Strict-feedback Nonlinear Sliding Mode Control for Battery Converters in DC Microgrids

In a DC microgrid, DC-DC converters are widely used as linking interfaces between DC power sources (or energy storage units) and the DC bus. Typically, linear controllers are widely adopted for these source DC-DC converters to control the power generation of the sources. However, the system's stability can hardly be guaranteed when constant power loads (CPLs), whose input impedances are negative, are connected to the microgrid due to unexpected interactions between sources and CPLs. In addition, as the variation of DC bus voltage is limited to a specific range by electrical standards, which indicates constrained states of the DC-DC converters, conventional nonlinear controllers would cause deteriorated power quality in static and dynamic processes. This paper proposes a novel strict state-constrained sliding mode control strategy for the source DC-DC converters to address the stability and power quality issues of the DC microgrid. The design methodology, stability analysis, and implementation of the proposed control strategy are discussed in detail. A 3-kW buck/boost converter, which is widely used as the source DC-DC converter in a DC microgrid, is designed and established in the lab. The simulation results verify the effectiveness of the proposed control strategy.