JPS6217950B2 - - 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 the drawback is that it requires a lot of reactive power from the power source to commutate the thyristor, which is a component of the cycloconverter, using the power supply voltage. There is. 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, _L01 and _L02 are DC reactors with intermediate taps, and LOAD is a load. Also, BUS is a three-phase electric line, C is a phase advance capacitor connected to △ or 〓, and TR is a power transformer. The control circuit includes an alternator CT _S that detects the three-phase alternating current at the receiving end, and a transformer P that detects the three-phase power supply voltage.
T, reactive power calculator VAR, control compensation circuit H _(S) ,
Current transformer that detects input current of positive group converter
CT _P , current transformer CT _N that detects the input current of the load converter, three-phase full-wave rectifier circuit DP, ON, adder A ₁ ~
A ₅ , operational amplifiers K ₀ to _{K 3} , comparators C ₁ to _{C 3} , absolute value circuit ABS, and phase control circuits PH-P and PH-N are used. The current transformer CT _P detects the AC input current of the positive group converter SS- P , and is a three-phase full-wave rectifier circuit DP.
The signal obtained through the converter becomes the detected value of the output current I _P of the positive group converter. Similarly current transformers CT _N and 3
Negative group converter SS-N by phase full-wave rectifier circuit DN
The output current I _N of is detected. I _P -I _N =I _L is determined by adder _A3 . This is the detected value of the load current. Also, adder A ₁ ,
The following calculation is performed using A ₂ , absolute value circuit ABS, and amplifier K ₀ (1/2 times). I ₀ =1/2·(I _P +I _N −|I _L |) This is the detected value of the circulating current. First, the operation of load current control will be explained. Compare the load current command I _L with the detected value I _L of the load current that actually flows, and control the phase control circuits PH-P and PH-N so that the cycloconverter generates a voltage proportional to the deviation ε ₃ . . The output phase α N of PH-N is α _N with respect to the output phase α _{P of} PH-P
The signal is input from amplifier _K2 to PH-N via inverting amplifier _K3 so as to maintain the relationship: =180° _-αP . In other words, SS-P output voltage V _P =K _V・V _S・cos
α _P and SS-N output voltage V _N =K _V・V _S・cos
Normal operation is performed with α _N =K _V · V _S · cos (180° - α _P ) being balanced at the load terminals. When the current command I _L changes 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 ₀ flows. Next, the operation of circulating current control will be explained. The power supply terminal has a current detector CT _S and a voltage detector.
A PT is installed, and its reactive power Q is calculated by VAR. The reactive power command value Q〓 is normally set to zero, and a deviation ε ₁ is generated by the comparator C ₁ . The control compensation circuit H _(S) normally uses an integral element in order to make the steady-state deviation ε ₁ zero, and its output I ₀ becomes the command value of the circulating current I ₀ . The deviation ε ₂ =I ₀ 〓−I ₀ is taken by the comparator C ₂ and sent to the adder via the amplifier K ₁ .
Fill in A ₄ and A ₅ . Therefore, the inputs to PH-P and PH-N are ε ₄ and ε
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 DC reactors L ₀₁ and L ₀₂ , and the circulating current
I ₀ flows. If I ₀ flows too much than the command value I ₀ 〓, ε
₂ decreases to make the differential voltage smaller. As a result, I ₀ is controlled to become I ₀ 〓. FIG. 2 is a configuration diagram showing a typical embodiment of the reactive power calculation circuit VAR used in the device shown in FIG. R, S, T are the R of the power supply 3-phase electric line BUS
Phase, S phase, and T phase are shown. PT is the voltage of each phase of the power supply υ _S
A transformer that detects _R , υ _SS , and υ _ST , and includes a tertiary winding △ that absorbs the third harmonic. _CTSR ,
CT _SS and CT _ST are current transformers that detect line currents i _SR , i _SS , and i _ST of each phase. The phase shifter PHS has each phase voltage υ
Unit voltage υ′ _S delayed by 90° with respect to _SR , υ _SS , υ _ST
R , υ′ _SS , υ′ _ST are obtained from the following relational expression. The multipliers M _R , M _S , M _T use the above unit voltages υ′ _SR , υ′ _S
S , υ′ _ST is multiplied by the detected currents i _SR , i _SS and i _ST of each phase, respectively, and q _R = υ′ _SR・i _SR
etc. are instantaneous reactive power. The thyristor that makes up the cycloconverter contains many harmonic components because it performs on/off operations. Therefore, the instantaneous reactive powers q _R , q _S , q _T cannot be used as they are. Normally, integration is performed every half cycle of the power supply frequency, and the average value is taken out to obtain the average reactive power Q. The integrators _INTR , _INTS , and _INTT integrate the instantaneous reactive powers _qR , _qS , and _qT, respectively, and are reset every half cycle of the power supply frequency. In addition, the sample and hold circuits S _R , S _S , and S _T are the integrators mentioned above.
The outputs of INT _R , INT _S , and INT _T are sampled and held just before reset, and the following values are obtained as a result. Q _R = 1/T∫ ^T _O q _R dt Q _S = 1/T∫ ^T _O q _S dt Q _T = 1/T∫ ^T _O q _T dt Here, T indicates the half cycle period of the power supply frequency. The sum of these three-phase reactive powers Q _R , Q _S , and Q _T and divided by 3 becomes the average reactive power Q of the power supply. In addition, zero cross detectors ZC _R , ZC _S , ZC _T , pulse generators EX _R , EX _S , EX _T and monomulti circuit
MM _R , MM _S , MM _T are the integrators INT _R , INT _S ,
INT _T reset signal and sample hold circuit
It generates sample timing signals for _SHR , _SHS , and _SHT . FIG. 3 shows the input and output signals of each circuit for the R phase. That is, a is the waveform of the R-phase voltage υ _SR detected by the transformer PT, b is the output signal waveform of the zero cross detector ZC _R , C is the output signal waveform of the pulse generator EX _R , and d is the monomultiple The output signal waveform of _MMR is shown. The signal C becomes the sample timing signal for the sample and hold circuit _SHR , and the signal d is generated after a delay of time t and is passed through the integrator INT _R.
Reset. The same applies to the other S phase and T phase. The reactive power Q detected in this way indicates the difference between the delayed reactive power of the cycloconverter and the leading reactive power of the phase advance capacitor, and as described above, by setting the command value Q=0, Q=0. controlled so that That is, when Q is smaller than zero (advanced), ε ₁ >0, and I ₀ 〓 is increased via the control compensation circuit H _(S) . Therefore, the circulating current I ₀ increases, increasing the delayed reactive power of the cycloconverter. Therefore, Q=0 as a result. Q
When is larger than zero (delay), conversely, ε ₁ <
0, and by decreasing I ₀ 〓, it is controlled so that Q=0 as well. The conventional reactive power compensation type cycloconverter device described above has the following drawbacks. (1) Transformer PT to detect reactive power of power supply
and current transformers CT _R , CT _S , CT _T shall be used. When the capacity of the device increases, these
It requires insulation ability to withstand high voltage and is expensive. (2) To remove the influence of harmonic components of the cycloconverter, it is necessary to perform integration and sample and hold every half cycle of the power supply frequency. Therefore, the circuit configuration becomes complicated. Also, approximately 1/2 of the sample hold time (half cycle period time)
Since the time becomes a dead time for detection, the response of the control system has to be delayed. In particular, as the output frequency of the cycloconverter becomes higher, fluctuations in the reactive power on the power supply side also become faster in synchronization with it. Therefore, in order for the control system to follow the rapid fluctuations and bring the power factor on the power supply side to 1, it is necessary to eliminate the dead time associated with the above detection. The present invention has been _made in view of _{the above} -mentioned points. The present invention aims to provide a method for controlling a compensated cycloconverter. FIG. 4 is a configuration diagram showing an embodiment of the reactive power compensation type cycloconverter device of the present invention. The other circuit configurations are the same as in FIG. 1 except for the reactive power detection means. The means for detecting the reactive power Q _CC will be explained below. In the figure, K〓 and K _Q are operational amplifiers, A ₆ and A ₇ are adders, SQ is a square calculation circuit, and SQR is a square root calculation circuit. Now, assume that the output signal of the amplifier K ₁ of the circulating current control circuit is sufficiently smaller than the output signal of the amplifier K ₂ of the load current control circuit. Therefore, the firing control angle α P of the positive group converter SS- _P and the firing control angle α _{N of the negative group converter SS-N} are α _N ≒180°−α _P
There is a relationship between Therefore, the output voltage of SS- P V _P =K _V・V _S・cos
α _P and SS-N output voltage V _N =K _V・V _S・cos α _N
is operated in a nearly balanced state at the load terminals.
It was previously stated that the magnitudes of V _P and V _N are proportional to the output voltage of amplifier K ₂ . In other words
cosα _P ≒−cosα _N changes in proportion to the output voltage of K ₂ . Therefore, by multiplying the output signal of _K2 by a constant using the amplifier K, the cosine value cos of the ignition control angle α can be obtained.
α is calculated. Here, in order to satisfy the condition -1≦cosα≦1, the amplifier K is also provided with a limiter function. The next square calculation circuit SQ calculates cos ² α, and the adder A ₆ calculates 1−cos ² α. This is further processed through the square root calculation circuit SQR.
sinα= ^√1−2 is obtained. On the other hand, as mentioned in the explanation of Fig. 1 that the output of the adder _A1 is the sum of the output current I _P of the positive group converter and the output current I _N of the negative group converter, this I _P +
The value of I _N and the output sin α of the above SQR are multiplied by the multiplier MLT. Its value I _REACT − _U = (I _P +
I _N )·sin α is the delayed reactive current of the U-phase cycloconverter CC-U shown here. When supplying alternating current to a three-phase load, cycloconverters CC-V and CC-W are similarly connected to the electric line BUS, but the respective delayed reactive currents I _REACT - _V , I _REAC
T - _W is obtained in the same way as the U phase. The adder _A7 sums the delayed reactive currents I _REACT - _U , I _REACT - _V and I _REACT - _W obtained in this way. By multiplying this by a constant using the amplifier K _Q , the delayed reactive power Q _CC of the entire cycloconverter can be obtained. The comparator _C1 compares the reactive power command value _Q〓C with the detected value of the delayed reactive power _QCC , and outputs a deviation _ε1 .
Here, Q〓 _C is set equal to the leading reactive power Q _C supplied to the phase leading capacitor C. The above deviation ε ₁ becomes the command value I ₀ 〓 of the circulating current of the cycloconverter of each phase via the control compensation circuit H _(S) , and as described in the explanation of Fig. 1, it is set so that Q _CC =Q 〓 _C. controlled by. Therefore, if we set Q〓 _C = Q _C , the lagging reactive power Q _CC of the cycloconverter and the leading reactive power of the phase advance capacitor will be equal, and as a result, the reactive power on the power supply side will be zero, and the power factor of the power supply will be 1. Become. FIG. 5 is a block diagram showing another embodiment of the device of the present invention. In the figure, SIN _P and SIN _N are K in Figure 4.
It is a combination of SQ, A ₆ and SQR, and the operation √1−
MLT _P which performs cos ² α, MIT _N is a multiplier, A ₈
is addition. That is, the sine value sinα P of the firing control angle α _P of the positive group converter SS- _P and the sine value sinα N of the firing control angle α _N of the negative group converter SS- _N are obtained separately, and the respective output currents I _P The delayed reactive current I _REACT - _U of the cycloconverter CC-U is obtained by multiplying by I and I _N . The relational expression is as follows. I _REACT - _U = I _P sinα _P + I _N sinα _N When the output voltage of the amplifier K ₁ of the control system for the circulating current I ₀ is sufficiently smaller than the output voltage of the amplifier K ₂ of the control system for the load current I _L , α _N ≒ 180°−α _P , and I _P sinα _P + I _N sin α _N ≒ (I _P + I _N )・sin α holds true. Therefore, since the impedance of the load LOAD is usually larger than the impedance of the DC reactors L ₀₁ and L ₀₂ and satisfies the above conditions, the detection circuit shown in FIG. 4 can also perform sufficiently accurate detection. As described above, in the device of the present invention, when detecting the reactive power Q _CC of the cycloconverter, the output current I _P of the positive group converter, the output current I _N of the negative group converter, and the sine value of the firing control angle α are used. However, since both are unrelated to the power supply frequency and are calculated at the DC level, detection is possible without the influence of harmonics associated with the switching operation of the thyristor. Therefore, there is no need to use a conventional sample and hold circuit, and the dead time can be completely eliminated. Rather, in the device of the present invention, the firing angle for controlling the cycloconverter is detected first, and then the reactive current I _REACT - _U that will flow is determined, so that control with even better followability is possible. Furthermore, it is not necessary to use the transformer PT, current transformers CT _SR , CT _SS , CT _ST, etc. used in conventional devices, and it is possible to provide a device with a simple configuration and low cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional reactive power compensation type cycloconverter device, Fig. 2 is a block diagram showing a typical example of the reactive power calculation circuit used in Fig. 1, and Fig. 3 is a block diagram of a conventional reactive power compensating cycloconverter device. 2 is a waveform diagram for explaining the operation, FIG. 4 is a configuration diagram of a reactive power compensation type cycloconverter device showing an embodiment of the present invention, and FIG. 5 is a diagram of a reactive power compensation type cycloconverter device showing an embodiment of the present invention. FIG. 2 is a configuration diagram of a cycloconverter device. BUS…3-phase power line, C…phase advance capacitor, TR
...power transformer, CC-U...U-phase cycloconverter, SS-P...positive group converter, SS-N...negative group converter, L ₀₁ , L ₀₂ ...DC reactor,
LOAD-U...Load, PH-P, PH-N...Phase control circuit, ABS...Absolute value circuit, K ₀ , K ₁ , K ₂ , K ₃ , K
〓, K _Q ...Operation amplifier, _C1 , _C2 , _C3 ...Comparator, _A1
~ _A8 ...Adder, H _(S) ...Control compensation circuit, CT _P ,
CT _N ...Current transformer, DP, DN...3-phase full-wave rectifier circuit,
SQ...square calculation circuit, SQR...square root calculation circuit,
MLT, MLT _P , MLT _N ...multiplier.

Claims (1)

[Claims] 1. In a circulating current type cycloconverter consisting of a positive group converter and a negative group converter that output variable frequency alternating current, a phase advance capacitor is connected to its power supply terminal, and the delayed reactive power of the cycloconverter and the advance of the phase advance capacitor are In the reactive power compensation type cycloconverter device that controls the circulating current of the cycloconverter so that the reactive power cancels each other, the phase control signal of the cycloconverter is controlled based on the comparative difference between the load current command and the actually flowing load current. The reactive power compensation type cycloconverter is characterized in that the delayed reactive power of the cycloconverter is detected and controlled from the phase control signal of the cycloconverter, the output current of the positive group converter, and the output current of the negative group converter. Control method.