JPS62281771A - Control system for reversible converter - Google Patents

Abstract

PURPOSE:To suppress unnecessary forward reverse change-over, by setting a detector for detecting that converter current is zero. CONSTITUTION:A reversible converter control circuit is composed of a voltage setting unit 8, a voltage regulator 9, a phase shifter 10, forward side and reverse side pulse amplifiers 11-12, a DC voltage detector 13, comparators 14-15, and the like, and by controlling the ignition phase of a power rectifier 3 and a power inverter 4, the DC output voltage of a reversible converter 2 is controlled to be constant, and the power rectifier 5 and the power inverter 4 are switching-controlled. In this case, a current transformer 16, a zero detecting comparator 17, AND gates 18-19, and a flipflop 20 are arranged. Then, whether the DC current of the converter 2 is zero or not is discriminated, and only when it is zero, the signal of high(H)level is applied to the AND gates 18-19. As a result, only when the DC current of the converter 2 is zero, output from the comparators 14-15 is made effective, and forward or reverse change-over is executed.

Description

Detailed Description of the Invention 6. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a control system for a reversible converter that supplies reversible DC power to at least one inverter for driving a motor.

[Conventional technology]

Supply constant DC power from the converter to the inverter,
Generally used is a method in which the alternating current is converted into alternating current with variable voltage and variable frequency through pulse width modulation (pwm) control using an inverter, thereby operating the motor at variable speed. In this case, in order to realize four-quadrant operation of the electric motor, it is necessary to process power in both directions of drive and regeneration, especially when using a DC distribution type inverter that supplies power to multiple inverters with one converter. In large-scale systems, it is economically advantageous to use reversible converters.

FIG. 2 shows a general example of a motor drive system using such a reversible converter and an inverter.

Here, 2 is a reversible converter, and a plurality of inverters 61 to 6n are provided for this, and electric motors 71 to 7n are individually driven at variable speeds via these inverters 61 to 6n. . In addition, in the same figure, 1 is an AC power supply, 5 is
4 is a forward converter, 4 is an inverse converter, and 5 is a smoothing capacitor.

The magnitude and polarity of the DC output voltage of the reversible converter 2 are always constant, but the magnitude of the DC current is different from that of the inverter 61.
The cost is reduced according to the size of the load of ~6n, and the direction of the nuclear current is opposite to each other during driving and during regeneration. That is, during driving, the forward converter 5 operates and direct current flows toward the converter 2 and inverters 61 to 6n, while during regeneration, the reverse converter 4 operates and direct current flows in the opposite direction to the above. This allows power to flow in both directions.

FIG. 3 shows a general example of such a reversible converter control circuit. Here, 8 is a voltage setting device (setting value VR),
9 is a voltage regulator (AV['t), 10 is a phase shifter, 11 is a 1@ side pulse amplifier, 12 is a reverse side pulse amplifier, 16 is a DC voltage detector, and 14.15 is a comparator.

The voltage regulator 9 performs a predetermined control calculation so that the deviation between the voltage setting value vR by the setting device 8 and the voltage actual value vF obtained via the detector 13 becomes zero, and the output is used to control the phase shifter 10. and cranial pulse amplifier 11. Reverse pulse amplifier 1
The DC output voltage of the reversible converter 2 is controlled to be constant by controlling the firing phase of the converter 3 or the inverter 4 through the converter 2. On the other hand, the voltage setting value vR and the voltage actual value vF are guided by comparators 14 and 15, and when VF>VR, the head side gate pulse is turned off and then the reverse side gate pulse is turned on, and when VF<VR, the reverse side gate pulse is turned on. Turn on the cephalic gate pulse after turning off the contralateral gate pulse.

In this way, voltage feedback control and forward/inverse converter switching control are performed.

[Problem that the invention seeks to solve]

While the control circuit described above has the advantage of a simple configuration, it requires a certain amount of switching off time to prevent mutual short-circuiting of the AC power supplies during forward and reverse switching, and during this time the voltage control system is also discontinuous. Because of this, there is a problem in that the DC voltage fluctuates transiently. In addition, because the conditions for forward and reverse switching are determined only by comparing voltages, forward and reverse switching may occur even if the voltage fluctuates temporarily due to load fluctuations, increasing voltage oscillations and making it difficult to control. There is also the problem that the system becomes unstable.

Therefore, it is an object of the present invention to provide a simple control system with stable operation by suppressing unnecessary forward and reverse switching.

[Failure to solve the problem]

A detection means is provided to detect when the DC current of the converter becomes zero.

[Effect]

When switching between drive and regeneration, the output DC current of the reversible converter automatically becomes zero, so by adding the detection results from the detection means to the conventional forward and reverse switching conditions, the demarcation switch can be turned off. To shorten time and avoid unnecessary switching and reverse switching.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.

As is clear from the figure, this embodiment has a current transformer 16,
It is characterized by the provision of a zero detection comparator 17, AND gates 18 and 19, and a flip-flop 20.

That is, the current transformer 16 detects a DC output current equivalent to the converter DC input current, and the zero detection comparator 1
7, it is determined whether the UKt current of the converter 2 is zero or not, and only when this is zero, a high (H) level signal is given to the analogue games 18 and 19. Therefore, only when the DC current of converter 2 is zero, comparator 14
．． The output from 15 becomes valid, thereby performing forward and reverse switching. In other words, when the inverters 61 to 6n switch from driving to regeneration or from regeneration to driving, the DC input current of the inverters 61 to 6n, that is, the converter 2
The output DC current of comparator 17 is always zero.
, and only in this case, AND gate 18
, 19 and in order.

Make the signal for reverse switching valid. Incidentally, the flip-flop 20 is used to temporarily store the output from the AND gates 18 and 19.

In this way, when there is converter output current, Y'ii.

No reverse conversion is performed, and therefore no operation occurs due to temporary voltage sensing due to load fluctuations, thus making it possible to suppress unnecessary forward and reverse switching.

Note that other points are the same as those in FIG. 3, so explanations will be omitted.

〔Effect of the invention〕

According to the present invention, an advantage is provided that simple and stable control can be realized simply by providing a detector that detects that the converter current is zero. It goes without saying that the present invention can be applied to either a system in which one reversible converter is combined with one inverter or a system in which one reversible converter is combined with a plurality of inverters.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a general example of a motor drive system using a reversible converter and an inverter, and Fig. 3 is a block diagram showing a general example of a reversible converter control circuit. It is a block diagram which shows an example. Symbol explanation 1...AC power supply, 2...Reversible converter, 6...Forward converter, 4...Inverse converter, 5...Curved smoothing capacitor , 61-6n... Inverter, 71-7n... Electric motor, 8...
...Voltage setting device?・Tune/voltage regulator (AVR), 10
... Phase shifter, 11 ... Top side pulse amplifier, 12 ... - - Reverse side Halsian 7', 13 ... Curved voltage detection! , 14.15... Comparator, 1
6...Current transformer, 17...Zero detection comparator, 18゜19...And gate, 2o
...Flip-flop, vR... Voltage setting value, vF... Actual voltage value. Agent Patent Attorney Akio Namiki Agent Patent Attorney Kiyoshi Matsuzaki 1 Tsuyoshi 2

Claims (1)

[Claims] A reversible converter comprising forward and reverse converters connected in antiparallel and supplying driving and regenerative reversible DC power to at least one inverter; and a reversible converter that detects the output DC voltage of the converter and sets a predetermined setting. control means for performing predetermined voltage control by selecting one of the reversible converters based on the comparison result; and detection means for detecting that the direct current of the reversible converter has become zero. , and makes the comparison result valid only when the direct current is zero to enable forward and reverse switching operations.