JPH0454873A - Power converter - Google Patents

Abstract

PURPOSE:To provide a voltage step-down function with an input current kept in sine wave form by connecting a voltage step-down chopper between a converter and an inverter, connecting a switch to short-circuit the input side and the output side of the voltage step-down chopper, and turning on the switch in boosting and turning it off in voltage step-down. CONSTITUTION:Converter output voltage raised to shape an input current into sine wave form is compared with a DC voltage command value. When the voltage must be lowered, a switch 54 is turned off to convert the input current into a sine wave with the action of a converter 3 and the DC voltage is lowered by the switching action of the switching element 51 of a voltage step-down chopper 55 and controlled with a control circuit 8 so as to be transmitted to an inverter 4. For smooth turning on and off, the switch is turned on and off when the switching element 51 is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power converter that drives an inverter by increasing and decreasing a DC voltage with an electric motor as a load.

[Conventional technology]

FIG. 2 shows an example of a power conversion device according to the prior art. In Fig. 2, 1 is a power source 2 is a reactor 6 is a smoothing capacitor 7 is a load motor 3 is a switching element 30 to
33, a converter section consisting of a rectifier circuit consisting of four diodes 40-43, and an adle 2 connected to its input side, and an inverter section 4 consisting of switching elements 34-39 and four diodes 44-49. ,
8 is a control circuit for controlling switching of the converter section 3 and the inverter section 4, and 9 is an operating frequency command.The operation will be explained below.

In the converter section 3, an input current is applied, a DC voltage ■de is applied, a zero cross ps signal of the power supply voltage is input to the control circuit 8, the input current becomes a sine wave, and the DC voltage is the V/FfF characteristic of the motor with the load 7. The switching of the switching elements 30 to 33 is controlled by the control circuit 8 so as to be equal to the DC voltage command value predetermined by the operating frequency command 9.

The inverter section 4 uses PWM corresponding to the operating frequency command 9.
/'' turn causes the switching element 34 in the control circuit 8
-39 are controlled and drive the load 7.

[Problem to be solved by the invention]

In order to operate the motor in a low speed range, the motor's V/1'
Low voltage is required to satisfy the characteristics.

However, in conventional converters, the input current is controlled in a sinusoidal manner by controlling the switching of the switching elements, and at the same time, the DC voltage is boosted by the boosting action of the reactor.

Therefore, the DC voltage is at its lowest when no switching is performed; l) The output voltage could not be lowered below the full-wave rectified voltage value. Also, at that time, it was not possible to make the input current sinusoidal.

Therefore, in order to satisfy the motor speed characteristics, the voltage had to be controlled low in the inverter section.

FIG. 3 shows a PWM pattern generation method using a sine wave/triangular wave comparison method.

If the amplitude of the triangular wave is 1, the amplitude of the sine waves ■ and ■ will be the voltage control rate Af1 + Al1. b) Diagram C) Diagram is a)
In the figure, groove patterns are shown for sine waves (■) and (2), respectively. Since K generates a low voltage, the voltage control rate must be reduced to I, like ν2, and the waveform contains many high frequencies with a narrow Norms width, resulting in high motor efficiency and low electromagnetic noise. Optimal 1? Unable to create turn.

[Means to solve the problem]

In the power converter according to the present invention, a step-down circuit is connected between a converter section and an inverter section, and a smoothing capacitor is connected to the input side and output side of the step-down circuit. A switch is connected so as to go around the switching element and reactor part that constitute /4'.

This switch is controlled to turn on when the voltage increases and turns off when the voltage decreases in accordance with the DC voltage command value, and the on/off operation of the switch is controlled so that it operates when the switching element of the step-down chopper is on. There is.

[Effect]

The power conversion device of the present invention compares the converter output voltage with the DC voltage command value determined by the operating frequency command, and when the result of the comparison does not require the step-down converter to step down the voltage, the step-down converter By stopping the operation of 4' and turning on the switch, on-resistance loss of the switching element and loss of the accelerator are eliminated, the input current is made into a sine wave in the converter section, and the converter output voltage becomes equal to the DC voltage command value. It is controlled by the control circuit as follows. When the voltage needs to be reduced in the step-down circuit, the switch is turned off in the step-down section, and the switching of the step-down circuit is controlled so that the DC voltage output becomes the DC voltage command value, and the input current is controlled in the converter section. A control circuit controls it so that it forms a sine wave. In addition, the switch is turned on and off when the switching element of the step-down converter is on so that it can be turned on and off smoothly.

〔Example〕

FIG. 1 is a schematic diagram of a power conversion device according to an embodiment of the present invention.

The same parts as those shown in FIG. 2 according to the conventional example are designated by the same reference numerals, and the description thereof will be omitted.

51Fi switching element, 52 is a reactor.

53 is a diode, 54/d switch, 6' is a smoothing capacitor, and 55 is a switching element 51. Reactor 52.
A step-down circuit consisting of diodes 53, 1/e, su,
A switch 54 connected to bypass the switching element 5 and the handle 62 that constitutes the step-down voltage regulator 55
This step-down section is composed of a step-down circuit A55, and a smoothing capacitor 6' is connected to the input side of the step-down section 50, and a smoothing capacitor 6 is connected to the output side of the step-down section 50.

Next, the operation will be explained.

In the converter section 3, as in the conventional example, the control circuit 8 controls the input current to have a sinusoidal waveform and the DC voltage to be equal to the DC voltage command value predetermined based on the V/T characteristics of the motor of the load 7 and the operating frequency command 9. The switching of the switching elements 30 to 33 is controlled.

However, since the converter section 3 alone cannot reduce the DC voltage below the full-wave rectified voltage, the step-down converter 55
It lowers blood pressure.

The boosted converter output voltage generated to make the input current sinusoidal is compared with the DC voltage command value, and when there is no need to step down, the operation of the switching element 61 of the step-down cap 55 is stopped and the switch 64 is Turn on. This is K
The actuator 52 for switching element 51 is rotated and the actuator 52 for on-resistance loss of switching element 5J is rotated.
It is controlled by the control circuit 8 so that the loss of the converter section 30 is eliminated and only the action of the converter section 30 is transmitted to the inverter section 4.

When it is necessary to lower the voltage, turn off the % switch 54.

It is controlled by the control circuit 8 so that the small input current is converted into a sine wave by the action of the converter part 30, and the DC voltage is stepped down by the switching action of the switching element 5 of the step-down switch 55 and transmitted to the inverter part. There is.

Further, the on/off operation of the switch is performed when the switching element 5 is on so as to be performed smoothly.

As a second embodiment, the same effect can be obtained even if the converter section is configured as shown in FIG.

〔Effect of the invention〕

As described above, by inserting a step-down chip between the inverter and the converter, it is possible to add a step-down effect while keeping the input current in the form of a sine wave, and the DC voltage can be controlled from low to high voltage. Therefore, there is no need for voltage control by the inverter, and the inverter can use the optimum power pattern for the motor as shown in Figure 3 (2), improving motor efficiency and reducing electromagnetic noise.

In addition, by controlling the switch in the step-down section, it is possible to bypass the step-down circuit 4, which is not necessary during step-up, and eliminate loss in the on-resistance and accelerator of the switching elements in the step-down section Δ. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a power conversion device according to a first embodiment of the present invention, FIG. 2 is a schematic diagram of a conventional power conversion device, and FIG. 3 is a schematic diagram of a PWM /+ turn of an inverter. FIG. 4 is a schematic diagram of a power conversion device according to a second embodiment of the present invention.

Claims (1)

[Scope of Claims] A converter unit connected to an AC power source and having a boost control and power factor control function, an inverter unit that converts DC of the converter unit into AC, and a control circuit that controls the converter unit and the inverter unit. A power conversion device comprising: a step-down chopper comprising a switching element, a reactor, and a diode is connected between the converter section and the inverter section, and a smoothing capacitor is connected to the input side and output side of the step-down chopper. A switch is connected to short-circuit the input side and the output side of the step-down chopper, and the switch is turned on when the voltage is increased and turned off when the voltage is stepped down in accordance with the DC voltage command value. Device.