JPH0154952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a reactive power compensation type cycloconverter that controls the fundamental wave power factor seen from the power source side to an arbitrary value.

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 supply because its component thyristor is commutated by current and voltage. be. Moreover, the reactive power constantly fluctuates in synchronization with the frequency on the load side. Therefore, in addition to increasing the capacity of power system equipment,
Reactive power fluctuations have various negative effects on electrical equipment connected to the same system.

Japanese Patent Application No. 119122/1984 describes a method of compensating for the reactive power of such a cycloconverter. This Japanese Patent Application No. 119122/1984 is concerned with the fact that there is dead time and detection delay associated with the detection of reactive power at the power receiving end, and that an integral element is used as a control compensation element in order to stabilize the control system and reduce the steady-state deviation to zero. etc., it is not possible to increase the response speed of the reactive power control system. Therefore, when the frequency on the load side is low, it follows relatively well and the reactive power at the receiving end can be controlled to zero, but as the frequency on the load side increases, the control delay becomes noticeable and the The reactive power remains by the amount of the control delay.

In addition, Japanese Patent Application No. 119122/1987 controls the circulating current of a cycloconverter to compensate for reactive power, but when comparing this with a conventional non-circulating current type cycloconverter, it is found that the circulating current is controlled by the amount of circulating current. The capacity of the converter will increase.

Therefore, the present invention has been made in view of the above, and an object of the present invention is to provide a control method for a reactive power compensation type cycloconverter which has a reactive power control system with good followability and which requires less increase in converter capacity. purpose.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a reactive power compensation type cycloconverter device for explaining the method of the present invention. In the diagram, BUS is the electric line of the 3-phase AC power supply,
C is or △ connected phase advance capacitor, TrU,
TrV, TrW are power transformers, CC-U, CC-V,
CC-W is a circulating current type cycloconverter,
V, W are loads, CNT-U, CNT-V, C
ONT-W is a load control circuit, and RI is a circulating current command circuit. The cycloconverter CC-U is composed of a positive group converter SS-P, a negative group converter SS-N, and DC reactors Lo ₁ and Lo ₂ .
CC-V and CC-W are similarly configured. The load current control operation and circulating current control operation will be explained below using a U-phase cycloconverter as an example.

First, the load current is controlled as follows.

The load current _ILU is detected by the load current detector _CTLU and compared with the command value _ILU . The phase control circuits PH-P and PH-N are controlled so that the cycloconverter generates a voltage proportional to the deviation ε ₂ =I _LU −I _LU . The output phase α NU of PH-N is input to the PH- _N via the inverting amplifier K ₃ from amplifier K ₂ so as to maintain the relationship α _NU = 180° − α pu with respect to the output phase α pu of PH-P. . That is, the output voltage of the positive group converter SS-P is Vp = kv・Vs・cosαpu, and the output voltage of the negative group converter SS-N is V _N =kv・Vs・cosα _Nu =
Normal operation is performed with kv×Vscos (180°−αpu) balanced at the load terminals. However, Vs is the power supply voltage and kv is the conversion constant. When the current command I _LU is changed sinusoidally, the deviation ε ₂ also changes accordingly, and the αpu and α _Nu are controlled so that a sinusoidal current flows through the load. In this normal operation, the output voltage of the positive group converter SS-P and the negative group converter SS
Since the -N output voltages are equally balanced, almost no circulating current Iou flows.

Next, the operation of circulating current control will be explained. circulating current
I _pU is detected by performing the following operation.
However, Ipu is the output current of the positive group converter SS-P, _INU is the output current of the negative group converter SS-N, |
I _LU | is the absolute value of the load current I _LU .

Iou=(Ipu+I _NU − | I _LU |)/2 Current detector CTpu, CT _NU , CT _LU absolute value circuit
The above calculation is performed using ABS, adders A ₁ and A ₂ , and amplifier Ko (=1/2 times).

The circulating current Iou detected in this way is compared with the command value Iou by the comparator _C1 , and the deviation ε ₁ =
Iou*−Iou is output. The deviation ε ₁ is input to adders A ₃ and A ₄ via an amplifier K ₁ . Therefore,
The inputs ε ₃ and ε ₄ to PH-P and PH-N are as follows, respectively. However, K ₃ =-1.

ε ₃ = K ₂・ε ₂ +K ₁・ε ₁ ε ₄ = −K ₂・ε ₂ +K ₁・ε ₁ Therefore, the relationship α _NU = 180° − αpu collapses, and K ₁・
The output voltage Vp of the positive group converter SS-P and the output voltage V _N of the negative group converter SS-N are proportional to ε ₁ .
becomes unbalanced. The difference voltage is the DC reactor
Applied to Lo ₁ and Lo ₂ , a circulating current I _pL flows.
If Iou flows too much than the command value Iou*, ε ₁ decreases, reducing the voltage difference. As a result, Iou is controlled to be equal to Iou*. The V and W phases are similarly controlled.

The circulating current command value Iou* is the circulating current command circuit.
Generated from RI. FIG. 2 shows a specific example of the circulating current command circuit, and the part surrounded by the broken line is RI.

In the figure, Kα _U , Kα _v , Kα _w , K _MU , K _Mv , K _Mw and
Ka is an operational amplifier, LMu, LMv, LMw are limiter circuits SQu, SQv, SQw are square calculation circuits,
SQRu, SQRv, SQRw are square root calculation circuits, Mu ₁ ,
Mv ₁ , Mw ₁ , Mu ₂ , Mv ₂ , Mw ₂ , Mu ₃ , Mv ₃ ,
Aw ₃ is a multiplier, DIV is a divider, AD ₁ to _{AD 9} are adders, and VR is a reactive power setter.

First, the phase control input voltages Vαu, Vαv, and Vαw of each phase cycloconverter are taken out and input to the circulating current command circuit RI. Vαu is the amplifier K ₂ in Fig. 1
This is the output signal of cosαpu and −
cosα Takes a value proportional to the average value of _NU . Therefore, by multiplying Vαu by a constant by the amplifier Kαu, the cosine value cosαu of the ignition control angle αu can be obtained. Next, the limiter circuit LMu determines the upper and lower limit values of the output signal of the amplifier Kαu in order to satisfy the condition -1≦cosαu≦1. This signal is squared by the square calculation circuit SQu and inputted to the adder _AD1 . In AD ₁ , the output signal of the SQu is subtracted from the unit DC voltage 1, and as a result, 1-cos ² αu is obtained. This is passed through the next square root calculation circuit SQRu to sinαu=
Find ^√1−2 . Similarly, sinαv from Vαv
Sinαw can be found from Vαw.

Next, the absolute value of the load current of each phase cycloconverter |I _LU |, |I _LV |, |I _LW | is detected, and the absolute value of the load current |I _LU |, |I _LV |, |I _LW | Input Mu ₂ , Mv ₂ , Mw ₂ . Adder AD ₅
is the absolute value of the U-phase load current | I _LU from the constant value I _M
Subtract | to find I _M − | I _LU |. The next operational amplifier K _MU multiplies the output signal of AD ₅ by (1/I _M ). As a result, k _U =( _IM − |I _LU |)/I _M is obtained. Similarly, kv=(I _M − | I _LV |)/I _M , k _W =
(I _M − | I _LW |)/I _M is found.

The multiplier _Mu1 multiplies the output signal sinαu of the square root calculation circuit _SQRU by the output signal ku of the operational amplifier _KMU , and ku・sinαu=( _IM− | _ILU |)/
I _M・sinαu is output. Similarly, by multiplier Mv ₁ , kv×sinαv=(I _M − |ILv|)/I _M・sinαv,
Also, by the multiplier Mw ₁ , kw・sinαw=(I _M − |
I _LW |)/ _IM・sinαw is output. Then, the above three values are added by the next adder AD ₄ .
A signal of ku・sinαu+kv・sinαv+kw・sinαw is obtained.

Moreover, the multiplier Mu ₂ is connected to the square root calculation circuit SQRu.
output signal sinαu and the absolute value of the U-phase load current |
It is multiplied by I _LU |, and |I _LU |・sinαu is output. Similarly, by the multiplier Mv ₂ , |I _Lv |・sinαv
Also, the multiplier Mw ₂ outputs |I _LW |·sinαw. Adder AD ₈ is multiplier Mu ₂ , Mv ₂ ,
It adds the output signals of Mw ₂ , |I _LU |・
Find sinαu＋｜I _Lv ｜・sinαv＋｜I _LW ｜・sinαw. The next adder AD ₉ subtracts the output signal of the adder AD ₈ from the output signal Icap* of the reactive power setting device VR, and inputs the output signal to the next divider DIV. The divider DIV is the signal a of the adder AD ₉ above.
is divided by the output signal b of the adder AD ₄ , and by multiplying by (1/2) by the next operational amplifier Ka,
The following value is obtained as Io*.

Io=1/2×Icap/*−(|
I _LU ｜・sinαu＋｜I _Lv ｜・sinαv＋｜I _LW ｜・sinαw）
/ku・sinαu+kv・sinαv+kw・sinαw This value Io* is a pre-stage signal of the command values Iou*, Iov*, Iow* of the circulating current of each phase cycloconverter, and will be temporarily called a pre-stage command signal.

The multiplier _Mu3 multiplies the preceding stage command signal Io* by the output signal ku of the operational amplifier _KMU , and the output signal Iou*=ku·Io* becomes the circulating current command value of the U-phase cycloconverter. Similarly multiplier
The output signal Iov*=kv・Io* of Mv ₃ becomes the circulating current command value of the V-phase cycloconverter, and the multiplier
The output signal Iow*=kw·Io* of Mw ₃ becomes the circulating current command value of the W-phase cycloconverter.

Here, the above-mentioned pre-stage command signal Io* is used in common for the U, V, and W phases, and the distribution coefficient ku,
KV and KW are involved. In case of U phase, ku=(I _M − |
For example, if I _M is set equal to the maximum value Im of the load current in I _LU |)/I _M , when |I _LU |=0, the coefficient ku=1
When Io _U *=Io* and |I _LU |=Im,
When the coefficient ku=0, Iou*=0. In other words, when the absolute value of the load current |I _LU | is large, the circulating current Iou
｜I _LU ｜ becomes small, then Iou
I try to make it flow as much as possible. Circulating current command values Iov* and Iow* are similarly given to the V-phase and W-phase.

Figure 3 shows the voltage and current vector diagram for one phase on the input side of the cycloconverter, where Vs is the current voltage, Is is the power supply current, and Icap is the phase advance capacitor C.
, Iccu, Iccv, and Iccw are the input currents of each phase cycloconverter, Issp is the input current of the positive group converter SS-P of the U-phase cycloconverter, I _SSN is the input current of the negative group converter SS-N, and I _REACT respectively represent the delayed reactive current of the entire cycloconverter.

In the case of a U-phase cycloconverter, at a certain instant, the positive group converter SS-P has a circulating current at the firing control angle αpu.
Iou and load current _ILU flow. Therefore, if the conversion constant of the converter is _k1 , the magnitude of the input current of SS-P is _k1 ·(Iou+| _ILU |). Further, a circulating current Iou flows through the negative group converter at an ignition control angle α _NU ≒180°−αpu. Therefore, the size of I _SSN is k ₁ · Iou. Therefore, the input current Iccu of the U-phase cycloconverter is as shown in the figure, and its circulating current component is
I _REACT-U is, I _REACT-U = I _SSp・sinαpu＋I _SSN・sinα _NU ≒k ₁
(2Io _U + | I _LU |)・sinαpu.

Similarly, the reactive current components I _REACT-v and I _REACT-w of the V-phase and W-phase cycloconverters are given as follows.

I _REACT-v ≒k ₁ (2Iov＋｜I _LV ｜
) sinαpv I _REACT-w ≒k ₁ (2Iow＋｜I _LW ｜
)・sinαpw Delayed reactive current of the entire cycloconverter I _REACT
is a combination of these, and is as shown in the following equation.

I _REACT = I _REACT-U + I _REACT-v + I _REACT-w ≒k ₁・(2Iou+｜I _LU |)・sinαpu+k ₁・(2Iov+
|I _Lv |)・sinαpu +k ₁・(2Iow+|I _LW |)・sinαpw Here, as mentioned above, the circulating currents Iou, Iov, Iow
are the outputs Iou*, Iov*, of the circulating current command circuit RI,
When controlled to be equal to Iow*, the above I _REACT becomes as follows.

I _REACT =k ₁・(2・Iou*+｜I _LU ｜)・sinαpu+k ₁
・(2・Iov*+｜I _Lv |)・sinαpv +k ₁・(2・Iow*+｜I _LW |)・sinαpw=2・k ₁
Io*(ku・sinαpu+kv・sinαpv +kw・sinαpw)+k ₁ (｜I _LU ｜・sinαpu+｜I _Lv ｜
sinαpv＋｜I _LW ｜・sinαpw) sinαpu≒sinαu, sinαpv≒sinαv, sinαpw≒
Considering that sinαw, I _REACT =k ₁ ·Icap*.

If Icap*=Icap/k is set to ₁ , I _REACT =
Icap, the lagging reactive current I _REACT of the entire cycloconverter and the leading reactive current of the phase advancing capacitor C cancel each other out, and the current I _S has only the in-phase component with the power supply voltage V _S . That is, the fundamental wave power factor at the receiving end is controlled to be 1.

If Icap*>Icap/k is selected as ₁ , I _REACT >Icap, and it can be explained that the delayed power is taken, and Icap
If you select <Icap/k ₁ , I _REACT <Icap, and you can set it to take progressive power. When other electrical equipment is connected to the same electrical line and the electrical equipment is drawing power either ahead or behind, it is useful to select Icap* accordingly.

The coefficients ku, kv, and kw for distributing the circulating currents Iou*, Iov*, and Iow* of each phase differ depending on how the normalization constant I _M is selected. In other words, if I _M ≫ Im is selected for the maximum value Im of the load current, then, for example, the coefficient ku becomes ku = I _M - |I _LU |/I _M ≒1, and the magnitude of |I _LU | Regardless, it becomes a constant value. Conversely, if you choose I _M < Im, |I _LU |=
When Im, ku becomes a negative value, and Iou*=ku・
Io* is also given a negative command value. Circulating current Iou*
Since it only flows in a certain direction, as a result Iou*
This is the same as giving a command of =0. load current
If I _LU , I _Lv , and I _LW are three-phase balanced sinusoidal currents, when the U-phase circulating current Iou is small, the V-phase circulating current Iov or the W-phase circulating current Iow becomes large, and as a whole, The reactive power of the cycloconverter is controlled to be constant. However, if the circulating current command value of any phase becomes negative, the above-mentioned relationship I _REACT =k·Icap* no longer holds true, and it becomes necessary to shift Icap*.

Therefore, the normalization constant I _M is the maximum value Im of the load current
It is most effective to choose a value equal to or slightly larger than . In particular, when I _M = Im, the load current I _U
When reaches the maximum value Im, the circulating current Iou = 0
For example, the output current of the positive group converter SS-P is
Ipu = I _LU + Iou = Im, and the current capacity is the same as that of a conventional non-circulating current type cycloconverter that does not flow circulating current.

As described above, according to the present invention, the value of the circulating current to be passed through the cycloconverter is calculated and given from the phase control signal and the detected value of the load current, which eliminates the detection delay associated with conventional reactive power detection. Therefore, time becomes less of an issue, and a control system with good followability can be constructed. Therefore, even if the frequency on the load side increases, as long as the response of circulating current control is within the allowable range, the reactive power at the receiving end can be controlled to zero, and the fundamental wave power factor on the power source side can also be reduced to 1. It is. In addition, elements required for reactive power control in the past, such as transformers and current transformers for power supply voltage or current detection, reactive power calculation circuits, control compensation circuits, etc., can be omitted, resulting in a simple configuration. It can be an economical device. Furthermore, since the circulating current of each phase is controlled in inverse proportion to the magnitude of the absolute value of the cycloconverter, the increase in converter capacity caused by the flow of circulating current is only a small amount, making the device more economical. be able to.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the reactive power compensation type cycloconverter device of the present invention, FIG. 2 is a block diagram showing a specific example of the circulating current type command circuit RI of FIG. 1, and FIG. It is a voltage current vector diagram for explaining the effect of the present invention. CC-U, CC-V, CC-W...Circulating current cycloconverter, U, V, W...Load, C...
Phase advance capacitor, CNT-U, CNT-V,
CNT-W...Control circuit, RI...Circulating current command circuit, SS-P...Positive group converter, SS-N...
... Negative group converter, Lo ₁ , Lo ₂ ... DC reactor, K ₀ , K ₂ , K ₁ , K ₃ ... Operational amplifier, A ₁ , A ₂ ,
A ₃ , A ₄ ... Adder, C ₁ , C ₂ ... Comparator, ABS...
... Absolute value circuit, VR ... Reactive power setting device, Kαu,
Kαv, Kαw, K _MU , K _Mv , K _MW , Ka ... operational amplifier, AD ₁ to AD ₉ ... adder, LMu, LMv, LMw
... Limiter circuit, SQ _U , SQ _v , SQ _W ... Square calculation circuit, SQRu, SQRv, SQRw ... Square root calculation circuit, M _U1 , Mv ₁ , Mw ₁ , Mu ₂ , Mv ₂ , Mw ₂ ,
Mu ₃ , Mv ₃ , Mw ₃ ... multiplier, DIV ... divider.

Claims (1)

[Claims] 1. In a three-phase output circulating current type cycloconverter in which a phase advance capacitor is connected to a power supply terminal, the sine value sinαu of the firing control angle of each phase converter is calculated from the phase control input signal of the cycloconverter.
Calculate sinαv and sinαw, and also calculate the absolute value of the three-phase load current |I _LU |, |I _LV |, |I _LW | and its normalization constant
From I _M , circulating current distribution coefficient ku = (I _M − | I _LU |) /
I _M , kv = (I _M − | I _LV |) / I _M , kw = (I _M − | I _LW
|)/I _M is calculated, and when the reactive current setting value at the receiving end is Icap*, the command values Iou*, Iov*, Iow* of the circulating current of each phase of the cycloconverter are
Iou*=kuIcap/*−｜ _ILU
｜sinαu−｜I _LV ｜sinαv−｜I _LW ｜sinαw/2(kusin
αu＋kvsinαv＋kwsinαw) Iov＊＝kvIcap／＊−｜I _LU
｜sinαu−｜I _LV ｜sinαv−｜I _LW ｜sinαw/2(kusin
αu＋kvsinαv＋kwsinαw) Iou＊＝kwIcap／＊−｜ _ILU
｜sinαu−｜I _LV ｜sinαv−｜I _LW ｜sinαw/2(kusin
A method for controlling a reactive power compensation type cycloconverter, characterized in that αu + kvsinαv + kwsinαw).