JPS5812542A - Overvoltage suppressing device in ac/dc interlock system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overvoltage suppression device in an AC/DC interconnection system, and particularly to an overvoltage suppression device in an AC/DC interconnection system suitable for preventing an increase in AC/DC voltage.

Generally, an AC/DC interconnection system is configured by connecting different AC systems with a direct feeder system interposed therebetween, and is known as, for example, a DC power transmission system or a frequency conversion station.

FIG. 1 is a block diagram showing an example of the above-mentioned AC/DC interconnection system. In this figure, numerals 1 and 2 indicate different AC systems, and between these AC systems 1 and 2, there is a forward converter 3, a DC reactor 4, and a DC power transmission +1!
J5, a DC reactor 6 and an inverter 7 are connected via a DC system 8. □To explain in more detail,
The forward converter 3 connects the first forward converter '31 to the first transformer 3.
2, the second forward converter 33 is connected to the AC system 1 via a second transformer 34, and receives a signal from the operation command device 9;
Based on this signal, the outputs of control circuits 35 and 36 that drive and control the first and second forward converters 31 and 33 are supplied to the forward converters 31 and 33, respectively, and the AC system 1 and transformer 32. A phase adjustment capacitor 37 is connected to the connection part with the forward converter 31.34 for supplying the reactive power necessary to stably operate the forward converter 31.33, and harmonics generated from the forward converter 31.33 are connected. It is configured by connecting an AC filter 38 that absorbs current. The DC power converted to DC in the forward converter 3 is transmitted to the inverse converter 7 via a DC system 8. This DC system 8 connects a closed circuit consisting of a DC reactor 41, a DC power line 51, a DC reactor 61, an inverse converter 71, and a DC power line 52 between the positive and negative electrodes of the first forward converter 31, and Between the positive and negative electrodes of the second forward converter 33, the DC power transmission line 52 and the inverse converter 7
3. A closed circuit consisting of a DC reactor 62, a DC power transmission line 53, and a DC reactor 42 is connected, and the power transmission line 52 is grounded on the forward converter 3 side. Further, the inverter 7 connects the first inverter 71 to another AC system 2 via the first transformer 72, and connects the second inverter 73 to the second transformer 74. Outputs of control circuits 75 and 76 that are connected to the AC system 2 via the AC system 2, take in signals from the operation command device 9, and drive and control the first and second inverters 71, 73 based on the signals. is supplied to the inverters 71 and 73, and the reactive power necessary to stably operate the inverters 71 and 73 is supplied to the connecting portion between the AC system 2 and the converters 2 and 74. A phase adjustment capacitor 77 is connected thereto, and an AC filter 78 is connected thereto to absorb harmonic currents generated from the inverse converters 71 and 73. Note that the two converters 31 and 33 are configured to transmit power with equal DC current values. Note that the forward converter 3 and the inverse converter 7 are controlled by control circuits 35, 36 .
By changing the phase angle of the drive pulses supplied from 75 and 76, the inverse can be easily converted.

The operation of the AC/DC interconnection system configured as described above will be explained with reference to FIGS. 2 and 3.

Figure 2 is a characteristic diagram showing the operating characteristics of the forward converter and the inverse converter.1 The horizontal axis represents the DC current Id, and the vertical axis represents the DC voltage I.
d is shown respectively. Fig. 3 is a time chart shown to explain the operation when one pole fails, and each horizontal axis shows time t, and each vertical axis shows voltages e, V, and current i of each part. ing. Generally forward converter 31
and 33 are subjected to constant current control, and inverse converters 71 and 73 are subjected to constant voltage control (or constant margin angle control), and stable operation is performed at point 0 in FIG. The direction of the current can be easily determined by manipulating the control angle regardless of the states of the two AC systems 1 and 2, as described above. Therefore, each of the control circuits 35, 36, 75, and 76 of the forward converters 31 and 33 and the inverse converters 71 and 73 is equipped with a constant current control circuit, a constant voltage control circuit, or a constant voltage control circuit. Therefore, the current setting value of the constant current control circuit of the inverse converters 71 and 73 is also the same as that of the forward converters 31 and 33! t<margin ΔIa is set smaller, and the above-mentioned power flow can be arbitrarily changed by manipulating ΔIa'. That is, the converters 31 and 33, 71 and 73 have -i&fi in forward and reverse directions by manipulating the control angle. Note that the symbol vDD indicates the output voltage of the forward converters 31 and 33, and VID indicates the input voltage of the inverse converters 71 and 73.

Incidentally, in order to operate a forward/inverse converter stably, generally a reactive power of about 50 to 60% of the active power is required, and for this reason, as mentioned above, the capacitor 3 for phase adjustment is required.
7.77, AC#r, and filter 38.78 are provided in each AC system 1 and 2 for supplying reactive power. Since the required amount of reactive power usually differs depending on the operating state of the DC system, the phase modulating capacitors 37 and 77 are each divided into several parts and turned on or off depending on the operating state.

Now, let's consider a case where one of the positive or negative poles is stopped due to a ground fault or other failure in the DC transmission line 51, 53.
Before the failure, the reactive power required by the converter is supplied and balanced by the phase adjustment capacitor 37.77 and the sound filter 38.78 capacitor, but when the negative pole fails and the power is stopped, the reactive power required by the converter is The reactive power generated by the converter is halved, the changeover switch for closing and opening the phasing capacitor 37.77 does not respond instantaneously, and the leading reactive current of the capacitor 37.77 is lower than the lagging reactive current required by the converter. Larger currents also increase the current voltage. The magnitude of this voltage increase ΔV
is Δ■=ΔQ−X8, (where Xs is the impedance of the AC system and ΔQ is the change in reactive power.

), and the larger the impedance X8 of the AC system, and the larger ΔQ, that is, the transmitted power of the DC system, the greater the risk of insulation of the materials connected to the AC system. To explain this in detail, we will explain the operation when a one-line ground fault occurs in a DC system based on the time chart shown in Figure 3. The voltage is almost zero, and the current i
Although dI increases by -1, the constant flow control of the control circuit 11 operates and returns to the set value.

- Upon detection of a single-ground fault (details not described), the converter immediately performs a gate shift (at time 1) and interrupts the fault current. (Time ``2''). On the other hand, the other pole operates normally without any change in direction. Therefore, the AC voltage e2 becomes reactive power because the control angle of one pole increases due to the occurrence of an accident, and time t.-1 , the voltage decreases by -tan during the period , but the faulty pole stops at time t, ′, the voltage increases conversely from time t2 onwards, and when the impedance Xs of the AC system is high, this voltage increase is equal to the rated value. , for example 30%
There are cases where it reaches even. Therefore, if the insulation of the AC system is weak, dielectric breakdown may occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overvoltage suppressing device for an AC/DC interconnection system that eliminates the drawbacks of the prior art described above and is capable of suppressing overvoltage and performing stable operation.

The present invention incorporates an AC voltage of a converter in a direct line system into a comparator circuit, outputs a switching command signal when the AC voltage exceeds a predetermined value, and outputs a switching command signal when the AC voltage exceeds a predetermined value. AC voltage, DC voltage, DC/current are taken into the control circuit, and this? The tjlJ +t11 circuit is based on these 1g issues at least directly m 'tttt
In addition to maintaining m k constant, the noise generated from the converter when receiving the switching command signal from the comparison circuit,
It is designed to change the dynamic force.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the Isho DVLJ of the present invention will be explained based on the drawings. Components that are the same as those of the conventional example will be described with the same reference numerals.

FIG. 4 is an explanatory diagram shown to explain the basic operation of the present invention. In this figure, the horizontal axis shows the DC current ■4
The vertical axis shows the AC voltage e, the dotted line indicates unipolar operation, and the solid line indicates multipolar i! I! i is shown respectively.

This figure shows the non-current filters 37 and '77 for reactive power supply of the converters 3 and 7, and the phase adjustment capacitors 38.
78 is set to the value at the rated operation of the DC system 8, and the power of the DC system is calculated. This shows how the voltage changes.

First, during rated operation, since it is a preliminary test operation, it is within the range of large victory in the diagram, and DC I! It current Ia=Ito, and the AC voltage at this time is e. It is. Normal control angle is α=19 degrees,
(in the inverter, α = 140 degrees), and the operating point is α
-+-=10 degrees (in Tonga chivalry, α=16 (1:) to α
, , =90 degrees (α=90g in the inverse converter). If one pole is stopped in this state, the operating point will be 0. (that is, the range indicated by the dotted line in the figure), and the voltage increases by, for example, ΔV, although it varies depending on the impedance Xs of the AC system. In this state, set the control angle of the healthy pole to α8. If the voltage is increased to near A, the operating point becomes O12, and the voltage rise can be suppressed. Furthermore, by increasing the direct current to Ia2' (or more), the alternating current voltage e can be maintained at the rated value co. Of course, the operating point in this case is 0
□' or 02.

Fuenkyoku was created focusing on the points mentioned above, and it detects the rise in AC voltage and controls it according to the magnitude of AC voltage.
The AC voltage rise is suppressed by changing the angle or the DC it'ti.

FIG. 5 is a block diagram showing the first column of the overvoltage suppressing device in the AC/DC yarn system according to the present invention. In this figure, the control of one converter at one end of the converter l! ! Although only i% is shown, it is assumed that the same circuit is provided in other converters. Furthermore, the same components as in FIG. 1 are given the same reference numerals and will be explained.

In FIG. 5, the comparator circuit 100 connects the AC system 1 to the AC system 1 via an AC voltage detection circuit 110 that detects the voltage of the AC system 1.
It is connected to the AC system 1 so that the voltage of the AC system 1 can be taken in. When the magnitude of this AC voltage exceeds a predetermined value, the switching command signal s t , o becomes logic II I 11.
o is output.

In addition, the control circuit JI6200 detects the current in the DC system and outputs a voltage that is proportional to this magnitude. A constant voltage control circuit 201 that takes in the electric signal from the current detection circuit 120 and the command value Iap from the operation command device 9 to keep the current in the DC system at a constant value, and a DC voltage detection circuit that detects the voltage in the DC system. a constant voltage control circuit 202 that takes in the voltage 1g from the circuit 130 and takes in the command value V a p from the operation command device 9 to keep the voltage of the DC system at a constant value;
The voltage signal from the AC voltage detection circuit 110 and the voltage signal from the @current detection circuit 120 are taken in, and from the current and AC voltage of the DC system, the converter 33 calculates the voltage required for commutation when the converter 33 is in reverse converter operation. a constant margin angle control circuit 203 that outputs a voltage corresponding to the minimum margin angle; and the constant current control circuit 2.
01, constant voltage control circuit 202, constant margin angle control circuit 203
A minimum voltage detection circuit 204 selects the output voltage of the circuit most suitable for the operation of the converter 33, and from the output voltage of this minimum voltage detection circuit 204, the magnitude of the output voltage is It is equipped with an automatic pulse phase shifter 207 that converts the pulse into a pulse having a control angle equal to vlJ. The function generating circuit 205 is a circuit that delays the control angle (when operating the forward converter) or advances it (when operating the reverse converter) depending on the magnitude of the AC voltage.
The delay/lead switching is based on the command Pr from the operation command device 9.
I'm starting to do better. This function generator 205
It may be a type having a simple proportional characteristic or a type having a non-Toga type characteristic such as an arccosine, and the characteristics and circuit examples thereof will be described in detail later. And comparison circuit 1
00 outputs a switching command signal S100 which is logic "1" when the magnitude of the AC voltage exceeds a certain level, and when the output of the comparator circuit 100 is logic "'θ"', the switch is turned off. The circuit 206 is connected to the lowest voltage detection circuit 204, and when the switching command signal of the comparison circuit 100 is logic ``1'', it is connected to the function generation circuit 205 and outputs the selected value of 1M. It has become.

The operation of the embodiment as described above will be explained below.

In this embodiment, if we now consider a case where the other pole fails and stops, the alternating current voltage will rise. When this voltage exceeds a certain predetermined value, the comparison circuit 100 operates and the switch circuit 206 switches to the output of the function generation circuit 205.

Therefore, when the converter 33 is operating as a forward converter, the control angle is delayed according to the magnitude of the AC voltage, while when operating as a reverse converter, the control angle is advanced, thereby nullifying the delay required by the converter. Since the electric power becomes larger, the leading reactive power caused by the AC filter 18, the phase adjustment capacitor 37, etc. is compensated, and the increase in the voltage of the AC system is suppressed. After a certain period of time has passed, a changeover switch (not shown) for the phase adjustment capacitor 37 is activated.
When a part of the capacitor 37 is disconnected, the current voltage decreases again, so the command signal output of the comparator circuit 100 becomes logic NO.
I+, and the switch circuit 206 switches to the lowest voltage detection circuit 204 again. In addition, in order to make this operation mW, the characteristics of the comparator circuit 100 are not simply to operate with a logic "1 pass" above a predetermined value and a logic "0'' below a predetermined value, but to have a hysteresis characteristic. ,
It is desirable that the transition from Ou→II II+ or 1″→″θ′” be made with different values.

By operating as described above, the converter 33 stops instantaneously, thereby suppressing the rise in the voltage of the current system, which insulates the equipment and reduces the operational responsibility of the arrester. It has the advantage of being lightweight.

Here, using FIGS. 6 and 7, the function generator 205
The details will be explained below. FIG. 6 is a characteristic diagram shown to explain the characteristics of the function generator 205 during the operation of the inverter. (I) of the same figure shows the control angle β (−π
-α), and (9) of the same figure is a diagram showing the relationship between the control angle α and the AC voltage. Same figure (III)
FIG. 2 is a diagram showing the relationship between the control angle α and the change in AC voltage. In these figures, the curve t1 shows the control angle to keep the DC voltage constant at the rated value 1 [p-u:], and t2 shows the control angle to keep the minimum value of the margin angle constant at rml++-17 degrees. It is.

By the way, in order for the converter to operate stably during reverse converter operation, the control advance angle β with respect to the AC voltage should be determined by the curve t2.
It must have a higher control angle.

Since it is normally operated with a constant DC voltage, when the AC voltage is about 1 [p, u] or more, the control angle changes along the curve t, and the operating point during rated operation is O. Further, in a range where the AC voltage is smaller than 1 (p, ul), the control angle β is controlled along the curve t2 in order to minimize the reactive power required by the converter.

Figure (2) shows Figure (I) modified by the control delay angle α. The details of the part higher than 1[:p, u] of the AC voltage are shown in Figure (]III. In Figure (nI), during normal operation, the control angle α is above the broken line t, and the control angle is only for suppressing overvoltage. It is desirable that the angle increase has a characteristic as shown by a solid line, for example.

On the other hand, when the transformer is operating as a forward converter, it changes with respect to the AC voltage at the direct connection point! The control angle of the device is as shown in Figure 7. figure(
In I), t is the DC voltage with the rated value 1 [p, u)
It shows the control delay angle α to keep it constant, and the operating point in the rated state is 0. In figure (I), the AC voltage is 1 [p, u)
The details of the higher portion may be shown, and the increase in the control angle for suppressing overvoltage may have a characteristic as shown by a solid line in the figure, for example.

FIG. 8 shows a specific circuit for producing a function generator having the characteristics shown by the solid lines in FIG. 6 (III) and FIG. 7 (company).

In FIG. 8, the function generator 205 is configured as follows. For the AC voltage IE21, a resistor R2 is connected between the output end and the input end of the operational amplifier OPo via a resistor R, thereby forming an inverter circuit INV.

The output terminal of this inverter circuit INV is connected to the positive input terminal of the operational amplifier OP1 via a resistor R8. A reference voltage set by a variable resistor VR is supplied to the positive input terminal of the operational amplifier OP1 via a resistor R2. A resistor R6 is connected between the input end and the output end of the operational amplifier OP t , and the output terminal thereof is connected to one end of a switch SW which is switched by a command P2 from the operation command device. The function generating circuit configured in this manner is used when operating as an inverse converter.

The AC voltage IE21 is still connected to the positive input terminal of the operational amplifier OP2 via the resistor R6, and the reference voltage set by the variable resistor VR2 is connected to the positive input terminal of the operational amplifier OP2 through the resistor R7. A resistor R8 is connected between the input terminal and the output terminal of the operational amplifier OP2, and the output terminal is connected to the switch S.
Connected to the other end of W. The function generating circuit configured in this manner is used when operating as a converter.

Note that the slopes of the straight lines shown in No. 691 (III) and FIG. 7 (6) are obtained by arbitrarily changing the values of gains R5/R2 and R7/R8 in operational amplifiers OP1 and OP2. Note that R,,=11,2
This is due to the relationship ゜Rs = R4 and Ra = R7.

FIG. 9 is a block diagram showing a second embodiment of the overvoltage suppression device in an AC/DC interconnection system according to the present invention. In this figure, the same components as in FIG. 5 are given the same reference numerals and will be explained.

Actual example ρ in Figure 9; differences from the example in Figure 5 are as follows:
In the control circuit 200, the signal from the function generation circuit 205 is supplied to the adder [208] via the switch circuit 206 which is switched by each switching command from the comparison 100, and the signal is supplied to the adder M2O3. The current command Iap from the operation command device d9 is supplied, the addition result is supplied to the constant current control circuit 202, and the output of the minimum voltage detection circuit 204 is directly supplied to the automatic pulse phase shifter 207. There are no other changes to the configuration.

In other words, in the implementation/critique shown in Figure 5, the control angle is changed according to the magnitude of the AC voltage, whereas in the "meiyu-kuri" method, the magnitude of the DC current is changed to increase the reactive power and reduce the overvoltage. This is to suppress the

The operation of the embodiment configured in this way will be described below.

Here, if the other pole stops due to an accident and the AC voltage increases, the output of the command signal 5100 of the comparator circuit 100 becomes 1.
”, the switch circuit 206 is turned on, and the adder 208 adds the current command 2, Iap from the operation command device 9 and the signal from the function generation circuit 205, and inputs it to the constant current control circuit 201. Then, the DC In addition to the addition of current, the reactive power also increases.As a result, the increase in AC voltage is suppressed.In this case, a current limiter is installed in the constant current control system to prevent overcurrent. It is desirable to take measures to prevent damage to the safety device due to overvoltage suppression.It is also good to coordinate the amount of increase in current for overvoltage suppression and the limiter value for overvoltage suppression in advance.

This embodiment also suppresses the increase in AC voltage. Since the increase in AC voltage is suppressed in this way, there is an advantage that the insulation of the equipment and the operational responsibility of the arrester can be reduced. Note that the time for increasing the DC current to suppress overvoltage is an extremely short time until the opening/closing switch of the phase modulating capacitor 37 operates, so there is no need to enlarge all the equipment.

FIG. 10 is a characteristic diagram showing an example of the characteristics of the function generator 205 used in FIG. u) are shown respectively.

This figure shows the current command value for a high part (change in sound pressure) from the rated value 1 (p, u) of sound pressure, and shows the increased change when the AC voltage increases. The DC current command value can be varied in proportion to the amount. Since this value is added to the Ω command value Iap from the operation command device, the DC current increases and the reactive power required by the converter can be increased. A relational generator having the characteristics shown in FIG. 10 can be obtained with a simple circuit shown in FIG.

In FIG. 11, the function generating circuit 205 generates an AC voltage I
E21 is supplied to the positive input terminal of the operational amplifier OPS via the resistor R0, and a variable resistor V is connected to this input terminal.
The reference voltage obtained through R is supplied through a resistor R8, and a resistor R81 is connected between the input terminal and the output terminal of the operational amplifier OP, and the function signal is taken out from this output terminal. It is configured as follows. With such a configuration, a signal system having characteristics as shown in FIG. 10 is naturally output. In addition, in this example,
Ro=Rt. This is due to the relationship between

As a third implementation, an overvoltage suppression device that suppresses overvoltage by combining the configuration of FIG. 5 and the configuration of FIG. 9 is inferior, but in this case, the current setting value is changed on the forward converter side. , it is preferable for operation to change the control angle on the inverter side. By operating in this manner, the reactive power can be changed over a wide range due to the synergistic effect of the change in the control angle and the change in the DC current, and the increase in the AC voltage can be suppressed.

In addition, the above-mentioned practical V is related to l#4, in which the DC current value or control angle is changed from the increase in AC voltage.
A similar effect can be expected by using the conventional accident detection signal, which causes an instantaneous stop of the transformer, as the switching command signal.

As described above, according to the present invention, in an AC/DC interconnection system, when the rise in AC voltage exceeds a predetermined value, the reactive power generated from the converter is changed, so that the "overvoltage" of the AC voltage is changed. This has the effect of suppressing this and ensuring stable driving.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional AC/DC interconnection system, Fig. 2 is an operating characteristic diagram showing the operating characteristics shown in Fig. 1, and Fig. 3 shows the operating state of a single-line ground fault in the configuration shown in Fig. 1. A time chart, FIG. 4 is an explanatory diagram left for explaining the basic operation of the present invention, FIG. 5 is a block diagram showing a first embodiment of the present invention, and FIG. 6 is a first MA example of the present invention. FIG. 7 is a characteristic diagram showing the characteristics of the function generator used for inverse converter operation, FIG. 8 is a characteristic diagram showing the characteristics of the function generator used for inverse converter operation, and FIG. FIG. 9 is a block diagram showing a second embodiment of the present invention, a characteristic diagram showing the first characteristic, and FIG.
FIG. 1 is a circuit diagram showing a specific circuit of a function generator having the characteristics of the 10-character diagram. 1.2...Current conversion station, 3,7...Form conversion station, 4,6
・・・Direct H') Naktor, 5...Power grid, 8...DC system, 1st (21st trial 2 Figure 3 Figure 'II; 4-121 1 compensation ￥, 6 units 7 units Cr ) Support (KPLL) 18 Figure 9

Claims (1)

[Claims] 1. In an AC/DC system connected to at least two AC systems by a forward converter that converts from AC to DC and an inverse converter that converts from DC to AC, an AC voltage in the AC system is taken in. , a comparison circuit that outputs a switching command signal when the AC voltage exceeds a predetermined value; An overvoltage suppression device for an AC/DC interconnection system, comprising: a control circuit that maintains constant reactive power and changes reactive power from the converter when receiving a switching command signal from the comparison circuit. 2. The control circuit transmits a signal from a function generator that changes the control angle of the AC/DC exchanger according to the value of the AC voltage to the converter via an automatic pulse phase shifter in response to a switching command signal from the comparison circuit. An overvoltage suppressing device in an AC/DC interconnection system according to claim 1, characterized in that the overvoltage suppressing device is configured to be able to supply a voltage to the AC/DC interconnection system. 3゜The control circuit adds a signal from a function generator that can vary the current setting value according to the value of the AC voltage to the current setting value taken into the constant current control device by the switching signal from the comparison circuit. An overvoltage suppression device in an AC/DC interconnection system according to claim 1, characterized in that it is configured as follows.