JPH03118769A - Power converter - Google Patents

Abstract

PURPOSE:To reduce the harmonic current components of currents to be supplied to an AC motor by operating the harmonic current components on the output side of a main power converter from the phase reference and amplitude refer ence of the output currents of the main power converter, and negating the harmonic current components. CONSTITUTION:The harmonic currents of a main inverter are sought in advance by subtracting main inverter basic currents from main inverter output currents. Next, a harmonic current arithmetic unit 21 is set so that it may output harmon ic current components according to them when an amplitude reference Im* and a current phase reference theta* are input. Here, a PWM control circuit 17 compares the currents outputted by a sub inverter 15 and detected with a current detector 6c with the harmonic currents outputted by the harmonic current arithmetic unit 21, and controls the gate signal of the sub inverter 15 so that it may negate the harmonic currents. Hereby, harmonic currents practically cease to flow to an induction motor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to a power converter that drives an AC motor or the like and is capable of reducing harmonic current components by 1%.

(Prior art) For large-capacity power converters that drive all AC motors, devices with high switching capabilities are expensive, so a 1200 square wave current source inverter device consisting of a swivel transistor or the like with low switching capability is used. Generally applied.

FIG. 6 shows an example of a variable speed drive device for an AC motor to which a 120' square wave current source inverter device is applied.

The device shown in Fig. 6 converts power from an AC power source 1 into a rectifier 2, a DC reactor A/3, and a 120' current-carrying type inperter 4.
Convert the variable frequency text into variable voltage AC power,
This is a device that drives an induction motor 5.

The current detected by the current detector 6a and the current reference signal set by the current amplitude setter 7 are compared and controlled by the current control circuit 8 to obtain a rectifier 20 phase reference signal. The phase control circuit 9 outputs a date pulse according to the phase reference signal.

Also, the frequency reference signal ω set by the frequency setter 10
0 is time-integrated using an integrator 1 to obtain the current phase reference θ* of the inverter. The pulse distribution circuit 12 has a current phase reference θ0
Outputs dart pulses accordingly.

As described above, AC power is once converted to DC power,
It is possible to convert the current into alternating current with a different frequency again and drive the induction motor 5 at variable speed.

(Problems to be Solved by the Invention) In the conventional device shown in FIG. 6, the current output by the inverter 4 is a 1200 square wave as shown in FIG. 7, and contains many harmonic currents.

This harmonic current may cause torque ripple or harmonic loss to the motor 5, or may cause resonance in the mechanical system.
There were problems such as overheating of the electric motor 5.

Also, the current on the AC power supply side is the same as in Figure 7.

Since the current is a 120° square wave, there is a problem in that harmonic current flows into the AC power supply.

Conventionally, a method is known in which an active filter is attached to the AC power source to absorb harmonic currents from the AC power source.

FIG. 8 shows an example of an active filter.The operation of the active filter 14 will be briefly explained.

The AC power supply 1 supplies power to a main power converter 13 that generates harmonics. Inverter 15 is connected in parallel to main power converter 13 . The current flowing through the main power converter 13 is detected by the current detector 6b, and the fundamental wave removal filter 16
Find the current of the harmonics.

The harmonic current flowing through the AC power supply 1 can be canceled by controlling the current in the PWM control circuit 17 so that the current detected by the current detector 6c matches the harmonic current.

When this active filter is applied to the output side of a power conversion device, the following problems occur.

Unlike the AC power supply 1, the impedance of the induction motor 5 is large, and the control system of the main power converter 130 is.

They are connected in parallel and are affected by nine active filters 14.

In addition, since the harmonic current is detected by the current detectors 6b and 6a, the control system for controlling the harmonic current is a closed loop control system, which may be unstable depending on the frequency output by the main power converter 13. There is an area where

Therefore, an object of the present invention is to provide a power converter device with less harmonic current.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a main power converter device including a current source inverter device, and a phase reference and a phase reference for the output current of the main power converter device. It is characterized by comprising a harmonic current calculating means for calculating a harmonic current component on the output side of the main power converter from an amplitude reference, and a sub power converter that is subjected to pwu control so as to cancel the harmonic current component. That is.

(Function) By configuring as described above, the harmonic current component of the output current of the main power converter can be canceled by the sub power converter, and the harmonic current of the current supplied to the AC motor can be canceled by the sub power converter. component can be reduced, and the rotational pulsation of the electric motor can be reduced. Further, since the harmonic current is calculated by calculation from the current amplitude reference and the current phase reference without performing current feedback, stable control is possible without closed loop control.

(Example) FIG. 1 is a block diagram showing one embodiment of the present invention.

This device corresponds to the device in which the main power converter 13 is exactly the same as the device shown in FIG. 6, with the addition of a sub power converter 18 and a transformer 20h.

The sub power converter 1B"ll will be explained below. The main circuit of the sub power converter 18 operates as a voltage source inverter consisting of a DC capacitor 19 and a sub converter 15.

The output of the sub-inverter 15 is connected in parallel to the output of the main inverter 4 via a transformer 20a.

The control circuit of the sub power converter 18 includes a harmonic current calculator 2
1, a current detector 6c%m, and a control circuit 17. The harmonic current calculator 21 calculates the harmonic current component of the current output from the main inverter 4 based on the current amplitude reference l;l set in the main power converter 13 and the current phase reference θ0.

FIG. 2 is a detailed diagram for explaining the operation of the harmonic current calculator 2.

The output current of the main inverter 4 can be determined as a function of the current amplitude reference l:n and the current phase reference θ0, as shown in the 29th case, without performing current detection.

The fundamental wave current of the main inverter 4 is calculated mathematically by the fundamental wave f7-1 of the inverter output current shown in FIG.

The harmonic current of the main inverter 4 can be found by subtracting the main inverter fundamental current from the main inverter output current.
The waveform is shown in figure (c). In this way, when the harmonic current component is determined in advance and the current amplitude reference l:n and current phase reference θ0 are input, the harmonic current calculator 2 outputs the harmonic current component accordingly. Set .

This will be explained using FIG. 1 again. The groove control circuit 17 compares the current output by the sub-inverter 15 detected by the current detector 6c with the harmonic current output by the harmonic current calculator 21, and controls the sub-inverter so as to cancel the harmonic current. Controls 15 dart signals.

By the above operation, almost no harmonic current flows through the induction motor 5, and driving with a sine wave current becomes possible.

The same components are used in the apparatus shown in FIG.

Sub-rectifier 22 that supplies DC capacitor 1911C power
Equivalent to adding .

In the embodiment shown in FIG. 1, when the output frequency of the main inverter 4 decreases, the charging/discharging time of the DC capacitor 19 becomes longer and the terminal voltage of the DC capacitor 19 fluctuates greatly, causing - When the voltage exceeds the withstand voltage rating of f7 19), the voltage decreases and the sub-I/parter 15 becomes unable to output current. In order to prevent this, the capacitance of the capacitor 19 must be increased, but this is uneconomical.

Therefore, as shown in FIG. 3, a sub-rectifier 22 capable of power regeneration is connected in parallel to the DC converter 19, and the energy for charging and discharging the capacitor 19 is supplied using the sub-rectifier 22''Ik. , suppresses voltage fluctuations of the DC capacitor 19.

Furthermore, another embodiment of the present invention will be explained using FIG.

In FIG. 4, components given the same numbers as in FIG. 3 are the same elements, and their explanations will be omitted.

The difference between this embodiment and the embodiment shown in FIG. 3 is that the sub-rectifier 22
The point is that it works to remove harmonic current flowing in the AC power supply. The harmonic current of the current flowing into the rectifier 2 is the current amplitude standard set by the current amplitude setting device 7! Second, the phase reference θ° output from the current control circuit 8 is determined by the same method as explained in FIG.

The field M control circuit 17a performs current control so that the current detected by the current detector 6d matches the harmonic current, thereby canceling out the harmonic current flowing through the AC power supply 1.

Further, another embodiment of the present invention will be explained using FIG.

In FIG. 5, components given the same numbers as in FIG. 1 are the same elements, and their explanations will be omitted.

The embodiment shown in FIG. 5 is different from FIG. 1 in that the sub power converter 18 operates as a current source inverter by a combination of a DC reactor 3a and an converter 15h. It is clear that the same effect as the first embodiment can be obtained in this example as well.

In the above description, an induction motor is used as an example of the AC motor, but the AC motor is not limited to the induction motor, but may be any other AC motor, or may be any AC load other than the electric motor. Furthermore, the capacity of the sub-inverter can be further reduced by multiple-connecting the main power converters and reducing harmonic components of the current output by the main power converters.

[Effects of the Invention] As explained above, according to the present invention, the harmonic components of the current output by the main power converter can be canceled out by the sub power converter having a smaller capacity than by the main power converter. It is possible to supply a sinusoidal current to the connected AC load.

Also, if it is a method to detect the current and find the harmonic components,
This constitutes a closed-loop control system, and there is an unstable region; however, in the present invention, the harmonic components are calculated from the set values of the main power converter. There are advantages that don't exist.

Furthermore, in a 120' square wave inverter, the current phase flowing through the load changes only every 60°, but according to the present invention, the current phase can be changed continuously, improving control response. .

Furthermore, since a sinusoidal current flows through the load, voltage spikes do not occur during commutation of the main power converter, the commutation period is shortened, and the power factor is improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the present invention in detail, and Figs. 3 to 5 show different embodiments of the present invention. Block Diagram,
FIG. 6 is a block diagram of a conventional device, FIG. 7 is an output current waveform diagram of the power conversion device shown in FIG. g6, and FIG. 8 is a block diagram showing an example of use of an active filter. J... AC power supply, 2... Main rectifier, 3... DC reactor, 4... Main inverter, 5... Induction motor, 6h to 6d... Current detector, 7... Current Amplitude setter, 8... Current control circuit, 9... Phase control circuit, 1
0... Frequency setting circuit, 11... Integrator, l J-
t4 Lux distributor, 13... Main power converter, 14...
・Active filter* J5. Jj &... Sub-inverter, 16... Basic pass removal filter, 411.11&
, 17b...Field M control circuit, 18...Sub power converter, 19...DC=7 capacitor, 20 &, :l
Ob-) U/S, 21, 278-! Harmonic current calculator, 22... sub-rectifier.

Claims (2)

[Claims] (1) A main power converter device consisting of a current source inverter device, and a harmonic current calculation that calculates a harmonic current component on the output side of the main power converter device from a phase reference and an amplitude reference of the output current of the main power converter device. A power conversion device comprising: a sub-power conversion device that is subjected to PWM control to cancel the harmonic current component. (2) A main power converter comprising a current source inverter device, and a first harmonic that calculates harmonic current components on the output side of the main power converter from a phase reference and an amplitude reference of the output current of the main power converter. wave current calculating means, a first sub power converter which is PWM-controlled to cancel the harmonic current component, and a first sub power converter that performs PWM control to cancel the harmonic current component; a second harmonic current calculation means that calculates a harmonic current component on the input side; and a second harmonic current calculation means that is PWM-controlled to cancel the harmonic current component on the input side.
What is claimed is: 1. A power conversion device comprising a sub power conversion device.