Power Control Based on State Space Strategies for Grid⁃Oriented Inverters with LCL Filters

Through a third⁃order mathematical model of grid⁃oriented LCL⁃type converters,this paper analyzes the complicated dynamic characteristics and resonance problems which may influence the system stability.To realize active damping for LCL filters and improve dynamic performance of current regulators,a state space current PI controller is proposed whose parameters can be tuned based on the polynomial equations approach.An extended state observer is integrated with the regulation scheme,where additional sensors are not necessary in contrast with conventional active damping strategies.Synchronous reference frame PLL(SRF⁃PLL)equipped with filter technology is proposed for grid voltage disturbance suppression.This method is then applied to establish a double⁃closed⁃loop power regulator that demonstrates improved performance compared with other controllers.The simulation results are displayed to illustrate the efficiency of the regulation methods.

Improved Model Predictive Direct Power Control of Grid Side Converter in Weak Grid Using Kalman Filter and DSOGI

When grid side converter(GSC)is connected to weak grid,the small signal instability can happen due to terminal characteristics of the GSC that are incompatible with the grid impedance.This issue is not of wide concern in previous studies of direct power control(DPC)of GSC.By small signal analysis,it is shown that the impedance characteristic of the conventional direct power control GSC is not compatible with the inductive grid impedance in weak grid due to its constant power load behavior.To solve the problem,instead of feeding the DPC controller with direct measured voltage and current,a Kalman filter(KF)is used to obtain filtered output current and a double second-order generalized integrator(DSOGI)is used to obtain filtered voltage at the point of common coupling(PCC).These strategies change the impedance characteristic of the GSC dramatically and make it suitable to operate in weak grid where SCR is 2,while the rapid power response is preserved.The proposed strategy is verified through simulation and controller hardware in loop(CHIL)tests.