JPS62144595A - Controller for current type inverter - Google Patents

Abstract

PURPOSE:To prevent the commutating failure accident of an inverter from being generated even if set current is suddenly changed owing to an external disorder or the like, by inserting a lamp function generator into the output circuit of a voltage regulator. CONSTITUTION:The input of set current signal for output generated from a voltage regulator 14, to a lamp function generator 30 is provided, and so the output of gradually varied set current signal is generated from the lamp function generator 30. Accordingly, even if the output signal of the voltage regulator is suddenly changed owing to an external disorder or the like, the suddenly changed signal is relaxed to be signal changed at the rate of a specified time change, and so DC intermediate circuit current can be prevented from being suddenly increased, and accordingly, the commutating condenser voltage of an inverter is also changed following a value corresponding with the DC interme diate circuit current. As a result, the inverter can be prevented from generating a commutating failure accident.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a control device for a current source inverter that operates an AC motor at variable speed by setting the ratio between the voltage output by the inverter and the frequency to a predetermined value.

[Prior art and its problems]

FIG. 3 is a control block diagram showing a conventional example of a current source inverter that drives a 4m motor at variable speed.

In FIG. 3, AC 1fif power from an AC power source 2 is converted into DC power by a thyristor rectifier 3, and then
The AC power is converted back into AC power by the inverter 5, and this AC power is used to drive the induction motor 6 at a desired speed. , a DC reactor 4 is inserted in the so-called DC intermediate circuit,
The pulsating portion of the DC intermediate circuit current meId flowing through this circuit is removed.

The inverter 5 has an impark thyristor 51, a commutating capacitor 52, and an inverter diode 53 on the positive 4iX 111111, and an inverter thyristor and ksfM, a capacitor edge, and an inverter diode 57 on the negative side.
commutation capacitors 52 and 5, respectively.
Direct current is converted into alternating current by sequentially turning on and turning on six inverter thyristors 51 and 55 using pressure in the light [' of 6]. Incidentally, the inverter diodes 53 and 57 are used to prevent the charges in the commutating capacitors 52 and 56 from being discharged to the induction motor 6, which is a load.

The operating speed of the induction motor 6 is set by a speed setting device 10. That is, the speed setting device 10 via the acceleration/deceleration calculator 11
The speed setting value obtained from is converted into a frequency setting value by the voltage/frequency converter 18 and is applied to the ring counter 1.The output from the ring counter 19 is then subjected to pulse amplification 6 and then to the inverter thyristors 51 and 55. given to each gate.

Therefore, the on/off order and on/off period of the six inverter thyristors 51 and 55 are controlled by this ring counter 19, and the inverter 5 outputs AC power at a frequency corresponding to the speed setting value. That will happen.

On the other hand, the speed set value outputted from the acceleration/deceleration calculator 11 is inputted to the function generator 12, and the set frequency of the ionization type inverter is the set voltage at one thread between the predetermined functions. is output from. Furthermore, since the output voltage of the inverter 5 is detected by the voltage transformer 23 and the rectifier 24, if the deviation between the above-mentioned set voltage and the output voltage is input to the voltage regulator 14, the output voltage from the voltage regulator 14 is A current setting value that makes the input voltage deviation zero is output. Therefore, when the deviation between the inverter current detected by the current regulator 21 and the rectifier n and this current set value is input to the current regulator 15, a control signal is sent from the current regulator 15 to make the input current deviation zero. By applying the output signal from the discharge current regulator 15 to the gate of each thyristor constituting the thyristor rectifier 3 via the phase shifter 16 and the pulse amplifier 17, the output of the thyristor rectifier 3 is adjusted. The voltage is controlled.That is, the thyristor rectifier 3 and inverter 5 are controlled by the illustrated control circuit, so that the induction motor &6 is given AC power with a voltage-frequency correlation determined by the function generator 12. That will happen.

The AC voltage applied to the induction motor 6 is ■1 frequency is F
If so, it is optimal to operate the induction motor 6 at variable speed to control the ratio of the two, that is, v/F, to be always constant. Therefore, the function generator 12 controls the input speed setting It is normal to output a set voltage proportional to the value.

In the conventional current source inverter control circuit shown in Figure 3,
As already explained, since the output of the voltage regulator 14 is input to the current regulator 15 as a set current, disturbances such as ζ
As a result, when the output of the voltage regulator 14 changes step-by-step, the inverter current may suddenly increase to 9, leading to commutation failure.

The cause of commutation failure is described below.As the commutation operation of current source inverters is well known, detailed explanation thereof will be omitted. There is a period of commutation type,
During this commutation type fx period, a commutation spike 1 pressure occurs.

Figure i4 is a waveform diagram showing the commutation spike voltage, where the solid line shows the commutation spike voltage waveform and the broken line shows the commutation capacitor voltage waveform. Now, the voltage of the induction motor 6 (line-induced voltage) is EM, the power factor angle of the motor is φ, the motor leakage inductance is subtracted, the DC intermediate circuit current is Id, and the capacitance of the commutating capacitor is C. The peak value Ep of the current spike voltage is given by equation (11).

The commutating capacitor voltage VC is equal to the commutating spike voltage Ep as shown in Figure 4, and this E.

As is clear from the formula fi1, the value of depends on the DC intermediate circuit current Id.

Diagram Zα5 is a diagram showing the reverse bias time of the inverter thyristor, where To represents the reverse bias time and c represents the commutation capacitor voltage. Expressing this reverse bias time To in a mathematical formula is as follows. The following equation (2) is obtained.

Here, Id is the DC intermediate circuit current, and C is the commutating capacitor! ! The fact that it is a tolerance amount is the same as in the case of equation (1).

Assume that the DC intermediate circuit current is commutated at a value of Id+, and the commutating capacitor voltage becomes VCI. If for some reason the DC intermediate circuit current suddenly increases to Idz, which is larger than Idt, the commutating capacitor voltage will still remain at VCt, so the reverse bias time To will be shortened as shown in equation (2). It is obvious that commutation failure may occur due to insufficient reverse bias time To. FIG. 6 is a waveform diagram showing the cause of commutation failure.

Figure 6(a) shows the change in the commutating capacitor voltage ■c, and Figure 6(b) shows the change in the DC intermediate circuit current 1 (10). In other words, at time 11, the DC intermediate circuit current commutates at a value of Idt, so that when the commutation capacitor voltage is VCI, the DC intermediate circuit current becomes Idz.
, the commutating capacitor voltage will still be VCI
Therefore, the reverse bias time T.

This indicates that there is a risk of commutation failure due to insufficient amount.

As mentioned above, in the conventional circuit shown in FIG.
If the output of the electric compression moderator 14 changes suddenly, the DC intermediate circuit tiId may change suddenly and the inverter 5 may fail to commutate, resulting in the inconvenience that the induction motor 6 cannot be commutated. be.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a current source inverter that can prevent inverter commutation failure accidents even if the set current changes suddenly due to disturbances or the like.

[Key points of the invention]

In this invention, when the set current changes suddenly due to disturbance etc., the DC intermediate circuit current also changes suddenly.
This method focuses on the fact that the idle bias time becomes short due to no voltage change, resulting in an Iit failure, and a ramp function generating means is inserted into the output circuit of the voltage μ node means.
The output of the ramp function generating means is applied as a set current to the current adjusting means to moderate the change in the DC intermediate circuit current.

Reduction of reverse bias time (this is intended to prevent commutation failure due to this).Furthermore, by changing the rate of change of the signal output from the ramp function generating means in accordance with the set frequency of the inverter, It is also intended to improve response.

[Embodiments of the invention]

FIG. 1 is a control diagram showing an embodiment of the present invention, and the content of the present invention will be explained below with reference to FIG.

In FIG. 1, AC power from an AC power supply 2 is converted into DC by a thyristor rectifier 3 and output to a DC intermediate circuit. A DC 11 accelerator 4 is inserted into the DC intermediate circuit, and after removing the pulsating portion of the current Id flowing through the DC intermediate circuit, the current Id is inputted to the inverter 54. The inverter 5 has a positive side inverter thyristor 51. Commutation capacitor 52, inverter diode 53, and negative inverter thyristor 5. It is composed of a commutating capacitor 56 and an inverter diode 57, and converts input current into alternating current. The current source inverter, which is composed of the above-mentioned cylindrical star rectifier 3, DC reactor 4, and invanitor 5, converts the AC power input from the AC power supply 2 into AC power of a desired voltage and frequency, and outputs the AC power. , the induction motor 6 can be operated at any speed.

The operating speed of the induction motor 6 is set to an arbitrary value by a speed setting device 10. The speed set value from this speed setter 10 is converted into a speed set value that changes at a predetermined rate of change by an acceleration/deceleration calculator 11, and is then passed through a function generator 12 and a voltage/frequency converter 1.
8 is input.

The voltage/frequency converter 18 converts the input speed setting value into a frequency setting value 1 and outputs it to the 11 ring counter 19. Based on this input, the ring counter 19 selects the six inverter thyristors 51 that make up the inverter 5.
The order and on/off period for turning on and off the + 55 are determined and outputted to the gates of each inverter thyristor 51 and 55 via a pulse intensifier.

Therefore, the inverter 5 outputs AC power at a frequency corresponding to the speed setting value set by the speed setting device 10. Note that commutation capacitor 52 r 5 that constitutes inverter 5
+j uses the Kyuden voltage to connect the inverter thyristor 5.
1155 + sequential commutation, and inverter diodes 53 and 57 are commutating capacitors 52156
This is to prevent the electric charge accumulated in the motor from discharging to the induction motor 6, which is a load.

The speed setting value input to the function generator 12 is a setting value that has a predetermined functional relationship with the setting frequency of the current source inverter.
This function generator 12 outputs the α pressure. Temptation 4
The voltage of the AC power applied to the motor 6 is ■, and the frequency is F.
It is well known that controlling the ratio between the two, that is, '17I2, to be always constant is optimal for variable speed operation of the induction motor 6. Therefore, the function generator 12 outputs a set voltage proportional to the input speed set value. Therefore, the voltage 1114M between the set voltage from the function generator 12 and the output voltage of the current source inverter detected by the instrument transformer n and the rectifier is sent to the voltage regulator 14, which is composed of a proportional-integral calculator. When input, this voltage regulator 14 outputs a set current signal that makes the input voltage deviation zero.

In the present invention, the set current signal output from the % voltage regulator 14 is input to the rung function generator, so a set current signal that gradually changes is outputted from the ramp function generator 530. The rate of change of this set current signal is set to a value corresponding to the set frequency of the current source inverter.
The speed setting value output from the acceleration/deceleration calculator 11 is guided to this ramp function generator I to change the slope of the output signal.

The current regulator 15, which is composed of a proportional-integral calculator, inputs the deviation between the set current output from the ramp function generator I and the inverter current detected by the current transformer 21 and the rectifier η. , outputs a control signal that makes this input current deviation zero. The output signal from this current regulator 15 is passed through a phase shifter 16 and a pulse amplifier 17 to a thyristor rectifier 3.
Since the output voltage of the thyristor rectifier 3 is controlled, the DC intermediate circuit current Id is applied to the gate of each thyristor composing the thyristor. FIG. 2 (A) shows the change in the kh current capacitor voltage ■c, FIG. 2 (B) shows the change in the output of the voltage A moderator 14, and FIG. The changes in the input of the current regulator 15 are shown in FIG. 2, and the changes in the DC intermediate circuit current 1d are shown in FIG. 2, and the horizontal axis is the time axis in both cases.

As is clear from FIG. 2, even if the output of the voltage regulator 14 suddenly changes in a step-like manner, the input to the current regulator 15 is moderated to keep changing due to the action of the ramp function generator I. Therefore, the change in the DC intermediate circuit current Id also becomes gradual. Corresponding to this increase in the DC intermediate circuit current Id, the commutation capacitor voltage vc also increases, so the reverse bias time To shown in equation (2) does not decrease, so the risk of commutation failure can be avoided. . Note that the time T shown in FIG. 2(a) corresponds to 60 degrees in electrical angle, so if one frequency increases, this time T becomes shorter. Therefore, there is no problem in increasing the rate of change, that is, the slope R, of the set current signal output from the ramp function generator I, and when operating the inverter at a low frequency, the set current signal has a gentle slope.

〔Effect of the invention〕

According to this invention, by providing the ramp function generating means on the output side of the voltage regulating means constituting the control device of the α-flow type inverter, the output signal of the voltage regulating means can be prevented from changing rapidly due to disturbances or the like. However, since the sudden change signal is relaxed into a signal that changes at a predetermined rate of change over time, it is possible to prevent the current from increasing rapidly in the DC intermediate circuit. It changes to follow the value commensurate with the intermediate circuit current. This makes it possible to avoid accidents where the inverter causes a commutation failure accident, but with a small investment of installing a ramp function generating means, it is possible to obtain a great effect of avoiding the possibility of interruption of operation of the current type inverter. I can do it. It goes without saying that the rate of change over time of the set voltage that is moderated by the ramp function generating means corresponds to the set frequency of the inverter.

[Brief explanation of drawings]

FIG. 1 is a control block section showing the embodiment ν1 of the present invention, and FIG. 2 is an operation waveform diagram showing the operation of each part in the circuit of the embodiment ν1 shown in FIG. 1. FIG. 1 shows a conventional example of a current source inverter that drives a motor at variable speed
tiIJ a block diagram, FIG. 4 is a waveform diagram showing the commutation spike voltage, FIG. 5 is a diagram showing the reverse bias time of the inverter, and FIG. 6 is a waveform diagram showing the cause of commutation failure. 2... AC power supply, 3... Thyristor rectifier, 4...
・DC reactor, 5... Inverter, 6... Induction motor. 10...Speed setter, 1]...Acceleration/deceleration calculator, 1
2...Function generator, 14...' wake-up pressure regulator, 15.
・・Current regulator, 16...# Phase controller, 17, 20...
- Pulse amplifier, 18... Voltage-frequency converter, 19
...Ring counter, 21...Current transformer, 22 Shiba・
... Rectifier, n... Instrument transformer % Addition... Ramp function generator, 51155... Inverter thyristor,
52, 56...K current capacitor, 53.57...
Inverter die Figure 2-J Figure 4 Figure 5 Figure 1 Electric Figure 6

Claims (1)

[Scope of Claims] 1) Voltage regulating means that operates according to a voltage deviation between a set voltage corresponding to a set frequency of a current source inverter and an output voltage of this current source inverter, and an output signal of this voltage regulating means and the The AC motor can be operated by controlling the ratio between the voltage and frequency output by the current source inverter to a predetermined value using a control device equipped with a current adjusting means that operates according to the current deviation from the current flowing through the current source inverter. What is claimed is: 1. A control device for a current source inverter that operates at variable speed, comprising ramp function generating means for changing the output signal of the voltage adjusting means at a predetermined rate of change over time. 2) In the control device according to claim 1, the ramp function generating means is a ramp function generating means that outputs a signal with a time change rate corresponding to a set frequency of the current source inverter. A control device for a current source inverter.