Research On Adaptive Sliding-mode Robustness Voltage Control Strategy And Performance Of Microgrid Inverter

As an excellent carrier for coordinating different renewable energy sources,microgrid has attracted much attention with the extensive use of new energy.In the islanding mode operation,the inverters of the microgrid need to be controlled cooperatively,and the system voltage and frequency are kept synchronized and the power is divided evenly in the steady state.However,the actual system has no ideal voltage support,and the inverter output is easily affected by load changes and nonlinear disturbances.The current inverter often adopts a droop control strategy with a double-loop control structure,and its characteristics are limited by the droop control loop coefficient,the dynamic response is slow and the output adjustment range is large.At the same time,the existing dual-loop control or PID voltage controller has low robustness and high steady-state output distortion rate under nonlinear disturbances.Therefore,it is of great significance to design an effective output voltage control strategy to improve the system’s transient disturbance suppression capability and steady-state output quality.This article first analyzes the current research status of parallel inverter control strategies under the islanded mode operation,and summarizes the current research deficiencies.Therefore,based on the droop control strategy,researches on dynamic performance optimization and system robustness performance improvement are carried out and effective solutions are proposed.Aiming at the optimization of dynamic performance,the improved droop control strategy based on virtual impedance and dynamic power compensation is compared and analyzed.It is difficult to have both rapidity and stability and the control effect is limited.The droop control is unable to flexibly change the voltage adjustment step due to its fixed coefficients.Therefore,according to the real-time power and voltage differential relationship,an improved droop control strategy based on sliding mode variable structure control terms is proposed.This strategy achieves rapid system stability by dynamically adjusting the droop reference voltage,the sliding mode controller can effectively resist external disturbances,and the power differential feedback can quickly reflect the trend of line output changes.In addition,the flexibility of voltage adjustment is related to the sliding mode control law.By designing an improved approaching law of sub-sub-speed change,the system can adaptively adjust the voltage step change rate according to the deviation between the actual value and the reference value.Simulations verify that the proposed control strategy achieves rapid output voltage stabilization and reduces sliding mode chattering.On the other hand,due to the perturbation of the internal filtering parameters of the inverter system and the disturbance of the nonlinear load current,the output waveform distortion is serious and it is difficult to meet the high-quality power supply requirements.Therefore,based on the mathematical model of the static two-phase coordinate system topology,a sliding mode variable structure voltage single-loop control strategy is proposed,which quickly expresses the current disturbance through the voltage switching gain term and tracks the system voltage output in real time.Aiming at the filter parameter perturbation,a parameter observer is designed to eliminate the system parameter dependence and realize the global robustness of the sliding mode;at the same time,combining the previous article to improve the reaching law and improve the speed of dynamic adjustment of the sliding mode.In order to reduce the jitter amplitude of the sliding mode system without losing the adjustment speed,an adaptive gain coefficient is designed to compensate for the uncertainty disturbance caused by the state change,and an adaptive virtual impedance term is added based on the sliding mode voltage control loop to realize the equal distribution of reactive power.Finally,simulation and experimental results show that the method has a fast response to filter parameter perturbation,current interference and good robustness performance.