JPS6056065B2 - Control method for reactive power compensation type cycloconverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a reactive power compensating cycloconverter such that the fundamental wave power factor as viewed from the power supply side is always 1.

A cycloconverter is a device that directly converts alternating current power at a constant frequency into 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.

Moreover, the reactive power constantly fluctuates in synchronization with the frequency on the load side. 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 a cycloconverter, C is a phase advancing capacitor, 5
5 is a thyristor bridge circuit, L.

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 so that the reactive power Q on the power supply side is always zero, thereby controlling the current 10 flowing through the DC resistor and the iristor Lo. 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 V, a current Icc flows through the cycloconverter c/c at a certain instant. The magnitude of Icc and the phase angle α are constantly changing in synchronization with the alternating current flowing through the load. In addition, the phase advance capacitor C has V
A constant current Icap, which is 900 ahead of s, is flowing. At this time, the reactive power compensator (thyristor bridge circuit 55 + DC reactor L.
-sin α, the power supply current 1,
has only the in-phase component with the voltage V. Even if the magnitude of I'cc and the phase angle α change, 10'■k
If lo is controlled, voltage V and current 1 will always be in phase, and the fundamental wave power factor seen from the power supply side will always be operating at 1. This conventional reactive power compensator is
Thyristor bridge circuit 5 separate from cycloconverter
5, it had the disadvantage of being expensive. 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 compensator such as the conventional thyristor bridge circuit described above. The objective is to provide a control method for a reactive power compensated cycloconverter that can always control the power factor to 1. FIG. 3 is a block diagram of an embodiment of the reactive power compensation type cycloconverter device of the present invention.

In the figure, BUS is the electrical line of the three-phase AC power supply, C is the Δ or connected phase advance capacitor, TrU, TrV, TrW are the power transformer, CC-U, CC-V, CC-W are the U phase, V phase, W phase circulating current type cycloconverter, LOA
Du, LOADv, LOAD are three-phase loads. Inside the U-phase cycloconverter CC-U is a positive group converter S.
S-P1 Negative group converter SS-N1 Consists of DC reactors LOl and LO2 with intermediate taps, and its control circuit includes a load current detector CTLU, an output current detector CTpu of the positive group converter, and an output current of the negative group converter. Detection V-TNUl adders A1 to A, comparators Q, C2,
C3, operational amplifier KO, Kl, K2, inverting circuit 1N■,
Absolute value circuit. ABSl phase control circuit PH-P, PH-N
is used. The V-phase and W-phase cycloconverters are similarly configured, and the control circuit CO surrounded by the two-dot chain line
NT-V and CONT-W are the U-phase control circuit CONT
- It is configured similarly to U. In addition, as a reactive power control circuit, a transformer PT that detects the three-phase AC voltage at the receiving end,
Current transformer CTSL reactive power calculation circuit that detects three-phase alternating current ■AR, . There is a reactive power setter Q*, a comparator C1, a control compensation circuit [1(s)], and a distribution circuit DIS.

First, the operation of load current control of the circulating current type cycloconverter will be explained using the U phase as an example.

Load current command 1L1u and actually flowing load current 1LU.
The detected values are compared, and the phase control circuits PH-P and PH-N are controlled so that the cycloconverter CC-U generates a voltage proportional to the deviation ε3.

With respect to the output phase α, Ll of PH-P, the output phase αNU of PH-N is changed from the amplifier K2 to the inverter 1NV through the inverting circuit 1NV so that αNu=180, maintaining the relationship of -α,u.
It is input to N. In other words, the output voltage of SS-P ■Pu=
Kv・■s-COSapu. l5SS-N output voltage V
NU=Kv●■・COSaNU=-VPU is the load terminal, and normal operation is performed in a balanced state. When the current command ILIu is changed in a sinusoidal manner, the deviation ε3 is also changed accordingly, and the αPu and αNU are controlled so that a sinusoidal current 1L flows through the load. In this normal operation, the SS-P voltage and the SS-N voltage are equal and balanced, so the circulating current is 1. There is almost no flow. The load currents of the ■phase and W phase are V, IL, . are similarly controlled.

Next, the control operation of the circulating current 10 will be explained.

Here again, the explanation will be given using the U-phase cycloconverter as an example. The circulating current 10u is detected as follows.

That is, the output current of the positive group converter SS-P. The sum of the detected value and the detected value of the output current 1NU of the negative group converter SS-N, subtracting the absolute value of the detected value of the load current 1LU, and multiplying by 112 is the circulating current 10u.
It is. The relational expression is as follows. The circulating current 10u obtained in this way is its command value 1.

Compared to U. The deviation E2=IOIu-100 is input to the adders A3 and A via the amplifier K1. Therefore, the inputs E4 and E5 to the PH-N are each as follows.

Therefore, the relationship αNu = 1800 - αPu becomes dull K,・
SS-P output voltage Vpu and S are proportional to E2.
The output voltage VNU of S-N becomes unbalanced.

The differential voltage is applied to the DC reactors LO1 and LO2, and a circulating current 10u flows. If IOLl flows too much than the command value 1 system, ε2 decreases and the differential voltage is reduced. As a result, the circulating current 10u is controlled to be equal to its command value I. Circulating current 1 of V-phase and W-phase converters.

v and IOw are similarly controlled according to the command values 10I1v and IO8w. On the other hand, reactive power control is performed as follows.

A current detector CT3 and a voltage detector PT are installed at the power receiving end, and their reactive power Q is calculated by VAR.

The specified reactive power value Q1 (is normally set to zero, and the comparator q
A deviation ε1 is generated by . Control compensation circuit H (
s), an integral element is normally used to make the steady-state deviation ε1 zero, and its output 10* becomes the command value for the circulating current. In other words, when the lagging reactive current IREACT for the three phases of the cycloconverter becomes smaller than the leading reactive current 1cap of the phase-advancing capacitor, the reactive power at the receiving end becomes advanced, and Q
is a negative value.

Therefore, ε1=Q*-Q=-Q is positive, and the integration circuit H
(s) to increase IO*. Then, IOu. via the distribution circuit DIS. IOIv. IM increases, increasing the circulating current of the cycloconverter. This circulating current is a delayed reactive current component when viewed from the power supply side, so
It serves to increase the above 1REA0. 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 = Q water - Q = -Q will be negative,
Reduces IO water and reduces circulating current. Here, the circulating current command value 10* is directly changed to the circulating current command value 1 for each phase.

Iu, I08v, I0Iw may be used, but in that case, the following drawbacks occur. Figure 4 shows the current of a three-phase load.

, ILV, output voltage Vu of the cycloconverter,
It represents the waveforms of Vv, Vw and the control phase angles α, U, α, V, of the positive group converter at that time. As shown in the figure, α, U, αPv, and αPw are 0 to 180. The range changes while shifting the phase. Note that the control phase angles of the negative group converter are αNU″.180n−α,
α, v≠180 phase-αPVlαNW≠1800-αP
It is changing while maintaining the relationship w. Point a (α
, o=00, αP■=αPw=1200), the circulating current is 1. When u, I0v, and I0w flow, the reactive current component is as follows.

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 U phase, α at point a. = 0, so no matter how much circulating current flows, the reactive current component is 1. U(REAC, > does not increase, and a wasted current is flowing. This wasted current increases the current capacity of the thyristor, which is a component of the cycloconverter. Therefore, if possible, at this time (a
It is preferable not to allow the circulating current 10u of the U-phase cycloconverter to flow. The distribution circuit DIS in Figure 3 is a cycloconverter for each phase.
Wood Wood vata circulating current command value 10u, I0v
, I0w are distributed in proportion to the sine value Slnα of the firing control angle α of the cycloconverter of each phase.

FIG. 5 is a block diagram showing a specific embodiment of the distribution circuit DIS. In the figure, KaO, Kav, Kαu are proportional amplifiers, LMu, LMv, LMw beam transmitter circuits, SQu
, SQv, SQw are square calculation circuits, A5U, A5V, A
5 is an adder, SQRLj, SQRv, and SQRw are square root calculation circuits, and Mu, Mv, and M are multipliers. VaO
is the output signal of the amplifier K2 in FIG. 3, which serves as a phase control signal for the U-phase cycloconverter CC-U. That is, αN exists between the phase control angle αPu of the positive group converter SS-P and the phase control angle αNU of the negative group converter SS-N.
u-. If we consider that the relationship 180−−αPu holds,
SS-P output voltage V, O and SS-N output voltage VN
As mentioned before, U can be expressed as follows. In other words, VQO can be considered to be proportional to the cosine value of the phase control angle αPO.

Therefore, returning to FIG. 5, the distribution circuit DIS will be explained.

The proportional amplifier KaO is for unitizing the phase control signal VaO.

Therefore, VauXKau=COsau. but,
The control signal VaO can be increased as much as desired according to the deviation E2, whereas the phase control angle αU is in the range of 00 to
Limited to 1800 range. That is -1 COs
It must be aOku1. The limiter circuit LMu takes this limit value into consideration. Next, its cosine value COs
αo is squared using a square calculation circuit SQu to obtain (COsau)2. The adder A5U converts the unit voltage 1 to the above (COsα
u) subtracts 2, resulting in 1-(COSαu)
2 is input to the square root calculation circuit SQRu. Therefore SQRO
The output is! 1-COsau)2, which is the sine value Sinαo
is found. The multiplier Mu is a compensation circuit H(s
) is multiplied by the sine value Sinau of the phase control angle αU of the U-phase cycloconverter, and the output 1.1 [J=■o tree・SinaO is the command for the circulating current 10u of the U-phase cycloconverter value.

Similarly, SinaVlsinai can be obtained from the phase control signals Vav and vaw of the V-phase and W-phase cycloconverters, respectively.

Therefore, the outputs of multipliers Mv and Mvv are respectively IOIv=
IO*●Sina, and I product = IO water/Sinaw. In this way, the circulating current 1 of the cycloconverter for each phase is
0u910v910w is the firing phase control angle α of the respective phase converter.

, αV, αi are distributed in proportion to the sine values of αi. Therefore, a large amount of circulating current flows in the cycloconverter of the phase that largely contributes to the reactive current component on the power supply side, and a small amount of circulating current flows in the cycloconverter of the phase that does not contribute much to the reactive current component. Therefore, unnecessary circulating current is not caused to flow, and efficient reactive power compensation can be performed. 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 proportion of the circulating current of the cycloconverter of each phase is determined by the sine value Sln of the firing control angle α of the cycloconverter of each phase.
Since the power is distributed and controlled in proportion to α, no wasteful circulating current is allowed to flow, and efficient reactive power compensation can be performed. 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 the drawing]

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 a concrete diagram of the distribution circuit of FIG. 3. It is a block diagram which shows an example. CC-U-CC-W... Circulating current type cycloconverter, TrU-TrW... Power transformer,
SS-P...Positive group converter, SS-N...
...Negative group converter, LOl, LO2...DC reactor, LOADu~LOADvq...
Load, BUS... Three-phase electric line, C...
Phase advance capacitor, CT,, CTNO, CTpu, CTL
u...Current transformer, PT...Transformer, C1
~C3... Comparator, A1 ~ Input... Adder, PH-P, PH-N... Phase control circuit, A
BS: Absolute value circuit, NV: Inverting circuit, 4 to K2: Amplifier, DIS:
・Distribution circuit, Kαo-Ka9...Amplifier, LM
Mw on u...Remitter circuit, SQu-SQw・
...Squaring calculation circuit, A5O-A5W...
Adder, SQRu-SQRw... Square root operation circuit, MO-Mw... Multiplier.

Claims (1)

[Claims] 1. In a circulating current type cycloconverter that supplies variable frequency alternating current for each phase to a multiphase load, a phase advancing capacitor is connected to its common power supply terminal, and the sum of the delayed reactive power of the cycloconverters of each phase is calculated. When the circulating current of the cycloconverter of each phase is controlled so that the leading reactive power of the phase advancing capacitor cancels each other, the proportion of the circulating current of the cycloconverter of each phase is controlled to ignite the cycloconverter of each phase. A method for controlling a reactive power compensation type cycloconverter, characterized in that the control is performed by distributing the angle in proportion to the sine value sin α of the angle α.