Improved weighted average current control of LCL grid‐connected inverter and analysis of its order reduction characteristics

Abstract

LCL grid-connected inverter is good at suppressing the high frequency current, but the inherent resonance frequency of the filter will lead to the resonance peak. Therefore, the active damping is commonly used to suppress the resonance effect. Since the weighted average current control can provide better bandwidth for the system with high frequency and has the characteristics of system reduction, it is often used to replace the traditional dual-loop current control in the application of LCL grid-connected inverter. However, the reduction of current resonance peak at the grid side by the weighted average current control is limited, so it is necessary to combine the grid voltage and capacitor current feedback loop to achieve the ideal results. In weak grid, the newly added feedback path would easily lead to the loss of system reduction, which results in the existence of transient variables in the transfer function affecting the stability of the control strategy. To solve this technical problem, this paper addresses a new control method of LCL grid-connected inverter based on weighted average current control. By adding a capacitor current feedback path, pole-zero cancellation of the control system is realised as to reduce the systematic order and improve the robustness of the controller under the time-varying weak grid.

A weighted average mixed feedback control method based on LCL‐type grid‐connected inverter

“…Conventional WAC Delay compensation 19 Pole-zero repositioning 20 Parameter optimization design 21,22 The open-loop transfer function TWAC ref from i ref to i WAC can be deduced from Figure 1 as follows:…”

“…This approach can partially accomplish reduced‐order control by compensating for the digital control delay, but the open‐loop phase margin still decreases with an increase in grid impedance. Yang et al 20 achieve pole‐zero cancelation by adding a capacitor current feedback path when not considering the impact of digital control delay. However, after considering the digital control delay, adding a lead compensator again still fails to perfectly achieve pole‐zero cancelation.…”

Research on the control strategy of LCL grid-connected inverters based on improved auto disturbance rejection

“…However, because of the existence of nonlinear factors such as the dead time effect, switching tube conduction voltage drop, and grid voltage fluctuations in grid-connected inverter systems, it is difficult for inverters to maintain good performance; thus, the research on inverters is of great significance. 5,6 At present, the main control strategies for grid-connected inverters include proportional integral (PI) control, proportional resonance (PR) control and repetitive control (RC). The PI controller has the advantages of simple design and easy parameter adjustment.…”

“…However, because of the existence of nonlinear factors such as the dead time effect, switching tube conduction voltage drop, and grid voltage fluctuations in grid-connected inverter systems, it is difficult for inverters to maintain good performance; thus, the research on inverters is of great significance. 5 , 6 …”