Improved low-cost sliding mode control of 4-leg inverter for isolated microgrid applications

Isolated microgrids including several sources of clean energy such as photovoltaic system can be considered as the auxiliary source of power generation. However, unbalanced condition is inevitable in typical microgrids due to asymmetric power generation and consumption. To supply load from different distributed generation, an interface 4-wire power converter is essential. A 4-leg inverter with suitable control method is a beneficial solution to support unbalanced loading condition. However, high reliable low-cost control method achieves more attention to avoid any power outage. As a result, a low-cost sliding mode control method is proposed in this paper to control the output voltages of the 4-leg inverter. The proposed method can provide fast dynamic response, fixed switching frequency, high robustness against model parameter mismatches, and external disturbances without any current sensors. Furthermore, to reduce the chattering of the sliding mode control method more effectively, an improved low-cost method with adaptive discrete coefficient is also proposed. Finally, to evaluate the performance of the proposed method, a 3-kW test bench with digital control board based on TMS320F28335 processor is provided.