JP3125354B2 - Active filter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an active filter which comprises power conversion means and compensates for reactive power and harmonics generated in a power system.

[0002]

2. Description of the Related Art FIG. 3 is a main circuit connection diagram showing a first example in which reactive power and harmonics generated in a power system are compensated by an active filter. In FIG. 3, a transformer 2 serving as an AC power supply supplies AC power to a load 4 via a bus 3, and if the load 4 is a rectifier circuit or an inductive load, etc. The power factor is reduced due to distortion or a reactive power source. Waveform distortion causes overheating, burnout, malfunction, and induction failure of communication lines and the like of power devices, and reduction in power factor causes increase in transmission loss and fluctuation of system voltage. Conventionally, a so-called LC filter composed of a capacitor and a reactor has been used. However, if the suppression effect changes due to the system impedance or the frequency of the harmonics fluctuates, the suppression capability is affected, and furthermore, it is excessive. There have been various inconveniences such as the LC filter itself being burned out by the load.

[0003] On the other hand, if the excellent control characteristics of a power converter composed of semiconductor switch elements are used,
It is also possible to eliminate the above-mentioned drawbacks of the LC filter and generate a current that cancels out only unnecessary harmonic currents.
Such a device that compensates for a harmonic current in a power converter using a semiconductor switching element is called an active filter. In FIG. 3, the active filter 5 as the power conversion means is connected to the output side of the transformer 2. A capacitor 6 is connected to the DC side of the active filter 5,
Further, a control device 7 for controlling the active filter 5 is attached. It connects the instrument transformer 9 for detecting the current transformer 8 and the power supply voltage V _S for detecting the load current I _L between the transformer 2 and the bus 3, the control device 7 and a power supply voltage V _S to be input to the load current I _L to detect the power factor of the harmonic currents and the load, to compensate for these compensation current I
_The active filter 5 outputs _C.

FIG. 4 is a main circuit connection diagram showing a second example in which reactive power and harmonics generated in a power system are compensated by an active filter. In an urban area, in order to reduce the occupied area of the substation, the transformer 2 and the bus 3 are often insulated with gas or solid and integrated with each other. Only the current transformer 8 is connected between the transformer 2 and the bus 3 and the active filter 5
Is difficult to connect, and the circuit configuration shown in FIG. 4 is often used. That is, the active filter 5 as power conversion means is connected in parallel with the load 4 via the bus 3, so that the power supply current I _S and the power supply voltage V _S are input to the control device 7 for controlling the active filter 5. , so that the active filter 5 outputs the compensation current I _C.

FIG. 5 is a circuit diagram showing a conventional example of a control device for an active filter. As shown in FIG. 5, the power supply current I _S having waveform distortion is input to the fundamental wave operation circuit 13, where the fundamental wave current component I _S0 of the power supply current I _S is calculated. The fundamental wave current I _S0 and the power supply current I _S that are the result of this calculation
Is a harmonic current, the current controller 14 outputs a control signal that makes the harmonic current zero. On the other hand the voltage regulator 11 outputs a control signal to match the voltage E _D of the DC-side voltage detection value or the capacitor 6 of the active filter 5 to the voltage command value E _D0, the multiplier 12
The output signal of the voltage regulator 11 is multiplied by the power supply voltage V _S to obtain an AC current command value, and the AC current command value is compensated for the fundamental wave current I _S0 by the loss of the active filter 5. Add by polarity. The comparator 16 performs pulse width modulation on the output signal of the current regulator 14 and the carrier signal output from the carrier oscillator 15 to control the active filter 5.

FIG. 6 is a circuit diagram showing the configuration of the fundamental wave operation circuit 13 used in the control device shown in FIG. In this circuit, I _U, I _{V, and} I _W are phase currents of the power supply current I _S , ω _mt is a phase signal of a desired harmonic, and these are input to each of the desired harmonics. The phase currents I _Um , I _Vm ,
I _Wm can be obtained. Therefore, if m = 1, the fundamental wave current of each phase can be obtained. Since the circuit shown in FIG. 6 is known, the description of its operation is omitted.

[0007]

As described above, unlike the first circuit shown in FIG. 3, the second circuit shown in FIG. 4 is a circuit for controlling a closed loop for performing positive compensation. For example, if there is an error in the operation of the fundamental wave operation circuit 13, an error occurs in the control command system, and this is detected and fed back, so that there is a disadvantage that the error is enlarged.

FIG. 7 is an operation waveform diagram illustrating the operation when the calculation error is on the lag phase side when the control circuit shown in FIG. 5 is applied to the second circuit shown in FIG. 7 shows a change in the fundamental wave current I _S0 , FIG. 7 shows a change in the fundamental wave current effective component I _P0 , and FIG. 7 shows a change in the fundamental wave current invalid component I _Q0 . That is, the fundamental wave current I _S0 shown in FIG. 7 can be decomposed into the fundamental wave current effective component I _P0 shown in FIG. 7 and the fundamental wave current invalid component I _Q0 shown in FIG. Here, when the phase of the fundamental wave current I _S0 is delayed by Δθ due to a calculation error, the fundamental wave current effective component I _P0 correspondingly decreases to I _P1 (see FIG. 7), and the fundamental wave current invalid component I _Q0 becomes Increase to _IQ1 (see FIG. 7). That is, since the control is performed so that the effective component decreases, the active filter 5 supplies the insufficient effective component to the load 4. However the DC side voltage E _D of the active filter 5 by the active filter 5 supplies the active component is lowered.
So taking the active component from the power supply side to maintain the dc side voltage E _D the command value E _D0, even if calculation error active component is eventually balanced. On the other hand, the ineffective portion increases as a result of the control, and this becomes the command value again. Therefore, the positive feedback is applied, the command value changes more and more in the delay direction, and the command value oscillates from the maximum value of the delay to the maximum value of the advance. Therefore, the device stops due to the overcurrent.

FIG. 8 is an operation waveform diagram illustrating the operation when the control error shown in FIG. 5 is applied to the second circuit shown in FIG. 8 shows a change in the fundamental wave current I _S0 , FIG. 8 shows a change in the fundamental wave current effective component I _P0 , and FIG. 8 shows a change in the fundamental wave current ineffective component I _Q0 . That is, the fundamental wave current I _S0 shown in FIG. 8 can be decomposed into the fundamental wave current effective component I _P0 shown in FIG. 8 and the fundamental wave current invalid component I _Q0 shown in FIG. Here, when the phase of the fundamental wave current I _S0 advances by Δθ due to a calculation error, the fundamental wave current effective component I _P0 correspondingly increases to I _P2 (see FIG. 8), and the fundamental wave current invalid component I _Q0 becomes It decreases to _IQ2 (see FIG. 8). That is, since the control is performed so that the effective component is increased, the active filter 5 takes this effective component from the power supply side. This becomes a rise of the DC side voltage E _D, but will compete with operation of the voltage regulator 11 in a conventional example circuit shown in FIG. 5,
DC-side voltage E _D from the difference of the control constant becomes overvoltage device would stop. On the other hand, the ineffective portion decreases and changes the command value in the forward direction, and this further increases the effective portion.

As described above, when the control of the active filter 5 is controlled by detecting the current flowing on the power supply side of the active filter 5 (see FIG. 4), if there is a calculation error, the error is reduced. Positive feedback occurs, resulting in an overcurrent or overvoltage, resulting in inconvenience of stopping the apparatus.

Therefore, an object of the present invention is to control the active filter with a current on the power supply side rather than the active filter, and to perform a stable compensation operation without causing abnormalities such as overcurrent and overvoltage even if there is a calculation error. To be able to do it.

[0012]

In order to achieve the above object, a control device according to the present invention connects a parallel circuit of a power converter and a load, which are constituted by semiconductor switch elements, to an AC power supply, and outputs the AC power supply. The fundamental wave component of the current is calculated by the fundamental wave calculating means, and the difference between the fundamental wave component and the AC power supply output current is calculated, while the voltage adjusting means for maintaining the DC voltage of the power converting means at a predetermined voltage. The output signal is multiplied by the output voltage of the AC power supply to obtain an AC current command value, and the AC current command value is converted to a difference between the fundamental wave component and the AC power output current to compensate for the loss of the power conversion means. And the added value is input to the current adjusting means, and the current adjusting means outputs a control signal such that the output current of the power conversion means matches the fundamental wave component. In the apparatus, adding means for adding the output signal of the voltage adjusting means directly or via the level determining means having set a dead zone to the AC power supply voltage, and detecting a zero point of the output signal of the adding means to generate a phase reference signal. And a phase reference signal generating means for outputting the phase reference signal to the fundamental wave calculating means.

[0013]

According to the present invention, an abnormality that occurs in an active filter due to a calculation error is captured by a change in the level of a DC voltage control system of the active filter. When the change in the command value due to the error is on the leading phase side, the error is corrected appropriately, so that the abnormal operation or stop of the active filter due to overvoltage or overcurrent is appropriately performed. In order to avoid the error, the DC voltage control signal is supplied to the phase reference of the fundamental wave operation circuit directly or through the level conversion means, thereby canceling the error.

[0014]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. The voltage regulator 11 and the multiplier 1 shown in FIG.
2. The names, applications, and functions of the fundamental wave operation circuit 13, the current regulator 14, the carrier oscillator 15, and the comparator 16 are the same as those of the conventional circuit described above with reference to FIG. .

In FIG. 1, the result of multiplying the output signal of the voltage regulator 11 by the power supply voltage V _S is used as an effective component command given to the active filter 5 to compensate for the loss of the active filter 5. The output signal of the circuit 13 is added, but the output signal of the voltage regulator 11 and the power supply voltage V _S are added in the adder 21 to change the zero cross point of the power supply voltage V _S. The effective amount is decreased when the calculation error as described above is delayed in phase side DC side voltage E _D of the active filter 5 decreases, so as to maintain a reduced dc side voltage E _D to the command value E _D0 The output signal of the voltage regulator 11 increases, and the phase reference signal generating means including the zero point detection comparator 22, the monostable circuit 23, and the counter 24 basically uses the phase signal ω _mt to change the reference phase in the leading direction. Output to the wave operation circuit 13. When the calculation error is on the leading phase side, the phase signal ω _mt for correcting the leading phase in the lagging direction is changed to the zero point detection comparator 22 by the operation opposite to the above.
And a phase reference signal generating means composed of a monostable circuit 23 and a counter 24 to output the fundamental wave operation circuit 13.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. In the circuit of the second embodiment, the output signal of the voltage regulator 11 is added via a level discriminating means 31 for setting a dead zone. 1 is different from the circuit of the first embodiment described above with reference to FIG.
Is the same as the circuit of the first embodiment described above. That is, in the circuit of the second embodiment, the phase is corrected only when the output signal of the voltage regulator 11 exceeds the dead zone range set in the level determining means 31.

[0017]

When an active filter as power conversion means is connected to a power system and the reactive power and harmonic current of the power system are compensated by the current detected from the power supply side of the active filter, the operation of the arithmetic unit is required. When the current shifts to the lagging phase or the leading phase due to a slight calculation error or the like, the shift may be enlarged due to the positive feedback operation, and the device may eventually stop due to overcurrent or overvoltage. ,
According to the present invention, the fact that the current has shifted to the lagging phase side or the leading phase side is detected from a change in the voltage adjustment means output signal of the DC side voltage control system which controls the DC side voltage of the active filter. The output signal of the adjusting means is supplied to the phase reference signal generating means directly or through the level converting means, and the fundamental wave operation circuit is controlled by the phase signal output from the phase reference signal generating means. Since an abnormal operation or stop of the active filter can be avoided due to the error, an effect of stably performing a harmonic and reactive power compensation operation in the power system can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a main circuit connection diagram showing a first example of compensating reactive power and harmonics generated in a power system with an active filter.

FIG. 4 is a main circuit connection diagram showing a second example of compensating reactive power and harmonics generated in a power system with an active filter.

FIG. 5 is a circuit diagram showing a conventional example of a control device for an active filter.

6 is a circuit diagram showing a configuration of a fundamental wave operation circuit 13 used in the control device shown in FIG.

FIG. 7 shows the control circuit shown in FIG.
Operation waveform diagram illustrating the operation when the calculation error is on the lag phase side when applied to the circuit of FIG.

FIG. 8 shows a control circuit shown in FIG.
Operation waveform diagram illustrating the operation when the calculation error is advanced and the phase is on the phase side when applied to the circuit of FIG.

[Explanation of symbols]

2 Transformer 3 Bus 4 Load 5 Active filter as power conversion means 6 Capacitor 7 Controller 11 Voltage regulator 12 Multiplier 13 Fundamental wave operation circuit 14 Current regulator 15 Carrier oscillator 16 Comparator 21 Adder 22 Zero point detection comparator 23 Monos level determination means sets the table circuit 24 the counter 31 the dead zone E _D DC side voltage I _C the compensation current I _L the load current I _P0 fundamental current active component I _Q0 fundamental current reactive component I _S power supply current I _S0 fundamental current V _S Power-supply voltage

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J 3/01 H02J 3/18

Claims (2)

(57) [Claims] 1. A parallel circuit of a power conversion means and a load comprising a semiconductor switch element is connected to an AC power supply, and a fundamental wave component of the output current of the AC power supply is calculated by a fundamental wave calculation means. While calculating the difference between the AC power supply output current and the AC power command output value by multiplying the output signal of the AC power supply by the output signal of the voltage adjustment means for maintaining the DC voltage of the power conversion means at a predetermined voltage. This AC current command value is added to the difference between the fundamental wave component and the AC power supply output current with a polarity that compensates for the loss of the power conversion means, and the added value is input to the current adjustment means, In an active filter control device configured to output a control signal such that the output current of the power conversion unit matches the fundamental wave component, the output signal of the voltage adjustment unit and the AC power supply voltage are Active means for detecting the zero point of the output signal of the adding means and outputting a phase reference signal, and providing the phase reference signal to the fundamental wave calculating means. Filter control device. 2. A parallel circuit of a power conversion means and a load comprising a semiconductor switch element is connected to an AC power supply, and a fundamental wave component of the AC power supply output current is calculated by a fundamental wave calculation means. While calculating the difference between the AC power supply output current and the AC power command output value by multiplying the output signal of the AC power supply by the output signal of the voltage adjustment means for maintaining the DC voltage of the power conversion means at a predetermined voltage. This AC current command value is added to the difference between the fundamental wave component and the AC power supply output current with a polarity that compensates for the loss of the power conversion means, and the added value is input to the current adjustment means, In an active filter control device that outputs a control signal such that the output current of the power conversion means matches the fundamental wave component, the level of the output signal of the voltage adjustment means is set to a predetermined level. Level discriminating means for passing the output voltage only when the output voltage is outside the band range, adding means for adding the output signal of the level discriminating means and the AC power supply voltage, and detecting the zero point of the output signal of the adding means to determine the phase. A control device for an active filter, comprising: a phase reference signal generating means for outputting a reference signal; and providing the phase reference signal to the fundamental wave calculating means.