Three-phase four-switch parallel type APF control method under voltage unbalance

Abstract

The invention relates to a three-phase four-switch parallel type APF (Active Power Filter) control method under voltage unbalance, which comprises the following steps: step 1, establishing a three-phase four-switch APF typical topology and determining a synchronous signal Usyn; step 2, calculating the phase angle difference Phi a of a phase A relative to the synchronous signal by means of the following formula shown in the specification on the basis of discretizing the synchronous signal; step 3, gaining the phase angle difference Phi b of a phase B relative to the synchronous signal according to the method shown in step 2; step 4, determining the APF compensating current amplitude Im according to the APF compensation capacity and determining the current reference value according to the phase angle difference relative to the synchronous signal; step 5, detecting the voltage difference value of an APF direct-current bus capacitor on the basis of obtaining the current reference value and introducing the current difference value as feedback compensation, thereby weakening the effect of unbalance caused by the voltage difference value of a direct-current bus split capacitor on APF compensation performance; and step 6, controlling APF two phases by using a current tracking PWM (Pulse-width Modulation) control strategy, naturally controlling a third phase, finishing the compensation to a system harmonic source and finally ensuring that the voltage of a power supply is consistent with current waveform.

Description

technical field [0001] The invention relates to a three-phase four-switch parallel APF control method under unbalanced voltage. Background technique [0002] With the development of smart grid technology, the proportion of renewable energy such as photovoltaic power generation and wind power generation has increased, and a large number of medium and high-power power electronic devices and nonlinear equipment have been widely used. The resulting harmonic and reactive power problems have become increasingly serious. Filter (APF) is an effective device to solve power quality problems such as grid harmonics and reactive power compensation. [0003] At present, most of the APF application research is carried out for the three-phase six-switch topology. In contrast, the three-phase four-switch APF has a simple structure, significantly reduces device costs and switching losses, and further reduces heat dissipation requirements and device volume; The specific internal relationship ...

AI Technical Summary

Problems solved by technology

[0004] At present, domestic and foreign studies on the application of three-phase four-switch inverters to APF are mostly focused on harmonic and reactive power detection and new control methods, such as the dq method based on synchronous reference coordinates and the instantaneous reactive power based on the dq method. The theoretical pq method, ip-iq method, and the method of combining pq and ip-iq, etc., all of these methods have certain limitations, such as low accuracy, complex algorithms, and difficulty in meeting real-time requirements, and many methods are Based on the premise of grid voltage balance, without considering voltage unbalance and short-term faults, the APF reference value generation method

[0005] The three-phase four-switch APF command current determination method based on DC side voltage information, but this method needs to first classify and judge the fault current, and also needs to use a special method to detect the phase angle information of the positive sequence fundamental wave voltage, the calculation is cumbersome and lacks Versatility

The midpoint voltage balance mechanism of the three-phase four-switch motor drive device in the αβ coordinate system needs to be controlled by Clark transformation and SVPWM, which is relatively complicated to realize

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