Nonlinear Robust Controller Design for a Grid-Connected PV System Using DPC Approach

A nonlinear robust controller based on the 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 robust controller is designed using the nonlinear backstepping theory based on the power dynamics rather than the usual current dynamics. One of the foremost advantages of this procedure is that the inner current control loop is eradicated here which consequently simplifies the modeling and controller design process. On the other hand, to generate the reference active power from the closed loop control of the dc-link voltage dynamics an outer voltage loop is used. To show the robustness of the designed controller, external disturbances are also considered within the system. The overall stability of the whole system is confirmed with the formulation of control Lyapunov functions (CLFs) at every design stage during the design of the controller. Finally, the performance of the designed controller is tested on a 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 provide better performance than the existing controller in terms of the total harmonic distortion (THD) of the injected current.