LCL-type grid-connected inverter parallel connection virtual impedance control method

Abstract

The invention relates to an LCL-type grid-connected inverter parallel connection virtual impedance control method. Under weak grid conditions, a parallel connection virtual impedance control method isprovided, difference is solved between grid-connected current ig and grid-connected instruction current parameters iref to obtain a signal ei, then difference is solved between the signal ei and a current signal fed back by an inverter side virtual impedance Zp(s), a and after double-current feedback control, a PWM modulating wave signal is generated to be transmitted into a PWM generator to generate a switch signal. After parallel connection virtual impedance, a system phase margin is increased, a harmonic is obviously lowered, the robustness and the interference resisting capability of thesystem are effectively improved, it is guaranteed that grid-inlet current is not greatly influenced by grid resistance, a parallel connection inverter can still normally work under the change of gridresistance wide ranges, the harmonic is small, and the applicability is good; in the dynamic response process of transforming a half load to a full load of the grid-connected virtual impedance, compared with a traditional method, the transition time is shorter, the overshooting amount is reduced, and stable running of a grid-connected inverter system is not influenced.

Description

technical field [0001] The invention relates to a grid-connected control method, in particular to a parallel virtual impedance control method for improving the phase margin of an LCL type grid-connected inverter under a weak grid. Background technique [0002] In recent years, in order to cope with the energy crisis and environmental pollution, the distributed generation (DG) that uses renewable energy (such as solar energy, wind energy, etc.) to generate electricity has taken an increasing proportion in the power system. The interface between energy and the grid and its interaction with the grid has become a hot topic of research. According to the provisions of the distributed generation grid connection standard Q / GDW480-2010, the ratio of the short-circuit current of the distributed generation grid connection point (PCC point) to the rated current of the distributed generation is not less than 10. When the short circuit ratio (SCR) is between 2 and 3, the grid behaves as ...

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Problems solved by technology

[0005] The present invention is aimed at the problem that the current high grid impedance will lead to resonance and phase-locked loop control weakening, and proposes a parallel virtual impedance control method for LCL grid-connected inverters to ensure that the system has good robustness under a wide range of grid impedance Control method of parallel virtual impedance of LCL type grid-connected inverter with high performance and dynamic performance and low cost

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