JPS6155346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power control type cycloconverter device that freely controls the fundamental wave power factor as seen from the power source side.

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

As a method of compensating for the reactive power of such a cycloconverter, Japanese Patent Application No. 119122/1983 has been filed.

FIG. 1 shows a block diagram of the reactive power control type cycloconverter device. Connect a phase advance capacitor C to the common power receiving terminal of the cycloconverters CC-U, CC-V, and CC-W so that the leading reactive current Icap of the phase advance capacitor C and the lagging reactive current I _REACT of the entire cycloconverter are equal. This is to control the circulating current of the cycloconverter of each phase.

In this reactive power control type cycloconverter device, between the power supply line BUS and each converter,
Power transformers TrU, TrV,
A TrW was installed, but the power transformer required a capacity that could also supply the delayed reactive power of each converter. That is, in addition to the power that can be supplied to the load, lagging reactive power opposite to the leading reactive power of the phase advancing capacitor C must be supplied to each cycloconverter via the power transformer. Therefore, the power transformer becomes large, heavy, and expensive.

The present invention has been made in view of the above, and an object of the present invention is to reduce the capacity of the power transformer and provide a more economical reactive power control type cycloconverter device.

FIG. 2 is a configuration diagram showing an embodiment of the reactive power control type cycloconverter device of the present invention.

In the figure, BUS is a three-phase power line, TrU, TrV, TrW
is the power transformer, CC-U, CC-V, CC-W are the circulating current type cycloconverter body, U, V, W
is a load, and C _pU , C _NU , C _pV , C _NV , C _pW , and C _NW are phase advance capacitors. The U-phase cycloconverter CC-U consists of a positive group converter SS-P, a negative group converter SS-N, and DC reactors L ₀₁ and L ₀₂ . The V phase and W phase are similarly configured.
CONT-U, CONT-V, CONT-W are control circuits for each phase cycloconverter, and control circuit CONT-U for the U-phase cycloconverter is an operational amplifier K ₀ ,
K ₁ , K ₂ , K ₃ , adder A ₁ , A ₂ , A ₃ , A ₄ , comparator
C ₂ , C ₃ , absolute value circuit ABS and phase control circuit PH−
It consists of P, PH-N. V-phase, W-phase cycloconverter control circuit CONT-V, CONT-
W is similarly configured.

Furthermore, at the receiving end there is a transformer that detects the power supply voltage.
PT, a current transformer CTs that detects the power supply current, a reactive power calculation circuit VAR, a reactive power setting device VR, a comparator _C1 , and a control compensation circuit H(S).

Conventionally, the phase advancing capacitor is connected all at once to the power receiving end, but the device of the present invention is different in that it is connected separately to the secondary sides of the power transformers TrU, TrV, and TrW.

Hereinafter, the operations of load current control and circulating current control will be explained using a U-phase cycloconverter as an example.

First, the operation of load current control will be explained. The U-phase load current _ILU is detected by the current detector _CTLU and compared with the command value I ^* _LU . The deviation ε ₃ =I ^* _LU −I
_L.U.
Phase control circuits PH-P and PH-N are used to generate a voltage proportional to the voltage from the cycloconverter CC-U.
control. PH for the output phase α _pu of PH−P
The output signal from amplifier K ₂ is input to PH-N via inverting amplifier K ₃ so that the output phase α _NU of −N maintains the relationship α _NU =180°−α _PU . In other words, the output voltage Vp of positive group converter SS-P = k
_V・Vs・COSα _pu and negative group converter output voltage V
Normal operation is performed with _N =k _V・V _S・Cosα _NU =k _V・Vs・Cos (180°−α _pu ) being balanced at the load terminals. When the current command I ^* _LU is changed in a sinusoidal manner, the deviation ε ₃ also changes accordingly, and the α _pu and α _NU are adjusted so that the sinusoidal current I _LU flows through the load.
is controlled. In this normal operation, the output voltage of the positive group converter SS-P and the output voltage of the negative group converter SS-N are equally balanced, so the circulating current I
_OU hardly flows.

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

The circulating current I _OU is detected by performing the following calculation. However, I _pu is the positive group converter SS
-P output current, I _NU is negative group converter SS-N
The output current, |I _LU |, is the absolute value of the load current I _LU .

I _OU = (I _pU + I _NU − | I _LU |)/2 That is, current detectors CT _pU , CT _NU , CT _LU ,
The above calculation is performed by adders A ₁ and A ₂ , amplifier K ₀ (=1/2 times), and absolute value circuit ABS.
The circulating current command value I ^* _OU is the output of the control compensation circuit H(S), which will be explained later. comparator
Compare the command value I ^* _OU with the circulating current I _OU obtained by the above calculation using C ₂ , and calculate the deviation ε ₂ = I ^* _OU - I _OU
seek. The deviation ε ₂ is input to adders A ₃ and A ₄ via amplifier K ₁ . Therefore PH-P and PH
The inputs ε ₄ and ε ₅ to -N are respectively 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 _NU = 180° − α _pu breaks down,
Positive group converter SS− is proportional to K ₁・ε ₂
The output voltage VP of P and the output voltage VN of the negative group converter SS-N become unbalanced. The differential voltage is applied to DC reactors L ₀₁ and L ₀₂ and a circulating current I _OU flows. If I _OU flows too much than the command value I ^* _OU , ε ₂ decreases and the differential voltage is reduced. As a result, I
_OU is controlled to be equal to I ^* _OU .

The load current control and circulating current control operations of the V-phase and W-phase cycloconverters are performed in the same manner.

Figure 3 shows a voltage and current vector diagram for one phase on the input side of the cycloconverter, where a is a voltage and current vector diagram on the input side of the U-phase cycloconverter;
b represents the input side voltage and current vector diagram of the V-phase cycloconverter, c represents the input side voltage and current vector diagram of the W-phase cycloconverter, and d represents the input side voltage and current vector diagram of the entire cycloconverter. This vector diagram was drawn at a certain moment when the load current was being controlled in a sinusoidal manner, and the magnitude and phase angle of the vector were constantly changing.

First, the vector diagram in FIG. 3a will be explained. I _SS
P is the input current of positive group converter SS-P and its magnitude is
K ₁ (I _OU + | I _LU |), and the phase angle is α _pU . However, k ₁ is the conversion constant of the converter.
Moreover, I _SSN is the input current of the negative group converter SS-N, the magnitude is k ₁ , I _OU , and the phase angle is α _NU ≒180°−
α _pU . I _CCU is the input current of the cycloconverter CC-U and is the vector sum of I _SSP and I _SSN . I _capU is the sum of the leading currents flowing through the phase advance capacitors C _pU and C _NU , and is a constant current that leads by 90 degrees with respect to the power supply voltage. Therefore, the power transformer
The current I _TRU flowing in the primary side of Tru is I _CCU and I _ca
The vector sum of _pU is as shown in the figure. I _TRU
When is separated into effective component I _SU and reactive component I _QU , it can be expressed as follows using load current I _LU , circulating current I _OU and phase angles α _PU and α _NU . However, it is treated as α _NU ≒180°−α _pU .

I _SU =I _SSP・cosαpu+I _SSN・cosα _NU ≒(I _SSP −I _SSN )・cosα _pU =k ₁ (I _OU + |I _LU |−I _OU )・cosα _pU =k ₁ |I _LU |・cosα _pU I _QU = I _SSP・sinα _pU +I _SSN・sinα _NU −Icapu ≒ (I _SSP + I _SSN )・sinα _pU −Icapu=k ₁ (I _OU + | I _LU | + I _OU ) sinαpu−Icapu=k ₁ (2I _OU +|I _LU |)・sinα _pU −Icapu The above equation holds even if the load current I _LU , circulating current Iou, and phase angle αpu change. In addition,
It goes without saying that the size of I _TRU is √ ² _SU + ² _QU .

FIG. 3b is a voltage-current vector diagram on the input side of the V-phase cycloconverter, and similarly, the effective component Isv and reactive component _IQV of the current I _TRV flowing to the primary side of the power transformer TrV can be expressed as follows. However, α _NV ≒
Let it be 180°−α _Pv .

Isv≒k ₁ |I _LV |・cosαpv I _QV ≒k ₁ (2Iov + |I _LV |)・sinαpv−Icapv Icapv is the lead that flows to the phase advance capacitors Cpv and _CNV connected to the secondary side of the power transformer Trv. The sum of currents, usually chosen equal to Icapu.

Furthermore, regarding the input side voltage and current vector diagram of the W-phase cycloconverter shown in Figure 3c, the effective component Isw and reactive component _IQW of the current I _TRW flowing to the primary side of the power transformer Trw are expressed as follows. Become. However, α _NW ≒180°−αpw.

Isw≒k ₁・|I _LW |・cosαpw I _QW ≒k ₁ (2Iow | I _LW |)・sinαpw−Icapw Icapw is the sum of the leading currents flowing through the phase advance capacitors Cpw and C _NW , and is usually selected to be equal to Icapu. Ru.

FIG. 3d shows a voltage-current vector diagram at the receiving end, where the power supply current Is is the vector sum of _ITRU , _ITRV , and _ITRW . In order for Is to be in phase with the power supply voltage Vs, the reactive components of the power transformer current I _QU , I
It is sufficient if the sum of _QV and I _QW becomes zero. That is, the circulating currents Iou, Iov, and Iow of each phase cycloconverter may be controlled so as to satisfy the following equation.

I _QU + I _QV + I _QW = 0 ∴Icapu + Icapv + Icapw = k ₁ (2Iou + | I _LU |)・sinαpu +k ₁ (2Iov + | I _LV |) sinαpvk ₁ (2Iow + | I _LW ) sinαpw In the example of Fig. 2, reactive power control is carried out as follows. That is, the voltage and current at the receiving end are detected by the transformer PT and the current transformer CTS, respectively, and the reactive power Q is calculated by the reactive power calculation circuit VAR. The comparator _C1 compares the output of the reactive power setting device VR, that is, the reactive power command value Q ^* , with the above-mentioned reactive power Q, and generates a deviation _ε1 =Q ^* −Q. Q ^*
is normally set to zero to control the fundamental wave power factor on the power supply side to unity. The deviation ε ₁ becomes the command value Io ^* of the circulating current via the control compensation circuit H(s). H(s) is ε
Integral elements are often used to reduce the steady-state error of ₁ to zero.

Circulating current Iou, Iov, of each cycloconverter
As mentioned earlier, Iow is the command value Iou ^* , Iow ^* ,
Controlled to be equal to Iow ^* . here
It is given as Iou ^* = Iov ^* = Iow ^* = Io ^* .

When Q ^* = 0 and the fundamental wave power factor at the power receiving end is leading, Q takes a negative value, and ε ₁ =Q ^* -Q=-Q takes a positive value. Therefore ε ₁ >0 is integrated by H(s) and Io ^* increases. Therefore, Iou=Iov=Iow
increases, increasing the delayed invalid component on the right-hand side of the previous equation.
Conversely, if the fundamental wave power factor at the receiving end lags, Q
has a positive value, and ε ₁ has a negative value. Therefore Io ^*
decreases, reducing the delayed invalid component on the right-hand side of the previous equation. In this way, it is controlled so that Q=Q ^* =0. Size of load current | I _LU |, | I _LV |, |
Even when I _LW | and the phase angles αpu, αpv, αpw change, _ε1 changes accordingly, and Io ^* is controlled so that Q=0. At this time
Io ^* satisfies the following formula.

Io ^* =Iou ^* =I ₀ v ^* =Iow ^* ≒Icapu+Icapv+Icapw−k ₁ (|I _LU | sinαpu+ | I _LV | sin αpv+ | I _LW |
sinαpw)/2k ₁ (sinαpu+sinαpv+sinαpw) Figure 4 shows the magnitude of the input side current (peak value of the sine wave input current) when performing reactive power control as described above, and Iccu is the U-phase cyclotron. Input current of converter CC-U, I _TRU is power transformer
This shows the primary current of Tru. The broken line k ₁ |I _LU | indicates the magnitude of the input current of CC-U when the circulating current Iou does not flow, and when the above-mentioned circulating current Iou flows, Iccu shown by the two-dot chain line Become.
The effective portion of Iccu is Iccu− _S , which is the effective portion of I _TRU mentioned above.
, Iccu− _S =k ₁ ·|I _LU |·cosαpu. Further, the invalid portion Iccu- _Q of Iccu is the invalid portion IQU of _the above-mentioned I _TRU with Iccpu=0, and becomes Iccu- _Q = k ₁ (2Iou+|I _LU |)·sinαpu. Therefore, the size of Iccu is √ ² − _S + ²

- _Q becomes the absolute value of the load current | I _LU |, circulating current
It changes as shown in the figure depending on Iou and phase angle.
If Iou=0, √ ² − _S ++ ² − _Q =
k ₁・|I _LU |, resulting in a broken curve. That is, it is shown that the input current Iccu of the U-phase cycloconverter increases as the circulating current Iou flows.

Therefore, in the conventional reactive power control type cycloconverter shown in FIG. 1, the capacity of the power transformer Tru is ks·Iccu·Vs [VA]. however
Vs is the power supply voltage and ks is the proportionality constant.

On the other hand, as I _TRU , only the current of the magnitude shown by the solid line in FIG. 4 flows through the power transformer Tru of the device of the present invention. The reason for this is that the phase advance capacitors Cpu and _CNU are installed on the secondary side of the power transformer Tru, so the reactive component of Iccu (Iccu- _Q (delay)) and Icapu
This is because the (advances) cancel each other out and the magnitude of the reactive component I _QU of the current I _TRU of the power transformer becomes smaller.

I mentioned earlier that I _QU = Iccu - _Q - Icapu.

Therefore, the capacity of the power transformer Tru is ks・
All you need to prepare is I _TRU・Vs [VA]. Since I _TRU changes from moment to moment, it is unclear at which point the value should be taken, but as a power transformer, it depends on the size of the heat capacity, so the average value or effective value of the waveform in Figure 4 can be used. You can decide from

The capacities of the V-phase and W-phase power transformers Trv and Trw are similarly improved.

Phase advance capacitor Cpu, C _NU , Cpv, C _NV ,
The capacitance of Cpw and C _NW should be 1/6 of the capacitance of the phase advance capacitor C, which is conventionally installed all at once.

As described above, according to the reactive power compensation type cycloconverter device of the present invention, it is possible to always control the fundamental wave power factor at the receiving end to 1, and moreover, the capacitance of the power transformer can be controlled without increasing the capacitance of the phase advance capacitor. can be significantly reduced.

Here, a three-phase output cycloconverter has been described as an example, but it goes without saying that the present invention can be similarly applied not only to a single-phase output cycloconverter but also to a two-phase or more polyphase output cycloconverter.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional reactive power control type cycloconverter device, Fig. 2 is a block diagram showing an embodiment of the reactive power control type cycloconverter device of the present invention, and Fig. 3 is an operation of the device of Fig. 2. Similarly, FIG. 4 is a waveform diagram showing the magnitude of input current to explain the operation of the device shown in FIG. 2. CC-U, CC-V, CC-W... Circulating current type cycloconverter body, Tru, Trv, Trw... Power transformer, U, V, W... Load, Cpu, C _NU ,
Cpv, C _NV , Cpw, C _NW ... Phase advance capacitor,
SS-P...Positive group converter, SS-N...Negative group converter, _L01 , _L02 ...DC reactor, CONT
-U, CONT-V, CONT-W...Current control circuit, VAR...Reactive power calculation circuit, VR...Reactive power setter, H(S)...Control compensation circuit, ABS...
… Absolute value circuit, K ₀ , K ₁ , K ₂ , K ₃ … Operational amplifier, A ₁ , A ₂ , A ₃ , A ₄ … Adder, C ₁ , C ₂ , C ₃ …
...Comparator, PH-P, PH-N...Phase control circuit,
CTs, CT _LU , CT _LV , CT _LW , CTpu, CTpv...
Current detector.

Claims (1)

[Claims] 1. In a circulating current type cycloconverter equipped with a positive group converter and a negative group converter to which power is supplied from a power line via a power transformer, a phase advancing capacitor is installed on the secondary side of the power transformer to connect the positive group converter and the negative group. What is claimed is: 1. A reactive power control type cycloconverter device, characterized in that the cycloconverter is connected separately to a converter, and the circulating current of the cycloconverter is controlled so that the reactive power at the receiving end matches a set value.