Pre-synchronization control method based on virtual impedance

Abstract

The invention relates to a pre-synchronization control method based on virtual impedance, and belongs to pre-synchronization control methods. The pre-synchronization control method comprises a virtual impedance unit Xv exists at the two ends of a grid-connected switch Sg; the voltage Upcc of a node PCC and the grid voltage Ug are detected; and virtual active power Pv and reactive power Qv of a virtual reactance unit are calculated, PI controllers enable the virtual active power Pv and reactive power Qv to approach 0, when both the virtual active power Pv and reactive power Qv are 0, the voltage amplitudes of the two ends of the grid-connected switch Sg are the same, the voltage phases of the two ends of the grid-connected switch Sg are the same and if the grid is connected at this time, the instant impact current of grid connection is low, and it is ensured that an inverter is connected to the grid smoothly and friendly. A traditional pre-synchronization control method includes two phase-locked loops and needs a relatively large amount of PI regulators, and a traditional control system is complex. According to the pre-synchronization control method of the invention, the phase-locked loops are omitted, control is simpler, and the method is not influenced by delay and control precision of the phase-locked loops; only two PI controllers are needed, the complexity of an algorithm is reduced; and the output voltage of the inverter and the grid voltage are the same in both the amplitude and the phase, the transient impact current is reduced, and seamless switching between off-grid and grid-connection is realized.

Description

technical field [0001] The invention relates to a pre-synchronization control method, in particular to a pre-synchronization control method based on virtual impedance. Background technique [0002] With the aggravation of the energy crisis and the increasingly severe environmental pollution, the distributed power generation system based on renewable energy has been developed rapidly. No small challenge. The control strategy based on virtual synchronous generator (Virtual Synchronous Generator, VSG) can participate in the frequency regulation and voltage regulation of the power grid, and can also operate independently and autonomously like a synchronous generator, which greatly improves the adaptation of microgrid and distribution network to distributed power. Therefore, the virtual synchronous generator algorithm has great development prospects. [0003] The microgrid has two different operating modes: off-grid and grid-connected. When the inverter based on the virtual syn...

AI Technical Summary

Problems solved by technology

[0005] The purpose of the present invention is to provide a pre-synchronization control method based on virtual impedance, which solves the problems of the traditional pre-synchronization method based on virtual synchronous generators, omits the phase-locked loop link, makes the control simpler, and is not affected by the delay and delay of the phase-locked loop. The impact of control accuracy, and can achieve the same amplitude and phase of the inverter output voltage and the grid voltage, reduce the transient impact current, and realize the seamless switch between off-grid and grid-connected

Images