JPH05932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a parallel operation device for a plurality of circulating current type cycloconverters.

[Technical background of the invention]

A cycloconverter directly converts alternating current power of a constant frequency into alternating current power of a different frequency, and is widely used in variable voltage variable frequency power supplies driven by alternating current motors. In particular, it is known that circulating current type cycloconverters can have a high upper limit value for output frequency ₀ (operation at input frequency ₁ or higher is also possible) (Japanese Patent Application Laid-Open No. 60-28772), and the range of its application is increasing. It is being expanded.

On the other hand, the cycloconverter has the disadvantage that it requires a large amount of reactive power from the power supply because its component thyristor is commutated by the power supply voltage.
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 has various negative effects on electrical equipment connected to the same system.

On the other hand, in Japanese Patent Publication No. 59-14988, a phase advance capacitor is connected to the receiving end of the cycloconverter, and the delayed reactive power of the cycloconverter is
The circulating current of the cycloconverter is controlled so that the leading reactive powers of the phase advancing capacitors cancel each other out, so that the fundamental wave power factor as seen from the power supply side is always 1.

[Problems with conventional technology]

FIG. 10 shows a configuration diagram of a conventional parallel operation device for a plurality of cycloconverters.

In the figure, BUS is the electrical line of the 3-phase AC power supply, SW _A ,
SW _B is the main switch, CAP-A, CAP-B are phase advance capacitors, CC-A, CC-B are circulating current type cycloconverters for 3-phase to 3-phase conversion, M _A , _MB are AC motors, CT _S1 , CT _S2 are current transformers, PT _S1 , PT _S2 are transformers, VAR ₁ , VAR ₂ are reactive power calculation circuits, C _Q1 ,
C _Q2 is a comparator, HQ ₁ HQ ₂ is a reactive power control compensation circuit,
ACR _A , ACR _B are circulating current control circuits, ALR _A ,
ALR _B is load current control circuit, PHC-A, PHC-
B is a phase control circuit.

The load current control circuit ALR _A detects the current (load current) supplied to the AC motor M _A , and adjusts the output of the cycloconverter CC-A via the phase control circuit PHC-A so that it matches the command value. Adjust voltage.

The circulating current control circuit ACR _A detects the current circulating inside the cycloconverter CC-A, and controls the phase control circuit PHC- so that it matches the command value.
Through A, the positive group of the cycloconverter CC-A,
Controls the differential voltage (voltage applied to the DC reactor) of the negative group converter.

A phase advance capacitor CAP-A is connected to the receiving end of _the cycloconverter CC-A, and a reactive current component I _{Q (} reactive power A circulating current command value I ^* _OA is given to _{the circulating current control circuit ACR A so} that it becomes zero.

The cycloconverter CC-B is configured similarly,
Again, the circulating current I _OB is controlled so that the reactive power Q _B at the receiving end becomes zero.

Such conventional parallel operation devices for cycloconverters have the following problems.

The phase advance capacitor must be installed separately for each cycloconverter, which tends to complicate the wiring and increase the installation area.

Due to an accident, one of the cycloconverters
If one or several units are gated and disconnected, the phase advancing capacitor connected to the receiving end of the cycloconverter causes the overall reactive power to advance, leading to a risk of an increase in the power supply voltage.

The capacity of the phase advance capacitor connected to the receiving end of each cycloconverter is designed so that the power factor at the receiving end becomes 1 when each cycloconverter takes on its maximum load (when the delayed reactive power reaches its maximum). be done. In other words, regardless of the operation mode of other cycloconverters, the capacitance of the phase advance capacitor is determined in such a way that the leading reactive power is sufficient to cancel out the maximum value of the delayed reactive power of the own cycloconverter. In this case, there was a drawback that a phase advancing capacitor with unnecessary capacity was also required.

Increasing the capacitance of the phase advance capacitor means that the capacitance of the power transformer, converter, etc. also increases, especially at light loads.
By passing unnecessary circulating current, inefficient operation was avoided.

In addition, if the capacity of the phase advance capacitor is selected so that the power factor at the receiving end is 1 when each cycloconverter is operated at the rated load, the circulating current command value of the cycloconverter becomes negative during overload operation. value, resulting in operation with zero circulating current. For this reason, the cycloconverter operates as a non-circulating current type cycloconverter, and the waveform distortion of the output current increases.
This forces the upper limit of the output frequency to be lowered.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems.The present invention reduces the capacity of the phase advancing capacitor to be connected to the power receiving end, improves operating efficiency during light load operation, and circulates even during overload operation. It is an object of the present invention to provide a parallel operation device for cycloconverters that maintains the characteristics of a current type cycloconverter and reduces the capacity of the cycloconverter.

[Summary of the invention]

In order to achieve the above object, the present invention connects a phase advance capacitor to a common power receiving end of a plurality of circulating current type cycloconverters, and circulates it to each cycloconverter so as to control the reactive power of the entire device. It gives a current command value. At this time, the optimum value for the phase advance capacitor is prepared in consideration of the operating mode of the entire system. As a result, the capacitance of the phase advance capacitor is reduced, and unnecessary circulating current is not passed through the system as a whole, allowing efficient operation.

In addition, if the sum of delayed reactive power of the entire cycloconverter exceeds the capacity of the phase advance capacitor due to overload operation, the circulating current command value given to each cycloconverter is set to zero regardless of the power factor at the receiving end. By maintaining the constant value to such an extent that the cycloconverter does not change, each cycloconverter can always operate without losing its characteristics as a circulating current type cycloconverter.

Furthermore, when the circulating current to be passed through each cycloconverter increases during light load operation, it is possible to reduce the number of stages of phase advance capacitors in accordance with the magnitude of the circulating current command value, thereby improving operational efficiency. .

Furthermore, when each cycloconverter is operated separately due to light load or overload, the distribution is made such that more circulating current flows to the cycloconverter with a lighter load, and less circulating current flows to the cycloconverter with a heavier load. By controlling
It becomes possible to prevent an increase in the current capacity of the converter.

[Embodiments of the invention]

FIG. 1 is a configuration diagram showing an embodiment of a parallel operation device for a plurality of cycloconverters according to the present invention.

In the figure, BUS is the electrical line of the three-phase AC power supply, CAP is the phase advancing capacitor, SW _A , SW _B , SW _C , SW _D are the main switches, CC-A, CC-B, CC-C, CC-D is a circulating current type cycloconverter with three-phase to three-phase conversion, M _A , M _B , M _C , and M _D are AC motors, CT _S is a current transformer, P _S is a transformer, VAR is a reactive power calculation circuit,
C _Q is a comparator, HQ is a reactive power control compensation circuit, DST
is distribution circuit, ACR _A , ACR _B , ACR _C , ACR _D is circulating current control circuit, ALR _A , ALR _B , ALR _C , ALR _D
are load current control circuits, PHC-A, PHC-B,
PHC-C, PHC-D are phase control circuits, C-SEL
is a phase advance capacitor switching control circuit.

First, circulating current type cycloconverter CC-A
The operation will be explained.

Figure 2 shows the circulating current type cycloconverter CC-
An example of the main circuit configuration diagram of A and AC motor M _A is shown.
In the figure, TrU, TrV, TrW are power transformers, CC−
U, CC-V, CC-W are U-phase, V-phase, W-phase cycloconverters, M _A is the armature of the AC motor, U
is U-phase armature winding, V is V-phase armature winding, W is W
This is the phase armature winding. U-phase cycloconverter
CC-U is positive group converter SSP, negative group converter
It consists of SSN and DC reactors L ₀₁ and L ₀₂ .

FIG. 3 shows an example of a control circuit configuration diagram of the cycloconverter shown in FIG. 2. In the figure, LIM is a limit circuit, AD ₁ to _{AD 9} are adders, C ₁ to C ₆ are comparators,
G _OU , G _OV , G _OW are circulating current control compensation circuits, G _LU ,
G _LV , G _LW are load current control compensation circuits, IOA ₁ to _{IOA 3}
are inverting amplifiers, PHP _U , PHN _U , PHP _V , PHN _V ,
PHP _W and PHN _W are phase control circuits.

The operation of the cycloconverter CC-A will be explained below with reference to the configuration diagrams of FIGS. 2 and 3.

The cycloconverter CC-A directly converts 3-phase AC into 3-phase AC with a different frequency, and can be divided into U-phase cycloconverter CC-U, V-phase cycloconverter CC-V, and W-phase cycloconverter CC-W. I can do it.

First, the operation of load current control and circulating current control of the U-phase cycloconverter will be explained.

The load current I _U is controlled as follows.

Load current I _U is detected by current detector CT _U and inputted to comparator C ₁ in FIG. The comparator _C1 compares the load current command value IU and _the load current detection value _IU , and outputs the deviation _εU =I ^* _U − _IU . The deviation ε _U is input to the next control compensation circuit G _LU and is proportionally amplified (differential or integral elements may be used to improve the control response). Let this constant of proportionality be K _U. The output K _U・ε _U of the control compensation circuit G _LU is the output of the adder AD ₁
Positive group converter SSP phase control circuit through
The signal input to PHP _U and changed to −K _U ·ε _U via the inverting amplifier IOA ₁ is input to the phase control circuit PHN _U of the negative group converter SSN via the adder AD ₂ .

Positive group converter SSP is the above phase control circuit PHP _U
A voltage V _P proportional to the input v〓 _P = K _U · ε _U is generated in the direction of the arrow in Fig. 2. Similarly negative group converter
SSN generates a voltage proportional to the input signal v〓 _N of the phase control circuit PHN _U in the direction of the arrow in the figure.

Here, assuming that the output signal from the circulating current control circuit is sufficiently small, v〓 _N = -K _U · ε _U = -v〓 _P. Therefore, the firing phase angle α _NU of the negative group converter SSN has the relationship α _NU =180°−α _PU with respect to the firing phase angle α _PU of the positive group converter SSP.

That is, when the positive group converter SSP generates a positive voltage V _P in the direction of the arrow in FIG. 2, the output voltage V _N of the negative group converter SSN generates a negative voltage, so that V _P = -V _N , The voltages are balanced at the intermediate terminal point of the DC reactor.

Therefore, for the load U, (V _F = V _N )/2=K _CP・(v〓 _P −v〓 _N )/2=K _C・K _U・
A conversion constant is applied to ε _U K _C.

If I ^* _U > I _U , the deviation ε _U will be a positive value, and the load U
The voltage applied to V _U =K _C・K _U・ε _U becomes a positive value, increases the load current I _U , and settles down to I _U ≒ I ^* _U. Conversely, when I ^* _U < I _U , the deviation ε _U becomes a negative value, and the U-phase output voltage V _U also becomes a negative value, reducing the load current I _U , and eventually I _U ≒ I ^* Become _U and calm down.

If the load current command value I ^* _U is changed in a sinusoidal manner,
The actual current I _U is also controlled in accordance with this, and a sinusoidal current can be supplied to the load U.

Next, the operation of circulating current control of the U-phase cycloconverter will be explained.

By detecting the output current I _P of the positive group converter SSP and the output current I _N of the negative group converter SSN by current detectors CT _P and CT _N , and performing the following calculation, U
Find the circulating current I _OU of the phase cycloconverter.

I _OU = (I _P + I _N − | I _U |)/2 Here, | I _U | means the absolute value of the detected value of the load current I _U.

The circulating current I _OU thus determined is input to the comparator C ₂ in FIG. 3 and compared with its command value I ^* _OU . The deviation ε _OU =I ^* _OU +I _OU is input to adders AD ₁ and AD ₂ via a control compensation circuit G _OU (referred to as a proportional element K _OU ).

Therefore, the inputs v〓 _P and α〓 _N to the phase control circuits PHP _U and PHN _U are as follows, respectively.

v〓 _P = K _U・ε _U +K _OU・ε _OU v〓 _N = −K _U・ε _U +K _OU・ε _OU Therefore, the relationship α _NU = 180゜−α _PU collapses, and K _OU・
The output voltage V _P of the positive group converter SSP and the output voltage −V _N of the negative group converter SSN become unbalanced by an amount proportional to ε _OU . V _P +V _N =K _C (v〓 _P + v〓 _N = K _C・K _OU・ε _OU is applied to the DC reactors L ₀₁ and L ₀₂ , and a circulating current I _OU flows.

If I ^* _OU > I _OU , the deviation ε _OU takes a positive value and increases the circulating current I _OU . Conversely, if I ^* _OU < I _OU , the deviation ε _OU becomes a negative value, and the DC reactor
The voltage V _P +V _N applied to L ₀₁ and L ₀₂ is set to a negative value to reduce I _OU . Eventually, it settles down to I ^* _OU ≒ I _OU .

V-phase, W-phase cycloconverter load current
I _V , I _W and circulating currents I _OV , I _OW are similarly controlled.

Other cycloconverters CC-B, CC-C,
CC-D is similarly controlled.

Next, the operation of reactive power control at the power receiving end of the device shown in FIG. 1 will be explained.

First, the reactive power Q _T at the receiving end of the entire device is detected. The current and voltage at the power receiving end are detected by the three-phase current detector CT _S and three-phase voltage detector _PTS shown in FIG. 1, and are input to the reactive power calculation circuit VAR. In VAR, the phase of the three-phase detection voltage is shifted by 90 degrees, and that value is multiplied by the detection current of each phase. Then, the addition end of the three phases becomes the detected reactive power value (instantaneous value) Q _T of the received power.

The reactive power detection value Q _T and its command value Q ^* _T are input to the comparator C _Q , and the deviation ε _Q = Q ^* _T − Q _T is determined.
The deviation ε _Q is input to the next control compensation circuit HQ to perform proportional amplification or integral amplification. The output of HQ I ^* _T is
This is the surgical ring current command value for the entire cycloconverter, but each cycloconverter has a distribution circuit.
Circulating current commands I ^* _OA , I ^* _OB , I ^* _OC , and I ^* _OD are given via DST. The distribution circuit DST will be explained later.
Here, it will be explained as I ^* _OA = I ^* _OB = I ^* _OC = I ^* _OD = I ^* _OT .

Circulating current command for cycloconverter CC-A
I ^* _OA is given. I ^* _OA is the limiter circuit in Figure 3
It is input to LIM and converted into a new command value I ^* _OA ′. Figure 4 shows the input/output characteristic diagram of the limiter circuit LIM. When the input I ^* _OA is 0, the output I ^* _OA '=0
And, when input I ^* _OA I _O(nax), output I ^* _OA ′=
I _O(nax) . The intermediate range, i.e. 0<I ^* _OA
<I _O(nax) , then I ^* _OA ′=I _OA .

The output I ^* _OA ′ of the limiter circuit LIM is the addition AD ₃ ,
These are input to AD ₆ and AD ₉ , and added to the minimum circulating current command value I ^* _OO , respectively. Therefore, the circulating current command value I ^* _OU of the U-phase cycloconverter is the following value.

I ^* _OU = I ^* _OA ′ + I ^* _OO Similar circulating current command values for V phase and W phase I ^* _OV and I ^* _OW
is given.

Also, other cycloconverters CC-B, CC-
Similar circulating current command values I ^* _OB , I ^* _OC ,
Given I ^* _OD , similarly through the limiter circuit,
These are converted into new command values I ^* _OB ′, I ^* _OC ′, I ^* _OD ′ and added to the minimum circulating current command value I ^* _OD to give the individual circulating current command value.

Detected value of reactive power at receiving end (delay is considered positive)
If Q _T is smaller than its command value Q ^* _T , the deviation ε _Q = Q ^* _T
−Q _T becomes a positive value, increasing the output I ^* _OT of the control compensation circuit HQ. Therefore, the circulating current command values I ^* _OA , I ^* _OB , I ^* _OC , and I ^* _OD given to each cycloconverter also increase,
Increase the actual circulating current.

If the circulating current of the cycloconverter increases,
The delayed reactive power Q _T at the receiving end increases, and finally Q _T
= Q ^* _T.

Conversely, when Q ^* _T <Q _T , the deviation ε _Q becomes a negative value, reducing the circulating current of each cycloconverter and reducing Q _T. As a result, it is controlled so that Q _T =Q ^* _T.

When the deviation ε _Q increases to a negative value, the output I ^* _OT of the control compensation circuit HQ becomes a negative value. Therefore, the circulating current command value I ^* _OA given to each cyclo converter,
I ^* _OB , I ^* _OC , and I ^* _OD also have negative values.

However, the output I ^* _OA ' of the limiter circuit LIM does not become negative and becomes I ^* _OA '=0. Therefore cycloconverter
I ^* _OU =I ^* _OA '+I ^* _OO =I ^* _OO is given as a circulating current command to the U-phase cycloconverter of CC-A, and the minimum circulating current _IOU≈I ^* _OO continues to flow. The same applies to the V phase and W phase.

Furthermore, other cycloconverters CC-B, CC-
Similarly, the minimum circulating current continues to flow in C and CC-D.

That is, since the circulating current is not interrupted, the characteristics of the circulating current type cycloconverter can be maintained.

Figure 5 shows an example of the operation mode of the device shown in Figure 1. In Figure 5a, Q _eap = constant is the leading reactive power taken by the phase advance capacitor CAP, and Q _CCL is the delay taken by the entire cycloconverter. The reactive power when the minimum value I _OO of circulating current is flowing as reactive power, Q _T shown in Figure 5 b is the reactive power at the receiving end of the entire device, and I ^* _OA ′ + I ^* _OO in Figure 5 c is This is the circulating current command value of the cycloconverter CC-A.

When Q _CCL <Q _eap , Q _T =0 can be achieved by flowing the circulating current of each cycloconverter.

When Q _CCL > Q _eap , for example, when several cycloconverters are operated with overload at the same time, the circulating current of each cycloconverter is controlled to the minimum value I ^* _OO as described above. As a result, the reactive power Q _T at the receiving end is delayed, and the condition of power factor = 1 is no longer satisfied.

Therefore, when the above-mentioned overload operation frequently occurs, it is necessary to prepare a phase advance capacitor CAP corresponding to the overload operation.

However, in general, they are operated for long periods of time at below rated operation, and temporary overload operation is often required. In particular, when several cycloconverters are operated in parallel, the overload operations described above rarely overlap.

If Q _CCL > Q _eap , Q _T will be delayed, but
Since the time is short and the proportion is small, there is little negative impact on the power supply system.

It is very rare that all cycloconverters are overloaded at the same time. Figure 5a
Q _CCL(nax) indicates the delayed reactive power value when all cycloconverters are operated with overload at the same time. In the conventional operation method, the entire advanced reactive power Q _eap of the phase advance capacitor was prepared to cancel out Q _CCL(nax) . Therefore, not only the capacitance of the phase advance capacitor becomes large, but also the circulating current flowing through the cycloconverter becomes large, and accordingly, the capacitance of the converter, power transformer, DC reactor, etc. is also required to be large.

On the other hand, in the device of the present invention, the capacitance of the phase advance capacitor can be determined by considering the operation mode of the entire cycloconverter, and the minimum required capacitance is provided, so a considerable reduction effect can be expected. Moreover, even if the value of Q _CCL becomes larger than the value of Q _eap , each cycloconverter is controlled so that the minimum circulating current flows, so that it can continue flowing without losing the characteristics of a circulating current type cycloconverter. I can drive. Therefore, the upper limit value of the output frequency can be set high, and a sine wave current with little waveform distortion can be supplied to the load.

FIG. 6 is a block diagram showing an embodiment of the distribution circuit DST of the device shown in FIG.

In the figure, ABS ₁ to _{ABS 4} are absolute value circuits, and OA _{1 to} ABS 4 are absolute value circuits.
OA ₄ is an operational amplifier, A ₁ to _{A 4} are adders and subtracters, ML ₁ to
_ML4 is a multiplier, and _AS1 to _AS4 are analog switch circuits.

The input of the distribution circuit DST is the output I ^* _OT of the reactive power control compensation circuit HQ shown in Figure 1 and each cycloconverter.
These are peak values I ^* _nA , I*nB, I* _nC , and I* _nD of the load current commands given to CC-A, CC ^- B, CC ^- _C , and CC ^- D. That is, the load current command values for the U phase, V phase, and W phase of the cycloconverter CC-A are given as shown in the following equations.

I ^* _U = I ^* _nA・sinωt I ^* _V = I ^* _nA・sin (ωt−2π/3) I ^* _W = I ^* _nA・sin (ωt+2π/3) However, ω is the output angular frequency.

The circulating current command I ^* _OA given to the cycloconverter CC-A is as follows.

The peak value I ^* _nA of the load current command is input to the absolute value circuit ABS ₁ and becomes |I ^* _nA |. Next, it is multiplied by (1/1 _MA ) via the operational amplifier _OA1 , and the adder/subtractor _A1 outputs 1-(|I ^* _nA |/ _IMA ).

This is input to the multiplier ML ₁ and multiplied by the output signal I ^* _OT of the reactive power control compensation circuit HQ mentioned above, and the circulating current command I ^* _OA is obtained as I ^* _OA = I ^* _OT × (1 - | I ^* / _nA | /I _MA ) is given.

Here, I _MA is selected to be the maximum value of the peak value I ^* _MA of the load current command, or a value slightly larger than that value.

Other cycloconverters CC-B, CC-C,
CC-D circulating current commands I ^* _OB , I ^* _OC , and I ^* _OD are also given as follows.

I ^* _OB = I ^* _OT × (1 − | I ^* / _nB | / I _MB ) I ^* _OC = I ^* _OT × (1 − | I ^* / _nC | / I _MC ) I ^* _OD = I ^* _OT × (1 - | I ^* / _nD | / I _MD ) Therefore, for example, if CC-A is lightly loaded and the other cycloconverters are heavily loaded, |I ^* _nA | will be much smaller than I _MA , and I ^* _OA is largely given. The load current peak value of other cycloconverters is |I ^* _nB
|≒I _MB , |I ^* _nC |≒I _MC , |I ^* _nD |=I _MD , and as a result, I ^* _OB , I ^* _OC , and I ^* _OD have small values.

That is, the overall reactive power Q _T is controlled by allowing a large amount of circulating current to flow through the cycloconverter with a light load and a small amount of circulating current through the cycloconverter with a heavy load. Therefore, only a small circulating current needs to flow through a heavily loaded cycloconverter, and the current capacity of the converter can be prevented from increasing.

Analog switches AS ₁ to _{AS 4} output circulating current commands I ^* _OA , I ^* _OB , I ^* _OC , when each cycloconverter stops operating, that is, when the gate is cut off.
This is to set I ^* _OD to zero individually.

Figure 7 shows a phase advance capacitor connected to the receiving end.
The CAP is divided into multiple stages, and the number of closing stages can be switched using switches MC ₁ , MC ₂ , etc. CAP ₁ , CAP ₂ , ... are three-phase advance capacitors.

FIG. 8 is a configuration diagram showing an embodiment of a switching control circuit that controls the switches MC ₁ , MC ₂ , . . . in FIG. 7. In the figure, HYS is a hysteresis circuit, MM ₁ ,
MM ₂ is a mono multi circuit, CN is an up/down counter, and SELECT is a selection circuit.

First, the output signal I ^* _OT of the reactive power control compensation circuit HQ of the apparatus shown in FIG. 1 is input to the hysteresis circuit HYS. I ^* _OT increases and the upper limit of hysteresis a
When the point is exceeded, a rising pulse is generated and the monomulti MM ₁ is struck. The count value of the counter CN is increased by one by the output signal of _MM1 , and as a result, the number of input stages of the phase advance capacitor CAP is decreased by one stage via the selection circuit SELECT. When the capacity of CAP decreases, the reactive power Q _T at the receiving end becomes delayed,
Decrease the output signal I ^* _OT of the above HQ. However, the reduced capacitance of CAP is determined to such an extent that it does not reach the lower limit point b of the hysteresis circuit HYS.

Conversely, the cycloconverter becomes heavily loaded,
When I ^* _OT decreases to below the lower limit value of hysteresis (point b), send a falling pulse to monomulti MM ₂ and decrease the count value of counter CN by one. Then, the number of input stages of the phase advance capacitor CAP is increased by one stage via the selection circuit SELECT.

FIG. 9 shows the relationship between the count value of the counter CN and the number of stages of switches MC ₁ to _{MC 4} to be closed when the phase advancing capacitor CAP is divided into four stages.

In this way, by controlling the number of closing stages of the phase advance capacitor CAP according to the magnitude of the circulating current command value I ^* _OT , the value of the circulating current flowing through each cycloconverter is not small, especially at light loads, and the conversion This reduces losses not only in the power supply transformer and DC reactor, but also improves the operating efficiency of the entire system.

It goes without saying that the present invention can be similarly carried out using a triangular connection type circulating current type cycloconverter (Japanese Patent Laid-Open No. 58-60328).

Further, even if a non-circulating current type cycloconverter is included in a plurality of cycloconverters, it can be operated in the same manner.

〔Effect of the invention〕

As described above, in the device of the present invention, a phase advance capacitor is connected to the common power receiving end of a plurality of circulating current type cycloconverters, and a circulating current command is given to each cycloconverter to control the reactive power of the entire device. giving value. At this time, the optimum value for the phase advance capacitor is prepared in consideration of the operating mode of the entire system. This reduces the capacitance of the phase advance capacitor, eliminates unnecessary circulating current in the system as a whole, and enables efficient operation.

In addition, if the sum of delayed reactive power of the entire cycloconverter exceeds the capacity of the phase advance capacitor due to overload operation, the circulating current command value given to each cycloconverter is set to zero regardless of the power factor at the receiving end. By maintaining the constant value so that the current does not change, each cycloconverter can be operated without losing its characteristics as a circulating current type cycloconverter.

Furthermore, when the circulating current to be passed through each cycloconverter increases during light load operation, the number of stages of phase advance capacitors to be turned on can be reduced in accordance with the magnitude of the circulating current command value, thereby improving operational efficiency.

Furthermore, when each cycloconverter is operated with a light load or a heavy load, distribution control is performed so that a large amount of circulating current flows through the cycloconverter with a light load, and a small amount of circulating current flows through the cycloconverter with a heavy load. By doing so, it becomes possible to prevent the current capacity of the converter from increasing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the cycloconverter parallel operation device of the present invention, FIG. 2 is a block diagram showing an embodiment of the main circuit of the cycloconverter of the device in FIG. FIG. 4 is a characteristic diagram for explaining the operation of the circuit in FIG. 3;
The figure is an operation mode diagram for explaining the operation of the device shown in FIG. 1, FIG. 6 is a configuration diagram showing an embodiment of the distribution circuit of the device shown in FIG. 1, and FIG. 7 is a phase advance diagram of the device shown in FIG. 1. FIG. 8 is a block diagram showing an embodiment of the main circuit of the capacitor; FIG. 8 is a block diagram showing an embodiment of the switching control circuit for the phase advance capacitor of the device in FIG. 1; FIG. 9 is an explanatory diagram of the operation of the circuit in FIG. 8. , FIG. 10 is a configuration diagram of a conventional parallel operation device for a plurality of cycloconverters. BUS...Electric line of 3-phase AC power supply, CAP...Phase advance capacitor, SW _A , SW _D ...Main switch, CC-
A~CC-D……Circulating current type cycloconverter,
M _A ~ M _D ... AC motor (load), CT _S ... Current transformer, PT _S ... Transformer, VAR ... Reactive power calculation circuit, O _Q ... Comparator, HQ ... Reactive power control compensation Circuit, DST...Distribution circuit, ACR _A to ACR _D ...Circulating current control circuit, ALR _A to ALR _D ...Load current control circuit, PHC-A to PHC-D...Phase control circuit,
C-SEL... Phase advance capacitor switching control circuit.

Claims (1)

[Scope of Claims] 1. An AC power supply, a plurality of circulating current type cycloconverters connected in parallel to the AC power supply, a plurality of loads receiving power from each of the cycloconverters, and a receiving end of the AC power supply. a phase advance capacitor connected all together to the cycloconverter, a means for controlling the output current (load current) of each of the cycloconverters, a means for controlling the circulating current of each of the cycloconverters, and the entire power receiving end of the AC power supply. Parallel operation of cycloconverters comprising means for giving a circulating current command value to the circulating current control means of each of the cycloconverters in order to control the reactive power of the cycloconverters, and means for preventing the circulating current command value from becoming smaller than a certain minimum value. Device. 2. Claim 1, characterized in that the circulating current command value given to the circulating current control means of each of the cycloconverters is distributed and given according to the magnitude of the peak value of the output current of each of the cycloconverters. Parallel operation device for the cycloconverter described in . 3. The method according to claim 1 or 2, characterized in that the phase advance capacitor is divided into multiple stages, and the number of input stages of the phase advance capacitor is controlled according to the magnitude of the circulating current command value. Parallel operation device for cycloconverters.