The DC energy router is a friendly interface for multiple energy sources. The bidirectional converter is the key component of the DC energy router to realize power interaction between ports. This paper focuses on magnetic integration and efficiency optimized control on the proposed bidirectional four-port energy router. First, the coupling characteristics of the topology of the four-port energy router are analyzed. Based on the decoupling parameter constraints, the operation principle and characteristics of the four-port energy router under extended phase-shift control are analyzed. In order to reduce the leakage inductance and ensure the decoupling characteristics of the four-port energy router, the magnetic integration analysis and design of the inductor are carried out and the finite element simulation verification of the transformer and inductor design are given. By simplifying the analysis of the system loss model, control based on optimized RMS current is determined. The Lagrange extremum method is used to figure out the efficiency optimization variable the four-port energy router achieves soft-switching under the same power, while the RMS current is the smallest. Finally, a four-port energy router simulation model and a prototype experimental platform are built to verify the correctness of analysis and effectiveness of optimal control strategy.

For modular multilevel converter-based battery energy storage systems (MMC-BESS), uneven power among batteries of SMs will be deduced by battery aging, battery fault, etc., which will degrade performance and even lead to system failure. For maintaining the balance of capacitor voltage, this paper analyzes the limits of the uneven power of batteries, which are presented as the current limits in this paper. According to analysis, an analytical method is proposed that only the dc and fundamental frequency components of the arm current are used to calculate current limits. With the current limits it is able to evaluate the reasonability of power distribution among batteries. Meanwhile, increase of fundamental frequency component will enhance the current limits, and the dc component determines the size relationship between the absolute values of the upper and lower current limits. Finally, simulation model and experiment prototype are built for verifying the theoretical analysis and current limits calculation method, and satisfactory results are provided.