Research On Control Method Of Three-phase Grid-connected Inverter

Inverter systems are widely used due to their advantages of modular structure,multiple redundancy characteristics,and high power quality.Traditional droop control methods,unable to accurately manage power due to the inverter’s regulation of output impedance,are rendered ineffective when asymmetric and nonlinear loads are present.This causes the negative sequence and harmonic power to be distributed inaccurately,and three-phase asymmetry and harmonic distortion can also be present in the bus voltage,thus compromising the power quality of the entire power supply system.To begin with,four classic parallel control strategies-constant power control,constant voltage constant frequency control,droop control,were studied and analyzed in order to address the issue of output power and current equalization in inverter control systems.This was done by examining the output impedance characteristics of low-voltage inverter power supplies,assuming that the output impedance was resistive.After constructing a simulation model,the pros and cons of traditional control strategies are examined.In the face of various load fluctuations,micro grid active access and passive disconnection,traditional control strategies do not offer enough redundancy to sustain system steadiness.And there is still significant room for improvement in synchronization and power regulation,as well as harmonics.In order to further optimize the redundancy of the system,it is necessary to introduce proportional control,quasi proportional resonance control,and virtual impedance control strategies.Then,based on a three-phase inverter circuit with quasi proportional resonance,a VSG quasi proportional resonance control method based on virtual impedance is constructed by introducing adaptive virtual resistors.This method achieves accurate power distribution in testing,has the advantages of appropriate redundancy,and good system robustness,and solves the circuit harmonic problem during active access and passive disconnection of the microgrid.However,the overall circuit design is relatively complex,and the data construction and adjustment of virtual impedance still need to be matched with the actual grid connection system to achieve the desired high efficiency.Moreover,the demand for circuit protection design is also higher than for general control strategy application circuits.In a grid connected environment,it is necessary to study more concise and effective control strategies to meet practical application requirements.Finally,LCL type inverters with stronger application capabilities are studied.Aiming at the high-frequency resonance and stability control problems of LCL inverters,an analytical method based on solving higher-order equations is studied to obtain the maximum damping performance of higher-order inverters.While selecting the maximum damping ratio,the damping characteristics of grid connected inverters with higher order filters are analyzed considering multiple factors including digital control delay time,the ratio of resonant frequency to sampling frequency,and feedback algorithms.The proposed analysis method can obtain the control parameters of the inverter,facilitating engineers or researchers to use higher-order filters to achieve excellent control performance of grid connected inverters.This method also has the ability to collaborate with other control strategies.