JPH01222318A - System for controlling inverter of reactive power compensation device - Google Patents

Abstract

PURPOSE:To sufficiently compensate a conventional reactive power as a whole by allotting respective objects of compensation to higher harmonic compensation and reactive power compensation with giving limitation and compensating respective objects of compensation. CONSTITUTION:A higher harmonic current detection part 11 and a reactive current detection part 14 are provided in a control circuit 7, and a high harmonic current ilh is inputted to a first inverter generation voltage operation part 12, whereby an inverter 5 is operated by the output voltage signal V1* and the action of PWM13. On the other hand, a reactive compensation current iq and a system voltage Va corresponding to a reactive compensation current are inputted to a second inverter generation voltage operation part 15 and an inverter 6 is operated by the output voltage signal V2* and the action of PWM16. Thus the control signals of respective inverters can independently be controlled without being reciprocally interfered, and efficient control is attained in accordance with inverter functions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aims to improve the efficiency of voltage-source inverter control by limiting the compensation target of each inverter in a reactive power compensation device using series multiplexed voltage-source inverters. The present invention relates to an inverter control method for a reactive power compensator.

[Problems to be Solved by the Invention] There are various methods for suppressing system fluctuations using reactive power compensators, and the widely used ones include the reactive power compensator that is connected to the countermeasure bus, or the reactive power that flows through the capacitor. There is a device that suppresses the voltage fluctuation of the countermeasure bus by controlling the current with a thyristor and compensating for the reactive power or its fluctuation, but recently Hitoyoshi, which uses an inverter, has replaced the reactive power compensator with the above configuration. ffl reactive power compensators are being realized.

As mentioned above, inverter-based systems do not require accelerator equipment or capacitor equipment, and are highly expected to make further progress in the future. As described above, when incorporating an inverter into a reactive power compensator, it has been considered to multiplex the inverters.

However, in the case of multiplexed inverters, if the control of each installed inverter is configured to significantly interfere with the operation of other inverters, the operation control will become unstable.

The present invention analyzes a reactive power compensation device using a series multiplexed voltage source inverter, limits the compensation targets for harmonic compensation and reactive power compensation, and performs compensation for each compensation target. This is intended to enable adequate reactive power compensation as a whole.

[Means to solve the problem] FIG. 1 shows a schematic block diagram of the apparatus of the present invention.

1 indicates the grid power supply, and 2 indicates the grid impedance. 10
indicates a load connected to the grid power supply 1, and between the load 10 and the grid power supply l, a first transformer is shunted in parallel to the grid,
A first inverter 5 is connected via the primary side of the transformer 3, a primary side of the second transformer 4 is connected in series with the secondary side of the transformer 3, and a second inverter 8 is connected to the secondary side of the second transformer 4. is connected.

Inverters 5 and 6 are now in series relationship. 7 is a control circuit, and the fl control circuit 7 includes a PT8 for detecting system voltage.
A voltage signal from the C70 and a current signal from the C70 for load current detection are input, and a generated voltage signal for the voltage generated by the first inverter 5 and the second inverter 6 is formed in the control circuit 7.

A schematic block diagram of the control circuit 7 is shown in FIG.

As shown in the figure, a harmonic current detector 14 is provided with the load current li as input, and a reactive current detector 14 with the receiving point voltage Va and load current i as input. is input to the first inverter generated voltage calculation unit I2, and the output voltage signal Vl causes s PW
The inverter 5 is operated by the operation of M13.

On the other hand, the reactive current tq corresponding to the reactive compensation current and the receiving point voltage (system voltage) Va are input to the second inverter generated voltage calculation unit I5, and the output voltage signal v2 is used to calculate PW.
The inverter 6 is operated by the operation of MIB.

As understood from FIG. 2, reactive power compensation, especially compensation for the fundamental wave component, is performed by the second inverter 8 in FIG. 1. The fundamental wave equivalent circuit of a system including the above device is shown in FIG. 3(a). Compensating for reactive power is equivalent to compensating for reactive current, and as shown in FIG.
From the load current ie and the phase difference, the compensated reactive current i
Find q.

When iq flows, the following equation can be found from the equivalent circuit.

Va = V2 + Liq ==---=
=-(1)at However, L is the shunt inductance equivalent to the leakage impedance of transformers 3 and 4, that is, the generated voltage signal v2 of the second inverter θ is calculated by the second inverter generated voltage calculation section in FIG. 15 and operate the inverter by PWM operation.

As can be understood from Fig. 2, harmonic current compensation is
This is done by the inverter 5 at in the figure. The harmonic equivalent circuit of a system including the above device is shown in FIG. 3 (c). Although it depends on the nature of the load and the circuit configuration, the harmonic current may vary by %5.7.
11. There are l-th order harmonics, but now let us consider zero-order harmonic compensation. As shown in Fig. 2, the load current ie is detected, and harmonic current 1ah is generated by, for example, Fourier transform.
n (the subscript n represents the harmonic order, the same applies hereinafter) is obtained, but 1. Using that current, the inverter generated voltage signal (n
(order) Van is given by the following formula.

Vln” KnJ'1 (Ihndt,,++
++-〇However, Kn: 4x”・n”・to”
・L =-・-@fo:! The reciprocal of Kn given by the main wave frequency equation (4), 1/Kn, is equal to the value of C of the LC series circuit having zero-order resonance with respect to the shunt inductance L.

From this, the voltage of the first inverter 5 for the 0th order is (
As shown in FIG. 3(C), it is considered that the inverter plays an equivalent role to the capacitor of the LC circuit. Therefore, the impedance of the device is considered to be zero for n-th harmonics, and harmonics can be compensated for.

This holds true for each out-of-stock harmonic by using equations (3) and (4), and the inverter output voltage signal V- is calculated by the first inverter generated voltage calculation unit 12 in FIG.
So, Vi”=I:Vtn” EK nJ' i Q h n d t −・−−
(2) and then operate the inverter using PWN operation.

[Effects of the Invention] According to the method of the present invention, the control signals of each inverter can be controlled independently without interfering with each other, and efficient control can be performed according to the inverter function.

[Brief explanation of the drawing]

FIG. 1 shows in block diagram form an embodiment of the invention. FIG. 2 shows a control circuit of the present invention. FIG. 3(A) shows an equivalent circuit for the fundamental wave, FIG. 3(B) shows an equivalent circuit for harmonics, and FIG. 3(C) is an explanatory diagram of equivalent conversion of the first inverter. 1...System power supply, 2...System impedance, 3,
4...Transformer, 5.6...1st. second inverter,
7...Control circuit, 8...PT19...CT, 1G
···load. Math 1 Zurou 2 Zuna 3 Diagram (mouth) (c)

Claims (1)

[Claims] (1) In a reactive power compensator configured by connecting in series a second inverter that compensates only reactive power and a first inverter that compensates only harmonic current in a parallel shunt with the grid, The inverter generated voltage signal V_2^*, which determines the output voltage of the power compensation inverter, is determined by V_2^*=V_a-L(d/dt)i_q in the second inverter generated voltage calculation section,
The inverter generated voltage signal V_1^*, which determines the output voltage of the inverter for harmonic current compensation, is determined in the first inverter generated voltage calculation section by V_1^*=ΣK_n∫(i_l_h_n)dt. Inverter control method for reactive power compensator including harmonic current compensation. However, V_a: grid voltage, L: shunt inductance, i
＿q: Compensation reactive current, K_n: 4π^2×n^2×f_
0^2×L, n: harmonic order, f_0: fundamental frequency,
i_l_h_n: Each harmonic current in load current i_l