A Bridgeless Isolated Half Bridge Converter Based EV Charger with Power Factor Pre-regulation

 Abstract

Conventional full bridge and half bridge converters are quite popular for front-end power factor preregulation (PFP) in EV (Electric Vehicle) battery chargers. DCM operation at high power causes increased oscillation in the circuit. These oscillation increase with parasitic components of circuit. During deep DCM operation, these oscillations are seen to be significant and contribute to harmonic content in the input current. Therefore, a power factor pre-regulation bridgeless isolated half bridge (HB) converter based electric vehicle (EV) charger with reduced LC oscillation in discontinuous conduction mode (DCM), is presented in this paper. To reduce LC oscillation, two diodes are used in series with minimum number of magnetic components. The design of proposed charger in DCM is illustrated to facilitate uniform battery current during constant current/constant voltage (CC-CV) charging. The inherent advantage of reduced conduction loss with bridgeless topology are achieved. The performance of this isolated HB converter based charger is shown for improved oscillation characteristics and power quality (PQ) operation at steady state and over a range of varying input voltages.

Index Terms— Battery Charger, Bridgeless HB Converter, Electric Vehicle, PF Pre-regulation, CC-CV Charging, Power Quality

Block Diagram:

Fig. 1 Configuration of isolated half bridge PFC converter fed EV Charger

Expected Simulation Results:

Fig. 2 Experimental Steady State Performance of charger (a) Source

Voltage vs, Source current is, battery voltage Vdc and battery current Idc (b)

BL operation of two switches during individual half cycle (c) Magnetizing

Inductor currents iLm1,2 with diode currents iD3,4 at secondary VC1,2 in DCM

(e) Improved Switch voltage and switch currents with reduced LC

oscillation in DCM

Fig.3 Experimental Performance of Proposed EV charger at varying source

voltage (a) rated to increased (260V) (b) rated to reduced (160V)

CONCLUSION

A new BL isolated HB converter with the most beneficial features such as reduced cost and high power density, is designed and implemented in this work for off-board EV charger. Due to lower part count in the circuit and DCM based operation, compactness of the charger is achieved. The presence of input diodes in series with PFC switches reduces the LC oscillation during zero inductor current period, which has been shown with improved waveform of switch voltage stress across the switches in DCM operation. This improves the harmonics spectrum of input current. An improved charging with low ripple is facilitated in CC-CV mode and very low supply current THD is observed i.e. 3.5% at rated source voltage. The performance of isolated PFP fed charger, is found adequate, as per the recommended regulations i.e. the IEC 61000-3-2 PQ standard, at steady state as well as at varying source voltage over wide range.

REFERENCES

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