JPH03256593A - Pwm power converter - Google Patents

Abstract

PURPOSE:To prevent voltage drop of a DC bus and to obtain a stable and highly accurate PWM converter with low cost by controlling the speed of an induction motor while interlocking with limitation of converter output. CONSTITUTION:When the output signal from a current controller/amplifier 9 for controlling the output current of a converter 5 is limited by a limiter 31, a limiter detector 33 detects the fact and provides a signal to a limit value setter 35. The limit value setter 34 detects the limited speed command 19a, performs deceleration with a predetermined acceleration and sets the speed command as a limit value in a limiter 32. Consequently, output current from an inverter 2 is limited thus preventing voltage drop of a DC bus 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a PWM power converter, and particularly to a technique for stabilizing control during overcurrent limitation.

[Conventional technology]

FIG. 3 is a diagram showing a conventional PWM power converter disclosed in, for example, Japanese Unexamined Patent Publication No. Sho 59-194 [i97]. In the figure, (1) is the induction motor, (2) is the DC bus (3)
This is an inverter that converts DC power into AC power and performs variable voltage and variable frequency control of the induction motor (1), and is a transistor inverter using forced commutation transistors and parallel diodes. (4) is a smoothing capacitor connected between the DC bus bars (3), and (5) is a converter device connected to the AC power source (6) to convert AC power into DC.

In addition, (7) is a reference voltage setting device, for example, an electric motor (
1) is set to a value corresponding to the DC voltage of the DC bus (3) when it is stopped (no load). (8) is a voltage detector that detects the voltage of the DC bus (3), and (9) uses the output signal (7a) from the voltage setting device (7) as a reference value, and the output from the voltage detector (8) ( 8a) is a voltage control amplifier for performing voltage feedback control with negative feedback, and the output signal (9a) of this voltage control amplifier (9) is a three-phase sine signal of R, S, and T synchronized with the AC power supply (6). An output signal (10a) from a three-phase sine wave generator (10) that generates a wave reference signal (10a), (1
0i), (10c) and the multiplier (IIA).

Calculations are performed using (IIB) and (IIG). That is, the output signal (9a) of the voltage control amplifier (9) is the three-phase sinusoidal reference signal (10a), (1ab), (1
0c), which is a value that determines the amplitude of the multiplier (118),
(IIB), (IIG) output signal (I], a)
, (llb), (IIC) are three-phase sinusoidal current reference signals.

Furthermore, (12A), (1,2B), (12(
:) is a current control amplifier, and current detectors (13A), (13B), and (13B) are provided in each phase of the AC power supply circuit.
Current signal (13a) from (13G).

(13b) and (13c) are used as negative feedback amounts to configure a current control minor loop, and a current control amplifier (12A) is constructed.
.

(12B), (12(:) output signal (12a)
, (12b), (12c) are sawtooth wave generators (14
) is compared and detected by the comparator (15) with the pressure modulation signal (14a) of the converter device (
Signals (15a) to (15f) that determine the switching timing of each transistor in 5) are output.

(16) is a transistor base drive circuit,
A switching circuit L'H (1
6a) to (16f) are given. That is, the converter device (5) is controlled as a sine wave PWM converter with a constant frequency.

Figure 4 is a diagram showing the voltage and current waveforms of one phase.If the motor (1) performs continuous operation and the DC voltage of the DC bus (3) drops below the reference voltage setting value, the current waveform will be It is in phase with the voltage sine wave waveform and is connected from the AC power supply (6) to the DC bus (
3), and if the motor (1) performs regenerative operation and the DC voltage of the DC bus (3) increases, the phase will be reversed and power will be transferred from the bus (3) to the AC power source (6). Regeneration.

Even in sinusoidal PWM control, the current contains a ripple component corresponding to the PWM frequency due to the sawtooth voltage; however, a relatively large three-phase AC reactor (17
) to obtain a smooth sinusoidal current. In this embodiment, current control is performed for one phase, but the control circuit can be simplified by performing current control for any two of the three phases and converting from two phases to three phases, for example.

Next, control of the inverter device (2) will be described. In Fig. 3 above, (18) is the speed detector, (19) is the speed command setter, (20) is the speed command setter (19) with the speed command (19a) from the speed command setter (19) as the reference value, and the speed detector ( 1
a speed control amplifier (22) for performing speed feedback control using the speed signal (18a) from 8) as a negative feedback amount;
) is a frequency command generator that generates a frequency command (22a) based on the output signal (20a) of the speed control amplifier (20) and the speed signal (18a) from the speed detector (18), and (23) is a speed command generator. The phase angle (23a) and the three a current command generator that outputs the amplitude (23b) of the phase sine wave current reference;
24) is a three-phase sine wave standard (24a) of U, V, W based on the frequency command (22a) and phase angle (23a),
(24b).

Three-phase sine wave generator that generates (24C), (25A),
(25B).

(25G) is a three-phase sine wave standard (24a), (24b
), (24c) and the amplitude of the three-phase sinusoidal current reference (23
b) is a multiplier that multiplies the above output signal (25a).
, (25b) and (25c) are three-phase sinusoidal current references.

Further, (26A), (268), and (26C) are current control amplifiers, and current detectors (27A), (27B), and (27B) are provided in each phase of the output circuit of the induction motor.
Current signal (27a) from (27G), (27b
), (27c) is used as a negative feedback amount to configure a minor loop of current control, and the current control amplifier (26A),
(26B), (25G) output signal (26a)
, (26b).

(26c) is the output modulation signal (2) of the sawtooth wave generator (28).
8) and a comparator (29), and a signal (29a) is sent from the comparator (29) to determine the switching timing of each transistor of the inverter device (2).
) to (29f) are output. Reference numeral (30) denotes a transistor base drive circuit, which applies switching signals (30a) to (30f) to the transistor bases so as to control the speed and current to a predetermined value.

In this embodiment, current control is performed for three phases, but the control circuit can be simplified by performing current control for any two of the three phases and converting from two phases to three phases.

[Problem to be solved by the invention]

The conventional PWM II force converter is configured as described above, and includes means for limiting the current amplitude command in order to protect the converter device. Therefore, the converter device (5
) is limited by the current limiting means, the converter device (5) cannot supply power to the inverter device (2), the voltage of the DC bus (3) decreases, and the voltage of the inverter and converter device decreases. There was a problem that control became unstable.

This invention was made to solve the above-mentioned problems. When the alternating current of the converter device is limited by the current limiting means, the speed of the induction motor is limited by the limiting means in conjunction with the alternating current of the converter device. By supplying power from the device to the load, we have developed a PWM power conversion device that prevents voltage drops on the DC bus, provides stable control of inverter and converter devices, and makes maximum use of the capabilities of the elements. The purpose is to obtain.

(Means for Solving the Problems) A PWM power converter according to the present invention includes a first power converter including a switching element and a parallel diode connected to an AC power source via an AC reactor, and a first power converter including a switching element and a parallel diode. A second power converter includes a switching element and a parallel diode connected to the converter via a smoothing capacitor, and converts AC power from the AC power source into DC power via the first power converter. Further, in the PWM power converter which converts into AC power of a predetermined frequency and voltage via the second power converter to drive an induction motor, the first
a first current command generating means for commanding the current on the alternating current side of the power converter; a first limiting means for limiting the magnitude of the current command to a predetermined value; 1
a limiter detecting means for detecting that the induction motor is limited by the limiting means; a speed command generating means for commanding the speed of the induction motor; a second limiting means for restricting the magnitude of the speed command; and the limiter detecting means. When it is detected that the large rice grain of the current command of the first power converter is limited by the first limiting means, the speed command of the induction motor at that time is set as the second limit value. and a value setting means.

[Effect]

In this invention, the limit value setting means for the magnitude of the speed command of the induction motor is such that when the magnitude of the current command on the AC side of the converter device is limited by the current limiting means, the limit detecting means detects this; Therefore, the magnitude of the speed command at that time is set in the speed limiting means as a limit value for the magnitude of the speed command of the induction motor, and in conjunction with the alternating current of the converter device being limited by the current limiting means. The speed of the induction motor is limited by speed limiting means. Therefore, when the supply of power from the converter device to the inverter device is restricted, the supply of power from the inverter device to the load is also restricted, and the load is driven by the power that can be supplied by the converter device. Therefore, a drop in the voltage of the DC bus is prevented, and the inverter and converter devices are stably controlled.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Third
In Fig. 1, parts that are the same as those in the figure are designated by the same reference numerals.
(31) is the control circuit of the converter device (5),
Three-phase sine wave reference signal (10a), (10b) (10
c) is a limiter for the output signal (9a) of the voltage control amplifier (9) that determines the amplitude of the output signal (9a), and the limit value is set, for example, based on the current withstand characteristics of the power conversion element.

(32) is in the control circuit of the inverter device (2),
This is a limiter for the speed command (19a) from the speed command setter (19), and the limit value is set by a limit value setter (34) to be described later. (33) is a limiter detector that detects that the output signal (9a) of the voltage control amplifier (9) is limited by the limiter (31), and (34) is the limiter detector (3).
The output signal (33a) of 3) causes the voltage control amplifier (9
) is limited by the limiter (31), this limit value setting device sets the speed command (1!la) at that time as the limit value of the limiter (32).

Next, the operation will be explained according to the flowchart shown in FIG. The limiter detector (33) is a limiter (31)
In step 521, it is determined whether the output signal (9a) of the voltage control amplifier (9) is limited by a limit value set according to the current withstand characteristics of the power conversion element, and an output signal (33a) is output. Next, the limit value setter (34)
By the output signal (33a) of the limiter detector (33),
When the output signal (9a) is limited by the limiter (31), the speed command (19a) at the time of restriction is detected, the predetermined acceleration is reduced, and then the speed command (19a) is
) is set as the limit value of the limiter (32) (steps 522 to 524). Further, if the output signal (9a) is not limited by the limiter (31) (step 522), it is set to a predetermined limit value set according to the current withstand characteristics of the power conversion element (step 525).

(Effects of the Invention) As described above, according to the present invention, since the speed of the induction motor is limited by the speed limiting means in conjunction with the alternating current of the converter device being limited by the current limiting means, the converter device When the supply of power from the inverter to the inverter is restricted, the supply of power from the inverter to the load is also restricted, and the load is driven by the power that can be supplied by the converter. Therefore, a drop in the voltage of the DC bus is prevented, the inverter and converter device are stably controlled, and a highly accurate and inexpensive device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a PWM power converter according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of an embodiment of the present invention, and FIG. 3 is a block diagram showing a conventional PWM power converter. Figure 4 shows voltage and current waveforms. (1) is an induction motor, (2) is an inverter device, (5)
is a converter device, (6) is a three-phase AC power supply, (9) is a voltage control amplifier, (19) is a speed command generator, (31)
, (32) is a limiter, (33) is a limiter detector,
(34) is a limit value setter. Figure 2 Figure 3 Written amendment to the procedure (voluntary) Relationship to the April 19, 1990 incident Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo
Name (601) Mitsubishi Electric Co., Ltd. Representative Moriya Shiki 4, Agent address: 4th floor, Nakayama Building, 1-9-13 Nihonbashi Honmachi, Chuo-ku, Tokyo Detailed description of the invention column in the specification. 6. Contents of the amendment (1) The statement "occurs" on page 6, line 10 of the specification is amended to "occur". (2) “Output modulation signal (28)” on page 7, line 1 of the specification
The description J is corrected to ``output modulation signal (28a) J.'' (3) The description ``switching'' on page 7, line 8 of the specification is corrected to ``switching.'' (4) In the 1st line of page 10 of the specification, [Setting is now available]
" has been corrected to "Because it is set." (5) The statement "power conversion...set" in the second and third lines of page 12 of the specification is corrected to "clear the limit value of the limiter (32)".

Claims (1)

[Claims] a first power converter including a switching element and a parallel diode connected to an AC power source via an AC reactor; and a first power converter including a switching element and a parallel diode connected to the first power converter via a smoothing capacitor. It has two power converters, converts AC power from the AC power supply into DC power via the first power converter, and converts it into DC power at a predetermined frequency and voltage via the second power converter. A PWM power converter that converts AC power into AC power and drives an induction motor, the first current command generating means commanding the AC side current of the first power converter, and the magnitude of the current command set to a predetermined value. a first limiting means for limiting the current command, a limiter detecting means for detecting that the magnitude of the current command is limited by the first limiting means, and a speed command generating means for commanding the speed of the induction motor; When the second limiting means for limiting the magnitude of the speed command and the limiter detection means detect that the magnitude of the current command of the first power converter is limited by the first limiting means, A PWM power conversion device comprising: limit value setting means for setting the speed command of the induction motor at that time as the second limit value.