JP2001136663A - Method of controlling self-excited system compensation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of controlling a self-excited system compensation device capable of improving its operating reliability, which compensates for reactive power and higher harmonic generated at a power system. SOLUTION: A compensation amount computing circuit 30 is inserted in a conventional self-excited system compensation device. The compensation amount computing circuit 30 monitors the ripple component of the voltage across a DC side capacitor 9 of a voltage type inverter 8 and restrains, the increase if the ripple component increases higher than its predetermined level, thereby preventing the voltage type inverter 8 from being broken by overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage type inverter in which the AC side is connected to a power system via an AC reactor, and the voltage type inverter compensates for reactive power and harmonics from a load on the power system. The present invention relates to a control method of an excitation type system compensation device.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a conventional example of this type of self-excited system compensator.

In FIG. 7, reference numeral 1 denotes a power system such as a commercial power supply or a private power generation facility; 2, a load of the power system 1;
CT, 4 for detecting the voltage of the power system 1, PT for detecting the voltage of the power system 1, 5 for a circuit breaker inserted between the self-excited system compensator described later and the power system 1, and 6 for an AC reactor 7 CT for detecting the current between the voltage-source inverter 8 and the power system 1, 9 is a capacitor connected to the DC side of the voltage-source inverter 8, and 11 is a three-phase to two-phase detection current of three phases from CT 3. conversion, extracts the compensation amount I _q of the converted compensation amount I _d and reactive power components of the active power component of current flowing coordinate transformation to the load 2 based on the detection voltage of the three phases of the detected current from PT4 was Compensation component extraction circuit, 12 is a DC voltage setting device for setting the voltage across capacitor 9, 13 is a DC voltage detector for detecting the voltage across capacitor 9, 14 is the set value of DC voltage setting device 12 and the DC voltage detector Adjust the deviation from the detected value of 13. In order to obtain the fundamental wave current signal I _d1 , a voltage adjuster comprising an adder 14a and an adjuster 14b is combined. The voltage adjuster 15 combines the compensation amount I _d and the fundamental wave current signal I _d1 to obtain the compensation amount I _d1. adders obtaining _d2, 16 is a coordinate conversion based on the detection voltage of the three phases from PT4 and the compensation amount I _q and I _d2, the coordinate transformation values further two phases - converting three-phase phase current command calculation circuit for obtaining a compensation current command value _{I r1, I s1, I t1} , 17 is an output rated voltage source inverter 8 along with compensation operation based on either the instantaneous value of the compensation current command value of the phase An output capacity limiting circuit for calculating a limit value for limiting the voltage-type inverter so as not to exceed the output rating; Current command values _Ir2 , I
A multiplying operation unit that outputs _t2 , 19 is the compensation current command value I
_r2, by adjusting operation of the deviation between the detected current at the I _t2 and CT6 current regulator to obtain a phase compensation voltage command value, 20 the voltage inverter synthesizes the detection voltage of said compensation voltage command value and PT4 8, an adder 21 for obtaining an output voltage command value to the pulse width modulation (PW) based on the output voltage command value of each phase.
M) A PWM operation circuit that performs an operation and generates a drive signal to each of the self-extinguishing elements forming the voltage source inverter 8.

In the self-excited system compensator shown in FIG. 7, a potential difference between the voltage of the power system 1 and the output voltage of the voltage source inverter 8 is applied to the AC reactor 7, and a current based on this potential difference is detected by CT6. An adjustment operation is performed to match the detected value with a compensation current command value derived from a compensation amount based on the active power component, the reactive power component, the negative phase component, and the like of the load 2 extracted by the compensation component extraction circuit 11. The adjustment operation compensates for reactive power, harmonics, flicker, and the like from the load 8 to the power system 1 based on required specifications.

[0005]

It is known that voltage flicker occurs in the power system 1 when an arc furnace facility is installed as the load 2 of the power system 1 and the arc furnace facility is operating.

In the self-commutated system compensator shown in FIG. 7, the above-described voltage is calculated based on the compensation amounts of the reactive power component and the active power component of the load 2 (arc furnace equipment) as the compensation amounts extracted by the compensation component extraction circuit 11. In order to more effectively compensate for flicker, the reactive power component and the variation of the active power component are used as new compensation amounts.

However, in order to compensate for the fluctuation of the active power, the ripple component of the voltage between both ends of the capacitor 9 increases, and as a result, the output voltage of the voltage source inverter 8 becomes equal to the output voltage command output by the adder 20. The value could not follow the value, and the voltage-source inverter 8 could be damaged by overcurrent.

When an inductive load is installed as the load 2 of the power system 1, the compensation component extraction circuit 11 extracts the reactive power component and the active power component of the load 2 (inductive load) as the compensation amount. From the amount of compensation, it is effective to mainly set the steady-state component of the reactive power component as a new compensation amount. Therefore, the voltage-source inverter 8 outputs a leading phase reactive power, thereby Compensation is performed by the excitation system compensator.

However, when the system impedance is large due to, for example, the power system 1 being formed by private power generation equipment, the voltage at the interconnection point becomes higher than the rated value due to the leading reactive power output from the voltage type inverter 8. There was fear.

Further, as the voltage at the interconnection point rises, P
The output voltage command value output from the addition calculator 20 via T4 increases, the PWM calculation operation in the PWM calculation circuit 21 is limited, and the output voltage of the voltage source inverter 8 is distorted. Or an undesirable non-theoretical harmonic current may flow through the load 2.

An object of the present invention is to provide a control method of a self-commutated system compensator which solves the above-mentioned problems.

[0012]

According to a first aspect of the present invention, a capacitor is provided on a DC side, and an AC side of a voltage type inverter using the capacitor as a voltage source is connected to a power system via an AC reactor. The voltage-source inverter performs an operation of matching a current generated by a potential difference between both ends of the reactor with a compensation current command value. In the control method, a ripple component included in a voltage between both ends of the capacitor is monitored, and when the ripple component exceeds a predetermined value, a compensation amount for a variation in an active power component of the load is limited. I do.

According to a second aspect of the present invention, a capacitor is provided on a DC side, and an AC side of a voltage source inverter using the capacitor as a voltage source is connected to a power system via an AC reactor, and a potential difference between both ends of the AC reactor is obtained. In the control method of the self-excited system compensator for compensating reactive power and harmonics from a load on the power system, the voltage-source inverter performs an operation of matching the generated current with a compensation current command value. The instantaneous value of the output voltage command value to the inverter is monitored, and when the instantaneous value exceeds a predetermined value, the amount of compensation for the steady portion of the reactive power component of the load is limited.

According to the first aspect, the increase in the ripple component of the voltage between both ends of the capacitor is detected, and the amount of compensation for the fluctuation of the active power component of the load is set to a limited value, and the increase in the ripple component is reduced. Since the followability of the voltage-source inverter is maintained by suppressing the voltage-source inverter, it is possible to prevent the voltage-source inverter from becoming overcurrent.

According to the second aspect of the present invention, an increase in the amplitude of the output voltage command value is detected, and the compensation amount for the steady portion of the reactive power component of the load is set to a limited value. Since the voltage-type inverter is operated while suppressing the increase, the output voltage of the voltage-type inverter can be prevented from being distorted.

[0016]

FIG. 1 is a circuit diagram of a self-excited system compensator according to a first embodiment of the present invention. The circuit having the same functions as those of the conventional circuit shown in FIG. The description is omitted by attaching the reference numerals.

That is, in the self-excited system compensator shown in FIG. 1, a compensation amount calculating circuit 30 using the output of the adding section 14a of the voltage regulator 14 as a limiting parameter is provided on the path from the compensating component extracting circuit 11 to the adding calculator 15. Is inserted.

FIG. 2 shows the compensation amount calculation circuit 30 shown in FIG.
3 is a detailed circuit configuration diagram of FIG.

In FIG. 2, reference numeral 31 denotes a compensation component extraction circuit 1
1, the compensation amount I _d of the active power component of the load 2 extracted by
A low pass filter for extracting the steady component, 32 adders for outputting a variation of the compensation amount I _d obtained by subtracting the constant component from said compensation amount I _d, 33 the capacitor 9 to be described later and the fluctuation A multiplication operation is performed with a correction value derived from a ripple component of the voltage between both ends, and the operation result is added to an addition operation unit 15
, An absolute value detector 34 for obtaining the absolute value of the ripple component of the voltage across the capacitor 9, and 35 for increasing the absolute value of the ripple component of the voltage across the capacitor 9. In the direction, the absolute value is reduced, and in the decreasing direction, a conditional filter that functions as a low-pass filter, 36 is a limit value setter that sets a ripple voltage limit value, and 37 is a conditional value that sets the ripple voltage limit value to the condition. When the value obtained by the division operation unit 37 is out of the range of 0% to 100%, the division operation unit 38 restricts the division operation to the multiplication operation unit 33 when the value obtained by the division operation unit 37 is out of the range.
Is a limiting circuit that outputs the signal to the other input.

That is, the self-excited system compensator shown in FIGS. 1 and 2 is a self-excited system compensator (also referred to as a flicker compensator) suitable for an arc furnace facility installed as the load 2 of the power system 1. The active power is changed between the power system 1 and the voltage source inverter 8 as shown in FIGS. 3A and 3B due to the fluctuation of the active power caused by the voltage flicker generated at this time. As a result, the voltage across the capacitor 9 fluctuates as shown in FIG. 3B. In order to prevent this fluctuation from increasing, the ripple voltage limit value preset by the limit value setting unit 36 is set. The calculated value of the division based on the absolute value detector 34 and the ripple component of the voltage across the capacitor 9 via the conditional filter 35 does not exceed the range of 0% to 100% (that is, within the ripple voltage limit value). Adjusting the correction value.

FIG. 4 is a circuit configuration diagram of a self-excited system compensator according to a second embodiment of the present invention. Components having the same functions as those of the conventional circuit shown in FIG. The description is omitted.

In other words, in the self-excited system compensator shown in FIG. 4, a compensation is made on the path from the compensating component extraction circuit 11 to the current command operation circuit 16 using the phase voltage command value output from the adder 20 as a limiting parameter. A quantity calculation circuit 40 is inserted, and the fundamental wave current signal I _d1 output from the voltage regulator 14 is directly used as one input to the current command calculation circuit 16.

FIG. 5 shows the compensation amount calculating circuit 40 shown in FIG.
3 is a detailed circuit configuration diagram of FIG.

In FIG. 5, reference numeral 41 denotes a compensation component extraction circuit 1
1, the compensation amount _Iq of the reactive power component of the load 2 extracted by
Low-pass filter for extracting a stationary component from 42 adders for outputting a variation of the compensation amount I _q obtained by subtracting the constant component from said compensation amount I _q, 43 is an output voltage command below said stationary component multiplication operation for multiplying calculating a correction value derived from the value, 44 a variation of the compensation amount I _d, adds the corrected steady current command arithmetic circuit 16 adding calculator to f output, 45 is an absolute value detector for calculating the absolute value of each output voltage command value to the voltage source inverter 8, that is, the maximum value for calculating the maximum value among the obtained absolute values. An arithmetic unit 47, a conditional filter for outputting the maximum value as it is in the increasing direction and a low-pass filter functioning for the maximum value in the decreasing direction; 48, a limit value setting device for setting the output voltage limit value;
49 is a division operator for dividing the output voltage limit value by the output value of the conditional filter 47, and 50 is a division operator 4
When the value obtained in step 9 is out of the range of 0% to 100%, the limit circuit limits the range to this range and outputs it to the other input of the multiplying operation unit 43.

That is, the self-excited system compensator shown in FIGS. 4 and 5 is suitable for a case where an inductive load is installed as the load 2 of the power system 1 (reactive power compensator). In this case, the voltage-source inverter 8 performs an operation of generating a leading-phase reactive power with respect to the lagging reactive power generated in the power system 1 at this time (FIG. 6).
(B)). Therefore, as shown in FIG. 6B, the voltage output from the voltage-source inverter 8 increases to be higher than the voltage of the power system 1.

For example, when the electric power system 1 is formed by private power generation equipment, its system impedance is generally large, and thus the voltage at the interconnection point is increased by the leading reactive power output from the voltage type inverter 8 (FIG. , b V _s) is increased in), so that the voltage output by the voltage source inverter 8 (FIG. 6 (b, so V _i) is further increased in b), which is the output the output voltage of the adding calculator 20 Increase the command value,
As shown in FIG. 6C, the top of the sinusoidal voltage command to the voltage source inverter 8 (the broken line in FIG. 6C) is PW.
The voltage type inverter 8 can output by PWM operation in the M operation circuit 21, and exceeds the lower limit value.
A non-theoretical harmonic current, which is undesirable for

That is, in order to prevent the voltage command value from increasing, the output voltage limit value set in advance by the limit value setter 48, the absolute value detector 45, the maximum value calculator 46, the conditional filter 47 The correction value to the multiplication operation unit 43 is adjusted so that the division operation value based on the output voltage command of the addition operation unit 20 via the above does not exceed the range of 0% to 100% (that is, within the output voltage limit value). .

[0028]

According to the self-excited system compensator of the first invention, the increase in the ripple component of the DC side voltage of the voltage type inverter is detected while the arc furnace equipment or the like as the load is operating, and the load of the load is detected. Since the amount of compensation for the variation of the active power component is set to a limited value, the increase in the ripple component is suppressed, and the followability of the voltage source inverter is maintained, so that the voltage source inverter can be prevented from becoming overcurrent. .

According to the self-excited system compensator of the second invention, when an inductive load is installed as a load,
An increase in the amplitude of the output voltage command value to the voltage type inverter is detected, and the amount of compensation for the steady-state component of the reactive power component of the load is set to a limited value. Since the inverter is operated, even when the system impedance of the power system is large, the output voltage of the voltage type inverter is distorted, and it is possible to prevent non-theoretical harmonic current from flowing through the power system and the load.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a self-excited system compensator showing a first embodiment of the present invention.

FIG. 2 is a partial detailed circuit configuration diagram of FIG. 1;

FIG. 3 is an explanatory diagram for explaining the operation of FIG. 1;

FIG. 4 is a circuit diagram of a self-excited system compensator according to a second embodiment of the present invention.

FIG. 5 is a partial detailed circuit configuration diagram of FIG. 4;

FIG. 6 is an explanatory diagram for explaining the operation of FIG. 4;

FIG. 7 is a circuit configuration of a self-excited system compensator showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power system, 2 ... Load, 3 ... CT, 4 ... PT, 5 ... Circuit breaker, 6 ... CT, 7 ... AC reactor, 8 ... Voltage type inverter, 9 ... Capacitor, 11 ... Compensation component extraction circuit, 1
2: DC voltage setting device, 13: DC voltage detector, 14: voltage regulator, 15: addition operation device, 16: current command operation device,
17 output capacity limiting circuit, 18 multiplication operator, 19 current regulator, 20 addition operator, 21 PWM operation circuit,
30: Compensation amount operation circuit, 31: Low-pass filter, 32
... Addition calculator, 33 Multiplication calculator, 34 Absolute value detector, 35 Conditional filter, 36 Limit value setting device 37
... Division arithmetic unit, 38 ... Limiting circuit, 40 ... Compensation amount arithmetic circuit, 41 ... Low-pass filter, 42 ... Addition arithmetic unit, 43
... Multiplication operation unit, 44 ... Addition operation unit, 45 ... Absolute value detector, 46 ... Maximum value operation unit, 47 ... Conditional filter, 48
... Limit value setting device, 49 ... Division calculator, 50 ... Limiting circuit.

Claims (2)

[Claims] An AC side of a voltage source inverter having a capacitor on a DC side and using the capacitor as a voltage source is connected to a power system via an AC reactor, and compensates for a current generated by a potential difference between both ends of the AC reactor. In the control method of the self-excited system compensator for compensating reactive power and harmonics from a load on the power system by the voltage-source inverter performing an operation to match the current command value, the voltage-source inverter includes the voltage across the capacitor. Controlling a self-excited system compensation device, wherein a ripple component that is monitored is monitored, and when the ripple component exceeds a predetermined value, a compensation amount for a variation in the active power component of the load is limited. 2. A voltage-source inverter having a capacitor on the DC side, and the AC side of the voltage-source inverter using the capacitor as a voltage source is connected to a power system via an AC reactor, and compensates for a current generated by a potential difference between both ends of the AC reactor. In the control method of the self-excited system compensator for compensating for reactive power and harmonics from a load on the power system, the voltage-type inverter performs an operation of making the voltage-type inverter match the current command value. Monitoring the instantaneous value of the voltage command value, and when the instantaneous value exceeds a predetermined value, limiting a compensation amount for a steady portion of the reactive power component of the load; Method.