JPH0525995U - Inverter control circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent an abnormal stop due to the operation of the overcurrent protection function or overheating of the motor for a load with a large starting torque. [Structure] The basic V / for operating the three-phase induction motor 3
The V / F pattern data storage circuit 7 is provided which can set the F pattern to an arbitrary V / F ratio for an arbitrary time only at the time of starting.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to frequency / voltage control of an inverter that operates a three-phase induction motor at a variable speed.

[0002]

[Prior Art]

 FIG. 3 is a circuit block diagram of a conventional inverter. In the figure, 1 is a three-phase commercial power supply, 2 is an inverter main circuit, 3 is a three-phase induction motor, 4 is a start-stop switch, 5 is a frequency setter, 6 Is a frequency control circuit, 7 is a V / F pattern data storage circuit, and 8 is a voltage control circuit.

Next, the operation will be described. The three-phase commercial power supply 1 is converted into a variable frequency and a variable voltage by the inverter main circuit 2, and the three-phase induction motor 3 is operated at a variable speed. In order to obtain a variable frequency and a variable voltage, the control unit uses the frequency control circuit 6 to convert the analog signal set in advance by the frequency setter 5 into a signal corresponding to the output frequency, and the signal is converted into the V / F pattern. It is applied to the data storage circuit 7 and the voltage control circuit 8. In the voltage control circuit 7, the output signal of the V / F pattern data storage circuit 7 and the output signal of the frequency control circuit 6 are used to create a signal corresponding to the output frequency and output voltage applied to the three-phase induction motor 3, and the inverter It is given to the main circuit 2. Normally, the relationship between the output frequency and the output voltage is set as shown in FIG. In the low frequency range, the slope of the graph can be changed as shown by the dotted line in order to correct the voltage drop due to the primary winding resistance of the three-phase induction motor, and the V that matches the three-phase induction motor and the load can be changed. / F pattern can be set.

Further, in the start-stop, when the signal is turned on by the start-stop switch 4, the acceleration starts from the starting frequency and then to the frequency set by the frequency setting device 5. The time required for acceleration and deceleration at which deceleration is started and stopped by the signal OFF is preset. (See Figure 5)

[0005]

[Problems to be solved by the device]

 The conventional inverter control circuit operates as described above. When operating a load with a large static friction torque (eg, pump, compressor, etc.), if the V / F pattern is set high in order to increase the starting torque, the low speed In the region, the three-phase induction motor 3 becomes overexcited, the inverter output current increases, the inverter overcurrent protection function works, and the three-phase induction motor overheats.

The present invention has been made in order to solve the above problems, and to obtain an inverter control circuit which can eliminate the need to increase the inverter capacity or the capacity of a three-phase induction motor more than necessary. With the goal.

[0007]

[Means for Solving the Problems]

 The inverter control circuit according to the present invention is provided with a circuit that can set an arbitrary V / F ratio for an arbitrary time only at the time of starting, with respect to a basic V / F pattern for operating a three-phase induction motor. .

[0008]

[Action]

 In the present invention, the means for changing the V / F pattern only at the time of starting increases the output voltage only at the time of starting, increases the torque generated by the three-phase induction motor, and starts accelerating, in response to the demand for a large starting torque due to the static friction torque. After that, it returns to the normal V / F pattern and acts to perform optimum V / F control.

[0009]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 11 is a one-shot multivibrator. Next, the operation will be described. FIG. 2 shows a time chart showing the operation. When the start-stop switch is turned on, the one-shot multivibrator 11 is turned on for t ₁ . This signal is input to the frequency control circuit 6 and the V / F pattern data storage circuit 7. The frequency control circuit 6 outputs a signal corresponding to f ₁ during t ₁ by the ON signal of the start-stop switch and the ON signal of the one-shot multivibrator 11. The V / F pattern data storage circuit 7 outputs data corresponding to v _ST to the voltage control circuit 8 during t ₁ . In the voltage control circuit 8, the output voltage signal corresponding to v _ST is given to the inverter main circuit 2 during t ₁ by the output of the frequency control circuit 6 and the output of the V / F pattern data storage circuit 7. After t _1, the V / F pattern is set in advance as in the prior art. Since the output frequency and the output voltage are controlled as described above, the torque generated at the start of the three-phase induction motor can be increased by outputting a voltage higher than the normal V 1 / F ratio during t ₁ . After it starts moving, it returns to the normal V / F pattern, so overexcitation in the low speed range can be prevented.

Example 2. Although one embodiment has been described by using the circuit diagram, it can be implemented by software using a microcomputer.

[0011]

[Effect of the device]

 As described above, according to the present invention, it is possible to increase the generated torque only at the time of starting, it is possible to prevent unnecessary capacity increase of the inverter and the three-phase induction motor, and it is possible to reduce the cost. can get.

[Brief description of drawings]

FIG. 1 is a circuit block diagram according to an embodiment of the present invention.

FIG. 2 is a time chart showing an operation according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional inverter control circuit.

FIG. 4 is a diagram showing an operation of a conventional inverter control circuit.

FIG. 5 is a diagram showing an operation of a conventional inverter control circuit.

[Explanation of symbols]

 1 Three-Phase Commercial Power Supply 2 Inverter Main Circuit 3 Three-Phase Induction Motor 4 Start-Stop Switch 5 Frequency Setter 6 Frequency Control Circuit 7 V / F Pattern Data Storage Circuit 8 Voltage Control Circuit 11 One-Shot Multivibrator

Claims (1)

[Scope of utility model registration request] 1. In an inverter device for operating a three-phase induction motor at a variable speed, a basic V / F pattern for operating the three-phase induction motor is set to an arbitrary V / F ratio for an arbitrary time only at the time of starting. An inverter control circuit, which is provided with means capable of performing.