JPH03256592A - Pwm power converter - Google Patents

Abstract

PURPOSE:To prevent increase/drop of voltage on a DC bus and to obtain a stable PWM power converter having high accuracy with low cost by interlocking load limitation between a converter and an inverter. CONSTITUTION:When the output signal from a current controller/limiter 9 for controlling the output current of a converter 5 is limited by a limiter 31, a limiter detector 33 provides a signal to a limit setter 34. The limit setter 34 detects a limited output signal 23b which is set as the 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 when current is limited.

[Conventional technology]

FIG. 3 is a diagram showing a conventional PWM power conversion device disclosed in, for example, Japanese Unexamined Patent Publication No. 59-194697. In the figure, (1) is an induction motor, and (2) is an inverter device that converts the DC power of the DC bus (3) to AC and performs variable voltage variable frequency control of the 8-conductor motor (1), allowing forced commutation. This is a transistor inverter that uses a parallel transistor and a parallel diode. (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). The output signal (IQa) from the three-phase sine wave generator (10) that generates the wave reference signal (1
0b), (10c) and a multiplier (IIA).

Calculations are performed using (IIB) and (IIG). That is, the pressure signal (9a) of the voltage control amplifier (9) is the three-phase sinusoidal reference signal (10a), (10b), (1
0c) is the value that determines the amplitude of the multiplier (11^)
, (11B), (IIC) output signal (Ila)
, (llb), (llc) are three-phase sinusoidal current reference signals.

Furthermore, (12A), (12B), (12G)
is a current control amplifier, and current detectors (13A), (13B), (1
Current signal (13a) from 3C).

(13b) and (13C) constitute a current control minor loop with negative feedback amount, and the current control amplifier (12A)
(12B), output signal (12a) of (12C),
(12b), (12C) are sawtooth wave generators (14)
The comparator (15) compares and detects the output modulation signal (14a) of the converter device (5).
) signals (15a) to (15f) are output that determine the switching timing of each transistor. (
1δ) is the base drive circuit of the transistor, which applies a switching signal to the base of the transistor so that the DC voltage of the DC bus (3) is equal to the reference output signal and the current is controlled in a sinusoidal manner. (16a)
~(16f) is given. In other words, 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, and the current waveforms are as follows: It is in phase with the power supply voltage sine wave waveform and is connected from the AC power supply (6) to the DC bus (
3), if the motor (1) performs regenerative operation and the DC voltage of the DC bus (3) increases, the phase will be reversed! Electric power is regenerated from (3) to the AC power source (6).

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 three phases, but the control circuit can be simplified by, for example, performing current control for any two of the three phases and converting from two phases to three phases.

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). The phase angle (23a) and a current command generator (24) that outputs the amplitude (23b) of a three-phase sine wave current reference;
) is the three-phase sine wave reference (24a) of U, V, W based on the frequency command (22a) and phase angle (23a), (2
4b).

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.

Mata, (26A), (268), (26C)
A current detector (27 A), (27
B), current signal (27a) from (27C),
(27b) and (27C) constitute a minor loop of current control with negative feedback amounts, and the current control amplifier (26
A), (26B), (26C) output signal (2
6a), (26b).

(2fic) is the output modulation signal (
28) and a comparator (29), and the comparator (29) outputs a signal (29) that determines the switching timing of each transistor of the inverter device (2).
a) to (29f) are output. (30) is a transistor base drive circuit, which applies switching signals (30aJ to (3Of)) to the base of the transistor 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, for example, performing current control for any two of the three phases and converting from two phases to three phases.

(Problems to be Solved by the Invention) The conventional PWM power converter is configured as described above, and includes current control means for each current amplitude command to protect the inverter and converter device. Therefore, if the alternating current of the converter device (5) is limited by the current limiting means, but the alternating current of the inverter device (2) does not reach the current limiting means, the converter device (5) supplies power to the inverter device (2). Since power cannot be supplied or regenerated into a power source, the voltage of the DC bus (3) decreases or increases, resulting in a problem that control of the inverter and converter device becomes unstable.

This invention was made to solve the above-mentioned problems, and when the AC current of the converter device is limited by the current limiting means, the AC current of the inverter device is limited by the current limiting device in conjunction with this. By limiting the supply of power from the inverter device to the load or the regeneration of power from the inverter device to the converter device, a drop or increase in the voltage of the DC bus is prevented and stable control of the inverter and converter device is performed. It is an object of the present invention to obtain a PWM power conversion device that can utilize the capabilities of the elements to the maximum extent.

[Means to solve the problem]

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 connected to the first power converter via a smoothing capacitor. a second power converter including a switching element and a parallel diode, which converts AC power from the AC power supply into DC power via the first power converter, and further includes a second power converter. PW that is converted into AC power of a predetermined frequency and voltage through a device
In the M power converter, first current command generating means commands the current on the alternating current side of the first power converter; first limiting means limits the magnitude of the current command to a predetermined value; limiter detection means for detecting that the magnitude of the current command is limited by the first limiting means; second current command generation means for commanding the current on the AC side of the second power converter; When the second limiting means for limiting the magnitude of the current 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; and limit value setting means for setting the magnitude of the current command on the AC side of the second power converter at that time as the second limit value.

[Effect]

In this invention, the limit value setting means for the magnitude of the current command on the AC side of the inverter device detects when the magnitude of the current command on the AC side of the converter device is limited by the current limiting means. As a result, the magnitude of the current command on the AC side of the inverter device at that time is set in the current limiting means as a limit value for the magnitude of the current command on the AC side of the inverter device, and the AC current of the converter device is In conjunction with the current limiting means limiting the AC current of the inverter device, the current limiting means limits the alternating current of the inverter device. Therefore, when the power supply from the converter device to the inverter device is restricted, the power supply from the inverter device to the load is also restricted, and conversely, the power supply from the converter device to the power source during regeneration is restricted. When the regeneration of the converter is restricted, the regeneration of power from the load to the inverter is also restricted, and the load is driven by the power that the converter can supply, preventing the DC bus voltage from dropping or rising. , inverter and converter devices are stably controlled.

〔Example〕

An embodiment of the present invention will be described below 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 sinusoidal reference signal (10a), (lob).

This is a limiter for the output signal (9a) of the current control amplifier (9) that determines the amplitude of (10c), 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),
The output signal (23) of the current command generator (23) determines the amplitude of the three-phase sine wave generator (24a), (24b), (24c) output from the three-phase sine wave generator (24).
b) is the limiter, and the limit value is set by the limit value setter (described later).
34). (33) is a current controlled amplifier (
A limiter detector (34) detects that the output signal (9a) of the limiter (9) is limited by the limiter (31). When the output signal (9a) of the current command generator (23) is limited by the limiter (31), the output signal (23b) of the current command generator (23) at that time is set as the limit value of the limiter (32), and the output signal When (9a) is not limited by the limiter (31), it is a limit value setting device that sets a predetermined limit value set according to the current withstand characteristics of the power conversion element.

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 current 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) uses the output signal (33a) of the limiter detector (33) to generate an output signal when the output signal (9a) is limited by the limiter (31). (23b) and further sets the output signal (23b) as the limit value of the limiter (32) (steps 522, 523).

Furthermore, if the output signal (9a) is not limited by the limiter (31) (step 521), it is set to a predetermined limit value set based on the current withstand characteristics of the power conversion element (step 524).

〔Effect of the invention〕

As described above, according to the present invention, since the alternating current of the inverter device is limited by the current limiting means in conjunction with the alternating current of the converter device being limited by the current limiting means,
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. Conversely, when the supply of power from the converter to the power supply is restricted during regeneration, the supply of power from the load to the inverter is also restricted, and the load is driven by the power that can be supplied by the converter. be done. Therefore, it is possible to prevent the voltage of the DC bus from decreasing or increasing, and the inverter and converter devices can be stably controlled, resulting in a highly accurate and inexpensive device.

[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. , FIG. 4 shows voltage and current waveforms. (1) is a visiting electric 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, (23) is a current command generator, (31)
(32) is a limiter, (33) is a limiter detector, (34)
) is a limit value setter. Note that the same reference numerals in the figures indicate the same or corresponding parts.

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. In a PWM power converter for converting into AC power, a first current command generation means for commanding the current on the AC side of the first power converter, and a first current command generating means for limiting the magnitude of the current command to a predetermined value. limiting means, limiter detection means for detecting that the magnitude of the current command is limited by the first limiting means, and a second current for commanding the current on the alternating current side of the second power converter. A command generating means, a second limiting means for limiting the magnitude of the current command, and the limiter detecting means, the magnitude of the current command of the first power converter is limited by the first limiting means. When this is detected, the magnitude of the current command on the AC side of the second power converter at that time is changed to the second power converter.
A PWM power conversion device comprising: limit value setting means for setting a limit value of the PWM power converter.