A Cascade Equivalent Method For Compensation Networks In Wireless Power Transfer Systems

In wireless electric vehicle charging systems,all kinds of compensation networks are applied to compensate for the leakage inductance of the loosely coupled transformer.Constant current and constant voltage outputs and zero phase angle(ZPA)input characteristics are important for the compensation networks.Constant current/constant voltage charging profile can extend the battery life and ensure its safety and durability.Additionally,ZPA operation can minimize the apparent power required of the inverter,enhance system power transfer capability,achieve soft switching,and improve system efficiency.So far,more than 10 types of compensation networks have been proposed in wireless power transfer(WPT)systems.And their analysis methods are different and complicated.To resolve these issues,this dissertation firstly analyzes the current and voltage transfer characteristics of the one-order,two-order,and three-order circuits.And then,a general cascade equivalent method is proposed.With the proposed method,an arbitrary compensation network is considered as consisting of multiple one-order,two-order,and/or three-order circuits in cascade.The proposed method can simplify the analysis of the output and input characteristics of all compensation networks.A compensation network is equivalent to a cascade connection of one reversed L-section circuit and multistage π circuit.And it can also be equivalent to a cascade connection of multistage T circuit to analyze the constant voltage output characteristic.Based on the proposed method,this dissertation analyzes the output characteristics of some widely-used compensation networks in inductive power transfer(IPT)and capacitive power transfer(CPT)systems.A double-sided LCC compensated IPT system with output power of up to 3.3 kW is implemented to verify the proposed method.To analyze the constant current and voltage outputs both with ZPA operations of a compensation network,it is considered as consisting of multistage reversed L-section circuit and multistage normal L-section circuit in cascade.Based on this method,the resonant conditions of some widely-used compensation networks in IPT and CPT systems are analyzed to get constant output current and voltage at two ZPA frequencies.A 3.3 kW IPT system with the LCC-S compensation network is built to demonstrate the proposed method.Based on the proposed cascade method,a unified compensation network with minimum passive component counts is proposed to improve the power density and decrease the loss and cost.According to the proposed simplest network,all the possible IPT and CPT topologies are analogized.And then,this dissertation analyzes the resonant conditions of the simplest IPT system and the parameter sensitivity.Finally,the simplest IPT system with the S-SP compensation network is illustrated to demonstrate the analysis.This research makes contribution to the analysis and design of arbitrary compensation networks.And,it will provide scientific guidance and theoretical foundation for the design of high efficiency,high power density,and low cost wireless electric vehicle charging systems.