Research On High Voltage Gain Multi-port Converter Based On Coupled Inductor

The power of photovoltaic(PV)system is affected by environmental factors and has characteristics such as intermittency and fluctuation,which affect the stability and safety of the system.Therefore,it is necessary to add energy storage devices in PV system to meet the demand of smooth output power in PV system.The traditional PV-battery system uses multiple independent single-input single-output converters to realize power conversion,which has the shortcomings of high cost,large size and difficult to achieve centralized control.Considering the low-voltage DC bus by using high voltage gain multi-port converter(MPC)can effectively improve the above shortcomings,therefore,it is important to study the high voltage gain MPC integrating PV,battery and high-voltage DC bus.Based on the coupled inductor technology,this thesis thoroughly studies the high voltage gain three-port converter(TPC)integrating PV and battery and its ports scalability.First,from the perspective of TPC topology construction,a non-isolated TPC topology integrating PV,battery and load is obtained by embedding a quasi-H-bridge battery storage port with bi-directional power flow characteristics in a conventional Boost converter,and a coupled inductor-based high-gain TPC is further proposed to realize the integration of PV,battery and high-voltage DC bus.The operation principle of the converter is analyzed in detail,the voltage gain expression of the converter is derived,and the correctness of the theoretical analysis is verified by simulation.Secondly,in order to reduce the switching losses and further improve the voltage gain of the converter,an improved high voltage gain TPC is proposed and studied.This converter has the advantages of low voltage stresses of switching devices and high efficiency by changing the high gain circuit structure to improve the voltage gain and achieve zero current switching of diodes.According to the port power characteristics of the converter,the operation principle of the improved high-gain TPC in different operation modes is analyzed,and the steady-state characteristics and parameter design of the proposed TPC are analyzed in detail.The correctness of the theoretical analysis of the proposed TPC is verified by a 200 W experimental prototype.Finally,in order to meet the integration of distributed multi-PV modules with battery,this thesis deduces a high voltage gain m-port PV power optimizer based on coupled inductor by ports extension of the improved high voltage gain TPC.The m-port power optimizer can extend the input ports to realize multiple PV modules connected to the system at the maximum power point operation state at the same time,and can also extend the bidirectional energy storage ports to realize the integration of multiple storage devices with PV and load.Taking the four-port power optimizer as an example,the operation principle under different operation modes is analyzed in detail and design a reasonable control strategy to enable the system to switch smoothly between different operation modes;the loss model of the system is established and the loss distribution is analyzed.The theoretical analysis is verified by an experimental prototype of 240 W.