Research on the Application of an SMES Based on Sliding Mode Control to Enhance the LVRT Capability of a Grid-Connected PV System

In this paper, a superconducting magnetic energy storage (SMES) device based on sliding mode control (SMC) is proposed for grid-connected photovoltaic (PV) systems that can effectively improve the ability of a PV system to withstand low-voltage ride-through (LVRT) during faults. SMC theory is selected as a nonlinear control technique, since the SMES has the characteristics of being multivariable and nonlinear and having strong coupling in the running process. Both the voltage outer loop and the current inner loop adopt the SMC strategy based on an exponential reaching law to increase the system startup speed and effectively reduce system jitter. Next, the SMES system based on SMC is used in a 100-kW class PV system. When a symmetrical fault or asymmetrical fault occurs suddenly in the grid-connected PV system, the SMES based on SMC can more significantly improve the power and voltage of the point of common coupling (PCC) and effectively suppress the voltage fluctuations of the DC link than the case of not using auxiliary measures or the use of a PI-SMES.