JPH0470870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a circulating current type cycloconverter device that supplies variable frequency alternating current to a single-phase or multi-phase load.

[Technical background of the invention and its problems] A cycloconverter is a device that directly converts alternating current power of a constant frequency into alternating current power of a different frequency, but the thyristor, which is a component of the converter, is commutated by the power supply voltage. Therefore, it has the disadvantage of taking a lot of reactive power from the power supply. In addition, the reactive power constantly fluctuates in synchronization with the frequency of the load side, which not only increases the capacity of the power system equipment, but also has various negative effects on electrical equipment connected to the same system. .

Countermeasures such as installing a reactive power compensator at the receiving end of the cycloconverter have been taken to address this problem, but the equipment becomes large-scale, increases the installation area, and also becomes expensive. .

In view of this, Japanese Patent Laid-Open No. 56-44382 (Reactive Power Compensation Type Cycloconverter Device) and the like were proposed to solve the above problems. That is, a circulating current type cycloconverter is used, and a phase advance capacitor is connected to the power receiving end of the cycloconverter, so that the leading reactive power taken by the phase advance capacitor and the lag reactive power taken by the cycloconverter cancel each other out. This system controls the circulating current of the cycloconverter, allowing the cycloconverter itself to function as a reactive power compensator, which was required in the past. Therefore, the conventional reactive power compensator is no longer necessary, and the device can be made smaller and lighter, and the cost can be reduced accordingly.

In the above-mentioned conventional reactive power compensation type cycloconverter device, the capacity of the phase advance capacitor at the power receiving end is determined based on when the cycloconverter is performing rated operation, and when overload operation is expected, , a phase advance capacitor with an appropriate capacity must be prepared in advance.

In other words, if you try to always control the input power factor at the receiving end to 1, the output capacity of the cycloconverter will be determined by the capacity of the phase advance capacitor, and overload operation will not be possible any further. .

Additionally, if you connect a phase advance capacitor with an excessively large capacity in advance in anticipation of overload operation, the circulating current that should flow through the cycloconverter at rated load or light load will increase, and the converter and power transformer will be damaged. This results in an increase in capacity, and furthermore, an increase in loss, resulting in an inefficient system.

[Object of the Invention] The present invention has been made in view of the above, and an object thereof is to provide a control method for a circulating current type cycloconverter that allows stable overload operation without increasing the capacity of the phase advance capacitor. do.

[Summary of the Invention] The present invention utilizes the features of the circulating current type cycloconverter (high output frequency upper limit) while performing overload operation, and is disabled so that the input power factor becomes 1 up to the rated load. Performs power control. Therefore, the phase advance capacitor should have a capacity sufficient to cancel out the delayed reactive power generated by the cycloconverter during rated operation.

During overload operation, reactive power control at the receiving end is stopped and control is performed so that the minimum circulating current continues to flow through the cycloconverter. This allows stable overload operation without interrupting the circulating current even during overload operation.

[Embodiment of the Invention] FIG. 1 is a configuration diagram of an embodiment of a cycloconverter device of the present invention.

In the diagram, BUS is the electric line of the 3-phase AC power supply, and CAP is
△ or the connected phase advancing capacitor, TR is the power transformer, CC is the circulating current type cycloconverter body LOAD is the load.

Cyclo converter body CC is positive group converter
It consists of SSP, negative group converter SSN, and DC reactors L _O1 and L _O2 with intermediate taps.

Also, as a control circuit, there is a load current detector CT _L , a positive group converter output current detector CT _P , a negative group converter output current detector CT _N , and a transformer PT _S that detects the three-phase AC voltage at the receiving end. Current transformer CT _S that detects phase alternating current, reactive power calculation circuit VAR, comparator
C ₁ , C ₂ , C ₃ , adder A ₁ , A ₂ , A ₃ , control compensation circuit
HQ(S), G _O (S), G _L (S), limiter circuit LIM, circulating current setting device V _O , operational amplifier K ₁ and phase control circuit
PHP and PHN are available.

First, the operation of load current control will be explained.

Input the detected value of the load current command I _L ^* and the actually flowing load current L _L to the comparator _C3 , and calculate the deviation ε ₃ = I _L ^* −
Find _L. The load current control compensation circuit compensates for the change ε ₃
Input to G _L (S) and perform proportional or integral amplification.
Here, for simplicity, G _L (S) is a proportional element (gain K _L )
Please continue with the explanation. Circulating current control circuit G _O
Assuming that the output signal from (S) is sufficiently small and ignoring it, the input signal of the phase control circuit PHP of the positive group converter SSP becomes v〓 _P = K _L · ε ₃ , and the output voltage V _P is V _P = k _V・V _S・cosα _P ∝v〓 _P. At this time, the phase control circuit PHN of the negative group converter SSN receives the output signal of the control compensation circuit G _L (S).
V〓 _{N = −K L ・}
A signal ε ₃ is given. Therefore, the output voltage of SSN
V _N becomes V _N =−k _V・V _S・cosα _N ∝−v _aN =V _P. where k _V is the conversion constant, V _S is the power supply voltage,
α _P , α _N are firing phase angles.

In other words, the output voltage V _P of the positive group converter SSP
Normal operation is performed with the output voltage V _N of the negative group converter SSN balanced at the load terminal. In this case, the firing phase angle of the two converters is α _N =
The relationship 180°−α _P holds true. For load LOAD, 2
Average value of output voltage of two converters V _L = (V _P +
V _N )/2 is applied.

If I _L ^* > I _L , the change ε ₃ is positive and causes V _P and V _N to increase in the direction of the arrow in the figure. Therefore, the load terminal voltage V _L increases, causing the load current I _L to increase.
Conversely, when I _L ^* < I _L , the change ε ₃ becomes a negative value, causing V _P and V _N to occur in the opposite direction to the arrow in the figure,
Make the load terminal voltage V _L a negative value to decrease I _L. Therefore, it finally settles down to I _L ^* ≒ I _L.

When the current command I _L ^* is changed sinusoidally, the deviation ε ₃ also changes accordingly, and the firing phase angles α _P and α _N are controlled so that the sinusoidal current I _L flows through the load.
In this normal operation, the voltage V _P of the positive group converter SSP is
Since the voltage V _N of the negative group converter SSN and the voltage V N of the negative group converter SSN are equally balanced, almost no circulating current I _O flows.

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

The circulating current I _O of the cycloconverter is detected as follows. In other words, the detected value of the output current I _P of the positive group converter SSP and the detected value of the output current I _N of the negative group converter SSN are summed, and then the load current is calculated.
The circulating current I _O is obtained by subtracting the absolute value of the detected value of I _L and multiplying it by (1/2). The relational expression is as follows.

I _O =(I _P + _IN − |I _L |)/2 The circulating current I _O obtained in this way is compared with its command value I _O ^* . The deviation ε ₂ =I _O ^* −I _O is input to the next circulating current control compensation circuit G _O (S), where it is comparatively amplified or integrally amplified. For convenience of explanation,
G _O (S) = K _O , that is, it is treated as only a comparison element.
The output signal of G _O (S) is input to adders A ₂ and A ₃ .

Therefore, the input voltages _v〓P and _v〓N to the phase control circuits PHP and PHN are as follows, respectively.

v〓 _P = K _L・ε ₃ +K _O・ε ₂ v〓 _N = −K _L・ε ₃ +K _O・ε ₂ Therefore, the relationship α _N ≒ 180° − α _P breaks down and becomes K _O・ε ₂ The output voltage of the positive group converter SSP is increased by the proportional amount
V _P and the output voltage V _N of the negative group converter SSN become unbalanced. The difference voltage V _P −V _N is the DC reactor
Applied to L _O1 and L _O2 , a circulating current I _O flows.

When I _O ^* > I _O , the deviation ε ₂ becomes a positive value,
Increase V _P and decrease V _N. Therefore, the differential voltage V _P
−V _N becomes a positive value, increasing the circulating current I _O.
Conversely, when I _O ^* < I _O , the deviation ε ₂ becomes a negative value, decreasing V _P and increasing V _N . Therefore, the differential voltage
V _P −V _N takes a negative value and reduces the circulating current I _O. Eventually, it settles down to I _O ^* ≒ I _O.

In such circulating current control, the output voltages V _P and V _N of the positive group and negative group converters change, but the load terminal voltage V _L is the average value of V _P and V _N , so the load current control is There is no effect.

On the other hand, reactive power control is performed as follows.

At the receiving end, a three-phase current detector CT _S and a three-phase voltage detector PT _S are installed, and a reactive power calculation circuit VAR is installed.
The reactive power Q is calculated by . The reactive power command value Q ^* is normally set to zero, and a deviation ε ₁ =Q ^* −Q is generated by the comparator C ₁ . The reactive power control compensation circuit H _Q (S) normally uses an integral element in order to make the steady bias ε ₁ zero, and its output I ^* _OQ is sent to the above-mentioned circulating current command value I through the adder A ₁ . It becomes _O ^* .

FIG. 2 shows a voltage and current vector diagram at the receiving end, representing one phase of a three-phase power supply. In the figure, V _S is the power supply voltage, I _cap is the leading current flowing to the phase advancing capacitor, I _CC is the input current of the cyclone converter, and I _S
represents its active ingredient and I _REACT represents its inactive ingredient.
Further, I _SSP represents the input current of the positive group converter, and I _SSN represents the input current of the negative group converter. If the current conversion constant of the converter is k ₁ , the above input current I _SSP
and I _SSN can be expressed as follows.

I _SSP = k ₁・I _P I _SSN = k ₁・I _NThis vector diagram represents the state when the load current I _L is supplied from the positive group converter SSP, and the output current I of the positive group converter _P becomes I _P = I _L + I _O , and the output current I _N of the negative group converter is I _N = I _O
It is becoming.

The input current I _CC of the cycloconverter is the vector sum of I _SSP and I _SSN , and its effective component I _S and reactive component I _REACT can be expressed as follows.

I _S = I _S SP・cosα _P +I _SSN・cosα _N =k ₁ (I _L +I _O )・cosα _P +k ₁ I _O cosα _N ≒k ₁ I _L・cosα _P I _REACT =I _SSP・sinα _P +I _SSN・sinα _N = k ₁ (I _L + I _O ) sin α _P + k ₁ I _O sin α _N ≒ k ₁ (I _L + 2I _O ) sin α _P However, the relationship α _N ≒ 180° − α _P was introduced. That is, the circulating current I _O flowing through the cycloconverter does not affect the active component I _S on the input side, but only the reactive component I _REACT . so that the reactive current I _REACT is always equal to the leading current I _cap of the phase leading capacitor.
By controlling the circulating current _I.sub.O , the current _I.sub.S supplied from the power source is always only the effective portion, and the fundamental wave power factor is maintained at unity.

Returning to Figure 1, when Q ^* > Q (delay _is a positive value), the deviation ε ₁ = Q ^* −Q becomes a positive value, and the , increases the circulating current command value I _O ^* . Therefore, the actual value of the circulating current I _O
≒I _O ^* increases and the input current of the cycloconverter
Increase I _REACT by the delayed reactive current of I _CC . Therefore,
The delayed reactive power Q at the receiving end increases and is controlled so that Q≈Q ^* . Conversely, if Q ^* <Q,
The circulating current I _O decreases, and as a result, Q also decreases and settles as Q≒Q ^* .

Figure 3 shows the load current I _L , circulating current I _O , and power factor P.
This represents the relationship of F.

When the load current I _L is zero, the cycloconverter
Only the circulating current I _O flows through CC, maintaining the relationship I _cap = I _REACT . Therefore, _IO becomes a large value. Load current I _L
As the value of IO increases, the value of the circulating current _IO decreases and continues to keep the input power factor at unity. When the load current I _L is further increased to exceed the rated current, the leading reactive power taken by the phase advance capacitor CAP becomes insufficient compared to the lagging reactive power taken by the cycloconverter CC.
The power factor at the receiving end is a lagging power factor. Therefore, the reactive power control deviation ε ₁ =Q ^* −Q takes a negative value, and the output of the control compensation circuit H _Q (S) also takes a negative value. However, when the output of H _O (S) is negative by the next limiter circuit LIM, the output I ^* _OQ of LIM is made zero.

On the other hand, another circulating current command ΔI _O ^* is given by the circulating current setting device V _O . This current command ΔI _O ^* is set to such a value that the circulating current of the cycloconverter CC is not interrupted.

Therefore, in reality, the adder output I _O ^* = I ^* _OQ + △I _O ^* is given as the circulating current command value, and the actual circulating current
_IO is also controlled accordingly.

Therefore, even if the load current I _L increases and exceeds the rated value, the circulating current I _O of the cycloconverter CC is
Controlled without interruption.

In this case, the power factor at the power receiving end is no longer 1 and becomes a lagging power factor as the load current I _L increases, but this does not pose a problem in systems where overload operation is rarely performed.

Although the apparatus shown in FIG. 1 has been described for a single-phase load, it goes without saying that it can be similarly applied to a two-phase or more polyphase load.

Further, the present invention can be similarly applied to a cycloconverter with a Δ connection.

Furthermore, for polyphase output cycloconverters,
It is also possible to distribute the circulating current for each phase.

It goes without saying that other applications are possible without changing the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, the features of the circulating current type cycloconverter (i.e., low output current distortion and high output frequency upper limit) can be maintained even during overload operation. This enables stable operation. Further, the power factor at the power receiving end can always be kept at 1 until rated load operation, and the capacitance of the phase advance capacitor connected to the power receiving end of the cycloconverter is not particularly increased. Therefore, there is only a slight increase in the capacity of power transformers and converters for overload operation.
Efficient driving becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the cycloconverter device of the present invention, FIG. 2 is a voltage-current vector diagram for explaining the device in FIG. 1, and FIG. 3 is a diagram for explaining the device in FIG. 1 as well. This is a diagram showing the relationship between the load current I _L , the circulating current I _O , and the power factor at the receiving end. BUS...3-phase AC power supply line, CAP...phase advancing capacitor, TR...power transformer, CC...cycloconverter body, LOAD...load, SSP,
SSN...Positive group and negative group converter, L _O1 , L _O2 ...
DC reactor, CT _S , CT _L , CT _P , CT _N ... Current detector, PT _S ... Voltage detector, VAR ... Reactive power calculation circuit, C ₁ , C ₂ , C ₃ ... Comparator, A ₁ ,
A ₂ , A ₃ ... Adder, H _Q (S) ... Reactive power control compensation circuit, G _O (S) ... Circulating current control compensation circuit, G _L (S) ...
...Load current control compensation circuit, LIM...Limiter circuit, VR _O ...Circulating current setting device, _K1 ...Operation amplifier, PHP, PHN...Phase control circuit.

Claims (1)

[Claims] 1. In a circulating current type cycloconverter that supplies variable frequency alternating current to a single-phase or multiphase load, a phase advance capacitor is connected to its power receiving terminal, and when the cycloconverter is operated up to the rated load, the delayed reactive power of the cycloconverter is The circulating current of the cycloconverter is controlled so that the leading reactive power of the phase advancing capacitor and the leading reactive power of the phase advancing capacitor cancel each other, and the circulating current of the cycloconverter is controlled so that the leading reactive power of the phase advancing capacitor cancels each other out. A method for controlling a cycloconverter, the method comprising: controlling the cycloconverter so that it is approximately constant.