JPH0683575B2 - Cycloconverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a cycloconverter device in which the capacity of a power transformer is reduced.

(Prior Art) A cycloconverter is a device that directly converts AC power of a constant frequency into AC power of another different frequency. However, since a thyristor, which is a constituent element of the cycloconverter, is commutated by a power supply voltage, a large amount of reactive power from the power supply There is a drawback to take. Further, the reactive power constantly fluctuates in synchronization with the frequency on the load side. Therefore, not only is the capacity of the power supply system equipment increased, but fluctuations in the reactive power adversely affect various electrical devices connected to the same system.

As a method of compensating the reactive power of such a cycloconverter, there is a technique disclosed in Japanese Patent Laid-Open No. 56-44382.

That is, a phase advancing capacitor that takes a certain amount of lead reactive power is installed at the power receiving end of the cycloconverter, and the circulating current of the cycloconverter is adjusted so that the delay reactive power of the cycloconverter is always equal to the lead reactive power of the phase advancing capacitor. It is a thing.

On the other hand, in this reactive power compensation type cycloconverter device, a power transformer is installed between the AC power source and each converter for the purpose of lowering or raising the voltage or for insulating the converter. As a result, a capacity that can supply the delayed reactive power of each converter was required. That is, in addition to the power that can be supplied to the load, the delayed reactive power that opposes the advanced reactive power of the phase-advancing capacitor must be supplied to the cycloconverter via the power transformer. Therefore, the power transformer is large and large in volume, and is expensive.

In view of this, JP-A-57-80267 was proposed. FIG. 4 shows a main circuit configuration diagram of the conventional cycloconverter device.

In the figure, BUS is a three-phase AC power line, TrU, TrV, TrW are power transformers, CAP _{U1 to} CAP _U4 , CAP _{V1 to} CAP _V4 , CAP _{W1 to} CAP _W4.
Is a phase advancing capacitor, CC-U, CC-V and CC-W are circulating current type cycloconverters, and U, V and W are three-phase AC loads.

U-phase cycloconverter CC-U is a positive group converter SS
It consists of P _U and SDP _U , negative group converters SSN _U and SDN _U, and DC reactor L _OU . The circulating current type cycloconverter has 12 so-called control phases (control pulses).

The V-phase and W-phase cycloconverters CC-V and CC-W are similarly constructed.

On the input side of the U-phase cycloconverter CC-U, the phase-advancing capacitor CAP is divided into four on the secondary winding side of the power transformer TrU.
_{U1 to} CAP _U4 are connected.

In this way, the phase advancing capacitors CAP _{U1 to} CAP _U4
Delay reactive power and phase advancing capacitor CAP _U1 taken by cycloconverter CC-U by connecting to the secondary winding side of TrU
~ The progress of reactive power taken by CAP _U4 cancels each other to some extent,
This has the effect of reducing the capacity of the power transformer TrU. The same applies to the V phase and the W phase.

FIG. 5 shows the current value on the input side of the cycloconverter CC-U of FIG. 4, where I _SSPU is the positive group converter SSP _U.
Input current, I _SSNU is the input current of negative group converter SSN _U , I _SSNU
capu1 and I _capu2 indicate the magnitude of the current in the phase advancing capacitors CAP _U1 and CAP _U2 .

When the loads U, V, and W are AC motors, almost no counter electromotive force is generated during start-up and low-speed operation, the output voltage of the cycloconverter is small, and the control phase angle α is operated at about 90 °. Therefore, the input current I of each converter
Most of _SSPU , I _SSNU, etc. can be regarded as delayed reactive current.

Therefore, the current I _Tr2 flowing in the secondary winding of the power transformer TrU
Is I _Tr2 = | I _SSPU −I _capu1 |, and the size of I _Tr1 of the current flowing through the primary winding of TrU is I _Tr1 = 2 × | I _SSPU + I _SSNU −I _capu1 − I _capu2 |

In this way, the capacity of the power transformer TrU can be reduced, but the advance currents I _{capu1 to} I _capu4 flowing in the phase advancing capacitors CAP _{U1 to} CAP _U4 have constant values, whereas the input current of each converter is constant. Since I _SSPU , I _SSNU, etc. change as shown in the figure according to the output current I _U , the current of the difference flows in the current transformer TrU.

It goes without saying that as the speed of the AC motor load increases, active power is consumed, and in addition to the reactive power, the active transformer TrU must also bear the active power.

(Problems to be Solved by the Invention) The conventional cycloconverter device described above includes a phase advancing capacitor.
By dividing CAP _{U1 to} CAP _U4 etc. and connecting them to the secondary winding side of the power transformer TrU etc., the capacity of the power transformer TrU etc. can be reduced to some extent.

However, while the current flowing through the phase-advancing capacitor has a constant value, the input current of each converter greatly changes according to the output current of the cycloconverter, so the reactive current of the difference must be borne by the power transformer. As a result, the effect of reducing the capacity was halved. In particular, the current situation is that the secondary current capacity of the transformer cannot be expected to be reduced so much.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cycloconverter device in which the capacity of a power transformer is significantly reduced.

[Structure of Invention]

(Means for Solving Problems) In order to achieve the above object, the present invention provides an AC power supply, a load device insulated for each phase, and a positive group for supplying a current for each phase of the load. A cycloconverter having a negative group converter, a first phase advance capacitor connected to an input side common terminal of each phase positive group converter of the cycloconverter, and an input side common terminal of each phase negative group converter of the cycloconverter. A second phase-advancing capacitor connected to and a power supply transformer interposed between the AC power supply and the cycloconverter constitute a cycloconverter device.

Also, the number of control phases of the cycloconverter (the number of control pulses)
Accordingly, the first and second phase advancing capacitors are further divided and configured.

(Operation) That is, when the number of output phases of the cycloconverter is three, the input side terminal of the positive group converter of each phase cycloconverter is connected to the common first phase advance capacitor, and the terminal is connected to the secondary of the power transformer. By connecting to the winding, the delay reactive component of the input current of the positive group converter for three phases and the first
The leading currents of the phase-advancing capacitors cancel each other out, and only effective power flows through the secondary winding of the power transformer. The input side of the negative group converter acts in the same manner, and as a result, the capacity of the power transformer can be significantly reduced.

At this time, the load of the cycloconverter is insulated for each phase to prevent a power supply short circuit.

When the number of control phases (the number of control pulses) of the cycloconverter increases, the first and second phase advancing capacitors can be further divided accordingly, and operation with a small output current ripple can be performed. Even in this case, the effect of reducing the capacity of the power transformer is the same.

(Embodiment) FIG. 1 is a configuration diagram showing an embodiment of a cycloconverter device of the present invention.

In the figure, SUP is a 3-phase AC power supply, MTR is a power transformer, CA
P ₁₁ and CAP ₁₂ are the first phase advancing capacitors, CAP ₂₁ and CAP ₂₂ are the second phase advancing capacitors, CC-U, CC-V and CC-W are circulating current type cycloconverters, and U, V and W are It is a three-phase AC load.

The U-phase cycloconverter CC-U is a positive group converter SSP _U ,
SDP _U and negative group converter SSN _U , SDN _U and DC reactor L _OU
(L _{OU1 to} L _OU5 ). The same applies to the V-phase and W-phase cycloconverters CC-V and CC-W.

CTs is a three-phase AC current detection transformer, PTs is a three-phase AC voltage detection transformer, VAR is a reactive power operation circuit, CT _U , CT _V , C
T _W is the output current detector, CT _PU , CT _NU , CT _PV , CT _NV , CT _PW , CT _NW
Is the output current detector of each converter.

FIG. 2 is a block diagram showing an embodiment of the control circuit of the apparatus shown in FIG.

In the figure, VRQ is a reactive power setting device, H _Q (s) is a reactive power control compensation circuit, G _OU (s), G _OV (s) and G _OW (s) are load current control compensation circuits, and G _U (s) ), G _V (s), G _W (s) are load current control compensation circuits, OC _{1 to} OC ₃ are circulating current calculation circuits, C _{1 to} C ₇
Is a comparator, A _{1 to} A ₆ are adders, and INV _{1 to} INV ₃ are inverting amplifiers, respectively.

The operation of the device of the present invention will be described below with reference to the embodiments shown in FIGS. 1 and 2.

First, the control operation of the load currents I _U , I _V , and I _W will be described. The U-phase cycloconverter CC-U will be described as an example.

The load current I _U detected by the current transformer CT _U, is input to a comparator C _3. The current detector I _U is compared with the command value I _U ^* by the comparator C ₃ , and the deviation ε _U = I _U ^* −I _U is obtained. The deviation ε _U is input to the next current control compensation circuit G _U (s) and amplified. One of the output signals of G _U (s) is input to the phase control circuit PHP _U of the positive group converters SSP _U and SDP _U via the adder A ₁ . The other one of the output signals of G _U (s) is the inverting amplifier IN.
Input to the phase control circuit PHN _U of the negative group converter SSN _U , SDN _U via V ₁ and adder A ₂ .

Now, assuming that the output signal from the circulating current control circuit G _OU (s) is sufficiently small and ignored, the above phase control circuit
The input signals vα _PU and vα _NU of PHP _U and PHN _U have the following relationship. However, G _U (s) is the proportional element K _U only.

vα _PU = ε _U · K _U vα _NU = −ε _U · K _U Also, assuming that the output voltage V _PU , V _NU of the positive group and negative group converters is positive in the direction of the arrow in FIG. Have a relationship.

V _PU = k _V · V _S · cos α _PU V _NU = −k _V · V _S · cos α _NU , where k _V is the conversion constant, V _S is the power supply voltage, and α _PU and α _NU are the positive and negative groups. It is a control phase angle of the converter.

Furthermore, since there is a relationship of cos α _PU = k · v α _PU and cos α _NU = k · v α _NU , V _PU = V _NU , and the control phase angle at this time has a relationship of α _NU = 180 ° −α _PU .

The voltage V _U applied to the load U is the average value of the output voltages V _PU and V _NU of the positive group and negative group converters.

_{V U = (V PU + V} NU) / 2 = k V · k · V S · ε U · K U i.e., the voltage V _U which is proportional to the current deviation epsilon _U is applied to the load.

When I _U ^* > I _U , the deviation ε _U has a positive value, and the output voltage V _U is increased, and the current I _U is increased, so that the deviation is finally controlled so that I _U ≈I _U ^* .

Conversely, when I _U ^* <I _U , the deviation ε _U becomes a negative value and V _U
To a negative value to reduce the current I _U and again I _U ≈ I _U ^*
When the current command value I _U ^* is changed in a sine wave shape, the actual current I _U is also controlled to a sine wave accordingly.

At this time, V _PU = V _NU is always satisfied, and the circulating current I _OU
There is no increase or decrease.

The V-phase and W-phase load currents _IV and _IW are controlled in the same manner.

Next, the control operation of the circulating currents I _OU , I _OV , and I _{OW will be explained} . Again, the U-phase cycloconverter CC-U will be described as an example.

The circulating current I _OU of the U-phase cycloconverter is the current transformer CT _PU
, And the output currents I _PU and I _NU of the positive group and negative group converters detected by CT _NU are input to the arithmetic circuit OC ₁ , and the following arithmetic operations are performed.

I _OU = (I _PU + I _NU − | (I _PU −I _NU ) |) / 2 where I _PU −I _NU = I _U.

In this way, the obtained circulating current detection value I _OU is input to the comparator C ₂ and compared with the circulating current command value I _O ^* _U. The deviation ε _OU = I _O ^* _U −I _OU is input to the current control compensation circuit G _OU (s) and amplified. The output signal of G _OU (s) is input to the phase control circuits PHP _U and PHN _U via adders A ₁ and A ₂ , respectively.

Therefore, the input signals vα _PU and vα _NU of the PHP _U and PHN _U are changed as follows. However, consider G _OU (s) = K _OU .

vα _PU = ε _U · K _U + ε _OU · K _OU vα _NU = −ε _U · K _U + ε _OU · K _OU Therefore, the output voltages V _PU and V _{NU of the} positive and negative group converters
_Causes the balance to be lost by the amount of ε _OU · K _OU , and increases or decreases the circulating current I _OU .

That is, when I _OU ^* > I _OU , the deviation ε _OU becomes a positive value, and V _PU > V _{NU correspondingly} . Therefore the circulating current I _OU
= I _OU ^* and calm down.

On the contrary, when I _OU ^* <I _OU , the deviation ε _OU becomes a negative value and V _PU <V _{NU accordingly} . Therefore, I _OU is reduced, and again, I _OU = I _O ^* _U is controlled.

The V-phase and W-phase circulating currents I _OV and I _OW are similarly controlled.

The circulating current command values I _O ^* _U , I _O ^* _V , and I _O ^* _W are given by the output signal from the reactive power control circuit H _Q (s).

Next, the operation of the reactive power control will be described. Yotsute in the installed current transformer CT _S and transformer PT _S in the receiving end of the cycloconverter, detects the three-phase alternating current and three-phase AC voltage, and inputs to the reactive power computing circuit VAR. The reactive power Q _S at the receiving end is
Phases of the power supply voltages v _R , v _S , and v _T are delayed by 90 °, and the phase currents i _R , i _S , and v _T are respectively multiplied and three phases are added to obtain. That is, Q _S = v _R ′ · i _R ＋ v _S ′ · i _S ＋ v _T ′ · i _T The instantaneous reactive power Q _S is detected by.

The reactive power detection value Q _S is input to the comparator C ₁ and compared with the command value Q _S ^* from the reactive power setter VRQ. The deviation ε _Q = Q _S ^*
-Q _S is input to the reactive power control compensation circuit H _Q (s) to perform integral amplification or proportional amplification. Normally, an integral element is used for H _Q (s) to make the steady deviation ε _Q zero.

The output signal of H _Q (s) becomes the command values I _O ^* _U , I _O ^* _V , and I _O ^* _W of the circulating current of the cycloconverter for each phase.

When Q _S ^* > Q _S , the deviation ε _Q becomes a positive value, and the circulating current command values I _O ^* _U , I _O ^* _V , and I _O ^* _W are increased. The actual circulating currents I _OU , I _OV , I _OW are, as described above, I _OU ≈ I _O ^* _U , I _OV ≈ I
Since the control is performed so that _O ^* _V , I _OW ≈ I _O ^* _W , the circulating currents I _OU , I _OV , and I _OW also increase, and the delayed reactive power Q _S at the receiving end is increased.
Is increased and Q _S becomes equal to Q _S ^* and calms down.

On the other hand, when Q _S ^* <Q _S , the deviation ε _Q becomes a negative value, and the circulating currents I _OU , I _OV , and I _OW of each phase are increased, and the delay reactive power Q _S at the receiving end is reduced, and It is controlled so that Q _S = Q _S ^* .

In this case, the reactive power detection value Q _S treats the delay as a positive value.

Further, in general, since the operation is performed with the input power factor = 1, the reactive power command value Q _S ^* is given as 0.

The cycloconverters CC-U, CC-V, and CCW use the power supply voltage for natural commutation, and therefore always take the delayed reactive power Q _CC . The delayed reactive power Q _CC depends on the values of the negative currents I _U , I _V , I _W , and the control phase angles α _PU , α _NU , α _PV , α _NV , α _PW , α _NW of the respective converters at that time. Although it changes depending on the value of, the circulating current of each phase cycloconverter as described above.
By adjusting I _OU , I _OV and I _OW , Q _CC can be _kept constant.

On the other hand, the phase advancing capacitors CAP ₁₁ , CAP ₁₂ , CAP ₂₁ , CA ₂₂ that are divided and connected to the secondary winding side of the power transformer MTR.
Takes a certain lead reactive power Q _cap , and the delayed reactive power Q
Only the active power P _S needs to be supplied from the power supply SUP by canceling out with _CC .

In the cycloconverter device of the present invention, CC-U
The input terminal of the positive group converter SSP _W positive group converter SSP _V and CC-W positive group converter SSP _U and CC-V, are connected to a common phase advancing capacitor CAP _11, leading reactive power of CAP _11
Sum of delayed reactive power of Q _cap11 and SSP _U , SSP _V and SSP _W Q _SSP1
Cancel each other out. At this time, Q _SSP1 can be expressed as the following equation.

Q _SSP1 ＝ k _Q (I _PU・ sinα _PU ＋ I _PU・ sinα _PV ＋ I _PW・ sinα
_PW ) However, k _Q is a proportional number When the loads U, V, W are armature windings of the AC motor, the speed electromotive force is small at startup and low speed operation, so the output voltage V _U , V _{V of the} cycloconverter , V _W is small and the control phase angle α _PU ≈ α _PV ≈ α _PW ≈ 90 ° is used for operation. At this time, the delayed reactive power Q _S taken by the cycloconverter becomes maximum and the circulating currents I _OU , I _OV , and I _OW become minimum values.

The phase advancing capacitors CAP ₁₁ , CAP ₁₂ ,, CAP ₂₁ , CAP ₂₂ are α _PU = α
_NU = α _PV = α _NV = α _PW = α _NW = 90 °, the load current
Q _cap = Q _cap11 + Q so as to cancel the delayed reactive power Q _CC of the cycloconverter when I _U , I _V , and I _W take the maximum value.
_{Prepare cap12} + Q _cap21 + Q _cap22 . Therefore Q _cap11 = Q _cap /
It becomes 4.

FIG. 3 shows the waveforms of the output currents I _OU , I _OV and I _OW of the positive group converters SSP _U , SSP _V and SSP _W and the delay reactive power Q _{SSP1 with} the circulating current I _OU = I _OV = I _OW ≈0. Represent. However, α _PU ≈ α
It is treated as _PV ≈ α _PW ≈ 0.

The delayed reactive power Q _{SDP1 of} the positive group converters SDP _U , SDP _V , SDP _W connected to the secondary line of the Δ result of the power transformer MTR is also the same. That is, Q _SDP1 = Q _SSP1 .

On the other hand, the output current I of the negative group converter SSN _U , SSN _V and SSN _W
NU , I _NV , I _NW are 180 ° out of phase with the current waveforms I _PU , I _PV and I _{PW in} Fig. 3, but the reactive power Q _SSN1 is Q _SSN1 = k _Q (I _NU · sinα _NU + I _NU・ Sinα _NV ＋ _INW・ sinα
_NW ) and the reactive power Q _SSN1 taken by the positive group converter
Matches

That is, Q _SSP1 = Q _SDP1 = Q _SSN1 = Q _SDN1 = Q _CC / 4. Phase-advancing capacitors CAP ₁₁ , CAP ₁₂ , CAP ₂₁ , CAP
_{If the} advance reactive power Q _cap taken by ₂₂ is prepared by the maximum value Q _CC (max) of the delayed reactive power Q _CC that can be taken by the cycloconverter, the circulating current I _OU , so that Q _CC = Q _cap is always maintained.
I _OV and I _OW flow, and Q _SSP1 = Q _cap11 is satisfied.

That is, the secondary side of the power transformer MTR, the reactive power Q _CAP11 and positive group converter SSP proceeds phase advancing capacitor CAP ₁₁ takes
_The delayed reactive power Q _SSP1 taken by _U , SSP _V , and SSP _W completely cancels each other, so that only the active current flows in the secondary winding of the transformer MTR.

The same applies to the other secondary windings.

The output terminals of the cycloconverters CC-U, CC-V, and CC-W are separated for each phase of the load, and short-circuit current does not flow even if the input side is shared.

The device of FIG. 1 has been described as a 12-pulse cycloconverter, but in a 6-pulse cycloconverter, it is sufficient to prepare the _first phase advance capacitor CAP ₁ and the second phase advance capacitor CAP _2. In the pulse cycloconverter, the first phase advancing capacitor is divided into four, and CAP ₁₁ , CAP ₁₂ ,
CAP ₁₃ and CAP ₁₄ are also used, and the second phase advancing capacitor is also divided into 4
₂₁ , CAP ₂₂ , CAP ₂₃ , and CAP ₂₄ may be used.

The apparatus of FIG. 1 has been described with respect to the circulating current type cycloconverter, but it goes without saying that the same can be applied to the power factor correction of the non-circulating current type cycloconverter.

〔The invention's effect〕

As described above, in the cycloconverter device of the present invention,
The secondary side of the power transformer MTR can completely cancel the reactive power, and it is possible to significantly reduce the capacity of the transformer. In particular, the current flowing through the secondary winding is only the effective current, and it is not necessary to increase the current capacity of the secondary winding as in the conventional device.

In addition, the number of power transformers is one-third that of conventional devices, and the cost can be reduced accordingly.

Furthermore, during light load operation, the current flowing through the power supply transformer is also reduced, and the loss is reduced accordingly, enabling efficient operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a cycloconverter device of the present invention, FIG. 2 is a block diagram showing an embodiment of a control circuit of the device of FIG. 1, and FIG. 3 is an operation of the device of FIG. FIG. 4 is a waveform diagram for explaining, FIG. 4 is a configuration diagram of a conventional cycloconverter device, and FIG. 5 is a waveform diagram for explaining the operation of the device of FIG. SUP… 3-phase AC power supply MTR… Power supply transformer CAP ₁₁ , CAP ₁₂ … First advance capacitor CAP ₂₁ , CAP ₂₂ … Second advance capacitor CC-U, CC-V, CC-W… Circulating current cyclone Converter U, V, W ... AC load SSP _U , SSP _U , SSP _W (Positive group converter) SDP _U , SDP _V , SDP _W (Positive group converter) SSN _U , SSN _V , SSN _W (Negative group converter) SDN _U , SDN _V, SDN _W (negative group converter) L _OU1 ~L _OU5 ... (DCR) L _OV1 ~L _OV5 ... (DCR) L _OW1 ~L _OW5 ... (DCR)

Claims (2)

[Claims] 1. A cycloconverter having an AC power supply, a load device insulated for each phase, a positive group converter and a negative group converter for supplying a current for each phase of the load device, and a cycloconverter of the cycloconverter. A first phase advancing capacitor connected to the input side common terminal of each phase positive group converter; a second phase advancing capacitor connected to the input side common terminal of each phase negative group converter of the cycloconverter; A cycloconverter device composed of a power supply and a power transformer interposed between the cycloconverter. 2. The cycloconverter device according to claim 1, wherein the first and second phase advancing capacitors are divided according to the number of control pulses of the cycloconverter.