Research On Improved Droop Control Of Microgrid Inverter Under Complex Operating Conditions

Droop control is one of the most commonly used control methods for microgrid inverters,which has the advantages of plug and play,seamless switching between on-grid and off-grid.However,the droop control inverter has poor anti-interference ability to the grid-side voltage in the grid-connected mode.As the load conditions in the micro-grid become more complicated,the AC bus voltage of the micro-grid is affected by the load operation.The phenomenon of wave and imbalance caused the inverter based on traditional droop control to have problems such as output power fluctuation and poor output current waveform quality.To this end,this article takes a three-phase inverter in a microgrid of a photovoltaic module plant as a research object,and improves droop control for different load conditions to improve the adaptability of droop control to the complex conditions of the microgrid.In this paper,by establishing a small-signal model for droop control of a three-phase grid-connected inverter,the in-depth analysis of the influence of the frequency,amplitude fluctuations and harmonics of the AC bus voltage of the microgrid under intermittent and nonlinear loads on the inverter is performed.A composite voltage feed-forward strategy based on instantaneous frequency detection and voltage amplitude PI compensation was proposed to realize real-time feed-forward of grid-side voltage.The proposed strategy greatly improves the ability of the inverter to resist grid-side voltage interference,and effectively improves the output power smoothness and current waveform quality of the inverter.In the three-phase unbalanced state of the microgrid AC bus voltage,the inverter output power stability and current balance cannot be achieved at the same time.To this end,this paper proposes an improved current-power step-by-step climbing algorithm in the negative-sequence voltage feed-forward outer loop.Under grid-connected conditions,the proposed algorithm can realize the coordinated control of output negative sequence current amplitude and output power fluctuation amplitude according to the control requirements of different applications.At the same time,it solves the problem of unstable output voltage of the pure negative sequence voltage feedforward control strategy under off-grid conditions.The Simulink model is built,and the simulation test results show that under intermittent and non-linear load conditions of the microgrid,the output power of the inverter based on the proposed composite feedforward droop control is stable,and the quality of the output current waveform is significantly improved.In the case of microgrids with unbalanced load conditions,the proposed current-power segmented hill-climbing algorithm can achieve coordinated control of output current waveform quality and output power smoothness,and ensure off-grid stability.Compared with the traditional droop control methods,the two improved methods have significantly improved the inverter output performance.Finally,a DSP28335 main control chip was used to set up a 10 k W inverter experimental platform,which was verified with the proposed composite feed-forward droop control,indicating the feasibility of the experimental platform and the correctness of the proposed algorithm.