Research On Key Technologies Of Quasi-Z-source Rectifier For On-board Integrated Charger Application

Electrical vehicles on-board integrated charger becomes the development trend of future electrical vehicles charger technology due to its highly integrated.The core concept is sharing the hardware of driving system and motor windings with the on-board charger.The on-board integrated charger has the advantages of high charging power and low cost.It has great potentials.Z-source converter has advantages of high reliability,low cost and high efficiency,which are very suitable for on-board integrated charger.This paper does research about the quasi-Z-source rectifier for electrical vehicles on-board integrated charger application.It solves the problems of integrating windings,dc-side second power frequency ripple and the soft-switched technology when single/three phase charger is realized using driving system.This paper does research about how to reconstruct motor windings,how to achieve the soft-switching technology for quasi-Z-source rectifier,how to design the parameters of quasi-Z-source network.The quasi-Z-source integrated charger uses the three-phase inverter achieving single-phase or three-phase controllable rectifier,and uses the quasi-Z-source network adjusting voltage.To solve the dc-side second power frequency ripple which causes the inductor current ripple and capacitor voltage ripple large,a method is proposed which is suitable for a single-phase on-board integrated charger.The quasi-Z-source on-board integrated charger uses the motor windings as the grid-side filter inductor.Based on the reconstruction method of motor windings,the electromagnetic model is built when the ac source flows through the motor windings.The motor torque in charging mode is analytically described,which solves the problem of motor rotating in charging mode.The reason of existing second power frequency ripple in single-phase system is given.The auxiliary circuits are added even the hardware of driving system has been fully used.The analytical relationship between the auxiliary circuits design parameters and how to eliminate second power frequency ripple is derived.The design flow of auxiliary circuits and quasi-Z-source network is given.The control strategy of how to eliminate dc-side second power frequency ripples for single-phase charger is given.The dc-side second power frequency ripples are eliminated and the capacitance and inductance of quasi-Z-source network are small.The capacitance is 30 times lower and the inductance is 3.5 times lower compared to other methods A single-phase quasi-Z-source on-board integrated charger prototype is designed and tested.The electrical vehicles on-board integrated charger is different from the design method of traditional charger.The power switches of integrated charger must be shared with the switches of electrical vehicles driving sys tem.The parameters of switches do not match the charging power.So the efficiency of on-board integrated charger is low.A soft-switched modulation for single-phase rectifier is proposed which is based on asymmetrical unipolar frequency doubling modulatio n.Each transition process in one switching frequency is analyzed.The analytical relationship between the quasi-Z-source network design parameters and how to achieve soft-switching technology is derived.The design flow of quasi-Z-source network and key parameters is given.All the switches on H-bridge can achieve full soft-switching and all the recovery current of diodes can be eliminated.The conclusion is verified by using the driving system,the highest efficiency increases by 2.8 percent than the hard-switching.The higher power can be got when three-phase ac source is connected with charger,but the single-phase soft-switching is not suitable for three-phase charging.So a soft-switched modulation suitable for three-phase quasi-Z-source integrated charger is proposed which is based on SVPWM.The shoot-through is inserted between zero vector and active vector to realize soft-switching.The equivalent circuit of each transition process and theoretical voltage and current waveforms are given.The quasi-Z-source inductors have effect on soft-switching technology in different output power which are analyzed.The optimal parameters are designed.The control strategy of achieving soft-switching for three-phase quasi-Z-source charger is given.The efficiency of system increases.Research shows that all switches in three phase bridges can realize soft-switching.And all diodes’ recovery currents are eliminated.The switch of quasi-Z-source network can achieve soft-switching.The quasi-Z-source inductor current works with discontinuous or boundary mode to achieve soft-switching technology.The inductance is small.The inductor current ripples are large in driving system with the shared quasi-Z-source inductors.To solve the problem of large battery output current ripple,the quasi-Z-source coupled inductor is designed.The theory of how to eliminate the dc-side inductor current ripple is analyzed.The coupled inductors of quasi-Z-source network suitable for realizing soft-switching technology are designed.On this basis,the capacitors of quasi-Z-source network are designed under driving mode,charging mode and V2 G mode.Finally,the three different modes experimental results verify that the dc-side current ripple can be eliminated in different modulations.And the t hree-phase quasi-Z-source integrated charger also can achieve soft-switching technology in charging mode.This thesis proposes a single-phase integrated charger which solves the problem of dc-side second power frequency ripple with small capacitance.The soft-switching technology is realized without auxiliary circuit.The battery charging and discharging current ripple is eliminated by using coupled inductor.This paper provides the theoretical guidance for the practical electrical vehicles on-board integrated charger applications using quasi-Z-source rectifier.