JPH04312373A - Inverter - Google Patents

Abstract

PURPOSE:To realize optimum and quickest deceleration and stop without stopping a decelerating operation by a method wherein, while an output frequency is lowered to decelerate a motor, a main circuit voltage level is detected and a deceleration time is varied in accordance with the detected voltage level and the shortest deceleration time is predetermined without performing an overvoltage protective operation. CONSTITUTION:When a motor 8 to which a load 7 is connected is quickly decelerated, a regenerative power from the motor 8 produced by the GD<2> of the load is returned to elevate the terminal voltage of a smoothing capacitor 3. The terminal voltage level is detected by a voltage detector 10 and the detected voltage level is inputted to a deceleration time determining circuit 14. The deceleration time determining circuit 14 generates a deceleration time instruction which is a parameter to change the deceleration time in accordance with the inputted voltage level and outputs it to an acceleration/deceleration control circuit 15. With this constitution, an overvoltage protective operation against the regenerative power can be avoided and the optimum and shortest deceleration time corresponding to the GD<2> of the motor can be automatically predetermined, so that smooth deceleration and stop can be realized.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for variable speed control of an electric motor, and more particularly to an inverter device with improved control characteristics during deceleration of an electric motor.

0002

2. Description of the Related Art Generally, when an inverter device is used to lower the output frequency and decelerate a motor, such as an induction motor, the induction motor enters a regeneration mode and the shorter the deceleration time, the larger the GD2 of the induction motor. The larger the value, the greater the regenerative power generated in the regeneration mode, and the higher the main circuit voltage.

[0003] In order to prevent this main circuit voltage from increasing,
Control is generally used in which the main circuit voltage is detected, and when the detected value reaches a certain value or more, the deceleration is stopped and the output frequency is kept constant. A conventional inverter device that performs such control is shown in FIG.

As shown in FIG. 4, a conventional inverter device includes an AC power supply 1, a rectifier 2 for converting the AC power from the AC power supply 1 into DC power, and a smoothing capacitor 3 for converting the DC power from the rectifier 2 into DC power. A main circuit consisting of an inverter circuit 4 that exchanges AC power with an arbitrary frequency via a frequency setter 5 that sets the output frequency, and generates a frequency reference signal based on the setting value from the frequency setter 5. an acceleration/deceleration time setter 9 that sets the acceleration/deceleration time of the motor 8 that drives the load 7, a voltage detector 10 that detects the DC voltage of the smoothing capacitor 3, and a frequency reference generation circuit 6. , an acceleration/deceleration control circuit 11 that controls acceleration/deceleration time based on each output signal from the acceleration/deceleration time setter 9 and the voltage detector 10, and an inverter circuit 4 based on the output signal from the acceleration/deceleration control circuit 11. PWM control
The control circuit includes a control circuit 12 and a base drive circuit 13 that drives and controls the transistors forming the inverter circuit 4 based on the output signal from the PWM control circuit 12. In this configuration, the voltage of the smoothing capacitor 3 is detected by the voltage detector 10, and the deceleration time is controlled according to the detected value.

For example, as shown in FIG. 5, when the detected voltage value reaches a predetermined value, the output frequency of the inverter device stops decreasing as shown at point P. When the voltage detection value becomes less than a predetermined value by stopping the deceleration, the deceleration operation is restarted according to the deceleration time. Further, due to the increase in the DC voltage (voltage at the smoothing capacitor 3) caused by the regenerated power accompanying this deceleration operation, the deceleration operation and the stop operation are repeated every time the detected voltage value reaches the predetermined value.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, deceleration and stopping are repeated due to regenerative overvoltage when the inverter device decelerates and stops, and depending on the partner machine, smooth deceleration and stop cannot be performed. There was a possibility that the system would be adversely affected. Furthermore, since the amount of regenerated electric power depends on the GD2 of the motor and the deceleration time, it is necessary to conduct a combination test using a system including an inverter and an actual machine in order to avoid overvoltage protection operation and perform deceleration and stop in the shortest possible time.

In view of the above problems, the present invention promptly detects an overvoltage state of regenerative power during deceleration, and
An object of the present invention is to provide an inverter device that can realize smooth deceleration operation. [Structure of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention first converts an AC power source into a DC power source, and in an inverter device that converts this DC power source into an AC power source having an arbitrary frequency, the output frequency and a control means for changing the deceleration time of the motor in accordance with the detection value detected by the voltage detection means. It is characterized by:

[0009]

[Operation] In the inverter device of the present invention configured as described above, the main circuit voltage level is detected while the output frequency is lowered and the motor is decelerated, and the deceleration time is changed according to this voltage level. By setting the shortest deceleration time without activating the overvoltage protection operation, it is possible to perform the optimum and shortest deceleration stop according to the GD2 of the motor without stopping the deceleration operation.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, there is an AC power supply 1 and a rectifier 2 for converting AC power from the AC power supply 1 into DC power.
The main circuit is composed of a smoothing capacitor 3 that smoothes the DC power from the rectifier 2, and an inverter circuit 4 that converts the DC power sent through the smoothing capacitor 3 into AC power having an arbitrary frequency. Furthermore, the inverter circuit 4 is constructed of a three-phase bridge circuit including transistors and diodes.

The control circuit also includes a frequency setter 5 that sets the output frequency, a frequency reference generation circuit 6 that generates a frequency reference signal based on the output signal from the frequency setter 5, and an electric motor that drives the load 7. an acceleration/deceleration time setter 9 for setting the acceleration/deceleration time of the motor 8; a voltage detector 10 for detecting the DC voltage of the smoothing capacitor 3; and a voltage detector 10 for detecting the DC voltage of the smoothing capacitor 3; Based on the deceleration time determination circuit 14 to determine the speed of the motor 8, the frequency reference value from the frequency reference generation circuit 6, the acceleration/deceleration time set value from the acceleration/deceleration time setting device 9, and the output signal from the deceleration time determination circuit 14, An acceleration/deceleration control circuit 15 that calculates the optimum acceleration/deceleration time, a PWM control circuit 16 that performs PWM control on the inverter circuit 4 based on the output signal from this acceleration/deceleration control circuit 15, and an output from this PWM control circuit 16. It is comprised of a base drive circuit 17 that performs on/off control of transistors forming the inverter circuit 4 based on signals. Deceleration operation control in the inverter device of this embodiment configured as described above will be described next.

When the motor 8 to which the load 7 is connected is suddenly decelerated, regenerated power is powered back from the motor 8 by GD2 of the load 7, and the voltage across the terminals of the smoothing capacitor 3 increases. This voltage level is detected by the voltage detector 10, and the detected voltage level is input to the deceleration time determining circuit 14. The deceleration time determination circuit 14 generates a deceleration time command coefficient K, which is a parameter for changing the deceleration time as shown in FIG. 2, according to the input voltage level, and outputs it to the subsequent acceleration/deceleration control circuit 15. Here, the deceleration time determining circuit 14 will be explained in detail. When the output frequency of the inverter device is f, the frequency during deceleration operation becomes fD fD = f-Δf*K. Here, Δf is the amount of change in frequency per unit time when decelerating from the maximum frequency fMAX in t seconds, and Δf=fM
It is expressed as AX/t.

[0014] Then, the detected value of the voltage detector 10 is OP1
In this case, the next frequency f to be output is determined by K determined by the detected value. When the detected value is OP1, deceleration is performed according to the deceleration time set by fD = f - Δf. Further, in the range from OP2 to OP3, fD = f, the frequency becomes constant, and deceleration is stopped. Further, a range larger than OP3 becomes an overvoltage protection operation region. Note that FIG. 3 shows frequency changes during deceleration and stop in this embodiment.

[0015]

As described above, according to the present invention, it is possible to reduce the output frequency, prevent overvoltage protection operation due to regenerative power when decelerating and stopping the motor, and reduce the GD2 of the motor.
Automatically sets the optimal and shortest deceleration time depending on the situation, allowing for smooth deceleration and stopping.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing deceleration time control in the embodiment shown in FIG. 1;

FIG. 3 is a graph showing frequency changes during deceleration in the embodiment shown in FIG. 1;

FIG. 4 is a schematic configuration diagram showing a conventional inverter device.

FIG. 5 is a graph showing frequency changes during deceleration in the inverter device shown in FIG. 4;

[Explanatory diagram of symbols]

1...AC power supply 2... Rectifier 4...Inverter circuit 7...Electric motor 8...Acceleration/deceleration time setter 9...Voltage detector 10...Deceleration time determination circuit 11...Acceleration/deceleration control circuit

Claims (1)

[Claims] Claim 1: In an inverter device that first converts an AC power source into a DC power source and then converts this DC power source into an AC power source having an arbitrary frequency, the main circuit voltage is detected when the output frequency is lowered and the motor is decelerated. An inverter device comprising: voltage detection means; and control means for changing the deceleration time of the electric motor according to a detection value detected by the voltage detection means.