JPH0640704B2 - Inverter parallel operation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a parallel operation method of inverters in which a cross current is suppressed in parallel operation of a plurality of inverters.

(Prior art) In parallel operation of multiple inverters that output AC voltage, not only control of load sharing between inverters but also suppression of cross current caused by voltage difference and phase difference between individual inverters is an important issue. is there.

In parallel operation of conventional inverters, a very complicated control method has been adopted to suppress cross current. FIG. 5 is a block diagram for explaining a conventional parallel operation method of inverters. The figure is a block diagram showing a single inverter that operates in parallel. In parallel operation, inverters having the same configuration are connected in parallel to the bus bar. In the figure, the output of the inverter 1 is connected to the parallel bus 2 and operated in parallel with other inverters to supply AC power to the load 3. The reference sine wave generation circuit 4 outputs the reference frequency F ₀ of the output of the reference oscillator 5.
And a reference sine wave F ₀ determined by the reference voltage Vr.
The reference sine wave F ₀ , the output voltage V ₀ and the error amplification circuit 6 are comparatively amplified to generate a sine wave signal F ₂ . The sine wave signal F ₂ controls the PWM (pulse width modulation) drive circuit 7, and the PWM drive circuit 7 controls the inverter 1 by turning on / off the switching element of the inverter.

Next, the control of the cross current between the inverters is performed as follows. Effective cross current detecting circuit 8 detects the effective lateral current component in phase or antiphase with respect to the output voltage V _0, also disable cross current detection circuit 9 detects an invalid horizontal flow component of the advance or delay of the output voltage V ₀ and 90 ° phase To do. Next, the signal detected by the effective cross current detection circuit 8 is applied to the voltage / voltage via the NO.1 damper 10.
It is converted into a minute frequency signal ΔF proportional to the signal detected by the frequency conversion circuit 11, and this minute frequency signal ΔF changes the reference frequency F ₀ by ΔF via the frequency addition / subtraction circuit 12. Further, the signal detected by the reactive cross current detection circuit 9 is converted into a minute voltage signal ΔV via the NO.2 damper 13, and this minute voltage signal ΔV is supplied to the voltage adding / subtracting circuit 14 from the reference voltage Vr of the voltage control loop. Change by ΔV.

Since the internal impedance of the inverter is considered to be almost pure reactance, the cross current caused by the voltage difference of the inverter becomes an ineffective cross current, and the cross current caused by the phase difference of the inverter becomes an effective cross current. Here, the minute voltage signal ΔV generated from the invalid cross current is set to be added to the reference voltage Vr when the invalid cross current is advanced, and is set to be subtracted from the reference voltage Vr when the invalid cross current is delayed. That is, when there is a voltage difference between the other inverters and a forward reactive cross current flows, the output voltage V _{0 of the} inverter is raised, and when a delayed reactive cross current flows, the output voltage V ₀ of the inverter is lowered and that of the other inverter. The voltage of is matched and the cross current is compensated. Next, the minute frequency ΔF generated from the effective cross current is subtracted from the reference frequency F ₀ when the cross currents have the same phase,
When the effective cross current has the opposite phase, the direction is set to be added to the reference frequency F ₀ . That is, if there is a phase difference between the other inverters and a cross current of the same phase is flowing, the frequency of the inverter will be lowered to match the phase with the other inverter, and if a cross current of the opposite phase will be raised, the frequency of the inverter will be increased and The phase of is matched and the cross current is compensated.

(Problems to be Solved by the Invention) In the prior art, it is necessary to detect the effective component and the ineffective component of the cross current, and the compensation of the effective cross current is a complicated circuit such as a voltage / frequency conversion circuit and a frequency addition / subtraction circuit. is necessary. Therefore, there is a drawback that the device is expensive.

It is an object of the present invention to solve the above problems and provide a simple and inexpensive inverter parallel operation system.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a plurality of error control circuits for controlling the output of an error amplification circuit for comparing an output voltage with a sine wave reference signal via a PWM drive circuit. In the parallel operation of the inverters in which the inverters are connected in parallel, a means for adding or subtracting the detection signal of the output current of the inverter to the input or the output of the error amplification circuit is provided, thereby reducing the output voltage of the inverter. The output current detection signal is applied to the error amplification circuit together with the output voltage detection signal after adding the signal from the sine wave generation circuit. When increasing the inverter output voltage, the current detection signal and the voltage detection signal In addition, the signal from the sine wave generation circuit is given to the error amplification circuit to control the cross current between the inverters. The method of transfer is the gist of the invention.

(Operation) In the present invention, the output of the inverter 1 is connected to the parallel bus 2 as shown in FIG. 1, other inverters (not shown) are also connected to the parallel bus 2, and a plurality of inverters are operated in parallel to load 3. Supply AC power. Furthermore, the output power V ₀
And the output current A ₀ are detected, and the inverter 1 is controlled through the error amplification circuit 6 and the PWM drive circuit 7 together with the reference sine wave generation circuit 4.

Originally, in the PWM inverter, the voltage waveform of the output of the inverter is controlled so as to have the same waveform as the reference signal used for the PWM control. Therefore, in the following description, the output waveform and the waveform of the reference signal will be compared and described.

Fig. 2 shows the operation of this inverter in parallel operation mode.
This will be described with reference to the vector diagrams of (a) and (b). For example, when two inverters are operated in parallel, a cross current flows between the inverters. Therefore, the output current A ₀ of the inverter includes a cross current component. As shown in FIG. 2 (a), the output current A ₀ is a combined current of the load current component A ₁ and the cross current component A ₂ . That is, the output current A ₀ is out of phase with the load current component A ₁ by θ ₁ . Here, for simplicity, the load is a resistive load.

Next, the reference sine wave signal in the control circuit of the inverter is the second
B ₁ shown in FIG. 3B has the same phase as the load current component A ₁ .
That output current _{A 0} detection signal A _'0 (current transformer in Figure 1
The signal obtained from 15) is out of phase by the reference sine wave signal B ₁ and θ ₁ . This is subtracted from the reference sine wave signal B ₁ θ ₂
Then, the reference signal B _{2 is obtained} , and the signal is out of phase by θ ₂ . At the same time, the level of the reference signal B ₂ also changes. In the present invention, since the inverter is controlled by this reference signal B ₂ (the signal from which the cross current component is removed), the output voltage phase and the output voltage level of the inverter are controlled corresponding to the cross current.

In the PWM inverter, the output voltage waveform of the inverter is controlled so as to have the same waveform as the reference signal. Here, when the output current increases with the detection signal as the reference signal, the output voltage is lowered. In other words, since this reference signal is added in the direction of decreasing the detection signal, the reference signal changes in the same direction for the cross current component included in the detection signal, which is the output current, and when the cross current increases, the reference signal changes so that it decreases. The output voltage is controlled. In addition, the cross current can be separated into the effective component and the reactive component.The effective component changes according to the output voltage phase of the inverter, and the reactive component changes according to the output voltage level.Therefore, the cross current component included in the detection signal The voltage phase and the voltage level of the reference signal are controlled so as to be smaller, and thus the output voltage phase and the output voltage level of the inverter are controlled corresponding to the cross current.

By subtracting the output current detection signal A ′ ₀ from the reference sine wave B _{1 in} this way, the output voltage phase and the output voltage level of the inverter are controlled corresponding to the cross current, and the cross current can be suppressed.

(Examples) Examples of the present invention will be described below with reference to the drawings.
Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 is an inverter for controlling on / off of a semiconductor switching element to convert direct current into alternating current, and 2 is an output of a plurality of inverters 1 (other inverters are not shown) connected to a parallel bus 2. Power is supplied to the other inverters and the load 3. Reference numeral 15 is a current transformer for detecting the output current.

In the parallel operation method of the inverters of this embodiment, the output voltage V ₀ and the output current A ₀ are detected, the output voltage signal V ′ ₀ and the output current signal A ′ ₀ are obtained, and the reference generated by the reference sine wave generation circuit 4 is used. 'subtracted _0, this output voltage signal V' output current detection signal a from the sinusoidal wave B _{1 0} compared amplified by the error amplifier circuit 6, a sine wave signal at the output of the error amplifier circuit 6 PW
The M drive circuit 7 produces a PWM signal, which controls the switching element of the inverter.

Here, by subtracting the output current detection signal A ′ ₀ from the reference sine wave B ₁ , the phase and voltage level of the output voltage V ₀ of the inverter can be controlled corresponding to the cross current, and the cross current can be suppressed. Become.

Next, FIGS. 3 and 4 are block diagrams showing other embodiments of the present invention.

The basic structure of each of the embodiments shown in FIGS. 3 and 4 is the first.
It has the same configuration as the basic configuration in the figure, but differs in the addition or subtraction processing of the output detection current.

In the embodiment shown in FIG. 3, after the addition processing of the output voltage detection signal V ′ ₀ and the output current detection signal A ′ ₀ is performed, the error amplification circuit 6 together with the reference sine wave B ₁ of the reference sine wave generation circuit 4 are processed. To the PWM drive circuit 7
The inverter 1 is controlled via. In this case, in order to match the polarity of _"0 output voltage detection signal V 'output current detection signal A to be subtracted from a reference sine wave B ₁ and _0,' and the ₀ output current detection signal A 'output voltage detection signal V with ₀ Is being added.

Further, in the embodiment of FIG. 4, which subtracts the output current detection signal A _'0 from the sinusoidal signal at the output of the error amplifier circuit 6. In this case, since the output current detection signal A ′ ₀ is subtracted from the sine wave signal output from the error amplification circuit 6, there is an advantage that the gain of the error amplification circuit 6 does not affect the output current detection signal A ′ ₀ .

(Effect of the invention) According to the present invention, in the parallel operation of the inverters in which a plurality of inverters controlled by the output of the error amplification circuit for comparing the output voltage and the sine wave reference signal are connected in parallel, By providing means for adding or subtracting the current detection signal to the input or output of the error amplification circuit, the phase and voltage level of the output voltage of the inverter can be controlled by a simple circuit in parallel operation of a plurality of inverters. Therefore, the voltage balance between the inverters can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a vector diagram for explaining the present invention, and FIGS. 3 and 4 are block diagrams showing other embodiments of the present invention. Fifth
The figure is a block diagram showing a parallel operation method of conventional inverters. 1 ... Inverter 2 ... Parallel bus 3 ... Load 4 ... Reference sine wave generation circuit 6 ... Error amplification circuit 7 ... PWM drive circuit 15 ... Current transformer

Claims (1)

[Claims] Claims: 1. In parallel operation of inverters in which a plurality of inverters controlled by a PWM drive circuit are connected in parallel to operate an output of an error amplification circuit for comparing an output voltage with a sine wave reference signal A means for adding or subtracting the detection signal of the output current of is added to or subtracted from the input or output of the error amplification circuit, so that when the output voltage of the inverter is lowered, the detection signal of the output current is output from the sine wave generation circuit. After adding the signal, it is given to the error amplification circuit together with the output voltage detection signal, and when raising the output voltage of the inverter, the current detection signal and the voltage detection signal are added, and the signal from the sine wave generation circuit is sent to the error amplification circuit. A method for parallel operation of inverters, characterized in that a cross current is controlled between the inverters.