JPS6322130B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for detecting problems caused by transformer saturation when starting an AC/DC converter in which a converter comprising a switch having forced commutation capability is connected to an AC system via a transformer. The present invention relates to a starting device that suppresses overcurrent in a converter.

The AC/DC converter station that connects the DC system and AC system is
It is configured as shown in FIG. In the figure, 1 is the power transmission line of the DC system, 2 is the converter connected to the DC system 1, 3 is the transformer connected to the AC side of the converter, and 4 is for connecting the transformer 3 to the AC system 5. It is a switch. The converter 2 is a so-called self-excited converter configured with a switch having forced commutation capability, and is configured as shown in FIG. 2, for example.
In FIG. 2, P and N are DC terminals, which are connected to the DC power transmission line 1. 20 is a smoothing capacitor connected between the lines of the DC terminal, 201, 202,
203, 204, 205, 206 are main thyristors, 221, 222, 223, 224, 225,
226 is an auxiliary thyristor, 211, 212, 21
3, 214, 215, 216 are freewheel diodes, 231, 232, 233 are commutating reactors, and 241, 242, 243 are commutating capacitors. Two main thyristors are connected in series, and AC output terminals U, V, and W are led out from the intermediate point. The AC output terminal is connected to the transformer 3. The operation of the self-commutated converter of FIG. 2 is well known.

Conventionally, a method for starting such a self-commutated converter is to charge the smoothing capacitor 20 to a predetermined value using a separate power source (not shown), and then apply a conduction signal to the thyristors in a predetermined order. It had been taken. When a conduction signal is applied to the thyristor, an AC voltage proportional to the DC voltage value of the smoothing capacitor 20 is generated at the AC output terminals U, V, and W of the converter. It is known that a large excitation current called inrush current flows. This exciting current is applied to the converter 20
flows through the main thyristor, the current carrying capacity of the converter increases and the device becomes larger. Therefore, it is necessary to suppress the inrush current at startup as much as possible. Inrush current increases as the voltage applied to the transformer increases, so in conventional self-excited converters that have an output transformer on the AC output side, in order to suppress the inrush current of the output transformer at startup, A startup method is used in which startup is performed with a low DC voltage, the voltage applied to the transformer is initially kept low, and the voltage is gradually increased. However, as shown in Figure 1, in a self-excited converter connected to a DC transmission line, the voltage of the DC transmission line directly becomes the DC voltage of the converter, so the conventional startup method is not recommended. I can't. Therefore, there was a drawback that an excessive current flowed through the arm of the converter at startup.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by supplying the inrush current of the output transformer from the AC system side, it is possible to convert It is an object of the present invention to provide a startup method that can suppress the current flowing through the converter and reduce the current capacity of the converter even when starting an excited converter.

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 3, 50 indicates an AC system. Reference numeral 21 denotes a starting signal generator, which gives a closing command to the shear breaker 4. 22 is a voltage detector that detects the voltage of the AC system 50, 23 is a phase detector that detects the phase of the voltage, and 24 is a device that compares the system side voltage phase and the converter gate pulse phase and detects the deviation thereof. 25 is a filter that converts the output signal of the phase difference detector into a DC voltage; 26 is a voltage frequency converter that converts the output voltage of the filter into a frequency; 2
7 is a gate pulse generator that frequency-divides the output of 26 to create a gate pulse for each thyristor of the converter, and 28 is a phase detector that detects the phase of the gate pulse. The loop made up of 24, 25, 26, 27, and 28 constitutes a phase locked loop. A phase-locked circuit is a circuit that generates a pulse synchronized with the phase of an input pulse, and for example, there is one described in the November 1973 issue of Denshi Kagaku "Basic Theory of PLL". 29 is a phase coincidence detector that outputs an output when the outputs of the two phase detectors 23 and 28 match, and 30 is a timer that generates an output after a certain period of time from the input signal 4. 31 is
When the output of 30 and the output of 29 are both output,
The AND logic circuit 32 that produces an output applies the gate pulse generated from 27 to each thyristor only when the output from 31 is output, and when there is no output from 32, the AND logic circuit 32 cuts off the gate pulse. It is a logic circuit.

Next, the operation will be explained. Until the activation signal is given, the voltage phase of the AC system is detected by 22 and 23, and this is compared with the gate pulse phase detected by 28 at 24. If the phase detected at 28 lags behind the phase detected at 23, the output at 24 will increase, and as a result, the DC output voltage at 25 will also increase, and the oscillation frequency at 26 will increase. As a result, the frequency of the gate pulse generated at 27 also increases and the gate pulse phase detected at 28 advances. Conversely, when the phase detected at 28 is ahead of the phase detected at 23,
The output of 24 becomes smaller, and as a result, the DC output voltage of 25 also becomes smaller, and the oscillation frequency of 26 decreases. As a result, the frequency of the gate pulse generated at 27 is reduced and the gate pulse phase detected at 28 is delayed. In this way, 24, 25, 26,
Due to the function of phase locking circuits 27 and 28, always
26 frequencies are determined so that the detection phase 23 and the detection phase 28 match. As a result, 2
The gate pulse phases are synchronized so that when a gate pulse is applied from 27 to each thyristor, a voltage having the same phase as 50 is generated in the system side winding 3. However, since no signal comes from 31, the gate pulse is blocked by 32. In this state, when input command 4 is issued from 21, activation is performed as shown in FIG. In FIG. 4, time t ₁ indicates the point in time when the input command is issued from 21 to 4. In response to this input command, the timer 30 generates an output at a time _t3 , which is a predetermined time _T0 after _t1 , and provides the output to the timer 31. 31 is given this signal and the output of 29, but 2
9, the phase synchronization circuit in the first half operates normally, and 23
It checks whether the phases of and 28 match, and if they match, an output is output. In FIG. 3, it is assumed that synchronization has been completed at time _t2 . Therefore, at time _t3 , both inputs of 31 are given, so 31 becomes 32 at time _t3 .
The gate pulse is deblocked. As a result, after time _t3 , the gate pulse generated by 27 is applied to each thyristor 2 as is. For example, the gate pulse of the U-phase main thyristor 201 in FIG. 2 is as shown in the same figure, and the part shown by the broken line comes out from 27 but is blocked by 32, and the part shown by the solid line is applied to the thyristor. As a result, as shown in the figure, the line voltage between UVs 3 and 3 is the system voltage applied as is from t ₁ to t ₃ , and from t ₃ onwards, the output voltage 2 is applied. The excitation current of 3 flows largely when the voltage is applied to 3, but then decreases and eventually reaches a steady value. This initial excessive current (so-called inrush current) flows from the system 50 through the shield breaker 4 and into the converter 2.
is blocked, so only the charging current of the smoothing capacitor 20 flows. This current flows through the freewheeling diode. At t ₃ , when a gate pulse is applied to the thyristor, 3
The excitation current of has reached a steady-state value, and therefore,
There is no need to supply an excessive excitation current from the converter.

In the above embodiment, the converter 2 is a six-phase converter, but it may be a multiplex converter that adds the outputs of a plurality of six-phase converters using an output converter. In this case, it goes without saying that the multiplexing transformer corresponds to the output transformer 3 of the present invention.

In the embodiment shown in FIG. 3, the timer 30
Although the configuration is such that the startup time is determined, the operation command may be given to 31 from another circuit instead of the timer. In this way, after the breaker 4 is turned on, until an operation command is received, the converter is in a so-called standby state, in which it does not operate, but can be placed in a floating state where it can be activated immediately upon receiving an operation command.

As described above, according to the present invention, there is no need to supply inrush current to the converter transformer from the converter side, so overcurrent at the time of starting the converter can be avoided. Another advantage of the present invention is that since the smoothing capacitor is charged from the AC system via the output transformer, there is no need to charge the smoothing capacitor from another power source before starting up. Even if there is no system, it can be activated independently and has the effect of waiting.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of an AC/DC converter station, Fig. 2 is a block diagram showing an example of a self-excited converter, and Fig.
The figure is a block diagram showing an embodiment of a starting device for an AC/DC converter according to the present invention, and FIG. 4 is a time chart at the time of starting by the starting device of the present invention. In the figure, 1 is a DC system, 2 is a self-commutated converter, 3 is a transformer, 4 is a switch, 5 and 50 are AC systems, 21 is a starting signal generator, 22 is a voltage detector,
23, 28 are phase detectors, 24 is a phase difference detector,
25 is a filter, 26 is a voltage frequency converter, 27
is a gate pulse generator, 29 is a phase coincidence detector,
30 is a timer, and 31 and 32 are AND logic circuits. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a device that starts a self-commutated converter that is installed between a transformer connected to an AC system via a power disconnector and a DC transmission line and converts DC power to AC power, the above-mentioned AC A phase detector that detects the voltage phase of the system, and a phase coincidence detector that detects that the phase difference between the detected phase of this phase detector and the phase of the gate pulse that controls the ignition of the conversion device is less than a certain value. a timer circuit that outputs an output after a certain period of time has elapsed since the generation of the closing signal for the breaker; and a circuit that provides the gate pulse to the conversion device when the timer circuit and the phase coincidence detector output the signal. A starting device for AC/DC converter equipment.