JPS5848116A - Tap switching controller at alternating current and direct current conversion station - Google Patents

Abstract

PURPOSE:To reduce DC transmitted electric power and to shorten the AC voltage drop time of a power inverter side, by performing extremely speedy tap switching when the AC bus voltage of a power rectifier side drops. CONSTITUTION:When the voltage of an AC bus 01 varies slightly, a tap switch 12 performs tap-by-tap upward switching as usual. For example, the AC bus voltage drops greatly and the winding voltage of a reference valve side is compared with the varying winding voltage of the valve side; when a maximum voltage tap selection part 11 detects the fact that the voltage deviation is greater than a prescribed value, the tap selection part 11 shifts into the state wherein a maximum voltage tap is connected, so a maximum voltage tap selection signal is sent to the switch of the tap switch 12 to perform switching to a maximum voltage tap position in known order. Then, a tap state detecting part 14 detects maximum voltage tap selection being performed to open a normally closed contact 15, thus completing the tap switching.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tap switching control device for a pulp transformer installed in an AC-DC converter station for DC power transmission.

Conventional tap switching control methods employ a constant control method for the pulp side winding voltage, which monitors the pulp side winding voltage and adjusts the valve 1 winding voltage based on voltage fluctuations on the AC system bus side. If the voltage fluctuates, the deviation between the reference valve side winding voltage and the current voltage is integrated, and if the integrated value exceeds a certain value, a control command is issued to the tap changer, and the transformation ratio is changed by changing the tap (tap raising). This method compensates for voltage fluctuations by changing the voltage and maintains a predetermined pulp side winding voltage after compensation. However, since it takes several seconds to change one tap of a tap changer, if the voltage compensation width is large, it will be necessary to change the tap several times. It will take seconds.

The effect this has on the operating characteristics of the AC/DC converter station will be discussed next.

Figure 1 is a graph showing the DC current-voltage characteristics during normal operation, where DCWILD/ is a straight line determined by the minimum value of the control angle α on the forward converter side, and as is already known, the following (1) Because it is expressed by the formula.

Vαm1n=1. JtRAa cowαwin --X
IDO---11) π (However, EAO is the winding voltage on the pulp side.)Also, constant current control is normally adopted on the forward converter side, and its characteristics are shown in direct @100. Therefore, the characteristics on the forward converter side are directly yato.
It is a combination of i and 100. Constant voltage control is usually adopted on the inverter side, but its characteristics are
Indicated by The direct current control area is the characteristic of the constant current control region on the inverse converter side. Normally, the target value is set to be 1096 or more lower than the constant current control target value. The characteristics of the inverter side are direct mco00 and -
It is a combination with 07.

Now, if the AC bus side winding voltage of the pulp transformer drops due to voltage fluctuations in the AC system, the tap changer will immediately turn off.
does not operate, so the pulp side winding voltage also decreases. In this case, the forward converter side performs constant current control as described above.
5, the control angle α is made small to keep the DC current l110 constant. However, if the voltage fluctuation width is large, the control angle α reaches the minimum value αmin and cannot be reduced further, resulting in an uncontrolled state. In this uncontrolled region, as can be seen from equation (1), the DC voltage vαmin fluctuates as the EAO changes due to fluctuations in the pulp winding voltage. Therefore, if the voltage is significantly reduced due to AC system voltage fluctuations, the DC voltage-current characteristic will be as shown in FIG. That is, in FIG. 2, the direct MA 101'
is the characteristic in which the control angle α is the minimum value on the forward converter side, the straight line m1oo is the characteristic in the constant current region, the straight line 8200 is the characteristic in the constant voltage control region on the inverse converter side, and the straight line 0/ is the characteristic in which the control angle α is the minimum value. This characteristic indicates the region of constant current control.

Comparing Figure 1 and Figure 1, it can be seen that the AC-DC conversion operating point P is determined by DC voltage - current due to AC system voltage fluctuations.
0 point P1, which means that is moving to pl, is a point,
Compared to PK, the DC current IDO has decreased by 10 or more, and the DC voltage vDC has decreased in proportion to the AC system voltage drop width. Therefore, if the operating characteristics shown in Figure 1 are obtained,
The DC power will be significantly reduced, resulting in a decrease in stability if DC power transmission is used as a system stabilization measure. Also, at the operating point P1, since the inverse converter side is under constant current control, the decreased forward converter side voltage VD
Control to advance the control advance angle blade to increase O.

If this is executed, the power factor of the inverter as seen from the AC system will be poor and the inflow delayed reactive power will increase. Therefore, the AC bus voltage on the inverter side also decreases, making it impossible to continue stable operation. This results in an increase in space.

In this way, in the conventional tap switching control method, since tap switching takes time, constant current control on the inverse converter side is selected due to AC system voltage drop until the tap switching is completed on the forward converter side. This will result in a drop in the AC voltage on the reverse converter side and a significant decrease in the DC transmitted power9.In order to deal with this, the control angle α at rated operation on the forward converter side can be increased. However, there is a drawback that the number of required phase adjustment equipment increases, and the number of required phase adjustment equipment also increases on the inverter side.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and by performing tap switching extremely quickly when the AC bus voltage on the forward converter side decreases, the DC transmission power decreases and the reverse converter side It is an object of the present invention to provide a tap switching control device that can shorten the AC voltage drop time on the side as much as possible.

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 3, OL is the AC system bus to which the primary winding of the pulp transformer (not shown) is connected, PT is the potential transformer, and io is the AC bus voltage on the primary side of the pulp transformer. // is the one that converts when the tap switching operation is performed in the tap correction circuit that converts the voltage into the pulp side winding voltage.
In other words, the reference pulp side winding voltage is compared with the pulp side winding voltage that fluctuates through the primary winding connected to the AC flow rate Hot. When the voltage deviation is larger than a predetermined value, the maximum voltage tap selection section outputs the maximum voltage tap selection signal, and the l unit switches to the maximum voltage tap according to the maximum voltage tap selection signal. The tap changer 13, which operates on a normal tap, is not corrected when the maximum voltage tap is not selected, and when the maximum voltage tap is selected, the corrected pulp side winding voltage is set as the reference pulp winding voltage. This is a well-known tap control unit that compares the two voltages, integrates the voltage deviation, and outputs a tap control command, that is, a tap avoidance signal, when the integrated value exceeds a certain value. Therefore, the tap up signal lags behind the maximum voltage tap selection signal. In addition, when the maximum voltage tap selection signal is sent to the tap changer /J, the university detects this and
This is a tap state detection unit that opens a normally closed contact /j that connects the tap control unit /J and the tap changer saw.

FIG. 3 is a block diagram showing the configuration of the -1 part of the tap changer saw in FIG. Tap N is the maximum voltage tap. A, B, C, and D are contacts of a switch that performs tap switching operations, and R is a resistor for suppressing short-circuit current during tap switching. In addition, Figures (a) to (c)
) shows the process in which switches A, B, C, and DK shift from the tap state to the maximum voltage tap state.

Next, the operation will be explained with reference to FIGS. 3 and 4.

The switching operation of the tap changer saw when the voltage of the AC bus 0/ changes slightly is a tap-up switching operation every 1 taps as in the past. In other words, in the case of this tap raising, if the initial state of the tap is at tap /, no tap change signal is output from the maximum voltage tap selection section // in Fig. 3, and the tap change signal is not output from the tap control section /J. By tap up signal]
The tap position moves from tap 1 to tap 1 via switches A, B, and C, resulting in the state shown in Figure 3(o). Since this tap switching operation is well known, the details will be omitted.

A state in which the AC bus voltage decreases significantly and the operating point shifts from point P in Figure 1 to point P1 in Figure 1, that is,
When the maximum voltage tap selection section ll compares the reference pulp side winding voltage and the fluctuated pulp side winding voltage and detects that the voltage deviation is larger than a predetermined value, the maximum voltage tap selection section ll / changes from the state of Fig. e (a) to Fig. 4 (
To transition to the state connected to the maximum voltage tap N shown in C), a maximum voltage tap selection signal is sent to the switches A, B, C, D K of the tap changer saw to select the maximum voltage tap in a known order. Switch to position. Then, the tap state detection unit/
1 is detected, the normally closed contact 13 is opened, and the tap switching operation is completed. In this case, if the normally closed contact 13 is opened, if the normally closed contact 13 is closed, the tap control unit 13 will detect that there is a residual deviation between the reference pulp side winding voltage and the corrected pulp side winding voltage. In this case, a tap-up signal may be sent to the tap changer saw, which may close switch A or C, causing a short circuit with the highest voltage tap N.

In addition, in this invention, the voltage of the maximum voltage tap N is
It shows the maximum voltage that restores the pulp side winding voltage to the reference pulp side winding voltage when the maximum predictable voltage drop of the AC bus voltage occurs.

As mentioned above, according to the present invention, when the AC system bus voltage drops sharply, the tap of the tap changer is forcibly switched to a higher tap, so that the voltage drop in the pulp side winding The decrease in DC transmission power and the decrease in AC voltage on the inverter side can be reduced as much as possible.

[Brief explanation of drawings]

Figure 1 is a diagram showing the DC current-voltage characteristics during normal operation of an AC-DC converter station, Figure 2 is a diagram showing the DC current-voltage characteristics when the forward converter side AC bus voltage decreases, and Figure 3 is a diagram showing the DC current-voltage characteristics when the forward converter side AC bus voltage decreases. FIG. 4 is a block diagram of a tap switching control device according to an embodiment of the present invention, and FIGS. 4(a) to 4(C) are block diagrams showing a high voltage tap switching process. 0/...AC bus, l~f, N...tap, 10...
・Tap correction circuit, ll・・Maximum voltage tap selection section, 1
2...Tap changer, 13...Tap control unit, /41...
・Tap status detection unit, ll... Normally closed contact. In the drawings, the same reference numerals indicate the same or corresponding parts. Agent Tsutomu Kuzuno - Figure 2, Figure 3, Figure 1, Figure 4

Claims (1)

[Claims] (1) A valve transformer connected to the AC flow rate 11, a tap changer for adjusting the valve side winding voltage of this pulp transformer, and a tap changer that changes the AC voltage of the AC bus when the tap change operation is performed. a tap correction circuit for converting into the pulp side winding voltage; connected to the tap correction circuit, the tap changer is connected to the tap changer when a voltage deviation between the pulp side winding voltage and the reference valve side winding voltage is larger than a predetermined value; a maximum voltage tap selection section that outputs a signal for switching the tap to the maximum voltage tap position; connected to the tap correction circuit; a tap control unit that sends a tap increase signal to the tap changer to change the taps one by one when the maximum voltage tap position is selected, and the tap control unit and the tap changer when the maximum voltage tap position is selected. A tap switching control iron quantity in an AC-DC converting station, characterized in that it is equipped with a tap state detection section that disconnects the connection from the AC/DC converter station.