Closed-Loop Control of a Three-Port Series Resonant Converter

The three port series resonant converter (3pSRC) is a promising topology especially for grid applications and onboard chargers. It offers galvanic isolation, high efficiency and enables a power dense design via the common multiport transformer structure. Typically, power flow is controlled by means of the switching frequency and/or the relative phase between the excitation of each transformer port. However a unique solution for the optimal combination of control variables for any unique set of port voltages and powers is non trivial. This paper proposes a control loop for naturally approximating such optimal control variables. The mathematical model used for calculating the power flow between the three ports is presented and a method for finding the switching frequency that best balances zero-voltage-switching (ZVS) and high efficiency for a given operation point is given. The control approach is demonstrated with a Silicon Carbide (SiC) based prototype for an on-board charger application.