| Recently, hybrid battery and ultracapacitor has growing applications in electrical vehicle, electric ship and distributed renewable energy generation to achieve higher overall performance. Most of the power electronics interface of hybrid battery and ultracapacitor is realized by connecting individual dc-dc converters. However, the advantages of using integrated power converters with multiple interfacing ports, which is defined as multi-port converter, instead of individual dc-dc converters are the following: (1) reduced cost due to less component count and associated circuits, (2) higher power density, (3) efficient thermal management, (4) improved reliability because of compact layout, (5) easier implementation of centralized control. Therefore it is important to develop multi-port converter for hybrid energy storage elements.; To date limited research has been conducted on multi-port dc-dc converter. In addition, the topologies reported in the literature have problems such as unidirectional power flow, no electric isolation, hard switching with low efficiency, etc., which limit the applications. Other than that, most of the researches only focus on open loop operation and lack of investigation on dynamic performance under varied load conditions.; This research proposed a novel three-port dc-dc converter topology for hybrid energy storage elements including ultracapacitor and battery. Compared with existing topologies, this topology has the advantages of bidirectional power flow, low voltage and current source input, electrical isolation, soft switching and less component count. The steady state equations are derived based on operation principles. Interacting between two input ports is a common issue for multi-port converter. However, it is rarely investigated before. The figures based on steady state equations clearly show the interactions and relationship between control variables and outputs. The proposed converter is capable of soft switching for all the six switching devices, which is a key contributing factor for high power efficiency and high power density. Soft switching conditions are derived based on operation principle.; Other than steady state analysis, dynamic modeling using state space averaging techniques will be provided. Unlike single input dc-dc converter, the dynamic model of multi-port dc-dc converter is basically a multi-input-multi-output (MIMO) system containing multiple interacting variables. The model becomes more complicated because derived transfer functions are not scalar but matrix. In addition, each output variable could be affected by two or more control variables depending on how many input ports. Based on the dynamic model, a double loop control system with decoupling network will be designed to achieve: (1) dc inductor current control, (2) over current protection, (3) improved dynamic response, (4) controlled dc bus voltage. A system-level power management strategy is proposed to coordinate the power flow between each energy storage element and main power source.; Finally, an experimental converter prototype of 6 kW is built to verify the above theoretical analysis. A software based phase shift modulation scheme is proposed due to absence of modulation hardware in the DSP. Guidelines for power stage components designing and selecting are presented. |
