JPH0568944B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a reactive power control type cycloconverter that can supply variable voltage, variable frequency alternating current power to a load, and can arbitrarily control reactive power using circulating current. This invention relates to a cycloconverter device that operates in parallel with a phase advance capacitor.

[Technical background of the invention and its problems] FIG. 1 shows an example of a conventional reactive power control type cycloconverter operated in parallel with a phase advance capacitor.

In Figure 1, BUS is a three-phase AC power supply bus, and the input transformer is passed through the main power switch MS.
In addition to supplying three-phase power to the TR, it is further connected to the phase advance capacitor CAP via the input switch SW.

Cycloconverter CC is positive group converter SSP,
Negative group converter SSN and DC reactor L ₀₁ ,
_L02 converts the three-phase power supplied via the power transformer TR into variable voltage variable frequency power and supplies it to the load LOAD.

The control circuit includes a transformer _PTS and current transformer _CTS that detect the receiving voltage and current, a reactive power detector VAR, converter output currents I _P and I _N , and a load current.
Current transformers CT _P , CT _N , CT _L that detect I _L , comparators C ₁ , C ₂ , C ₃ , adders A ₁ , A ₂ , and control compensation circuit
G _L , G _O , H _Q , inverting amplifier OA, phase control circuit PH
-P and PH-N are available.

First, the load current I _L is controlled as follows.

That is, the load current detection value I _L and its command value I _L ^* are compared by the comparator C ₁ , and the deviation ε ₁ =I _L ^* −I _L is input to the next control compensation circuit _GL .

The control compensation circuit G _L is designed taking into account the stability or responsiveness of the control system, but for the sake of simplicity, only a proportional element (amplification factor K ₁ times) will be explained here.

The above deviation ε ₁ is multiplied by K ₁ , one is input to the phase control circuit PH-P of the positive group converter via the adder A ₁ , and the other is input to the inverting amplifier (amplification factor 1).
It is inverted at OA and input to the phase control circuit PH-N of the negative group converter via the adder _A2 .

Here, assuming that the output signal from the control compensation circuit G _O of the circulating current control system is sufficiently small, the firing phase angle α _N of the negative group converter SSN is compared to the firing phase angle α _P of the positive group converter SSP. is α _N =180°−α _P , and the output voltages V _P and V _N of both converters are as follows. However, V _S is the power supply voltage and k _V is the conversion constant.

V _P =k _V・V _S・cosα _P ……(1) V _N =−k _V・V _S・cosα _N =−k _V・V _S・cos(180°−α _P ) =V _P ……( 2) i.e. the output voltages V _P and V _N of both converters
match, and the voltage V _P −V _N applied to the DC reactors L ₀₁ and L ₀₂ becomes zero (actually, only the ripple of the output voltage is applied, but to simplify the explanation, we ignore this ripple) ), so almost no circulating current I _O flows.

The average value (V _P +V _N )/2 of the output voltages V _P and V _N is applied to the load terminal, and the load current I _L is controlled by controlling the average value.

When I _L ^* > I _L , the deviation ε ₁ becomes a positive value,
After being multiplied by K ₁ , K ₁ ·ε ₁ is input to the phase control circuit PH-P, and -K ₁ ·ε ₁ is input to the phase control circuit PH-N.

As a result, the output voltages V _P and V _N of the converter increase in the direction of the arrow in the figure, and their average value (V _P +V _N )/
2, thereby controlling the load current I _L to increase in the direction of the arrow so that I _L =I _L ^* .

Conversely, when I _L ^* < I _L , it is controlled in the same way,
The load current I _L is always controlled to match the command value I _L ^* .

When the load current command value I _L ^* is changed in a sinusoidal manner, the actual load current I _L follows it and becomes a sinusoidal current.

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

The circulating current I _O can be determined from the detected values of the positive group converter output current I _P , the negative group converter output current I _N and the load current I _L by performing the following calculation.

I _O = (I _P + I _N − | I _L |)/2 ... (3) Here, | I _L | is the absolute value of I _L.

Comparator C ₃ compares the circulating current detector I _O and its command value I _O ^* , and calculates the deviation ε ₃ = I _O ^* − I _O by the following control compensation circuit G _O (for simplicity, the amplification factor K is a proportional factor of ₂ ). Furthermore, the control compensation circuit G _O
When the output signals K ₂ and ε ₃ are input to the adders A ₁ and A ₂ , the inputs vα _P and vα _N of the phase control circuits PH-P and PH-N are as shown in the following equations.

vα _P ＝K ₁・ε ₁ +K ₂・ε ₃ ...(4) vα _N ＝K ₁・ε ₁ +K ₂・ε ₃ ...(5) Therefore, the above K ₂・ε ₃ increases the cost of both converters. The output voltage becomes unbalanced, and V _P ≠ V _N.

When I _O ^* > I _O , the deviation ε ₃ = I _O ^* − I _O becomes a positive value, and V _P > V _N , and a differential voltage V _P − V _N is applied to DC reactors L ₀₁ and L _02. being used to increase the circulating current _IO .

Conversely, when I _O ^* < I _O , ε ₃ becomes a negative value, V _P < V _N , and the circulating current I _O decreases, and finally I _O = I _O ^* . calm down.

Although the output voltages V _P and V _N of both converters change with the circulating current control, the voltage applied to the load (V _P +V _N )/2 is not affected, and the load current control is performed as described above. be exposed.

Next, reactive power control at the power receiving end of the cycloconverter will be explained.

Since a phase advancing capacitor CAP that takes a certain amount of leading reactive power is connected to the power receiving end, if the lagging reactive power taken by the cycloconverter CC is controlled to be equal to the leading reactive power mentioned above, the input fundamental wave power factor will always be the same. 1, and only active power is supplied from the power supply.

First, the voltage and current at the receiving end are detected by the transformer PT _S and current transformer CT _S , and the reactive power detector
Find the reactive power Q at the receiving end using VAR.

The reactive power detection value Q and its command value Q ^* are compared by the comparator _C2 , and the deviation _ε2 =Q ^* -Q is input to the next control compensation circuit _HQ .

An integral element is used as the control compensation circuit H _Q ,
Control is performed so that the steady-state component of the deviation ε ₂ becomes zero.

The output I _O ^* of the control compensation circuit H _Q becomes the command value of the circulating current I _O.

When viewed from the power supply side, the circulating current I _O of the cycloconverter CC always appears as delayed reactive power without affecting the active power component. Therefore, by controlling the circulating current I _O , the reactive power at the receiving end can be Power Q can be controlled.

Normally, the reactive power command value Q ^* at the receiving end is set to zero, but in some cases it may be set to a leading or lagging power factor. Note that the reactive power detection value Q will be described here assuming that the delay is a positive value.

When Q ^* > Q, the deviation ε ₂ = Q ^* −Q becomes a positive value, and the command value of the circulating current is determined via the control compensation circuit H _Q.
Increase I _O ^* .

Since the circulating current I _O is controlled to match the command value I _O ^* , the delayed reactive power taken by the cycloconverter CC increases, and the delayed reactive power Q at the receiving end increases.
increase.

Conversely, when Q ^* < Q, the deviation ε ₂ becomes a negative value, reducing the circulating current I _O = I _O ^* , reducing the delayed reactive power taken by the cycloconverter CC, and finally Q = Q ^* I feel calm.

If the reactive power command value Q ^* is set to zero, Q = 0.
Therefore, the fundamental wave power factor at the power receiving end can always be kept at 1.

As described above, the conventional reactive power control type cycloconverter supplies variable voltage, variable frequency AC power to the load while always keeping the fundamental wave power factor at the receiving end at 1 by connecting phase advance capacitors in parallel. However, the phase advance capacitor must have a capacity equivalent to the input KVA of the cycloconverter, and a large inrush current flows when the phase advance capacitor is turned on.

Although a series reactor is inserted in the phase advance capacitor to suppress inrush current, there is still an inrush current that is about three times the advance current in steady state.

It is possible to suppress the inrush current of the power supply by starting the cycloconverter and turning on the phase advance capacitor after the lagging current flows, but it is possible to suppress the inrush current of the power supply.
In the control circuit shown in the figure, since the control compensation circuit H _Q includes an integral element, there is a time delay from when the phase advance capacitor is turned on until the delayed current flows to the cycloconverter. cannot be suppressed sufficiently.

In other words, in Figure 1, the phase advance capacitor
Before CAP is turned on, Q is delayed reactive power (Q > 0) due to the excitation current of input transformer TR, and if reactive current command value Q ^* is set to zero, deviation ε ₂
becomes negative, and the output I _O ^* of H _Q has a negative saturation value as shown by the solid line in FIG.

This causes an operation to reduce the circulating current I _O , but since the circulating current I _O cannot become negative, I _O becomes I _O = 0 as shown by the solid line in Fig. 4, and is removed from the power supply. The input current I _S (leading current is indicated by + and lagging current is indicated by -) is a lagging current corresponding to the excitation current of the input transformer TR.

In this state, when the closing switch SW is turned on at time _t1 , a large advance current I _CAP flows through the phase advance capacitor CAP.

As a result, the output Q of the VAR becomes negative, the deviation ε ₂ becomes positive, and the circulating current command value I _O ^* also changes in the positive direction.

However, since the control compensation circuit H _Q includes an integral element, it takes time △t for I _O ^* to reach the required positive command value from the negative saturation value, so that the circulating current I Since _O also rises after time t has elapsed, the leading current I _CAP of the inrushed capacitor
Therefore, the input current I _S from the power supply becomes an excessive inrush current, which causes a problem in the power supply system and power equipment.

[Object of the Invention] The present invention is a reactive power control type cycloconverter that improves the power factor of a power supply by connecting phase advance capacitors in parallel, and which speeds up the rise of reactive power when the phase advance capacitor is turned on to reduce the inrush current of the power supply. It is an object of the present invention to provide a reactive power control type cycloconverter device equipped with a starting circuit that suppresses reactive power.

[Summary of the Invention] The present invention operates a reactive power control type cycloconverter in parallel with a phase advance capacitor, which supplies variable voltage variable frequency AC power to a load and can arbitrarily control delayed reactive power using a circulating current. In a cyclo-converter device that improves the power reception rate by using a cycloconverter, a circulating current control starting circuit is provided that starts the circulating current control operation in synchronization with the input of the phase advance capacitor. By accelerating the rise, the leading current to the phase advance capacitor is quickly compensated for by reactive power, suppressing the rush current from the power supply and improving the power factor of the power supply.

[Embodiments of the invention] An embodiment of the present invention is shown in FIG.

Figure 2 shows the phase advance capacitor current compared to Figure 1.
A current transformer CT _C that detects I _CAP and an analog switch circuit H _IC that converts its analog output to contact operation are added, and the above contact constantly shorts the integrating capacitor in the control compensation circuit H _Q. At the same time, the short circuit of the capacitor is released by contact operation to start the control operation, and the other aspects are the same as in FIG.

Details of the above starting circuit are shown in FIG.

In other words, the output of current transformer CT _C consisting of current transformers CT _r , CT _s , CT _t for each phase is the rectifier for each phase.
Absolute current value at ABS _r , ABS _s , ABS _t |I _rc |, |I _sc
|, |I _tc | and added by adder B1,
The output operates the analog switch and opens contact SW _a .

Contact SW _a is inserted in parallel between the input and output of the operational amplifier OP of the control compensation circuit _HQ and always shorts the integration capacitor C, so before the phase advance capacitor CAP is turned on (before time t ₁ ) is the output of H _Q I _O ^* is the fourth
It is zero as shown by the dotted line in the figure.

When the phase advance capacitor CAP is turned on at time _t1 and the capacitor current I _CAP rises, the analog switch circuit
Since HI _C operates and opens contact SW _a , the short circuit of integrating capacitor C is released, control compensation circuit H _Q starts control operation, and I _O ^* changes from zero to the required value as shown by the dotted line in Figure 4. starts to rise immediately from time t ₁ , thereby increasing the circulating current of the cycloconverter
I _O also rises immediately from time t ₁ as shown by the dotted line, so the capacitor current I _CAP is immediately compensated by the circulating current I _O of the cycloconverter, and the power supply input current
I _S also attenuates immediately from the inrush current as shown by the dotted line.

This suppresses the inrush of power supply current when the phase advance capacitor is turned on, and the input fundamental wave power factor is immediately controlled to 1.

In FIG. 2, the turning on of the phase advance capacitor is detected by the capacitor current I _CAP , but it can also be detected directly from the operation of the turning on switch.

[Effects of the Invention] As explained above, according to the present invention, in a reactive power control type cycloconverter that improves the power factor of a power supply by connecting phase advance capacitors in parallel, the reactive power is Since the integral operation of the corresponding circulating current control circuit is stopped and started at the same time as the phase advance capacitor is turned on, there is no time delay in the rise of the circulating current, and this reduces the inrush current of the phase advance capacitor. It is possible to immediately compensate for the lead current caused by the power supply, thereby suppressing the inrush power from the power supply, and to immediately bring the power factor of the power supply to 1, thereby making it possible to start up smoothly without adversely affecting the power supply system.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a row of conventional reactive power control type cycloconverters operated in parallel with a phase advance capacitor, FIG. 2 is a system diagram showing an embodiment of the present invention, and FIG. FIG. 4 is a circuit diagram showing details around the analog switch circuit, and a time chart showing the operation of the present invention in comparison with a conventional case. BUS...Power bus, MS...Main power switch,
TR...Input transformer, CC...Cycloconverter, LOAD...Load, CAP...Phase advance capacitor,
SW……Phase advance capacitor input switch, VAR…
...Reactive power detector, HI _C ...Analog switch circuit, G _L , G _O , H _Q ... Control compensation circuit.

Claims (1)

[Claims] 1 A cycloconverter that improves the power reception rate by operating a reactive power control type cycloconverter in parallel with a phase advance capacitor, which can supply variable voltage and variable frequency alternating current power to the load and arbitrarily control delayed reactive power using circulating current. A cycloconverter device characterized in that the converter device includes a circulating current control starting circuit that starts the circulating current control operation in synchronization with the input of the phase advance capacitor.