amplified by the error amplifier 13 and inverted by the inverter 17 to create a DC current command. Next, the line voltage of the three-phase AC power supply is detected via the isolator 8. Further, the oscillator 18 generates AC signals each having a phase difference of 120 ° for each command cycle. The AC signal is subjected to a product-sum operation with the three-phase line voltage, and the calculated phase error signal is pi (proportional
(Integration) After being calculated by the calculator 16, the oscillator 1 is used as a frequency command.
8 is output. Based on this frequency command, the oscillator 18 changes the frequency of the AC signal output for each command cycle and controls so that the phase error signal becomes zero. A series of these operations will be described below.

For example, 3 detected by the isolator 8
The line voltage of the phase power supply is the RS phase: ers = Esin (ω1t1
), ST phase: est = Esin (ω1t1 + 120
°), TR phase: etr = Esin (ω1t1 −120
), And the AC signal from the oscillator 18 is s1 = -co
s (ω2t2), s2 = -cos (ω2t2 + 120 °),
When s3 = -cos (ω2t2 -120 °) is set, the phase error signal: A is

## EQU1 ## A = ers × s1 + est × s2 + etr × s3 = − (Esin (ω1t1) × cos (ω2t2) + Esi
n (ω1t1 + 120 °) x cos (ω2t2 + 120 °)
+ Esin (ω1t1 −120 °) × cos (ω2t2 −1
20 °)).

Next, the relationship between the line voltage of the three-phase AC power supply and the AC signal will be described with reference to FIG. First, when the phase of the AC signal is stable in a state in which the phase of the AC signal is advanced by 90 ° with respect to each line voltage, the respective multiplied waveforms are α1, α2, α3, and as a result, the phase error signal: A = 0. Therefore,
There is no change in the frequency command output from the pi calculator 16. Further, when the phase of the AC signal advances from the stable state as compared with each line voltage, the respective multiplied waveforms are β1, β2,
β3, and as a result, the phase error signal: A <0.
Therefore, the frequency command output from the pi calculator 16 becomes small. As a result, the oscillator 18 operates so that the phase of the AC signal is delayed, and as a result, A = 0 is stabilized. Further, when the phase of the AC signal is delayed from the stable state as compared with each line voltage, the respective multiplied waveforms are γ1, γ2, γ3, and as a result, the phase error signal: A> 0. Therefore, the frequency command output from the pi calculator 16 becomes large. As a result, the oscillator 1 is arranged so that the phase of the AC signal advances.
8 operates and, as a result, stabilizes at A = 0. In this way, the frequency command output from the pi calculator 16 changes in proportion to the value of the phase error signal: A, and the phase error signal: A =
Stabilizes with a frequency command of 0.

The AC signals s1, s2, and s3 have the same frequency with a phase difference of 180 ° with respect to the phase voltages et, er, and es of the three-phase AC power supply. Therefore, by multiplying by the DC current command that has been inverted by the inverter 17, the AC current commands iR *, iS having the same phase and the same frequency can be obtained.
*, IT * can be created. Further, since the pi calculator 16 plays the role of a low-pass filter, the AC signal generated from the oscillator 18 is hardly affected by high-frequency power supply voltage distortion. Therefore, even if the power supply voltage is distorted, the AC current command is not affected. Therefore, the AC current command that does not affect the power supply voltage distortion is subtracted from the current detection value detected by the current detector 6 by the subtractor 20, and further amplified by the error amplifier 10 to create the AC voltage command, and the PWM control circuit 9 Entered in. Based on the AC voltage command, the PWM control circuit 9 pulse-width modulates the input signal with the carrier signal to generate ON / OFF control signals for the transistors Tr1 to Tr6. In this way, the input / output AC current of the converter 4 is feedback-controlled with respect to the AC current command, so that the AC current i having a sine wave as shown in FIG.
R, iS, and iT.

[0012]

As described above, according to the present invention,
Even when the power supply voltage is distorted, a distortion-free AC current command can be generated and feedback-controlled, and the regenerative current is also distorted. Therefore, it is possible to eliminate the adverse effect on the power supply.

[0013]

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of a motor control power conversion device capable of power regeneration according to 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 an alternating current flowing through a converter.

FIG. 4 is a system configuration diagram of a conventional power converter.

[Explanation of symbols]

1 3 phase AC power supply, 2 inverter circuit, 3 AC motor, 4 converter, 5 smoothing capacitor, 6 current detector, 7 choke coil, 8 isolator, 9 P
WM control circuit, 10,13 amplifier, 11 reference power supply,
12, 20 Subtractor, 14, 19 Multiplier, 15 Adder, 16 pi (proportional / integral) calculator, 17 Inverter,
18 oscillators, 21 converters.

Claims (1)

[Claims] 1. A three-phase AC voltage including a plurality of transistors and a plurality of diodes connected in anti-parallel to the plurality of transistors, the converter PWM-controlling the plurality of transistors according to an input AC voltage command. In a power conversion device for reversibly converting into a DC voltage, means for detecting an AC current input to and output from the converter and outputting an AC current detection value, and a DC current command based on the DC voltage output from the converter. Means and line voltages ers, est, of the three-phase AC power supply of the converter
a means for detecting the value of etr and outputting the detected value of the line voltage, and three AC signals s1, s2, which have different phases by 120 °,
The oscillation means for generating s3, the line voltage detection value and the AC signal are A = ers × s1
+ Est × s2 + etr × s3, a means for performing a sum-of-products operation and outputting a phase error signal A, a means for outputting to the oscillating means a calculated value obtained by performing a proportional / integral operation on the phase error signal A as a frequency command, and the alternating current Means for multiplying a signal and the direct current command to generate an alternating current command; and means for feedback controlling the alternating current based on the error between the detected alternating current value and the alternating current command, The means is a power conversion device that sets the frequency of the AC signals s1, s2, s3 to a frequency based on the frequency command.