JP3261010B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A plurality of transistors and a plurality of transistors are used as a DC power supply for an inverter for operating a motor used as a drive source of a machine tool at a variable speed so as to regenerate operating energy of the motor to an AC power supply when the motor is decelerated. 2. Description of the Related Art A power conversion device including a plurality of diodes each connected in anti-parallel and having a converter capable of performing reversible conversion using this transistor has been put to practical use. However, in recent years, there has been a problem that regenerating a regenerative current having a large amount of distortion to an AC power supply may cause adverse effects such as malfunction of other machines.

[0003] In order to solve this problem, it has been conventionally realized to regenerate a sinusoidal current with little distortion to a power supply by using a power converter shown in FIG. In this conventional power converter, a three-phase AC power supply 1 is connected to a converter 4 via a choke coil 7. The choke coil 7 has a role of smoothing a current ripple due to switching of the converter 4 of the AC current input / output to / from the converter 4. The converter 4 converts the three-phase AC voltage,
DC voltage Vdc is generated. The DC voltage Vdc is connected to a smoothing capacitor 5 for smoothing the DC output voltage of the converter 4. 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 AC current input / output to / from the converter 4 is insulated and detected via the current detector 6, and based on the detected value, feedback control is performed so that the input / output AC current becomes a sine wave. As another means for detecting a current, a current detection resistor is used.

Here, 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.
, And the subtractor 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 DC current command. Also, 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 to generate an AC signal having the same phase and the same frequency as the three-phase AC power supply voltage.
The AC signal and the DC current command are multiplied by a multiplier 19 to generate AC current commands iR *, iS *, and iT *.
This AC current command is supplied to the current detector 6 by the subtractor 20.
Is subtracted from the current detection value detected in step (1), and is further amplified by the error amplifier (10) to generate an AC voltage command, which is input to the PWM control circuit (9). In the PWM control circuit 9 based on the AC voltage command, the input signal is pulse-width-modulated by a carrier signal, and the transistors Tr1 to Tr6 are turned on / off.
An F control signal is created. The operation of the PWM control circuit 9 is generally used for the control circuit of the inverter, and the detailed description is 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 (power running) and deceleration (regeneration) of AC motor 3, currents iR, iS, and iT flowing through each phase of converter 4 have the same phase and the same frequency as the power supply voltage waveform as shown in FIG. Sine wave.

[0005]

In the above-described conventional power converter, a current command is generated by converting a line voltage of a three-phase AC power supply voltage into a phase voltage. 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 has as its object to provide a power converter capable of realizing a regenerative current with little distortion without affecting power supply voltage distortion.

[0006]

In order to solve the above-mentioned problems, the present invention comprises a plurality of transistors and a plurality of diodes connected in anti-parallel to the plurality of transistors, and responds to an input AC voltage command. And a converter that performs PWM control on these transistors
A power converter that reversibly converts a phase AC voltage into a DC voltage
A means for detecting an AC current input to and output from the converter and outputting an AC current detection value; a means for generating a DC current command based on a DC voltage output from the converter; and a line for a three-phase AC power supply of the converter Voltage ers, est, e
means for detecting tr and outputting a line voltage detection value, oscillating means for generating three AC signals s1, s2 and s3 having phases differing by 120 °, and converting the line voltage detection value and the AC signal. A means for performing a product-sum operation of A = ers × s1 + est × s2 + etr × s3 to output a phase error signal A, and outputting a calculated value obtained by performing a proportional / integral operation on the phase error signal A to the oscillation means as a frequency command. Means, means for multiplying the AC signal and the DC current command to generate an AC current command, and means for feedback-controlling the AC current based on an error between the AC current detection value and the AC current command. And the oscillating means includes AC signals s1, s2.
, S3 are the frequencies based on the frequency command.

[0007]

An AC current command for feedback-controlling a current input to and output from the converter is created by multiplying three AC signals having phases different by 120 ° with a DC current command corresponding to the DC voltage of the converter. The AC signal is obtained by calculating a phase error signal, which is a result of a product-sum operation of a line voltage detection value of a three-phase AC power supply and the AC signal, by pi (proportional / integral).
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 so as to be stable. Therefore, the AC signal always has the same phase and the same frequency as each phase voltage of the three-phase AC power supply. Also, pi
The arithmetic unit 16 plays a role of a low-pass filter when performing a pi operation on the phase error signal. For this reason, the frequency command that is the result of the pi operation has little effect on high-frequency power supply distortion.
Therefore, the AC current command obtained by multiplying the AC signal proportional to the frequency command by the DC current command is a sine wave that is not affected even if the power supply voltage is distorted. Therefore, the AC current input to and output from the converter is feedback-controlled based on the AC current command which does not affect the distortion of the power supply voltage, so that the current flowing through the converter is always a sine wave AC current without distortion.

[0008]

FIG. 1 is a diagram showing an example of a power converter according to the present invention in correspondence with FIG. 4, and the same components are denoted by the same reference numerals and description thereof is omitted. The operation of the control circuit D within the dotted line will be described below. This circuit is realized using a microprocessor or the like, and its operation is realized by software. First, the reference power supply 11 shown in FIG.
, And the subtractor 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 creates a DC current command whose polarity is inverted by the inverter 17. Next, the line voltage of the three-phase AC power supply is detected via the isolator 8. Further, the oscillator 18 generates an AC signal having a different phase by 120 ° for each command cycle. The AC signal is subjected to a product-sum operation with the three-phase line voltage, and a phase error signal, which is the operation value, is expressed as pi (proportional
Integral) After calculating by the calculator 16, the oscillator 1
8 is output. On the basis of this frequency command, the oscillator 18 changes the frequency of the AC signal output every command cycle and controls the phase error signal to be zero. A series of these operations will be described below.

For example, 3 detected from the isolator 8
The line voltage of the phase power supply is set to 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 expressed as s1 = -co
s (ω2t2), s2 = −cos (ω2t2 + 120 °),
Assuming that s3 = -cos (ω2t2−120 °), the phase error signal: A is

A = ers × s1 + est × s2 + etr × s3 = − (Esin (ω1t1) × cos (ω2t2) + Esi
n (ω1t1 + 120 °) × 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 advanced by 90 ° compared to each line voltage and stabilized, 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. Also, when the phase of the AC signal has advanced from the stable state compared to the line voltages, the respective multiplied waveforms are β1, β2,
β3, resulting in a phase error signal: A <0.
Therefore, the frequency command output from the pi calculator 16 becomes smaller. 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 increases. As a result, the oscillator 1 is set so that the phase of the AC signal is advanced.
8 operates, and as a result, A = 0 is stabilized. The frequency command output from the pi calculator 16 in this manner changes in proportion to the value of the phase error signal: A, and the phase error signal: A =
It is stabilized by the frequency command becoming 0.

The AC signals s1, s2, and s3 have the same frequency which is 180 ° out of phase with respect to each phase voltage et, er, es of the three-phase AC power supply. Therefore, by multiplying the DC current command inverted by the inverter 17 with the DC current command, the AC current commands iR *, iS having the same phase and the same frequency are obtained.
*, IT * can be created. Further, since the pi calculator 16 functions as 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, it does not affect the AC current command. Therefore, the AC current command that does not affect the power supply voltage distortion is subtracted by the subtractor 20 from the current detection value detected by the current detector 6 and further amplified by the error amplifier 10 to create an AC voltage command. Is input to In the PWM control circuit 9 based on the AC voltage command, the input signal is subjected to pulse width modulation by a carrier signal to generate an ON / OFF control signal for the transistors Tr1 to Tr6. In this manner, the input / output AC current of the converter 4 is subjected to feedback control with respect to the AC current command, so that the sine wave AC current i as shown in FIG.
R, iS, and iT.

[0012]

As described above, according to the present invention,
Even if the power supply voltage is distorted, an AC current command without distortion can be generated and feedback-controlled, and the regenerative current also has no distortion. Therefore, it is possible to eliminate an adverse effect on the power supply.

[0013]

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing one embodiment of a motor control power conversion device capable of performing power regeneration according to the present invention.

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

FIG. 3 is a diagram showing a relationship between a power supply voltage and an alternating current flowing to 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) operator, 17 inverter,
18 oscillators, 21 converters.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-47279 (JP, A) JP-A-3-107373 (JP, A) JP-A 4-222463 (JP, A) JP-A-6-222 54545 (JP, A) JP-A-63-274374 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/48 H02P 7/63

Claims (1)

(57) [Claims] 1. A three-phase AC voltage converter comprising a plurality of transistors and a plurality of diodes connected in anti-parallel to the plurality of transistors, and performing PWM control on the plurality of transistors in response to an input AC voltage command. A power converter that reversibly converts the DC voltage into a DC voltage, a unit that detects an AC current input and output by the converter and outputs an AC current detection value, and generates a DC current command based on the DC voltage output by the converter. Means, line voltages ers, est,
means for detecting etr and outputting a line voltage detection value; and three AC signals s1, s2,
an oscillating means for generating s3, and the line voltage detection value and the AC signal are expressed by A = ers × s1
A means for performing a product-sum operation of + est × s2 + etr × s3 to output a phase error signal A; a means for outputting a calculated value obtained by performing a proportional / integral operation on the phase error signal A to the oscillation means as a frequency command; Means for multiplying a signal and the DC current command to generate an AC current command; and means for feedback-controlling the AC current based on an error between the AC current detection value and the AC current command. The means is a power converter that sets the frequency of the AC signals s1, s2, and s3 to a frequency based on the frequency command.