Nonlinear backstepping controller design for a three-phase grid-connected photovoltaic system using DPC approach

A new direct power control (DPC) approach for a voltage source inverter (VSI) based three-phase grid-connected solar photovoltaic (PV) system is proposed in this paper. The proposed DPC is designed using the nonlinear backstepping control scheme based on the power dynamics rather than the conventional dp current dynamics. As a result, the inner current control loop is eradicated in this paper which simplifies the system modeling and controller design and enhances the transient performance. Conversely, the outer voltage loop is used to generate the active power reference from the closed loop control of the dc-link voltage dynamics. The proposed controller is designed recursively based on the Lyapunov function theory and overall stability of the whole system is confirmed with the formulation of control Lyapunov functions (CLFs) at every design stage of the controller. Finally, the performance of the designed controller is tested on a three-VSI based three-phase grid-connected PV system under different operating conditions. The performance is also compared with an existing controller and it is clear that designed controller can better performance than the existing controller in terms of the total harmonic distortion (THD) of the injected current and quality of power.