Feedforward control method to improve adaptability of lcl type grid-connected inverter to grid

Abstract

The invention discloses a feedforward control method for improving the adaptability of an LCL type grid-connected inverter to a power grid. The method comprises the steps that 1, a capacitance current ic, a network connecting current ig and a grid-connected point voltage vpcc are detected to obtain sampling signals ics, igs and vgs of the capacitance current ic, the networking current ig and the grid-connected point voltage vpcc; 2, the sampling signals are input to a current controller, and vrl is output after operational processing; 3, the signal vgs is input into a grid-connected coupling point voltage low-order harmonic selector, and vr2 is output through data processing; 4, vr1 and vr2 are added, a modulation signal vm is obtained and input to a PWM generator, and a PWM signal is generated to control a switching tube of an inverter topology. Feedforward control is carried out by selecting grid-connected point voltage low-order background harmonics, the stability of a grid-connected inversion system and power grid voltage low-order background harmonic suppression are considered, and the adaptability of the system to the power grid impedance wide range changes is improved.

Description

technical field [0001] The invention relates to a control method of an LCL type grid-connected inverter, in particular to a feedforward control method for improving the adaptability of the LCL type grid-connected inverter to a power grid. Background technique [0002] Under the background of the gradual shortage of traditional fossil energy and the increasingly serious pollution, the application of grid-connected power generation of new energy such as photovoltaic and wind energy has made great progress. With the continuous improvement of the penetration rate of new energy sources such as photovoltaic and wind energy, grid-connected inverters pose great challenges to the stability and power quality of distribution networks. The locations where distributed inverters are connected to the public grid are widely distributed, and the common grid-connected inverters are resistive and inductive. A large number of grid-connected inverters gradually weaken the public grid into a time...

AI Technical Summary

Problems solved by technology

For the LCL grid-connected inverter, the wide-range time-varying grid impedance will reduce the open-loop gain and bandwidth of the inverter system, and affect the steady-state error and dynamic response of the grid-connected current

Especially when the inductive reactance of the power grid is large, the resonant frequency of the LCL filter drops rapidly, and the resonant conjugate pole shifts to the left, resulting in a significant reduction in the phase angle margin, generating a large number of low-frequency harmonics, and even causing the resonance divergence of the incoming current to cause instability

In addition, due to the effect of a large number of nonlinear loads in the public power grid, the actual grid voltage often has a large number of low-frequency harmonics, and the distorted grid voltage is a real-time disturbance to the grid current, which affects the quality of the grid current.

Considering that the LCL grid-connected inverter needs to suppress its own resonance peak and improve its own phase angle margin, the parameters of the PI regulator are relatively small, and it is difficult to take into account the stability and robustness of the system

Considering the low-order harmonic suppression of grid-connected current, there is mutual coupling between the LCL current control and low-order harmonic suppression of the grid-connected system, that is, mutual dependence and mutual restriction, and the sampling and calculation delay will further deteriorate the grid-connected current.

Under the condition of weak power grid, there are still few researches on the consideration of grid-connected current control and low-order harmonic suppression of LCL type grid-connected inverter system, and the existing control schemes are slightly insufficient.

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