Sliding mode control for rectifier stage of solid state transformer

Solid state transformer (SST) enabled microgrid is the trend of microgrid. The aim of rectifier stage of SST is to absorb sinusoidal input current and maintains constant dc-link voltage. In the SST over scheme, dual active bridge is employed to supply the dc bus, which behave as a constant power load for the rectifier stage. The constant power loads have a characteristic of negative incremental impedance, which may degrade the stability of rectifier stage of SST if the rectifier is not properly controlled. This paper proposes a sliding mode control (SMC) scheme for the rectifier stage with constant power load. The proposed SMC is able to stabilize the dc-link voltage and guarantee the input current sinusoidal in the presence of significant variations in the load power. A sliding mode power observer is constructed to improve the performance of rectifier stage. The proposed SMC is validated by simulation in MATLAB/Simulink for stabilizing the rectifier stage with constant power load. the simulation result of conventional PI controller is also given for comparison. Simulation studies prove the SMC has better performance that conventional PI controller. Unity power factor and precise regulation of the DC voltage are achieved by SMC, even in cases of load power change.