Model-Based Active Damping Control for Three-Phase Voltage Source Inverters With LCL Filter

This paper presents a robust model-based active damping control in natural frame for a three-phase voltage source inverter with LCL filter. The presence of the LCL filter complicates the design of the control scheme, particularly when system parameters deviation is considered. The proposed control method is addressed to overcome such difficulties and uses a modified converter model in a state observer. In this proposal, the converter model is modified by introducing a virtual damping resistor. Then, a Kalman filter makes use of this model to estimate the system state-space variables. Although the state estimates do not obviously match the real world system variables, they permit designing three-current sliding-mode controllers that provide the following features to the closed loop system: 1) robust and active damping capability like in the case of using a physical damping resistor; 2) robustness because the control specifications are met independently of variation in the system parameters; 3) noise immunity due to the application of the Kalman filter; and 4) power loss minimization because the system losses caused by the physical damping resistor are avoided. An interesting side effect of the proposed control scheme is that the sliding surfaces for each controller are independent. This decoupling property for the three controllers allows using a fixed switching frequency algorithm that ensures perfect current control. To complete the control scheme, a theoretical stability analysis is developed. Finally, selected experimental results validate the proposed control strategy and permit illustrating all its appealing features.