JP2859930B2 - Harmonic compensator - Google Patents

Description

The present invention relates to an improvement of a harmonic compensator provided in a system line between a power supply system and a load facility.

[Prior Art] A three-phase PWM converter, an AC reactor connected in series to a power supply on the AC side of the three-phase PWM converter,
The active filter composed of a DC capacitor connected between the terminals on the DC side of the phase PWM converter is equipped with a higher-order filter to eliminate the ripple current generated by the active filter itself. Is generally configured.

In such a harmonic compensator, resonance may occur between the impedance of the power supply system and the high-order filter, and the compensation characteristics may be degraded. A method of feedbacking the power supply side harmonic current as a control method to suppress such resonance by an active filter was reported in "Study on Active Filter Control Method" as 566 in the 1987 IEEJ National Convention. I have.

Hereinafter, such a conventional harmonic compensator will be described with reference to the drawings. FIG. 3 is a main circuit configuration diagram of a three-phase AC power supply system including a conventional harmonic compensator, and FIG. 4 is a block diagram of a system at the time of harmonic compensation.

In FIG. 3, reference numeral 3 denotes a system impedance.
The phase AC system power supply 1 supplies power via a system impedance 3 to a load 2 such as a thyristor Leonard device via a load-side AC reactor 8. This system line has three phases
A harmonic compensator composed of an active filter including a PWM converter 5, an AC reactor 4, and a DC capacitor 6 and a high-order filter 8 is connected.

In FIG. 4, reference numeral 33 denotes a feedback control function G for the harmonic component I _SH of the power supply current, 31 denotes a transfer function GAF of the active filter, 32 denotes a power supply side harmonic inflow impedance Z, and a power supply side harmonic inflow impedance Z It is represented by the following formula from the impedance Z _f of the harmonic impedance Z _s and higher filter 7 strains.

In a system configured with such a transfer function, a load current harmonic component I _LH and an IG obtained by multiplying a power supply current harmonic component I _SH by a feedback control function G are added, and these are added to the active filter transfer function GAF. Input.

_{Assuming that} the difference between the output IF and the load current harmonic component I _LH is the input of the power source side harmonic inflow impedance Z, the output becomes the power source current harmonic component I _SH .

Here, if a proportional differentiation circuit is employed as the feedback control function G, resonance occurring between the impedance of the power supply system and the high-order filter 7 can be suppressed, and the compensation performance can be improved. When a proportional differentiating circuit is employed, the feedback function G becomes a transfer function of the proportional differentiating circuit and is represented by the following equation.

Here, K: Gain of proportional differentiator T: Time constant of proportional differentiator

[Problems to be solved by the invention]

In FIG. 3, a vector sum of a compensation current flowing into the three-phase PWM converter 5 and a filter current flowing into the high-order filter 7 is used to cancel a harmonic component of the load current flowing into the load 2. The wave compensation detects a load current, a system voltage, and a power supply current, sends them to an arithmetic circuit (not shown), generates a current command signal corresponding to a harmonic current compensation command, and generates a current command signal corresponding to the harmonic current compensation command. Comparing the magnitude with the compensation detection current signal proportional to
According to the result, on / off control of the switching elements S1 to S6 of the three-phase PWM converter 5 is performed.

For example, when the magnitude comparison result of the signals is: current command signal> compensation detection current signal, the switching elements S1 to S6
Is turned on, the DC capacitor 6,
A discharge circuit is formed through one of the switching elements S1 to S6 and the AC reactor 4, and the compensation current rapidly rises, instantaneously reaches the current value commanded by the current command signal, and further exceeds the command value.

For this reason, the magnitude comparison result of the signals is inverted to the current command signal <compensation detection current signal, and one of the switching elements S1 to S6 is turned off. As a result, a charging circuit is formed this time through the AC reactor 4, any one of the diodes D1 to D6, and the DC capacitor 6, and the compensation current falls rapidly, falls below the command value after reaching the command value,
Go back to the beginning.

As described above, the switching element is repeatedly turned on / off so that the compensation current having a steeper gradient than the change in the magnitude of the current command signal can be alternately passed above / below the current command value. Harmonic compensation is performed following the signal.

However, when the value of the load-side AC reactor 8 shown in FIG. 3 is small, the overlapping angle of the load currents I _LU , I _LV , and I _LW becomes small, and the waveform of the load current becomes close to a rectangle from a trapezoidal shape. The types of high-order harmonics overlap, and the rising and falling portions have a steep gradient.

For this reason, the waveform of the current command signal generated as a compensation command for detecting and calculating this current waveform and canceling out the harmonic component is:
It has a saw-toothed peak as shown in FIG. 2 (a) and a steep positive and negative slope.

In the current command signal at the time of commutation of the load current as shown in FIG. 2A, a time timing corresponding to a position slightly past the peak portion of the sawtooth wave (a position slightly to the right of the peak portion in the figure). When there is a compensation detection current signal of the magnitude of the signal and there is a comparison with the current signal on the positive side above the horizontal center line in the figure, the current command signal is in the lower right direction from the peak portion. The signal magnitude is compared as the current command signal <compensation detection current signal, or when comparing with the current signal on the negative side below the horizontal center line in the figure, The command signal rises steeply to the upper right from the peak, and the current command signal>
A magnitude comparison is made as the compensation detection current signal. Then, the switching element is turned off or on to invert the magnitude comparison relationship of this signal, and the compensation current flows rapidly to act to fall below or exceed the current command value so as to follow the current command to compensate for the harmonic current. I do.

However, the gradient of the rising and falling waveforms of the compensation current is limited by the AC reactor 4 having a finite value provided in the three-phase PWM converter 5, and the gradient of the waveform of the compensation detection current signal is changed to the waveform of the current command signal. When the slope becomes gentler than the slope, the current command value that changes with a steep slope during the same elapsed time becomes a compensation current that changes with a gentle slope as time passes. Unless it reverses and crosses with a gradient opposite to the change gradient of the compensation current, the compensation current cannot exceed or fall below the current command value, and the magnitude comparison relationship between the current command signal and the compensation detection current signal is determined. Since the switching element cannot be reversed during the period of the positive or negative change gradient, which is the same in both directions, the switching element does not repeat on / off following the change in the current command, and the switching element does not. Current is the thing that can not follow the instantaneous compensation command.

As a result, many harmonics are not suppressed and remain in the power supply system. Among them, high-order harmonics are also used by the high-order filter 7 provided for removing the ripple current generated by the active filter itself, and also serve as a filter function. Even if the suppression is performed, the low-order harmonics cannot be suppressed, and the resonance between the higher-order filter 7 and the power supply impedance 3 expands, and even if the gain of the feedback function G is increased, the expanded resonance increases. There was a problem that it could not be suppressed.

An object of the present invention is to provide a harmonic compensator that solves the above-mentioned problem and suppresses harmonics from low to high.

[Means for solving the problem]

A harmonic compensator according to the present invention is a harmonic compensator provided in a system line between a power supply system and a load facility. The harmonic compensator is connected in series with a three-phase PWM converter and each of the AC phases of the three-phase PWM converter. , A DC capacitor connected between the DC side terminals of the three-phase PWM converter, a high-order filter provided alongside a power supply side of the AC reactor, and control for controlling the three-phase PWM converter A control means for calculating instantaneous real power and imaginary power of the load equipment; a means for detecting a lower-order AC component from the instantaneous real power and imaginary power; Means for generating a first current command signal from the low-order AC component, means for calculating the instantaneous real power and imaginary power from the power supply current to generate a second current command signal, Means for inputting and performing proportional differentiation to generate a third current command signal, means for adding the third current command signal and the first current command signal to generate a current command signal, Means for comparing a signal and a compensation current detection value flowing in the AC reactor to generate each phase switching element of the three-phase PWM converter, wherein the high-order filter is provided in parallel with a power supply side of the AC reactor. In this case, the high-order harmonic current cannot be suppressed by the three-phase PWM converter during the commutation of a load having a small AC reactor value.

[Action]

In the harmonic compensator according to the present invention, utilizing the band pass from the instantaneous real power and imaginary power of the load current,
By detecting the lower harmonic components to obtain the first current command signal, the waveform of the first current command signal conventionally has a saw-toothed peak and a gradient as shown in FIG. 2 (a). The peaks and the gradients of the steep waves are gradually changed sinusoidally as shown in FIG. 2 (b) due to the bandpass, so that the AC reactor 4 having a finite value causes the AC reactor 4 to have a finite switching frequency. Most low-order harmonic components are suppressed,
Practically sufficient low-order compensation performance can be obtained.

Higher-order harmonic components can be suppressed by a higher-order filter. Also, in spite of suppression by the active filter, low-order harmonic components remain, and when resonance occurs between the power supply impedance and the high-order filter, the power supply current is generated from the instantaneous real power and imaginary power of the power supply current. It can be suppressed by the second current command signal and the third current command signal obtained by proportionally differentiating the value of the second current command signal.

As described above, harmonic current compensation during commutation of a load having a small value of the AC reactor can be favorably performed.

〔Example〕

Hereinafter, an embodiment will be described with reference to the drawings. The main circuit configuration diagram of the three-phase AC power supply system including the harmonic compensator according to the present invention is as shown in FIG. 3 as in the conventional case, and FIG. 1 is the harmonic compensator according to the present invention. 1 shows a block diagram of a control device of an embodiment of the device.

A three-phase AC system power supply 1 supplies power to a load 2 such as a thyristor Leonard device via a system impedance 3 and a load-side AC reactor 8, and a load current is supplied to each phase of the load 2.
I _LU , I _LV and I _LW are flowing. A high-order filter 7 and an active filter are connected to this system line in parallel with the load 2. The active filter includes a three-phase PWM converter 5, an AC reactor 4 for connecting each AC-side phase terminal to a system line, and a DC capacitor 6 connected between the DC-side terminals of the three-phase PWM converter.

3-phase PWM converter 5 on, consists off Switching element S ₁ to S ₆ and the diode D ₁ to D _6, each of the switching elements S ₁ to S ₆ are connected in parallel with diodes D ₁ to D _6, respectively Above, connected as a three-phase bridge circuit,
Switching element S ₁ to S ₆ by the switching signal V _G supplied from the control unit is on, and performs off has been harmonic compensation.

The AC reactor 4 inserted in series on the AC side of the three-phase PWM converter 5 is for limiting the rise of the current of the three-phase PWM converter 5, and the DC capacitor 6 connected to the DC side is This is for stabilizing the voltage on the DC side of the three-phase PWM converter 5 and is normally charged to a voltage which is about twice the AC side voltage of the three-phase PWM converter 5 which is equal to the voltage of the three-phase AC system power supply 1. Have been.

Now, in the main circuit configuration shown in FIG. 3, the load current flowing into the load 2 is represented by I _LU , I _LV , I _LW , and the compensation current flowing into the active filter, that is, the three-phase PWM converter 5 is represented by I _U , I
_V , I _W and the filter current flowing into the high-order filter 7 are I _FU ,
If I _FV , I _FW , power supply currents I _SU , I
_SV and _ISW are obtained by adding the load current, the compensation current, and the filter current in a vector manner. Therefore, it is only necessary that the vector sums I _U + I _FU , I _V + I _FV , I _W + I _{FW of} the compensation current and the filter current cancel the harmonic components of the load currents I _LU , I _LV , and I _LW , respectively.

In order to perform the harmonic compensation as described above, three-phase to two-phase conversion as described below is performed, and the concepts of real power and imaginary power are introduced. Showa about this concept
The paper was published as "Generalized Theory of Instantaneous Reactive Power and Its Application" in Paper 58-B60 published in IEEJ Transactions on Volume 103, Volume B, Issue 7, July 1983, etc. I do.

The concept is as follows. First, the three-phase load currents I _LU , I _LV , and I _LW and the system voltages e _U , e _V , and e _W are _converted into two-phase currents I _{L α} using the following equations (3) to (5). , I _{L β} and voltages e _α , e _β .

Here, [C] is a three- or two-phase transformation matrix.

Using the two-phase voltage and current obtained from the above equations (3) to (5), the real power p and the imaginary power q are obtained from the following equation (6).

These real power p and imaginary power q are expressed by the following (7),
According to equation (8), DC component and low-order AC component respectively And higher order exchange Is decomposed into

Here, 2-phase load current I _{L α,} I _L low-order harmonics content of _β is real power low-order AC component of And low-order AC component of imaginary power , And can be separated through a band-pass filter.

Next, a description will be given of a control device shown in FIG. 1 configured based on the above-described principle.

Power calculating circuit 11 receives the load current I _LU, I _LV, the load current signal i _LU proportional to I _LW, i _LV, and i _LW, system voltage e _U, e _V, and e _W, (3) ~ (6) the instantaneous real power p ₁ and the instantaneous imaginary power q ₁ is calculated according to equation these bandpass filter
Send to 12.

Bandpass filter 12 removes a DC component and higher-order AC components therefrom, and sends the low-order AC component _1L of instantaneous real power of the low-order AC component _1L and instantaneous imaginary power to sign inverting circuit 13. The sign inverting circuit 13 inverts these signs and outputs them to the current command value calculating circuit 14 as the real power command signal p ₁ ^* and the imaginary power command signal q ₁ ^* .

These are the original forms of the current command signal generated in the current command value calculation circuit 14. That is, the low-order harmonic active power is controlled based on the real power command signal p ₁ ^* obtained by the equation (9), and the low-order harmonic active power is controlled based on the imaginary power command signal q ₁ ^* obtained by the equation (10). Reactive power is controlled.

The current command value calculation circuit 14 receives the real power command signal p ₁ ^* , the imaginary power command signal q ₁ ^*, and the system voltages e _U , e _V , and e _W and receives the above equation (3) and the following (11) to According to equation (13), two-phase current command signals i _α1 ^* , i _β1 ^* are obtained, two-phase to three-phase conversion is performed to generate current command signals i _U1 , i _V1 , i _W1 and adder circuit 1
Output to 5.

[C] ^-1 is the inverse transformation matrix of [C].

Then, the power calculation circuit 21 supply current I _SU, I _SV, the power source current signal i _SU proportional to I _SW, i _SV, i _SW and, system voltage e _U,
In response to e _V and e _W , the instantaneous real power p ₂ and the instantaneous imaginary power q ₂ are calculated according to the equations (3) to (6), and these are sent to the high-pass filter 22.

The high-pass filter 22 removes the DC component from these,
AC component of instantaneous real power And instantaneous imaginary power AC To the sign inversion circuit 23. The sign inverting circuit 23 inverts these signs and outputs them to the current command value calculating circuit 24 as the real power command signal p ₂ ^* and the imaginary power command signal q ₂ ^* .

The current command value calculation circuit 24 receives the real power command signal p ₂ ^* , the imaginary power command signal q ₂ ^*, and the system voltages e _U , e _V , and e _W and receives the above equations (3), (13) and The two-phase current command signals _iα2 ^* , _iβ2 ^* are obtained according to the equations (16) to (17), and the two-phase to three-phase conversion is performed to generate the current command signals _iU2 , _iV2 , _iW2 and proportional differentiation. Output to the circuit 25.

The proportional differentiating circuit 25 obtains the current command signals i _U2 , i _V2 , i _W2 and obtains the third current command signal based on the transfer function of the equation (2).
i _U2 ′, i _V2 ′ and i _W2 ′ are calculated and output to the adder circuit 15.

The adder circuit 15 adds the current command signals i _U1 , i _V1 , i _W1 and the current command signals i _U2 ′, i _V2 ′, i _W2 ′ in each phase, respectively, and outputs the current command signals i _U ^* , i _V ^* , i _W ^* is generated and sent to the current control circuit 16.

The current control circuit 16 is the current command signal _{^{i U *, i V *,}} i W * with compensation current I _U, I _V, the compensation detected current signal i _U proportional to I _W, i _V, i _W
For example, when i _U ^* ≧ 0 and i _U ≦ i _U ^* , the switching element S ₄ of the three-phase PWM converter 5
Was on, i _U ^* ≧ 0 and i _U> i _U ^* turns off the switching element S ₄ when made in, also i _U ^* <and i _U ≦ i _U ^* becomes time 0, turns off the switching element S ₁ The switching signal V _G is generated, and the switching elements S _{1 to} S ₆ are turned on and off by the switching signal V _G , and the current instantaneous value of each phase of the harmonic compensator is controlled.

In this way, the low-order harmonic components are compensated by the current command signal _{i U1, i V1, i W1} , harmonic components of higher order can be compensated by higher-order filter. In addition, the resonance caused by the power supply impedance and the higher-order filter causes the current command signals i _U2 ′, i _V2 ′
i _W2 ′.

〔The invention's effect〕

As described above in detail in one embodiment, the harmonic compensator according to the present invention detects a lower-order harmonic using a bandpass even when the load-side AC reactor connected to the load is small. By doing so, good compensation can be achieved, and higher order harmonics can be compensated for by higher order filters.

In addition, the increase in low-order harmonics, which could not be compensated, due to the power supply impedance and resonance caused by the high-order filter can be suppressed by detecting the power supply current.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control device of an embodiment of a harmonic compensator according to the present invention, FIG. 2 is a waveform diagram showing a compensation current command signal, and FIG. 3 is equipped with such a harmonic compensator. FIG. 4 is a block diagram of a system at the time of harmonic compensation, while FIG. 4 is a main circuit connection diagram of a three-phase AC power system. 1 ... 3 phase AC system power supply, 2 ... load, 3 ... system impedance, 4 ... AC reactor, 5 ... 3 phase PWM converter, 6 ... DC capacitor, 7 ... high order filter, 8 ... Load-side AC reactor, 11, 21 Power calculation circuit, 12 Bandpass filter, 22 High-pass filter, 13, 23 Sign reversing circuit, 14, 24 Power command calculation circuit, 15 Addition Circuit, 16 ... Current control circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02J 3/01 H02M 5/27 H02M 7/48 G05F 1/70

Claims (1)

(57) [Claims] 1. A harmonic compensator provided in a system line between a power supply system and load equipment, comprising: a three-phase PWM converter; and a series line connected to each phase on the AC side of the three-phase PWM converter. An AC reactor, a DC capacitor connected between the DC side terminals of the three-phase PWM converter, a high-order filter provided alongside a power supply side of the AC reactor, and a control device for controlling the three-phase PWM converter, The control device includes means for calculating instantaneous real power and imaginary power of the load equipment, means for detecting a lower-order AC component from the instantaneous real power and imaginary power, and a lower-order AC component of the instantaneous real power and imaginary power. Means for generating a first current command signal, means for calculating the instantaneous real power and imaginary power from the power supply current to generate a second current command signal, and inputting the second current command signal. Proportional derivative Means for generating a third current command signal, means for adding the third current command signal and the first current command signal to generate a current command signal, and applying the third current command signal to the AC reactor. A means for generating a switching signal for each phase of the three-phase PWM converter by comparing the detected value of the flowing compensation current with the high-order filter provided on the power supply side of the AC reactor so that the AC reactor is used. A high-order harmonic current compensating means that cannot be suppressed by the three-phase PWM converter during the commutation of a load whose load is small.