JPS5914987B2 - Control method for reactive power compensation type cycloconverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a reactive power compensation type cycloconverter, which controls the fundamental wave power factor as viewed from the power source side to always be 1.

A cycloconverter is a device that directly exchanges alternating current power at a constant frequency with alternating current power at a different frequency, but it has the disadvantage that it takes a lot of reactive power from the power source because its component thyristor is commutated by the power supply voltage. be.

Also, the reactive power on the load side constantly fluctuates in synchronization with this frequency. This not only increases the capacity of power supply system equipment, but also has various negative effects on electrical equipment connected to the same system. Figure 1 shows a typical conventional reactive power compensator, where BUS is a three-phase AC power line,
c/c is 5 cycloconverter, C is a phase advancing capacitor, 55 is a thyristor bridge circuit, and Lo is a DC reactor.

The reactive power Q on the power supply side is detected, and the firing angle of the thyristor bridge circuit is changed to control the current 10 flowing through the DC reactor Lo so that it is always zero. FIG. 2 is a vector diagram showing the relationship between the voltage for one phase of the electric line BUS and the current flowing through each part of this conventional reactive power compensator.

With respect to the power supply voltage Vs, a current of Icc j5 flows through the cycloconverter c/c at a certain instant. This Ic
The magnitude of c and the phase angle α are constantly changing in synchronization with the alternating current flowing through the load. Further, a constant current Icap, which is 900 ahead of Vs, flows through the phase advance capacitor C. At this time, the reactive power compensator (thyristor valve 0 circuit 55 + DC reactor Lo) is
By flowing a delayed current of ap-Icc-slnα, the power supply current Is has only an in-phase component with the voltage Vs. Ic
Even if the magnitude of c and the phase angle α change, accordingly,
If 10'klo is controlled, the voltage Vs.5 and the current Is will always be in phase, and the fundamental wave power factor seen from the power supply side will always be 1 during operation. This conventional reactive power compensator requires a thyristor bridge circuit 55 in addition to the cycloconverter, so it has the disadvantage of being expensive. '0 The present invention has been made in view of the above points, and eliminates fluctuations in the reactive power of the cycloconverter without providing a special reactive power compensation device such as the conventional thyristor bridge circuit, and improves the The purpose of the present invention is to provide a control method for a reactive power compensation type 5 cycloconverter that can always control the fundamental wave power factor to 1.3.
The figure is a configuration diagram of an embodiment of a reactive power compensation type cycloconverter device of the present invention.

In the figure, BUS is the electrical line of the 3-phase AC power supply, C is △ or the connected phase advance capacitor, CC-U, CC-V, CC-
W is a circulating current type cycloconverter of U phase, phase, and W phase, respectively, and LOADu, LOAD, and LOADw are three-phase loads. The U-phase cycloconverter CC-U consists of a positive group converter SS-P1, a negative group converter SS-N1, and a DC reactor LO, LO2 with an intermediate tap.
Its control circuit includes a load current detector CTLUl, an output current detector for the positive group converter CTPUl, an output current detector for the negative group converter CTNUl, adders A1 to A4, and a comparator C.
,,C2,C3, operational amplifier K. ,K,,K2, inversion circuit 1N, absolute value circuit ABSl phase control circuit PH-P,P
H-N is used. The phase and W phase cycloconverters are similarly configured, and the control circuits PHC- and PHC-W surrounded by two-dot chain lines are the U-phase control circuit PHC-U.
It is configured in the same way. In addition, as a reactive power control circuit, a transformer PTSL that detects the 3-phase AC voltage at the power receiving end, an AC transformer CTSL that detects the 3-phase AC current, and a reactive power calculation circuit A
Rl reactive power setter Q1 comparator C1, control compensation circuit H (
s), there is a selection circuit SLC. First, the operation of load current control of the circulating current type cycloconverter will be explained using the U phase as an example.

The phase control circuit P is configured to compare the detected value of the load current command 11u and the actually flowing load current 1LU, and generate a voltage proportional to the deviation ε3 from the cycloconverter CC-U.
Controls HP and PH-N. PH-P output phase αP
With respect to
The signal is input to the PH-N via the PH-N. In other words, SS-? Output voltage Pu=k・Vs−COSapu (output voltage NUkvOS″COSaNU=−VPU of 5SS-N is the load terminal, and normal operation is performed in a balanced state. When the current command RLU is changed in a sinusoidal manner, The deviation ε3 also changes accordingly, and the above αPu and αNU are controlled so that the sinusoidal current L flows through the load.In this normal operation, the voltage of SS-P and the voltage of SS-N are equal and balanced. Therefore, the circulating current 10 hardly flows.The phase and W phase load currents 1L and ILW are similarly controlled.

Next, circulating current 1.

The control operation will be explained. Here again, the explanation will be given using the U-phase cycloconverter as an example. Circulating current 1.

U is detected as follows. That is, take the sum of the detected value of the output current 1p0 of the positive group converter SS-P and the detected value of the output current 1N[J of the negative group converter SS-N, then subtract the absolute value of the detected value of the load current 1LU, %
Multiplied by this is the circulating current 1. It is U. The relational expression is as follows. 10u=(Ip+IN-11L1)/2 Circulating current 1 thus obtained.

U is its command value 17). compared to Deviation ε2=1
7) U-10U is input to adders A3 and A4 via amplifier K. Therefore, the inputs ε4 and ε, to the PH-N are as follows.

ε4 yo K2ε3+K biε2 ε5=-K2・ε5+K, ε2 Therefore, the relationship αNu=180°−αPu collapses and K biε
SS-P output voltage Pu and SS-
The output voltage VNU of N becomes unbalanced.

The differential voltage is applied to the DC reactors LO and LO2, and a circulating current 10u flows. Is IOu the command value 1? ) If the current flows too much than u, ε2 decreases and the voltage difference becomes smaller. As a result, the circulating current 10u is its command value 1*0u
is controlled to be equal to . The circulating currents 10v and IOw of the phase and W-phase cycloconverters and their command values δ and IOw are similarly controlled in accordance with the command values 1δ and δW.

On the other hand, reactive power control is performed as follows.

A current detector CT8 and a voltage detector PT are installed at the power receiving end, and their reactive power Q is calculated by AR.

The reactive power command value q is normally set to zero, and a deviation ε1 is generated by the comparator C1. Control compensation circuit H(s
), an integral element is usually used to make the deviation ε, zero, and its output 1δ becomes the command value for the circulating current. That is, when the lagging reactive current IREACT of the three phases of the cycloconverter becomes smaller than 1 cap of the leading reactive current of the phase-advancing capacitor, the reactive power at the receiving end becomes a leading one, and Q takes a negative value.

Therefore, ε1-σ1Q-1Q is positive, and the integration circuit H(
s) to increase I♂. Then, selection circuit SL
* * *10u via C
,10,I0w also increases, increasing the circulating current of the cycloconverter.

Since this circulating current is a delayed reactive current component when viewed from the power supply side, it serves to increase REACT. Conversely, if the circulating current flows too much and the reactive power at the receiving end lags, Q will be a positive value and ε1=B-Q-1Q will be negative, reducing IO and reducing the circulating current. .

*Here, the circulating current command value 10 may be used as the circulating current command values 1♂U, I♂V, I♂W for each phase, but in this case, the following drawbacks occur.

Figure 4 shows the waveforms of the three-phase load currents 1LU, IL, ILW, the output voltages Vu, V, W of the cycloconverter, and the control phase angles αPu, αP, αPw of the positive group converter at that time. As in, αPu, αPv and α
Pw changes in the range of 0° to 180° while shifting the phase. Note that the control phase angles of the negative group converters are αNu−. 1800-αPu, αPuZl8O-αN
It changes while maintaining the relationship of V, αNwZl8σ - αNW. Point a in this figure (αPuO゜, αPv=αPw=
120°), when a circulating current of 10u, I0, I0 flows, the reactive current component is 10U (REACT)
1k110US11αPU3OlO(REACT)0k
110VsinaPV0(?/2)゜k110v10W
(REACT)0k110WsinαPw: (Tsutomu 72)
゜k110w However, K1 is a proportionality constant.

This means that even if the same circulating current is passed, the effect will differ depending on the control phase angle of each phase. For example, in the case of the U phase, αu=0 at point a, so no matter how much circulating current is passed, the reactive current component 10U (REACT) does not increase, and a wasteful current is passed. This wasted current increases the current capacity of the thyristor, which is a component of the cycloconverter. Therefore, if possible, at this time (
At point a), the circulating current of the U-phase cycloconverter is 10[
J! It is better not to let it flow. FIG. 5 shows the selection circuit SL
This shows the operation mode of C. First, X1=αPu−
Create a signal of αP, X2 = αP - αPW, X3 = αPw - αPu, then Y, =
X1・X2+X1・X2,Y "2X2・X3+X2・X
I'm making 3.

In the mode of Y, = 1, the selection circuit SLC is I♂→17)
A signal is connected to u, and a circulating current of 10 u is caused to flow through the cycloconverter CC-U in the range α, u = 60° to 12σ. Similarly, in * *Y2=1 mode, IO−+IO,
In the mode of Y3=1, the I♂→I2M signal is connected.

That is, three-phase cycloconverters CC-U, CC-
Among V and CC-W, the cycloconverter whose control phase angle α is closest to 90° is selected, and the circulating current is passed through it.

Therefore, unnecessary circulating current is not caused to flow, and efficient reactive power compensation can be performed. Figure 6 shows vector diagrams of voltage and current on the power supply side at point a in Figure 4, where (a) shows the case where no circulating current flows, and (b) shows the voltage
A vector diagram is shown when a circulating current is passed only through the phase cycloconverter.

In Figure 6a, Iccu, ccv, ccw are each U
It represents the input current vector of the phase, phase, and W-phase cycloconverter, and its magnitude and phase angle are as follows. Iccu=k・11Lu1Aapu:-0Ic
c2k・11L1 Otsu-αNv=180°-αPv=60
゜Iccw=k-11Lw1Z-αPw=120k: proportional constant, Phase cycloconverter CC- supplies load current IL from the negative group converter (IL has a negative value at point a in Figure 4) ) Therefore, the phase angle of 1 cc of input current is αNV2180°-αP=60°.

The input current Cc of the entire cycloconverter is the input current 1ccu, ccv, 1 of the above-mentioned phase cycloconverter.
It becomes the vector sum of ccw.

Therefore, by flowing a constant leading reactive current called the phase advancing capacitor Icap, the 5 human power current 1s supplied from the power supply is
is a vector sum of current 1cc (51cap).

Here, if the input current Icc of the entire cytalo converter is divided into effective components 1P0WER and REACT, it can be expressed as in the following equation.

01P0WER11CCU'COSaPU+ICC゜6
OSaN+Iccw′COSapw=K3{11Lu卜COSapu+(IL卜COsαN+11Lw1・CO
SαPw}IREACTOLCCU'SlflαPu+
Icc゛SlnαNV+1CCW′SlnaPW=k・
{11Lu1・Sinapu+I[LvI−SinaN
v + 11Lw1 - Sinapw} In Figure 6a, the leading current Cap of the phase advancing capacitor is larger than the lagging current 1Q of the cycloconverter, so the input current 1s leads the power supply voltage Vs by the phase angle δ. .

FIG. 6b shows a vector diagram when a circulating current of 10 V is applied to the V-phase cycloconverter by CC-V so that Icap=CC-Q.

By flowing a circulating current of 10 to CC-V, the input current of the phase cycloconverter becomes I'Ccv (7).
REACT) is expressed as follows.

1'Cc(POWER)0kIILV1゜C0SaN'
CCV(R,EACT)::k(11LV1+2゜0v
)゜sinapv That is, the effective portion remains unchanged and the invalid portion increases by 2k10vsinap.

As a result, the reactive component 15REACT of the input current Icc of the entire cycloconverter is expressed by the following equation.

IhEACTOk{11LU1゜sin αPu+IIL
vlsinapv+11LwI-Sinapw-F2l
O・Sinapv}The circulating current is set to 10v so that this value EACT is equal to the leading current Icap of the phase advancing capacitor.
By controlling , the input current 1 s from the power source can be kept in phase with the voltage s (power factor = 1). Figure 4a
From point b to point b, the circulating current 10 of CC-V is determined by the magnitudes of load current 1LU, ILV, ILW and control phase angle αPu.
, αP, and αPw are controlled to the following values. 1
1cap・0u0? {? -11Lu1゜S1naPU2・Slna
pvk-11L;゜sinapv-11Lw1゜S1naPW
}Similarly, from point b to point c, the circulating current 10u of the U-phase cycloconverter CC-U is controlled, and from point c to point d, the circulating current 10w of the W-phase cycloconverter CC-W is controlled, and the power factor of the power source is can always be held at 1.

As described above, the reactive power compensation type cycloconverter device according to the present invention can control the fundamental wave power factor as viewed from the power source side to always be 1 without using a conventional special reactive power compensation device.

In addition, the selection circuit selects the cycloconverter with the control phase angle α closest to 90I among the cycloconverters with multi-phase output to flow the circulating current, which eliminates the flow of wasteful circulating current and improves the efficiency of reactive power. Compensation can be made. In the embodiment, a three-phase output cycloconverter has been described, but it goes without saying that the present invention can be applied to a two-phase or more polyphase output cycloconverter.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a typical conventional reactive power compensator, Fig. 2 is a vector diagram for explaining the operation of Fig. 1, and Fig. 3 is a block diagram of a typical conventional reactive power compensator.
The figure is a block diagram of one embodiment of the reactive power compensation type cycloconverter device of the present invention, FIG. 4 is a waveform diagram of each part for explaining the operation of FIG. 3, and FIG. 5 is the operation of the selection circuit of FIG. 3. The mode diagram, FIG. 6, is a vector diagram of voltage and current on the power supply side at point a in FIG. 4. CC-U-CC-W... Circulating current type cycloconverter, SS-P... Positive group converter, SS
-N...Negative group converter, LO,,LO2...
...DC reactor, LOADu-LOAI) w.
...Load, BUS...3-phase power line, C.
... Phase advance capacitor, CTs, CTNu, CTp
u...Current transformer, PT...Transformer, VA
R...Reactive power calculation circuit, C1 to C3...
... Comparator, A1-A4 ... Adder, PH-P
, PH-N... Phase control circuit, ABS...
...Absolute value circuit, IN...Inversion circuit, KO-K
2...Amplifier, SLC...Selection circuit.

Claims (1)

[Claims] 1 It has a circulating current type cycloconverter that supplies variable frequency alternating current for each phase to a multiphase load, and a phase advance capacitor is connected to its common power supply terminal to nullify the delay of the cycloconverter of each phase. In a reactive power compensation type cycloconverter that controls the circulating current of the cycloconverter of each phase so that the sum of power and the leading reactive power of the phase-advanced capacitor cancel each other, the cycloconverter of each phase is operated. A method for controlling a reactive power compensation type cycloconverter, characterized in that a cycloconverter whose phase has a control phase angle α closest to 90° is selected and its circulating current is controlled.