JPS6155343B2 - - Google Patents

Description

[Detailed Description of the Invention] In the present invention, the fundamental wave power factor seen from the power supply side is always 1.
The present invention relates to a method of controlling a reactive power compensation type cycloconverter to achieve the following.

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. . 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 causes various adverse effects on electrical equipment connected to the same system due to reactive power fluctuations.

Conventionally, as a device for compensating for fluctuations in reactive power of such a cycloconverter, a reactive power compensator has been connected to a power receiving end of the cycloconverter. Since this reactive power compensator compensates for fluctuations in reactive power, it must have a high control response speed, and is made of semiconductor elements such as thyristors and is expensive.

FIG. 1 is a block diagram of a conventional reactive power compensation type cycloconverter device. In the figure, CC is a circulating current type cycloconverter, SS-P and SS-N are its positive group and negative group converters, L _O1 and L _O2 are DC reactors with intermediate taps, and LOAD is a load. Further, BUS is a three-phase electric line, and C is a phase advance capacitor connected to △ or 〓. The control circuit includes a current transformer CT _S that detects the three-phase alternating current, a transformer PT that detects the three-phase power supply voltage, a reactive power calculator VAR, a control compensation circuit H(s), a load current detector CT _L , and a positive Output current detector CT _P of group converter SS-P, output current detector CT N of negative group converter SS- _N , switch circuit SW, Schmitt circuit SH, comparators C ₁ to C ₅ ,
Operational amplifier K ₀ to K ₃ , phase control circuit PH-P, PH
-N is used. First, the operation of load current control will be explained.

Load current command I _L ^* and actual flowing load current I _L
The detected values are compared and the phase control circuits PH-P and PH-N are controlled so that the cycloconverter generates a voltage proportional to the deviation _ε3 . The output phase α _N of PH-N is α _{N =}
The signal is input from the amplifier _K2 to the PH-N via the inverting circuit _K3 so as to maintain the relationship of 180° _-αP . In other words, the output voltage of SS-P is V _P =k _V V _S・cosα _P and SS-
N output voltage V _N =k _V V _S・cosα _N =k _V V _S・cos
(180° - α _P ) is normal operation with the load terminals balanced. When the current command I _L ^* is changed sinusoidally, the deviation ε ₃ also changes accordingly, and α _P and α _N are controlled so that a sinusoidal current I _L flows through the load. In this normal operation, the SS-P voltage and the SS-N voltage are equally balanced, so almost no circulating current I _O flows.

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

For example, load LOAD from positive group converter SS-P
When supplying current I _L to negative group converter SS
The current I _N flowing through -N is nothing but a circulating current I _O. Conversely, load LOAD from negative group converter SS-N
When supplying current I _L to , it is a positive group converter.
The current I _P flowing through SS-P becomes the circulating current I _O.
The Schmitt circuit SH detects the direction of the load current I _L and switches the mode of the switch circuit SW. When I _L is in the positive direction, SW is closed to the N side, and when I _L is in the negative direction, SW is closed to the P side. That is, it detects the circulating current I _O of the cycloconverter CC.

On the other hand, a current detector CT _S and a voltage detector PT are installed at the power supply terminal, and their reactive power Q is calculated by VAR. The reactive power command value Q ^* is normally set to zero, and a deviation _ε1 is generated by the comparator _C1 . The control compensation circuit H(s) normally uses an integral element in order to make the deviation ε ₁ zero, and its output I _O ^* becomes the command value of the circulating current I _O . The deviation ε ₂ =I _O ^* −I _O is taken by the comparator C ₂ and inputted to the comparators C ₄ and C ₅ via the amplifier K ₁ .

Therefore, the inputs ε ₄ and ε to PH-P and PH-N
₅ are as follows. However, K ₃ =-1.

ε ₄ =K ₂・ε ₃ +K ₁・ε ₂ ε ₅ =−K ₂・ε ₃ +K ₁・ε ₂ Therefore, the relationship α _N = 180° − α _P breaks down K ₁・ε ₂
SS-P output voltage V _P and SS-N are proportional to
The output voltage V _N becomes unbalanced. The differential voltage is applied to the DC reactors L _O1 and L _O2 , and a circulating current I _O flows. If I _O flows too much than the command value I _O ^* , ε ₂ decreases, reducing the voltage difference. As a result, I _O is controlled to become I _O ^* .

FIG. 2 is a vector diagram showing the relationship between the voltage V _S for one phase of the power supply shown in FIG. 1 and the current of each part.

The phase advancing capacitor C with respect to the power supply voltage V _S
A constant lead current called Icap flows. Now considering the mode in which the load current I _L is supplied from the positive group converter SS-P, the circulating current I _O flows and the current Iccp flows from the power supply to SS-P.
A current of I _CCN flows into -N. I _CCP has a magnitude proportional to the sum of the load current I _L and circulating current I _{O and} has a phase angle α _P , and I _CCN has a magnitude proportional to the circulating current I _O and has a phase angle α _N = 180° − α _P. . Strictly speaking, α _N deviates from 180° − α _P by a value proportional to K ₁ · ε ₂ , but the deviation is small, so in the vector diagram, α
The explanation will be given as _N = 180°−α _P. As can be seen from this vector diagram, if the circulating current I _O is controlled so that the lagging reactive current component of the input current I _CC of the cycloconverter is equal to the leading reactive current of the phase advancing capacitor C, the current I _S supplied from the power supply is It becomes in phase with the voltage V _S and can be operated with a fundamental wave power factor of 1. The reactive current component at this time satisfies the following equation.

Icap=k ₁ (I _L + I _O ) sinα _P +k ₁ I _O sinα _N = K ₁ (I _L + I _O ) sin α _P +k ₁ I _O sin (180°−α _P )=k ₁ (I _L +2I _O ) sin α _P, that is, in FIG. 1, when the reactive power at the receiving end is leading, Q becomes negative and ε ₁ becomes positive. Therefore I
_O ^* is also positive and increases the circulating current I _O. Also, if the reactive power at the receiving end is delayed, Q is positive and ε ₁ = Q ^*
-Q=-Q. Therefore, I _O ^* also becomes negative, reducing the circulating current I _O. If an integral element is used in the control compensation circuit H(s), it is possible to control ε ₁ =0, and Q ^* =
Q=0.

The load current I can be controlled in the same way even in the mode where the current is supplied from the negative group converter SS-N to the load LOAD.
Even if the magnitude of _L and the phase angles α _P and α _N change in synchronization with the output frequency on the load side, the circulating current I _O changes accordingly, and the reactive power at the receiving end is maintained at zero. In other words, the fundamental wave power factor as seen from the power supply side is always 1.

This conventional device has the following problems. In other words, the Schmitt circuit SH detects the direction of the load current I _L as a means of detecting the circulating current I _O , which is the key point of reactive power control, the detected value of the output current I _P of the positive group converter SS-P, and the negative group converter SS. Since a switch circuit SW is used to switch the detected value of the -N output current I _N according to the output signal of the Schmitt circuit SH, the shift in the switching point becomes a problem and accurate reactive power control cannot be performed. .

In particular, when the absolute value of the load current I _L becomes small, the ripple component becomes relatively large, and the load current I
Detecting the direction of _L becomes very difficult. Furthermore, if a filter circuit is inserted before the Schmitt circuit in order to reduce the influence of the ripple, the time delay will increase the deviation of the switching point, making it impossible to accurately control the reactive power.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a control method for a reactive power compensation type cycloconverter, which enables accurate reactive power control by continuously detecting the circulating current I _O of the cycloconverter. With the goal.

FIG. 3 is a configuration diagram showing an embodiment of the reactive power compensation type cycloconverter device of the present invention.

In the figure, TR is a three-phase power transformer having two secondary windings, and the two secondary windings are connected to a positive group converter SS-P and a negative group converter SS-N, respectively.

In addition, L _O1 and L _O2 are DC reactors for suppressing the pulsation of the circulating current, and their intermediate terminals are connected to the load.
Connected to LOAD.

Further, a phase advance capacitor C connected to a △ or △ connection is connected to the receiving end of the three-phase power supply.

The AC current transformer CT _P ' and the three-phase full-wave rectifier circuit DP detect the output current I _P of the positive group converter SS-P, and a specific example thereof is shown in FIG.

In Figure 4, R, S, and T indicate the three-phase power output terminals from the transformer TR, and the positive group converter
Connected to SS-P. CT _P1 and CT _P2 are AC current transformers that detect an R-phase current i _R and an S-phase current i _S , respectively. Note that the T-phase current i _T is uniquely determined from the relationship i _R +i _S +i _T =0 once the i _R and i _S are determined, so a T-phase AC current transformer is not necessary.

The three-phase full-wave rectifier circuit DP is composed of rectifiers _D1 to _D6 , the output terminals of which are connected to a resistor R.

One terminal of current transformer CT _P1 (use as pole terminal)
is connected to the connection point of rectifiers D ₁ and D ₄ , and the current transformer
The pole terminal of CT _P2 is connected to the connection point of D ₂ and D ₅ . Then, connect the pole terminals of CT _P1 and CT _P2 , and connect them to the connection point of D ₃ and D ₆ .

An explanation will be given by taking as an example a case where i _R =10A and i _S =-6A as certain instantaneous values. The current transformer ratio is 1:1.

From the three-phase equilibrium condition, i _T =−(i _R +i _S )=−4A
flows. That is, among the thyristors S ₁ to _{S 6} that are the constituent elements of the positive group converter SS-P, S ₁ , S ₅ ,
This is the mode in which _S6 is conducting. At this time, the output current I _P of converter SS-P is 10A.

On the other hand, current transformer CT _P1 is a current source of i _R = 10A, CT _P2
becomes a current source of i _S =-6A, so the rectifier D ₁ ,
D ₅ and D ₆ become conductive, and current flows at a rate of 10 A, 6 A, and 4 A, respectively. Therefore, a current of I _P '=10 A flows through the resistor R, and the output current of the positive group converter SS-P is detected. In addition, at this time, the rectifier
The current flowing through _D6 corresponds to the T-phase current i _T =-4A.

According to this method, the output current I _P of the positive group converter SS-P can be detected from the AC input current, and there is an advantage that there is no need to use a DC current transformer or an isolation amplifier, which are complex and expensive. .

The present invention will be explained by returning to FIG.

The AC current transformer CT _N ' and the three-phase full-wave rectifier circuit DN detect the output current I _N of the negative group converter SS-N, and their configuration is the same as that shown in FIG. 4.

Further, A ₁ , A ₂ , and A ₃ are adders/subtractors, ABS is an absolute value circuit, and K ₀ is a proportionality constant.

First, adder/subtracter _A1 converts the positive group converter SS−
P output current detection value I _P ′ and negative group converter SS−
Take the sum I _P ′+I _N ′ of the output current detection value I _N ′ of N,
Input to the next adder/subtractor _A2 . Further, the difference I _P '-I _{N ' between I P ' and I N ' is} taken by the adder/subtractor _A3 and inputted to the absolute value circuit ABS. Then, the adder/subtractor _A2 converts the sum of I _P ' and I _N ' from I _P '+I _N ' to I _P '-I
The absolute value |I _P '-I _N '| of _N ' is subtracted, and the value is multiplied by 1/2 by the amplifier _K0 to obtain the detected value of the circulating current _I0 . Note that the output I _P ′−I _N ′ of the adder/subtractor A ₃
is the detected value of the load current _IL .

Figure 5 shows load current I _L and positive group converter SS-P.
The waveforms of the output current I _P of the negative group converter SS-N, the output current I _N of the negative group converter SS-N, and the circulating current I _O are shown.
The value obtained by subtracting I _N from I _P is equal to the load current, and by adding I _P and I _N it becomes the sum of the absolute value of the load current |I _L | and twice the circulating current I _O. Recognize. Therefore, the load current I _L and the circulating current I _O
I _L = I _P −I _N I _O =1/2・(I _P +I _N −|I _L |) =1/2・(I _P +I _N −|I _P −I _N |) It will be done. The circuit shown in FIG. 3 performs this calculation and continuously detects the load current I _L and the circulating current I _O.

The load current control and reactive power control are as explained in the apparatus shown in Fig. 1, and the detected value of the circulating current I _O is compared with its command value I _O ^* , and the reactive power at the receiving end is controlled. can be made zero.

As described above, the present invention performs continuous detection without using conventional switch circuits or the like when detecting circulating current. Therefore, there is no problem of switching point shift and accurate reactive power control can be achieved. Also, even if the load current I _L includes ripple, I _P +
After the calculation of I _N -|I _L | is canceled, the circulating current I _O can be detected accurately, and from this point of view as well, the control accuracy of reactive power can be improved.

Furthermore, in the present invention, it is sufficient to detect the output current I P of the positive group converter SS- _P and the output current I _N of the negative group converter SS-N, and these can be detected by installing a detector on the AC input side. It can be achieved. Therefore, it is not necessary to use conventional expensive and complicated DC current transformers, and an economical device can be provided.

Although FIG. 3 describes a cycloconverter with a single-phase output, the same can be done with a cycloconverter with a multi-phase output. In that case, instead of controlling the reactive power of each phase of the cycloconverter separately, by controlling the same circulating current to flow in each phase so as to make the reactive power at the common receiving end zero, the capacity of the cycloconverter can be reduced. And the capacitance of the phase advance capacitor can be small.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional reactive power compensation type cycloconverter device, Fig. 2 is a vector diagram for explaining the operation of Fig. 1, and Fig. 3 is a reactive power compensation type cycloconverter device showing an embodiment of the present invention. A block diagram of the cycloconverter device, FIG. 4 is a block diagram showing an embodiment for detecting the output current of the positive group converter of FIG.
FIG. 5 shows the load current I _L for explaining the present invention,
3 is a waveform diagram of a positive group converter output current I _P , a negative group converter output current I _N , and a circulating current I _{O. FIG} . TR...Power transformer, CC...Circulating current cycloconverter, SS-P...Positive group converter,
SS-N...Negative group converter, L _O1 , L _O2 ...DC reactor, LOAD...Load, BUS...Three-phase electric line, C...Phase advance capacitor, CT _S , CT _P ',
CT _N ′...Current transformer, PT...Transformer, VAR...Reactive power calculation circuit, _C1 to _C5 ...Comparator, PH-P, PH
-N...Phase control circuit, ABS...Absolute value circuit,
_K0 to _K3 ...Amplifier, _A1 to _A3 ...Adder/subtractor, DP,
DN...3-phase full-wave rectifier circuit, H(s)...compensation circuit.

Claims (1)

[Claims] 1. In a circulating current type cycloconverter that outputs a variable frequency alternating current, a phase advance capacitor is connected to its power supply terminal, and the lagging reactive power of the cycloconverter and the leading reactive power of the phase advance capacitor cancel each other out. In the reactive power compensation type cycloconverter device that controls the circulating current of the cycloconverter, the detected value of the output current I _N of the negative group converter is subtracted from the detected value of the output current I _P of the positive group converter of the cycloconverter. The output current of the positive group converter is determined from the sum of the detected value of the output current I _P of the positive group converter and the _detected value of the output current I _N of the negative group converter. The detected value of the circulating current I _O of the cycloconverter is the value obtained by subtracting the absolute value of the value (I _P −I _N ) obtained by subtracting the detected value of the output current I _N of the negative group converter from the detected value of I _P. A method for controlling a reactive power compensation type cycloconverter, comprising controlling the load current I _L and the circulating current I _O.