JPH0221218B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power control type cycloconverter device that can be controlled so that the fundamental wave power factor as viewed from the power source side is always 1.

A cycloconverter is a device that directly converts AC power with a constant frequency into AC power with a different frequency, but since the thyristor, which is a component of the cycloconverter, is commutated by the power supply voltage, it requires a lot of energy from the power supply. The drawback is that it consumes a lot of reactive power.

Furthermore, since the reactive power constantly fluctuates in synchronization with the frequency of the load side, it not only increases the capacity of the power supply system equipment, but also has various adverse effects on electrical equipment connected to the same system. Therefore, Japanese Patent Application No. 119122/1983 was filed as a method for compensating for the reactive power of such a cycloconverter.

FIG. 1 is a block diagram of a conventional reactive power control 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 3-phase electric line, and C is a phase advance capacitor connected in △ or Y. 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 amplifiers K ₀ to _{K 3} , phase control circuit PH-P, PH-
N is used. First, the operation of load current control will be explained.

The phase control circuit compares the detected value of the load current command I ^* _L and the actually flowing load current I _L and generates a voltage from the cycloconverter that is proportional to the deviation ε ₃ .
Controls PH-P and PH-N. The output phase α N of PN- _N is α _N = 180°- with respect to the output phase α _P of PH-P.
From amplifier K ₂ to inverting circuit K ₃ to maintain the relationship α _P
The signal is input to the PH-N via the PH-N. i.e. SS-P
Output voltage of V _P = kvV _S・cosα Output voltage of _P and SS-N V _N = kvV _S・cosα _N = kvV _S・cos (180°−α _P ) is normal operation with balance at the load terminal. will be carried out. 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, current flows from negative group converter SS-N to load LOAD.
When I _L is being supplied, the current I _P flowing through the positive group converter 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 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 deviation ε ₁ zero, and its output I ^* _O becomes the command value of the circulating current I _O. Deviation ε ₂ by comparator C ₂
= I ^* _O − I _O taken through amplifier K ₁ to comparators C ₄ and C ₅
Enter.

Therefore, the inputs ε ₄ and ε ₅ to PH-P and PH-N, respectively, 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 is broken by the amount proportional to K ₁・ε ₂ The output voltage V _P of SS-P and the output voltage V _N of SS-N become unbalanced. The differential voltage is applied to 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 and the above-mentioned differential voltage becomes smaller. 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.

I _cap for the phase advancing capacitor C with respect to the power supply voltage V _S
A constant leading current flows. 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 from the power supply.
The current of I _CCP goes from the power supply to SS-P again I _CCN
current flows into it. I _CCP is the load current I _L and the circulating current
The phase angle α _P is proportional to the sum of I _O and I _CCN is proportional to the circulating current I _O , and the phase angle α _N = 180°−
becomes _αP . Strictly speaking, α _N deviates from 180°−α _P by a value proportional to K ₁ ·ε ₂ , but since the deviation is small, it will be explained as α _N =180°−α _P in the vector diagram.
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 is 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.

I _cap = k ₁ (I _L + I _O ) sinα _P + k ₁ I _O sin α _N = K ₁ (I _L + I _O ) sin α _P + k ₁ I _O sin (180° + α
_P )=k ₁ (I _L + _2IO ) 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 _IO . Also, if the reactive power at the receiving end is delayed, Q will be positive and ε ₁ =Q ^* −Q=−
It becomes Q. Therefore, I ^* _O also becomes negative, reducing the circulating current _IO . 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 _L can be controlled in the same way even in the mode where current is supplied from the negative group converter SS-N to the load LOAD.
Even if the magnitude and phase angles α _P and α _N change in synchronization with the output frequency on the load side, the circulating current will change accordingly.
_IO also changes 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, and 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, making it extremely difficult to detect the direction of the load current I _L. Also,
In order to reduce the effect of the ripple, a filter circuit is inserted before the Schmitt circuit SH.
The time delay in the filter circuit increases the shift in the switching point, which again has the disadvantage that accurate reactive power control cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reactive power control type cycloconverter device that eliminates the above-mentioned shift in switching points and enables accurate reactive power control.

In this invention, the circulating current of the cycloconverter
The above objective was achieved by indirectly controlling I _O and load current _IL . Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3 is a configuration diagram of a reactive power control type cycloconverter device showing one embodiment of the present invention.
TR is a three-phase power transformer with two secondary windings, each of which is a positive group converter.
Connected to SS-P and negative group converter SS-N. In addition, L _O1 and L _O2 are DC reactors to suppress the pulsation of the circulating current, and their intermediate terminals are connected to the load.
Connected to LOAD. Further, a Y-connected or Δ-connected phase advancing capacitor C is connected to the receiving end of the three-phase power supply.

A current transformer for current detection is installed at the receiving end of the 3-phase AC power supply.
CT _S , a transformer PT for voltage detection is installed,
The reactive power Q of the power supply is calculated from the outputs of both by a reactive power calculator VAR. Reactive power Q is the value obtained by shifting the phase voltage V _S by 90° to the input current i _S of each of the three phases.
It is obtained by multiplying by V _S ' and adding it for three phases. The set value Q ^* of reactive power and the detected value Q of reactive power are compared, the deviation ε _q (=Q ^* −Q) is generated by the comparator _C1 , and the control compensation circuit H(S)
Outputs the command value I ^* _O of the circulating current _IO via the An integral element is normally used in the control compensation circuit H(S) in order to make the deviation ε _q zero.

On the other hand, the command value I ^* _L of the load current I _L is obtained by multiplying the output signal sinωt of the sine wave pattern generator PTG and the peak value command I _n by a multiplier ML.

I ^* _L = I _n・sinωt ... determined by (1).

_D1 is a half-wave rectifier circuit that outputs the positive half-wave value I ^* _LP of the load current command value I ^* _L . _K1 is an inverting circuit, which, together with the half-wave rectifier circuit _D2 , outputs a value I ^* _LN that is an inversion of the negative half-wave value of the load current command value I ^* _L .

A ₁ and A ₂ are adders, which respectively calculate the command value I ^* _P of the output current I P of the positive group converter _SP and the command value I * N of the output current I _N of the negative group converter SS ^- _N using the following equation. Output as follows.

I ^* _P = I ^* _LP + I ^* _O I ^* _N = I ^* _LN + I ^* _O ......(2) Comparator _C2 compares the command value I ^* _P of the positive group output current and the detected value I _P
The deviation ε _P (=I ^* _P − I _P ) is calculated by comparing _the
Input to PH-P.

In addition, the comparator _C3 compares the command value I ^* _N of the negative group output current with the detected value _IN , calculates the deviation _εN (=I ^* _N − _IN ), and outputs the result via the amplifier _KN. Input to the phase control circuit PH-N of the negative group converter.

CT _P and CT _N are positive group converter output currents, respectively
This is a DC current transformer for detecting I _P and negative group converter output current I _N.

Next, the operation of the reactive power control type cycloconverter device shown in FIG. 3 will be explained.

The following relational expression holds true between the positive group converter output current I _P , the negative group converter output current I _N , the load current _IL , and the circulating current I _O.

I _P −I _N =I _L ...(3) I _P +I _N =2I _O + |I _L | ...(4) Here, the deviations ε _P and ε _N are controlled to be sufficiently small as described above. ^In _{the case of} ^_ _{_ _ _} ), (4), (5), and (6), I _L = I ^* _LP −I ^* _LN ……(7) I _O = 1/2 {2I ^* _O + I ^* _LP + I ^* _LN − | I ^* _LP −I ^* _LN |} ...(8)

Here, as mentioned above, I ^* _LN is the inverted value of the negative half-wave value of the load current command value I ^* _L , so I ^* _LP − ^{I *} _LN = I ^* _L ...(9) holds. do. Also, since I ^* _LP + I ^* _LN = | I ^* _L | ...(10), equations (7) and (8) are respectively I ^* _L = I ^* _L ... (11) I _O = I ^* _O ...(12) becomes. Therefore, control is performed so that the load current I _L and its command value I ^* _L are equal, and the circulating current I _O and its command value I ^* _O are equal.

Figure 4 shows the load current command value I ^* _L , the circulating current command value I ^* _O , and the positive group converter output current command value I ^* _P.
FIG. 3 is a waveform diagram illustrating the relationship between output current command value I*N of the negative group converter and output current command value I ^* _N of the negative group converter.

Here, when the reactive power command value is set to Q ^* =0, the fundamental wave power factor at the receiving end is controlled to be 1. In other words, when the power factor becomes a leading power factor, the reactive power Q becomes a negative value, so the command value I ^* _O of the circulating current increases, and as a result, the cycloconverter
The delayed reactive power consumed by CC increases, and the reactive power Q settles to zero. Conversely, when the power factor is lagging, the reactive power Q becomes a positive value, so the command value I ^* _O of the circulating current decreases, and as a result, the cycloconverter
The delayed reactive power consumed by CC decreases, and the reactive power Q also settles to zero. Note that at this time, the current I _cap flowing through the phase advancing capacitor C is kept at a constant value.

By the way, in the device shown in Figure 3, the half-wave rectifier circuit
The load current command value I ^* _L is divided into the positive group side and the negative group side by D ₁ and D ₂ and processed, and the output current of the positive group converter SS-P and negative group converter SS-N is directly controlled. Since the configuration is controlled, the accuracy is improved.

In other words, the load current command value I ^* _L is processed as it is without being divided, and the signal obtained by adding the signal after the circulating current I _O control and this load current command value I ^* _L is used to control the positive group converter SS-N. If the phase control is performed, the load current control system (SS-P, SS-N and
LOAD) and circulating current control system (loop formed between SS-P and SS-N)
Mutual interference will occur between the two.

On the other hand, in the device shown in Fig. 3, for example, the signal that intervenes from the load current command value I ^* _L to the phase angle α _P (α _N ) is I ^* _LP ′ I ^* _P (I ^* _LN ′ I ^* _N ) are only signals related to control of positive group converter SS-p (negative group converter SS-N). Therefore, problems such as the occurrence of mutual interference as described above do not occur, and highly accurate control can be performed.

In the above-described embodiment, a cycloconverter with a single-phase output was shown, but it goes without saying that the present invention can be similarly applied to a cycloconverter with a multi-phase output. In this case, instead of mutually controlling the reactive power of each phase, if the same circulating current is applied to each phase in order to control the reactive power of the common receiving end to zero, the cycloconverter The capacitance of the capacitor and the capacitance of the phase advance capacitor can be reduced.

In the embodiment shown in FIG. 3, since circulating current detection unlike the conventional device is not performed, a Schmitt circuit associated with circulating current detection is not required. Therefore, it is possible to eliminate the shift in the switching point that occurs due to the insertion of the Schmitt circuit. Furthermore, since the DC current transformer for detecting the load current, which was required in the conventional device, is not required, there is an advantage that the device can be provided at a low cost.

As explained in detail above, according to this invention,
Since reactive power control can be performed without detecting circulating current, there is an excellent effect of eliminating deviations caused by switching of circulating current and enabling accurate reactive power control.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional reactive power control type cycloconverter device, Fig. 2 is a vector diagram for explaining the operation of Fig. 1, and Fig. 3 is a reactive power control type cycloconverter device showing an embodiment of the present invention. FIG. 4 is a waveform diagram showing the relationship among the load current command value, the circulating current command value, the positive group converter output current command value, and the negative group converter output current command value. 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 calculator, C ₁ , C ₂ , C ₃ ... Comparator, A ₁ , A ₂ ... Adder, K _P , K _N ... Amplifier, PH-P...Positive group converter phase control circuit, PH-N...Negative group converter phase control circuit, PTG...Pattern generator,
ML...multiplier, _K1 ...inverting circuit, _D1 , _D2 ...
Half-wave rectifier circuit, H(S)...compensation circuit.

Claims (1)

[Scope of Claims] 1. Leading reactive power of a phase advance capacitor connected to the receiving end of a circulating current type cycloconverter composed of a positive group converter and a negative group converter and a lagging reactive power of the cycloconverter are mutually canceled. In the reactive power control type cycloconverter device that controls the circulating current of the cycloconverter, control compensation is performed to calculate the circulating current command value from the deviation between the reactive power detection value of the electric line and the predetermined reactive power measurement value. A positive group converter current command value is the sum of a positive half-wave value of a load current command value and the circulating current command value, and the positive group converter current command value and a detected value of the output current of the positive group converter are a first comparator that outputs a deviation signal; a negative group converter current command value that is the sum of the inverted value of the negative half-wave value of the load current command value and the circulating current command value; a second comparator that outputs a deviation signal between the detected value of the output current of the negative group converter; and a second comparator that outputs a deviation signal between the detected value of the output current of the negative group converter; The output current of the negative group converter is determined based on a deviation signal from a positive group converter phase control circuit that performs phase control of the positive group converter and the second comparator so that the output current of the negative group converter matches a group converter current command value. A reactive power control type cycloconverter device comprising: a negative group converter phase control circuit that performs phase control of the negative group converter so as to match the negative group converter current command value.