JPS6236455B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an operation control method for an AC/DC converter,
In particular, the present invention relates to a control method for an AC/DC converter that is suitable for eliminating the fault without stopping the converter when a DC line ground fault occurs.

[Background of the invention]

The prior art of the present invention will be explained by taking a general DC power transmission system shown in FIG. 1 as an example. In Figure 1, 1 and 1' are AC systems, 2 and 2' are conversion transformers,
3 and 3' are AC/DC converters, 4 and 4' are DC reactors, 5 is a DC transmission line, 6 is an operation command device for commanding the operating state of the DC transmission system, and 7 and 7' are control devices. In general, the method of operating an AC/DC converter in such a system is as shown in FIG.
The (rectifier) side is operated stably with constant current control, and the inverter 3' (inverter) side is operated stably with constant voltage control or constant margin angle control, and point A shown by the current i _d - voltage v _d characteristics in Figure 2 is in operation. It becomes a point. When a ground fault occurs on a DC transmission line in such a system, for example at point f in Figure 1, the conventional method is to temporarily stop the converter, wait for the ions (=arc) at the ground fault point to disappear, and then restart the converter. There is a method of starting up, which was proposed in Japanese Patent Publication No. 48-33825. Specifically, in the latter method, when a ground fault occurs, due to the DC voltage drop, both the forward converter 3 and the inverse converter 3' enter constant current control, and therefore operate as a rectifier, and there is no constant current at the fault point. Difference Δ between the current command values of the constant current control circuits on the forward converter side and the inverse converter side
Since only a current of I _d (current margin) will flow, this is a method in which ΔI _d is set to zero and the current flowing to the fault point is made zero. This is shown in FIG. 3, where V _f is the voltage at the fault point, i _r is the direct current on the forward converter side, and i _i is the DC current on the inverse converter side.

[Problem that the invention seeks to solve]

However, with these conventional technologies, the former has the disadvantage that the power transmission is stopped for a long time because the converter is stopped, while the latter operates as a rectifier for both converters, so there is no need to stop, but the forward/reverse converter If there are variations between control devices, the current at the fault point cannot necessarily be reduced to zero even if ΔI _d is zero, and since an oscillatory current flows at the time of a fault due to the inductance and capacitance of the DC transmission line, it is impossible to reduce the current to zero. It's difficult to do. Therefore, even with the latter method, it is difficult to completely eliminate accidents.

The present invention has been made in view of the above points, and its purpose is to provide a control method for an AC/DC converter that eliminates the drawbacks of the prior art and can reliably eliminate accidents without stopping the converter. It is in.

Furthermore, another object of the present invention is that after ion annihilation,
An object of the present invention is to provide a control method for an AC/DC converter that can smoothly return to a steady state.

[Means for solving problems]

A feature of the present invention is that when a ground fault occurs on a DC line, the inverter also enters constant current control due to the voltage drop in the DC line.
The constant current setting value on the inverse converter side is made larger than the constant current command value on the forward converter side.

By the way, during the accident period, the converter is in a nearly zero power factor operating state, so the reactive power required by the converter increases, and if the AC system is weak, the operation becomes unstable. Furthermore, if the set value of the DC voltage is high when restarting after the accident time has ended, there is a possibility that an overvoltage will occur in the DC power transmission line.

Therefore, another feature of the present invention is that, in addition to the above features, when a ground fault fault is detected, the constant current command value of the forward/inverse converter and the constant voltage command value of the inverse converter are
The reason for this is that each value is set to be smaller than the value before the accident was detected.

[Effect]

As described above, when the constant current setting value on the inverse converter side is made larger than that on the forward converter side, the polarity of the voltage of the DC power transmission line is reversed. That is, since there is a period in which the current and voltage at the fault point are zero, the ions can be automatically extinguished. Therefore, after that, the relationship between the current setting values cannot be restored to the original state, and the normal operating state can be restored. Therefore, the converter does not need to be stopped due to an accident.

Furthermore, due to the second feature, during the accident period it is possible to operate with a small current that does not cause intermittent current, and when returning to normal operating conditions,
Since the constant voltage command value of the inverter is set small in advance, the voltage does not rise suddenly, and therefore the original state can be returned smoothly without generating an overvoltage.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. FIG. 4 shows a control circuit in one of the forward/reverse converters, and it is assumed that a similar circuit is provided in the other converter. Since the same numbers as those _in FIG. An adder adds the output values with the polarity shown, 72 is a DC voltage deviation amplifier, and this V _p and 7
0, 71, and 72 constitute a constant voltage control loop.
73 is a DC current transformer, and 74 is a value obtained by adding the current command value I _p of the operation command device 6 and the current margin (0 when the converter is in forward converter operation, ΔI _d when inverse converter operation), which will be described later. An adder that adds I _pr (= I _p : in the case of a forward converter) or I _pi (= I _p −ΔI _d : in the case of an inverse converter) and the output of this DC current transformer 73 with the polarity shown. I _pr or I _pi and 73,
74 and 75 constitute a constant current control loop. Therefore, I _pr and I _pi are herein referred to as current command values of the constant current control loop. 76 is a minimum value detection circuit that selects the lower value of the output values of the DC voltage deviation amplification device 72 and the DC current deviation amplification device 75, and as mentioned above, generally on the forward converter side, the DC current deviation increase Drawer 7
5 is a DC line voltage deviation amplifier 7 on the inverter side.
The output value of 2 is selected. Therefore, in the event of a ground fault, the DC voltage decreases, and as a result, the output of the inverter 75 becomes smaller than that of 72, resulting in constant current control. 77 is an automatic pulse phase shifter that provides control pulses to the converter; 101 is a polarity inversion circuit;
102 is a timer with time T, and 103 is a switching circuit which is normally set to the A side according to the signal from the timer 102, but when a DC line ground fault occurs, the polarity reversal circuit is switched to the B side.
It moves to the side. Reference numeral 104 denotes an adder that adds the current command value I _p of the operation command device 6 and the output of this switching circuit 103 with the polarity shown. The operation of this circuit will be explained with reference to FIG. In the figure, v _f is the voltage at the fault point, i _r is the DC current on the forward converter side, i _i is the DC current on the inverse converter side, P is the DC line ground fault fault detection signal, and I _pr is the forward converter side. The current command value of the constant current control loop, I _pi , indicates that on the inverter side. First, when a ground fault occurs at time t ₀ , a ground fault detection signal P is sent from a well-known ground fault detection device that detects the fault by detecting changes in current or voltage.
becomes “1” at t ₁ . With this signal, the timer 103 becomes "1", and the switching circuit 103 is switched to set the current command values of the constant current control loop to I _pr and I _pi as shown. In other words, as an example of making the current setting value on the inverse converter side larger than that on the forward conversion side, on the rectifier side, the setting value is decreased by ΔI _d , and on the inverse converter side, the setting value is increased by ΔI _d . let

As a result, the polarity of the voltage on the DC transmission line is reversed,
The polarity of the voltage v _f at the fault point is also reversed. When the time T corresponding to the extinction time of the ions at the accident point has elapsed, the timer 103 becomes "0" again, and due to the operation of the switching circuit 103, I _pr and I _pi return to the state before the accident, so that the DC transmission line The voltage also returns to its original polarity.
At this time, the current at the fault point always passes through a point where the current on the forward converter side equals the current on the inverse converter side, so it becomes zero transiently, and the voltage polarity is also reversed, so the voltage v _i at the fault point also It will always be zero. In this way, with the ions at the fault point extinguished, the current at the fault point is reduced to zero,
Since the voltage is set to zero, accidents are definitely eliminated.

As described above, according to the present invention, there is no need to stop the converter, and even if an oscillating current occurs, the current at the fault point can be reduced to zero, so that the fault can be reliably eliminated.

Another embodiment of the invention is shown in FIG. This sixth
The figure shows an operation command device 6 for controlling the command values of DC current and DC voltage in accordance with the embodiment of the invention shown in FIG.
This shows the command value creation circuit.

In other words, when a DC line ground fault occurs, the converter is in a nearly zero power factor operating state, so the reactive power required by the converter increases, and in a DC transmission system connected to a weak AC system, this reactive power As a result, the voltage at the AC/DC interconnection point may drop due to an increase in the voltage, which may cause the grid to become unstable. And, when recovering from a DC ground fault,
When the inverter returns to the constant current control loop, if the DC voltage setting is high and changes rapidly, overvoltage may occur on the DC transmission line. This is a circuit with a

To explain according to the figure numbers, 61, 61', 6
1'' and 61 are setting devices for setting the operating current command value I _p1 , minimum operating current command value I _pn , operating voltage command value I _p1 , and minimum operating voltage command value V _pn , respectively. 62 is a switch, and 63 is a setting device. Operating current command value I _p1
64 is a _switch ;
are the operating voltage command value V _p1 and the minimum operating voltage command value V _pn
a maximum value selection circuit that selects the larger value among the
Reference numeral 66 is a timer that operates similarly to the timer 102 in FIG. 4, and the time is T ₁ >T.

To explain the operation of this circuit, when a ground fault occurs and the timer 66 operates, the switching circuits 62, 6
4 changes from the on state to the off state, and the current command value I
_p is the minimum operating current command value I _pn within a range in which the DC system is not interrupted, and the voltage command value V _p is the minimum operating voltage command value V _pn which is the lowest possible voltage value. Therefore, even if the converter is in a zero power factor operating state during the accident time, the necessary reactive force does not increase and stable operation can be performed even in a weak AC system. In addition, actions to eliminate accidents,
That is, I _pr <I _pi is the same as above. Furthermore, even when the DC voltage is restored after the fault has been removed, the original state will be restored from the minimum DC voltage command value, so no overvoltage will occur on the DC line, and stable operation will be performed.

Further, when changing the above-mentioned current command value and voltage command value, the details of how to change them have not been described, but it is preferable to change them slowly over time. As described above, by implementing the present invention, even if a ground fault occurs in a DC line, power can be stably transmitted without stopping the converter and without causing abnormal phenomena.

The above explanation has been made with reference to the DC power transmission equipment configured as shown in Figure 1, but this is not applicable to the case where two sets of opposing The same effect can be obtained even if it is implemented between conversion stations. Further, the same effect can be obtained when two sets of forward converters and two sets of inverse converters are connected in series, and these converter groups are connected by a DC power transmission line.

〔Effect of the invention〕

As described above, according to the present invention, even when a ground fault occurs, the fault can be reliably removed without stopping the converter, and furthermore, it can be smoothly restored after the fault.

[Brief explanation of the drawing]

Figures 1 and 2 are system diagrams and operation explanation diagrams of DC power transmission, which is the subject of the present invention, Figure 3 is a waveform diagram of various parts when a DC transmission line ground fault occurs, and Figure 4 is a diagram of the DC power transmission system according to the present invention. FIG. 5 is an operation waveform diagram of FIG. 4, and FIG. 6 is a control circuit showing another embodiment of the present invention. 70... DC voltage converter, 71... Adder, 72...
DC voltage deviation amplifier, 73... DC current transformer, 7
4... Adder, 75... DC current deviation amplifier, 76...
Minimum value detection circuit, 77... automatic pulse phase shifter, P...
DC line ground fault detection signal, I _p ... current command value,
v _p ...Voltage command value, ΔI _d ...Current margin command value,
101... Polarity inversion circuit, 102... Timer, 10
3...Switching circuit, 104...Adder.

Claims (1)

[Scope of Claims] 1. A forward converter that is subject to constant current control is connected to one end of a DC line, and the other end of the DC line is subject to constant voltage control during steady state and constant current control when the voltage of the DC line decreases. In the AC/DC conversion equipment connected to an inverse converter, the constant current command value of the inverse converter is made larger than the constant current command value of the forward converter when a ground fault fault is detected in the DC line. A control method for AC/DC conversion equipment. 2. In claim 1, after the detection of the ground fault accident, when a predetermined time period necessary for ion extinction at the fault point has elapsed, the current command value of the forward/inverse converter is restored to the value before the occurrence of the fault. A control method for AC/DC conversion equipment, characterized in that: 3 A forward converter that is controlled by constant current is connected to one end of the DC line, and an inverse converter that controls constant voltage during steady state and controls constant current when the voltage of the DC line drops is connected to the other end of the DC line. In the AC/DC conversion equipment, when a ground fault fault is detected in the DC line, the constant current command value of the inverse converter is made larger than the constant current command value of the forward converter, and the constant current command value of the forward/inverse converter is A method for controlling AC/DC conversion equipment, characterized in that a current command value and a constant voltage command value of the inverter are each made smaller than values before the accident detection. 4 In claim 3, after the detection of the ground fault fault, when a predetermined period of time necessary for ion extinction at the point of fault has elapsed, the constant current command value of the forward/reverse converter and the constant voltage of the inverter A control method for AC/DC conversion equipment characterized by returning each command value to a value before an accident occurred.