JPS609429B2 - How to control cycloconverter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for controlling a cycloconverter, and in particular,
The present invention relates to a control method for switching and operating each of anti-parallel connected forward and reverse thyristor converters constituting a cycloconverter in accordance with the polarity of an output current.

FIG. 1 is a circuit diagram showing the main circuit section of a cycloconverter.

The main circuit of the cycloconverter consists of a thyristor converter 1 for positive side switching and a thyristor converter 2 for negative side switching.

When converters 1 and 2 are operated alternately for a fixed period of time using an AC power supply AC having a frequency f, an AC voltage having a frequency different from that of the AC power supply AC is obtained. The electric motor 3, which is a load, is driven by this frequency-converted AC power source. In Fig. 1, each converter is illustrated schematically, but
Actually, it has arms for the number of AC phases. converter 1,
No. 2 is capable of controlling the output voltage in a sine wave shape by changing the cosine cosQ of the firing phase Q into a sine wave, and the motor current also becomes a sine wave.

By the way, when the polarity of the current is switched, it is transferred from the appropriate converter 1 to 2 or from converter 2 to 1, so it is necessary to switch the operation of the converter accordingly. In the non-circulating current type, the switching occurs after one current disappears.
It is necessary to initiate the other ignition, otherwise a short circuit would occur across both converters. Therefore, conventionally,
It was necessary to set the switching time (the period during which the output currents of both converters are held at zero) to be sufficiently long to take into account cases of bad technique. However, as a result of this, when the output current passes through zero, the current waveform becomes distorted from a sine wave because the current period becomes longer. In particular, when the output frequency is high, the proportion of the zero current period in one cycle of the output current becomes longer, resulting in increased waveform distortion, which may cause problems with motor torque ripple. Particularly in the rolling industry, there are cases where an AC motor is required to have as low ripple as a DC motor, and to meet such requirements, high-speed switching is required. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a cycloconverter that does not cause current short circuits while minimizing switching time.

In order to achieve this object, the present invention maintains the control delay angle Q of the thyristor converter to be made conductive after switching to a predetermined value or more for a predetermined period of time from immediately before the start of ignition of the converter. .

Before explaining the embodiments, the principle of the present invention will be explained. A power supply short circuit occurs when current is flowing through one converter, which should become zero over time.
The next time the other transducer should conduct fires, which is a rare but possible occurrence based on the uncertainty in detecting zero current in the transducer. It is. Thus, a power supply short circuit occurs when the gate of the next converter to be turned on is removed when operation is transferred from one converter to another.

When a short circuit occurs in the power supply, the power supply lines are short-circuited through the thyristors of the converters 1 and 2, and an excessive current flows through the closed circuit. However, as a result of study, the inventors found the following fact. That is, when releasing the gate cutoff of the converter to be turned on next, the control delay angle Q of that converter is 9.
A large value such as 0 degrees means that even if a short circuit occurs in the power supply, no large current will flow in the shorted open circuit; conversely, if Q is 3
If the value is as small as 0 degrees, the initial ignition will generate an overcurrent, which may cause the fuse to blow. Each of FIGS. 2a, b, c, and d, FIG. 3, and FIG. 4 is an explanatory diagram for specifically explaining the above facts.

Figure 2 a, b, c, and d are the main circuits of a cycloconverter that obtains single-phase AC at a different frequency from a three-phase AC power supply, and the period during which the current in the positive converter continues to flow. In the figure, the short-circuit mode is shown when the gate suppression of the reverse transducer is released and its firing is initiated.

Figures 2a and 2b show short circuits (dashed lines in the figure) created by conduction between thyristors RP and TN', and Figures 2c and d show short circuits created by conduction between thyristors TN and SP', respectively. . Figures 2b and 2d show the current circulation over time. FIGS. 3a, b, and c show the thyristor conduction period and the period in which each short circuit occurs at that time (however, overlapping is ignored). Figure 3a shows the thyristor conduction period, and Figure 3b shows the power supply phase voltage from RP to TP and R.
The conductive state of N' to TN' is shown, and FIG. 3c shows the conductive state of RN to TN and RP' to TP, although FIG. The short-circuit current flows due to the power supply voltage included in the short-circuit, and the short-circuit prevention DC reactor and the reactance of the AC power supply suppress its rise. Therefore, the magnitude of the short circuit current is proportional to the time-integrated amount of the power supply voltage acting on the short circuit. The hatched areas in Fig. 3b and c are proportional to this voltage-time integral, and the
The reason for this is when the difference between the two AC power supplies included in the short circuit is positive, and when the short circuit current changes in a sinusoidal manner, the voltage that allows the short circuit current to flow in the direction of increasing, e is included in the short circuit. When the difference between the two AC power sources is negative and the short circuit current changes in a sinusoidal manner, it indicates that the voltage is such that the short circuit current can flow in a decreasing direction. Each figure in Figure 3 shows that the gate is shut off when the firing phase angle QF of the positive side converter is 150 degrees, and that the reverse side converter is firing at the firing phase angle QR = 150 degrees while the positive side current does not disappear. The case where ignition is started at 90 degrees is shown.
In this case, either e comes first, or even if reason comes first, the next largest e appears, so even if a short circuit occurs, the current quickly disappears and the short circuit is recovered. . On the other hand, Fig. 4 a, b, and c show the case where the gate is cut off at QF = 150 degrees as described above, and the reverse side converter starts firing at QR = 30 degrees before the positive side current disappears. shows.

In this case, ■ precedes, and because it is large, an excessive short-circuit current occurs. This is the reason for the above-mentioned difference in firing angle. Therefore, in the present invention, the occurrence of overcurrent is prevented in the following manner. That is, when the gate of the converter is released, a restriction is imposed so that the control delay angle Q of the converter does not become less than a certain value, and the first ignition is performed. At this time, if a short circuit occurs in the power supply as shown in Figure 5a, a certain amount of current will flow through the converter, which should already be non-conducting (the gate signal is cut off), so this should be considered. Either the phase of the converter on the side whose gate has been detected and whose gate has been released is controlled to a sufficiently large value, for example, 150 degrees (hereinafter referred to as gate shift), or the gate of that converter is shut off again. In this way, the current in the short-circuit open circuit can be quickly extinguished. On the other hand, in the case where a power supply short circuit does not occur as shown in Figure 5b, no current flows through the converter, which should already be non-conducting, so this is detected and from then on, the control delay angle Q Remove the restrictions and allow the device to perform its intended actions.

FIG. 6 is a block diagram showing an embodiment of the present invention.

The embodiment shown in FIG. 6 shows an example in which the present invention is applied to the main circuit configuration shown in FIG. In FIG. 6, the control device includes a current deviation intensifier 4 that increases the deviation between the current command signal (sine wave signal) from the previous stage and the output signal of the current detector 5, and the output signal of the intensifier 4 and the bias A switching circuit 6 that selects and outputs the signal from the setter 8 according to the signal from the OR circuit 22.
, 7, a limiter circuit 9 that limits the upper limit of the signals from the switching circuits 6 and 7 while the signal from the logic circuit 18 is being issued;
10. Automatic pulse phase shifter 1 for controlling the firing phase of the thyristor converters 1, 2 in response to signals from yield transmitter circuits 9, 10. 1, 12, in response to signals from flip-flop circuit 17. Switch circuits 13 and 14 that pass or block the output signals of the automatic pulse phase shifters 11 and 12, a polarity determination circuit 15 that determines the polarity of the current command signal, a current detection circuit 16, and current command reversal and current zero. The flip-flop circuit 17 whose output signal is switched according to the AND condition of signal to output, and
a logic circuit 18 that issues a signal so that the limiter circuits 9 and 10 operate for a predetermined period of time from the time when the signal disappears;
Current detectors 19 and 2 that detect input currents of converters 1 and 2
0, when current flows through converter 1 while the gate signal of converter 1 is cut off, or when current flows through converter 1 during the period when the gate signal is supplied to converter 2, and when converter 2
If current flows through converter 2 while the gate signal is cut off,
Alternatively, a power supply short circuit detection circuit 21 that issues a signal when current flows through the converter 2 during a period when a gate signal is supplied to the converter 1, and a logic that outputs the logical sum of the signals from the detection circuit 21 and the logic circuit 18. It consists of switch circuits 23 and 24 that cut off the signal from the flip-flop circuit 17 so as to cut off the gate signals of the converters 1 and 2 when a signal is issued from the sum circuit 22 and the detection circuit 21.

The operation of the embodiment of the present invention having the above configuration will be described next.

First, the current deviation amplifier 4 receives a current command signal (sine wave),
A signal corresponding to the deviation of the current detection signal is output, and the automatic pulse phase shifters 11 and 12 are outputted according to this signal.
Since the ignition phase of No. 2 is controlled, the output current of the converter is controlled in a sinusoidal manner so as to be proportional to the current command.

The operation at the time of forward/reverse switching, which is the object of the present invention, will be explained. When the magnetism of the current command is reversed, this indicates that the gutter discrimination circuit 15
from there to the flip-flop circuit 17.

However, until the current in the converter becomes zero, the output signal of the flip-flop circuit 17 remains unchanged and is not inverted.
The logic circuit 18 detects this period and applies a signal to the switching circuits 6 and 7 via the OR path 22. Then,
The switching circuits 6, 7 select the signal of the bias setter 8 and apply it to the automatic pulse phase shifters 11, 2, so that the firing phase of the suitable transducer is gate shifted to a sufficiently large value. This causes the converter current to dissipate rapidly. Then, since a signal is generated from the current zero detection circuit 16, the output signal of the flip-flop circuit 17 is inverted. Accordingly, the signal applied from the logic circuit 18 to the switching circuits 6 and 7 disappears, but at the same time, a signal is sent from the logic circuit 18 to the limiter circuits 9 and 1 for a predetermined period of time. As a result, the output signal of the multiplier 4 passes through the switching circuits 6 and 7,
Since the limiter circuits 9 and 10 operate, their size (c
(equivalent to osQ) has a limited upper limit and cannot be used as an automatic pulse phase shifter 1.
Added to 1 and 12. On the other hand, flip-flop circuit 1
Since the output signal of 7 has been inverted, the switch circuits 13,
The operation of step 14 is reversed, and the gate of the converter on the side that was previously suitable for conduction is cut off, and the gate cutoff of the side that should be made conductive next is released. In this way, the transducer to be turned on next is started with the control delay angle Q maintained at a value greater than a certain value. Here, if a power supply short circuit occurs, current will flow through the converter which should be non-conductive, and this is detected by the power supply short circuit detection circuit 21.

This detection is performed by the flip-flop circuit 17 and the current detector 1.
Based on the signals 9 and 20, it is determined whether or not current flows during the gate cutoff period. When a power supply short circuit is detected in this way, the signal is transmitted to the switching circuits 6 and 7 via the OR circuit 22, and the output signal of the switching circuit is switched to the signal from the bias setting device 8 to perform gate shift. Let it happen. As a result, the current in the shorted closed circuit quickly decreases and disappears. Therefore, occurrence of overcurrent is prevented. The same thing can be done not only by gate shifting but also by gate blocking.

In that case, as shown by the broken line in FIG. 6, the gate is cut off by applying the signal from the detection circuit 21 to the switch circuits 23 and 24 and cutting off both output signals from the flip-flop circuit 17. After the power supply short circuit is recovered, the operation can be stopped or automatically restarted.

The former case is realized by providing a storage element in the detection circuit 21 and configuring the output signal of the detection circuit to be held as is when a power supply short circuit is detected. In the latter case, once recovery from the power supply short circuit is detected, the gate shift and cutoff are basically canceled, but for safety reasons, the gate shift and cutoff are not canceled immediately, but are canceled after a predetermined period of time. This can be achieved by providing a time delay element in the detection circuit 21 and configuring the detection circuit 21 to continue outputting a signal for a certain period of time after the short circuit is recovered. Although not shown in the figure, the output signal of the detection circuit 21 is interconnected with those of other phases, and if a power supply short circuit is detected in one phase, the currents of all other phases are simultaneously The structure is such that the operation is performed so that the value becomes zero. On the other hand, if a power supply short circuit does not occur, the detection circuit 21 will not emit any signal.

Since the signal applied from the logic circuit 18 to the limiter circuits 9, 10' disappears after a predetermined time, the operation of the limiter circuits 9, 10 is stopped, and the output signal of the multiplier 4 is automatically pulse phase shifted. It is transmitted to the vessels 11 and 12. After this, normal operation is performed. Since it operates as described above, no overcurrent will flow even in the unlikely event of a short circuit in the power supply.

Therefore, according to the present invention, even if the switching time is set to the shortest possible time, no overcurrent will flow in the unlikely event of a short circuit in the power supply, and the short circuit in the power supply can be safely recovered.

In the above embodiment, when the gate cutoff is released, the upper limit of the signal applied to the automatic pulse phase shifters 11 and 12 is limited by the limiter circuits 9 and 10 so that the firing delay angle Q does not become smaller than a certain value. However, it is not limited to such things, for example, when the gate cutoff is released, the firing angle Q may be controlled to maintain a predetermined value for a predetermined time from that point onwards. The present invention can be applied and similar effects can be obtained.

Further, in the above embodiment, an example in which the present invention is applied to a cycloconverter has been described, but similar effects can be obtained even if the present invention is applied to a Leonard device that controls a DC motor.

The configuration of the Leonard device is the same as the -phase component of the cycloconverter, and by performing the same operation as described above, it is possible to quickly switch between electric power and regeneration.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the main circuit of the cycloconverter.
Figure 2 a, b, c, d, Figure 3 a, b, c, and Figure 4 a, b, c are explanatory diagrams showing the principle of the present invention, and Figure 5 a, b are power supply short-circuit diagrams. FIG. 6 is a block diagram illustrating an embodiment of the present invention. 1, 2... Thyristor converter, 3... Electric motor, 4... Current deviation amplifier, 5... Current detector, 6, 7...・Switching circuit, 8...
・Bias setting device, 9, 10...Limit circuit, 11, 12...Automatic pulse phase shifter, 13, 1
4...Switch circuit, 15...Sacrifice discrimination circuit, 16...Current cloud detection circuit, 17...
...Flip-flop circuit, 18...Logic circuit, 19,20...Current detector, 21...
Power supply short circuit detection 9, 20...Current detector, 21.
...Power short circuit detection circuit, 22...OR circuit, 23, 24...Switch circuit. Leopard's figure rare Otsuzu tea 3 figures rare - figure 菟zu fig.

Claims (1)

[Claims] 1. Two power converters configured with controlled rectifying elements are provided, these power converters are connected in anti-parallel, and an AC power source and a load are connected through the anti-parallel connected circuit. A method for controlling a cycloconverter capable of supplying alternating current power of a frequency different from the frequency of the alternating current power source to a load by alternately operating these power converters for a fixed period of time using an alternating current power source, A cycloconverter characterized in that the control delay angle of the power converter to be turned on next when the operation is transferred to the power converter is maintained at a predetermined value or more for a predetermined period of time from immediately before the gate cutoff of the power converter is released. Control method. 2. A cycloconverter control method according to claim 1, wherein the control delay angle is 90 degrees or more. 3. It has two power converters composed of controlled rectifying elements, these power converters are connected in anti-parallel, and an AC power source and a load are connected through the anti-parallel connected circuit, and these power converters are connected in parallel. In a method of controlling a cycloconverter that can supply alternating current power of a frequency different from the frequency of the alternating current power source to a load by operating the converters alternately for a fixed period of time using an alternating current power source, one power converter operates the other power converter. The control delay angle of the power converter to be turned on next when transferring the power converter is maintained at a predetermined value or more for a predetermined time from immediately before the gate cutoff of the power converter is released, and in response to the detection of a power supply short circuit during the predetermined time. A method for controlling a cycloconverter, characterized in that a gate shift or a gate cutoff is executed for the power converter on the side to be made conductive. 4. The cycloconverter control method according to claim 3, wherein the detection of the power supply short circuit is based on a detected value of a current flowing into the cycloconverter.