JPS6111533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a harmonic current compensator using a static inverter to generate a pulse width modulated output voltage that simulates a control input signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a harmonic current compensator that can be applied to a power grid without generating an inrush current.

FIG. 1 shows the principle structure of a harmonic current compensator according to the present invention. A load 2 that generates harmonic current is connected to a power supply system 1 . Reference numeral 3 designates a known pulse width modulation type inverter, which is shown here in its basic configuration by an inverter main circuit section 31, a modulation signal generator 32, a comparator 33, and a pulse amplifier 34. This pulse width modulation type inverter 3
is connected to the power supply system via the reactor 4. The inverter 3 generates an output voltage V _AF that simulates the control input signal e _io and supplies a compensation current I _AF to the system 1 via the reactor 4 . Now, assuming that the load current is I _Z , the system current is I _S , the system voltage is V _S , and the inductance of reactor 4 is L _S , I _Z = I _S + I _AF ... (1) V _AF = V _S + L _S dI _AF /dt...(2) There is a relationship.

The control input signal e _io given to the inverter 3 is the sum of the first input signal e ₁ corresponding to the system voltage V _S and the second input signal e ₂ given according to the harmonic current to be compensated. It will be given to you. That is, e _io =e ₁ +e ₂ (3). Furthermore, when the system voltage V _S can be expressed as V _S = |V _S | sinθ ...(4), the first control input signal e ₁ is given as e ₁ = λ ₀ sinθ ...(5) . However, when θ is the system angular frequency and time is t, θ=ωt, and λ ₀ is the output voltage ratio, which is a value corresponding to the output voltage |V _S |. When e ₂ =0 and therefore e _io =e ₁ , the fundamental wave of the output voltage V _AF of the inverter 3 matches the system voltage V _S expressed by equation (4). Therefore, if the second control input signal e ₂ is kept at zero and the inverter 3 is operated, the inverter 3 will generate an output voltage equal to the system voltage, so if the inverter is turned on to the power system 1 in this state, it will almost cause an inrush voltage. No current is generated.

The second control input signal e ₂ is the inverter output current target value I ^* _AF calculated according to the harmonic component to be compensated included in the load current I _Z and its actual value I
A deviation from _AF can be provided by a guided current regulator 5.

FIG. 2 shows an arithmetic circuit for determining the current target value I ^* _AF . 6 is a reference signal sinθ that detects the system voltage V _S and represents the phase of the system voltage.
This is a circuit that generates and cosθ. 7 is a current detector for detecting the actual load current value _IZ . Reference numeral 8 denotes a fundamental wave component calculator that calculates the magnitude A ₁ of the fundamental wave effective component and the magnitude B ₁ of the fundamental wave reactive component included in the actual load current value I _Z . In this case, coefficient A ₁ is the magnitude (amplitude) of the fundamental wave effective component, and coefficient B ₁ is the magnitude (amplitude) of the fundamental wave reactive component.
is based on the following formula based on Fourier analysis:
That is, it is calculated according to A ₁ =1/π∫ ² 〓 ₀ I _Z ·sinθdθ B ₁ =1/π∫ ² 〓 ₀ I _Z ·cosθdθ. The output of the multiplier 9 is the fundamental wave effective component A ₁ sin θ included in the load current I _Z , and the output of the multiplier 10 is the fundamental wave active component B ₁ cos θ included in the load current I _Z. The output of adder 11 is the current target value I ^* _AF applied to current regulator 5 (FIG. 1), which is given by the following equation.

I ^* _AF = I _Z - (A ₁ sin θ + B ₁ cos θ) ...(6) The current regulator 5 sets the actual current value I _AF to this target value I
^* Generate an output voltage e ₂ that matches _AF . Therefore, control is performed such that I _AF =I _Z -(A ₁ sin θ+B ₁ cos θ) (7). In other words, Equations (1) and (7)
As can be seen from the following relationship: I _S =A ₁ sin θ + B ₁ cos θ (8), no harmonic current flows through the power supply system 1.

In the embodiment shown in FIG. 2, only the harmonic current is compensated, but in the embodiment shown in FIG. 3, the fundamental reactive current is also compensated at the same time. According to FIG. 3, the circuit 60 extracts the reference signal from the system voltage V _S
sinθ is derived, and based on this, the fundamental wave effective component calculator 80 calculates the magnitude A ₁ of the fundamental wave effective component included in the load current actual value I _Z detected by the current detector 70. calculate. This calculated value A ₁ is multiplied by the reference signal sinωt by a multiplier 90 . At the mixing point 110, a difference is formed between the actual load current value I _Z and the output value A ₁ sinωt of the multiplier 90, and this difference becomes the current target value I ^* _AF , that is, I ^* _AF = I _Z −A ₁ sinωt ...(9). Due to the action of the current regulator 5, I _AF = I ^*
Control is performed so that _{the AF} occurs, and as a result, the system current I _S
As expressed by I _S =A ₁ sinωt, only the fundamental wave active current is present, and compensation for harmonic current and fundamental wave reactive current generated by the load is performed.

Note that a capacitor may be used instead of the reactor 4 in FIG.

As described above, according to the present invention, the control input signal e _io for the static inverter is divided into the first signal e 1 corresponding to the voltage V _S of the power supply system and the first signal e ₁ corresponding to the harmonic current to be compensated. Since it is given as the sum of the second signal _e2 , just by keeping the second signal _e2 at zero,
The output voltage fundamental wave of the static inverter matches the voltage of the power supply system. Therefore, if the compensator is turned on after starting the static inverter by keeping the second signal _e2 at zero, the output voltage of the static inverter and the power system voltage are in equilibrium, so , no inrush current flows through inductive or capacitive impedance. The harmonic current compensation operation can be started by releasing the zero holding of the second signal e ₂ after the completion of the input.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of the device of the present invention, and FIGS. 2 and 3 are block diagrams showing different embodiments of an arithmetic circuit for determining the target value of the compensation current in the device of the present invention. 1... Power supply system, 2... Load, 3... Pulse width modulation inverter, 4... Reactor, 5... Current regulator.

Claims (1)

[Claims] 1. A static inverter that generates a pulse-width modulated output voltage that simulates the control input signal is connected to the power system via an inductive or capacitive impedance to compensate for the harmonic currents that the load causes in the power system. The control input signal is a first signal having a value corresponding to the voltage of the power supply system, and a first signal that is kept at zero during the turning-on process of the static inverter, and a harmonic current that is to be compensated after the turning-on process is completed. A harmonic current compensator characterized in that the harmonic current compensation device is configured to provide the harmonic current as a sum with a second signal having a corresponding value.