JPS5926191B2 - Current source inverter disturbance prevention circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a disturbance prevention circuit for a current source inverter.

In general, current source inverters control the current, so they do not have the disadvantages of a constant voltage inverter such as fuse blowing in the event of a short circuit or commutation failure, and the current is automatically controlled by the action of the current minor loop. Although it has the excellent feature of preventing abnormal rises and ensuring stable operation at all times, it has the disadvantage that the frequency is quite high and disturbances are likely to occur, especially under light loads.

Conventionally, measures to prevent this disturbance have been taken, such as providing a reactor on the output side of the inverter and passing a dummy current, but this has resulted in problems in terms of efficiency and economy.

This disturbance phenomenon is caused by the control delay caused by the DC reactor inserted in the forward conversion section and inverse conversion section of the current source inverter, and this control delay is compensated by correcting the frequency using the signal accompanying the disturbance phenomenon. Various methods have been considered to achieve this. This conventional method for preventing disturbances is based on a differential signal of current or a differential signal of voltage. However, this control delay is caused by the power factor changing first when the load changes, then the DC voltage on the inverse conversion side changing, and then the current changing. Therefore, conventional current and output voltage detection has the disadvantage of causing a delay. An object of the present invention is to provide a disturbance prevention circuit with excellent quick response by detecting the power factor and applying the differential value to the oscillator as a correction signal.

The illustrated embodiment will be specifically described below.

In the figure, 1 is an AC power supply. 2 is a forward conversion circuit,
It receives input from an AC power source 1 and performs output control based on phase control of the component thyristor elements.

Reference numeral 3 denotes an inverse conversion circuit which receives the output from the forward conversion circuit 2 as an input via a constant current reactor 4, and its output is supplied to a load motor 5.

A phase shifter 6 supplies a phase control command for the thyristor in the forward conversion circuit 2 based on a command from the current controller 7.

This current controller □ receives input from a current transformer 8 that detects the current between the AC power supply 1 and the forward conversion circuit 2, and operates the current transformer 8, the current controller T, the phase shifter 6, and the forward conversion circuit 2. It constitutes a current minor loop. Reference numeral 9 denotes a voltage controller, and as its input, the output of the inverse conversion circuit 3 is guided through a transformer 10, and at the same time, the output from the command unit 11 is guided through a ramp function generator 12.

13 is a power factor detector which obtains a load voltage command through the transformer 10 and at the same time obtains a load current command through a current transformer 14 and a rectifier 15 in sequence.

A differentiator 16 differentiates the output signal from the power factor detector 13.

17 is a V/F converter that controls the distributor 18 based on the input from the ramp function generator 12 and the differentiator 16;
The frequency of the inverse conversion circuit 3 is regulated.

That is, when the load power factor is maintained constant, no output is obtained from the differentiator 16, but when the load power factor changes, an output is obtained from the differentiator 16.

By the way, the output from this differentiator 16 is the V/F converter 1
This is to control the pulse generation phase of No. 7 in the direction of compensating for the change in power factor. In the above configuration, first, the signal given by the command unit 11 is sent to the voltage controller 9 and the V/F converter 1 while the ramp function generator 12 prevents sudden changes in the command.
7 is given.

At this time, the voltage controller 9 compares the output signal of the ramp function generator 12 and the detection signal of the inverse converter 3, and regulates these signals so that they match. On the other hand, the current controller 7 compares the output of the voltage controller 9 and the output from the current transformer 8 to control the current, which is applied to the transfer device 6 and controls the output voltage of the forward conversion circuit 2. Then, the output of the ramp function generator 12 is given to the V/F converter 17, converted into a pulse signal, and distributed into three phases by the distributor 18, regulating the firing period of each thyristor of the inverse conversion circuit 3. . On the other hand, the power factor detector detects the power factor by detecting the load voltage and load current using the transformer 10, current transformer 14, and rectifier 15, respectively, and when the power factor changes, the amount of change is A corresponding output from the differentiator 16 is obtained. In this way, when the motor 5 is being driven by the current source inverter circuit mainly composed of the forward conversion circuit 2 and the inverse conversion circuit 3 in a normal state due to the disordered L, the change in power factor that causes the disorder is caused. If this occurs, an output is immediately obtained from the differentiator 16, and this output automatically controls the V/F converter 17 in the direction of preventing disturbance. That is, the pulse frequency from the distributor 18 is automatically shifted in the direction of preventing disturbance. Although the above embodiment shows an example in which the output of the differentiator 16 is supplied to the V/F converter 17, the output from the differentiator 16 is supplied to the ramp function generator 12. You can also expect young fruit to have a similar effect. As mentioned above, current source inverters generally have high frequencies, and disturbances are likely to occur particularly at light loads.

This is because when a disturbance such as a load change occurs, the voltage control loop inevitably has a delay due to the DC reactor connecting the forward conversion circuit and the inverse conversion circuit, making it impossible to respond quickly. When this disturbance is about to occur, attempts are made to detect it and provide a correction signal to the inverse conversion control frequency to cover the delay of the voltage control loop, but conventional methods detect the change in current, It detects the amount of change in the output voltage, and inputs the differential change value of the current and output voltage into an oscillator (V/F converter) to prevent disturbances. However, when there is a load change that causes disturbance, the load factor changes first, and then the load voltage and load current change. Therefore, since the configuration according to the present invention detects the change in the power factor and detects the process leading to the occurrence of disturbance, it is possible to prevent the occurrence of disturbance due to detection delay, and it is possible to prevent the occurrence of disturbance due to detection delay. Compared to the disturbance prevention means, this method has the practical advantage of being able to reliably prevent disturbances without causing a decrease in the child's rate.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the present invention. 2... Forward conversion circuit, 3... Inverse conversion circuit, 4... DC reactor, 13... Power factor detector, 16...・Differentiator.

Claims (1)

[Claims] 1. In a circuit configuration in which a DC reactor is interposed between the output side of a forward conversion circuit that receives AC input and the input side of an inversion circuit, and load power is supplied from the output side of the inversion circuit, the connection between the inversion circuit and the load is It is equipped with a power factor detector that detects the power factor based on voltage and current, and a differentiator that changes the output according to changes in the output of this power factor detector.The output of this differentiator is used to calculate the firing period of the inverse conversion circuit. A disturbance prevention circuit for a current source inverter that has a circuit configuration that is one of the control elements.