JPS5819185A - Inverter device - Google Patents

Abstract

PURPOSE:To enable to improve the response of an inverter device and to steadily operate the device by switching the device between a pulse width modulation type and a pulse amplitude modulation type during the period between speed varying time and constant speed time. CONSTITUTION:A control circuit 5 of a power inverter and a control circuit 8 of a power reactor are usd by a switching circuit 9 differently according to the signal of a signal source 10. That is, while a motor 6 is accelerating or decelerating, the control circuit 5 is operated to control the output voltage in pulse width modulation, while the thyristor of the power reactor 7 is fully conducted by a control circuit 8 of a power reactor. When the motor 6 is rotated at a constant speed, the control circuit 5 switches the transistor of a power inverter 4 in response to the set frequency, while the thyristor is controlled in phase by the control circuit 8, thereby controlling the voltage charged in a smoothing condenser 3 and controlling the pulse amplitude modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an inverter device for controlling variable speed operation of an AC motor.

In general, when an electric motor is operated at variable speed using the inverter device, there are two main control methods: pulse width modulation method (hereinafter referred to as PWM method) and pulse amplitude modulation method (hereinafter referred to as PAM method). Figure 1 shows an inverter device based on the PWM method. In the figure, (1) is an 8-phase power supply, and (2) is a diode bridge forward conversion section that converts alternating current into direct current. 3) is a smoothing capacitor, (4) is an inverse converter that converts direct current to alternating current, (5) is a control circuit for this inverse converter (4), and (6) is an electric motor.

In this PWM method, the output voltage of the motor (6) is controlled by an inverse converter (4) and a control circuit (5) to obtain an appropriate voltage for each frequency through a chopper control circuit and the waveform is This is shown by PI in the figure2.Thus, it is possible to control the voltage according to the switching speed of the transistor, so it has excellent coordination, but on the other hand, it has the disadvantage that the noise level of the motor is high (Fig. 2). 1 shows an inverter device using the PAM method, where the same reference numerals as in FIG. This is a control circuit for the forward converter (7).This PAM method is a method for controlling the amplitude of the output voltage of the motor (6,). (3) Since the charging voltage is controlled, the output waveform will be as shown at P2 in the figure, and although the response will be worse than the above PWM method, the noise level of the motor will be lower, resulting in quieter operation. [,However, the control method for inverter devices is the PWM method when speed is required, such as in machine tools, etc. Although it is generally accepted that the quiet PAM method is used for 1" knobs and blowers, the PWM method produces noise (Z l ii-,,-
The disadvantage of the PAM method is that it requires compromises in terms of responsiveness.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. By using a signal that determines the operating state of the electric motor, it is possible to detect when the electric motor changes speed, such as acceleration or deceleration. uses a highly responsive PWM method,
In addition, the PA allows for quiet operation after reaching constant speed operation.
The purpose is to provide an inverter device that combines the advantages of the PWM method and the PAM method, respectively, so as to switch to the M method.1. I'm here.

An embodiment of the present invention will be described below with reference to FIGS. 8 and 4.

In the figure, the same reference numerals as in Figures 1 and 2 indicate the same or equivalent parts, and (9) is a switching circuit that switches between PWM and PAM systems, and the head is a signal source that indicates the operating state of the electric motor (5). , this signal source QG can be easily obtained from the digitally configured control circuits (5) and (8).
For example, when the electric motor (6) is outputting a command signal to accelerate or decelerate to a set speed, the level is high, and after the electric motor (6) reaches the set speed, the level is low. The switching circuit (9) is used to selectively use the control circuit (5) of the inverse conversion section and the control circuit (8) of the forward conversion section according to the signal from the primary signal source QO (1).
That is, when the electric motor (6) is accelerating or decelerating, the control circuit (5) of the inverse conversion section operates to perform PWM control on the output voltage, while the control circuit (8) of the forward conversion section controls the thyristor of the forward conversion section (7). When the electric motor (6) becomes fully conductive and operates at a constant speed, the control circuit (6) of the inverse conversion section switches the transistors of the inverse conversion section (4) according to the set frequency, while the control circuit of the forward conversion section switches the transistors of the inverse conversion section (4) according to the set frequency. (8) controls the phase of the thyristor to control the voltage charged to the smoothing capacitor (3), resulting in h1 control.

FIG. 4 is a graph diagram for explaining an example of the operating pattern of the electric motor operated at variable speed by this inverter device. In this figure, the horizontal axis t represents time, and the vertical axis N represents the rotational speed of the electric motor. There is.

Now, the electric motor starts rotating and accelerates in a section M, then reaches a predetermined rotation speed and operates at a constant speed in a section B, then in a section C it does not accelerate, and then in a section it runs at a constant speed. - Then, in section E, the vehicle is decelerated and stopped.

At this time, in each section M, c3sE, where acceleration and deceleration are performed, the operation is switched to highly responsive operation using the PWM method, and in each section B%D, where constant speed operation is performed, the operation is switched to quiet operation using the PAM method. The advantages of each control method are fully utilized to control the variable speed operation of the electric motor.

The above-mentioned motor can be operated by switching to the PWM method when the rotation speed of the motor changes, and to the PAM method when the motor is running at a constant speed. It has a high responsiveness (and has the effect of controlling operation to ensure quiet operation).

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an inverter device using the PWM method, FIG. 2 is a block diagram of an inverter device using the PAM method, FIG. 8 is a block diagram of an inverter device according to an embodiment of the present invention, and FIG. 4 is a block diagram of an inverter device using the PAM method. It is a graph diagram explaining a variable speed operation pattern. In the figure, (1) is an 8-phase power supply, (2) is a forward conversion unit, (
3) is a smoothing capacitor, (4) is an inverse conversion section, (5) is a control circuit for the inverse conversion section, (6) is a motor, (7) is a forward conversion section, (8) is a control circuit for the forward conversion section, (9) is a switching circuit, Q
(I is a signal source. In the figure, the same i symbol indicates the same or equivalent part.

Claims (1)

[Claims] A determining means for determining whether the operating state of the electric motor is constant speed operation or speed changing operation, and a determination signal output from this determining means are input, and the pulse amplitude is determined by the constant speed operation signal. An inverter device equipped with a switching means for switching the distribution motor to be operated using the pulse width modulation method for operation with varying speeds;