High-Frequency-Linked Three-Port Converter With Optimized Control Strategies Based on Power System Load Flow Concepts for PV-Battery Systems

This article proposes an optimized modulation and control strategy for high-frequency-linked three-port converters (HFL-TPCs), which is conceptually derived from the generalized load flow equations of a typical power system. The power system analogy explains why single phase shift (SPS) modulation results in higher reactive currents that reduce the overall converter efficiency. The SPS converter also loses zero-voltage switching (ZVS) at lower power operations. The proposed optimized quintuple phase shift (QPS) modulation method allows dynamic control of duty cycles of the HF square wave voltages that potentially control the real and reactive power flows of the HFL-TPC. The QPS modulation phase variables are applied to derive the generalized models of the HFL-TPC using a harmonic analysis approach. Harmonic analysis and the optimized modulation strategy greatly simplify the theoretical analysis of the HFL-TPC compared to a piecewise time-domain approach. A detailed power loss model of the HFL-TPC is also discussed. To verify the practical feasibility of the proposed optimized modulation strategies, a 60-V, 400-W HFL-TPC is built and tested. Simulation and experimental results show that the proposed modulation method reduces reactive power, improves efficiency, and maintains the ZVS operation over a wide voltage and power range.