A Power Decoupling Circuit For LLC Single Stage On-Board Charger

Power density and efficiency are main specifications of on-board charger(OBC)for EV.Single stage OBC has advantages in efficiency and cost,but there exists secondorder ripple on DC side because of topology and function requirements.It causes large charging current ripple and influences battery lifetime.If bulky electrolytic capacitors are applied to solve this problem,power density will be much lower.Appling active power decoupling(APD)circuit in single stage OBC can significantly achieve minimization of power pulsation with higher power density.In order to solve the double line frequency ripple of the LLC single-phase OBC,this paper first analyzes the relationship between the volume of the APD energy storage capacitor and the APD topology.After comparing between several topologies,the Bidirectional Buck/Boost is chosen as the APD circuit and its control strategy is analyzed.Secondly,the paper analyzes and calcualtes the system phase shift in the LLC-type car charger.The influence of the phase shift on the decoupling effect is evaluated.Finally,a hybrid control strategy avoiding phase shift influence is investigated.By sampling the DC side signal and controlling with a proportional resonance controller,it can realize zero static error control for double line frequency component of charging current.As the inner control loop,APD inductor current is controlled to ensure the APD working in the stable region.The outer loop is APD capacitor voltage control which fixes the DC part of APD capacitor voltage equaling to half of battery voltage.Thus,the three-loop control strategy can realize power decoupling better.Based on the topology and calculation,this paper designed the active power decoupling circuit and built an experimental prototype.The working waveform of the circuit proved the rationality of the control strategy and theoretical analysis.