Onboard Unidirectional Automotive G2V Battery Charger using Sine Charging and its Effect on Li-ion Batteries

 ABSTRACT

The use of on-board battery chargers is common in electric and plug-in hybrid electric vehicles (EV/PHEV) for charging the battery from the utility power grid. To reduce the mass and cost of the charger while charging Li-ion batteries used in these vehicles, various cost-effective topologies are being proposed. This paper introduces two unidirectional battery charger topologies with a novel single-stage control that generates rectified sinusoidal charging currents to the battery, eliminating the need for bulky dc bus electrolytic capacitors used in conventional systems. Eliminating the electrolytic capacitors results in reduced size, mass, and cost of the charger and improved reliability. The paper presents simulations of voltage and current waveforms during normal operation and an accelerated cycle charge/discharge testing of battery cells with low-frequency current ripple to determine the impact on Li-ion battery capacity and life. The test results demonstrate the negligible impact of sine charging on Li-ion battery performance.

KEYWORDS

battery charger, sine charging, Li-ion

Schematic Diagram:

                 Fig. 1. Electrical schematic diagram of Isolated Unidirectional Charger Topology 1

Expected Simulation Results:

Fig. 2: Simulation Results of the Charger topologies with sinusoidal

                                     charging scheme (a) Topology 1 (b) Topology 2

                                      Fig. 3. Battery measured static capacity versus cycle # test results
                                                     sinusoidal charging and DC charging

                             Fig. 4. Battery capacity versus # of days test has been running to
                                               show impact of shelf life on loss of capacity

Fig. 5. Roundtrip charge discharge efficiency for 1C (16A) DC

                                  and sine charging and 1C (16A) 80% DOD DC discharge

Fig. 6. Battery HPPC resistance for an 80A, 10 second discharge

                                                 pulse at 100 and 800 cycles

Fig. 7. Battery open circuit voltage at 100 and 800 cycles

Fig. 8. Battery impedance versus frequency at 100 and 800 cycles

CONCLUSION

In battery chargers for EV/PHEVs the DC link capacitor volume can be significantly reduced by eliminating the electrolytic capacitor. This enables higher power density chargers with reduced mass, cost and improved reliability if current ripple at twice the line frequency can be tolerated by the battery. The impact of this low frequency ripple has been studied experimentally and the results support the use of the sinusoidal charging technique allowing 120Hz ripple into the battery as an alternative to DC charging. Two unidirectional battery charger topologies utilizing this sine charging technique with a single stage control have been simulated to verify the control strategy and charger performance. The first topology uses the conventional boost stage and would be more suitable for power < 1kW. As the power levels increase, the diode bridge losses significantly degrade the efficiency, so heat management might become an issue [10]. The second topology uses the bridgeless boost PFC configuration where the input diode rectifier input is replaced by two diodes and two switches. These are suitable for higher power levels >1kW due to their better efficiency. However, this topology introduces more EMI into the circuit.

REFERENCES

[1] D. Gautam, F.Musavi, M. Edington, W. Eberle, and W. G. Dunford, “An automotive on-board 3.3 kW battery charger for PHEV application,” in Proc. 7th IEEE Veh. Power Propulsion Conf., Chicago, IL,2011.

[2] W. Ruxi, F. Wang, L. Rixin, N. Puqi, R. Burgos, and D. Boroyevich, "Study of Energy Storage Capacitor Reduction for Single Phase PWM Rectifier," in Applied Power Electronics Conference and Exposition,2009. APEC 2009. Twenty-Fourth Annual IEEE, 2009, pp. 1177-1183.

[3] T. Shimizu, T. Fujita, G. Kimura, and J. Hirose, "A unity power factor PWM rectifier with DC ripple compensation," Industrial Electronics, IEEE Transactions on, vol. 44, pp. 447-455, 1997.

[4] Linlin Gu; Xinbo Ruan; Ming Xu; Kai Yao; , "Means of Eliminating Electrolytic Capacitor in AC/DC Power Supplies for LED Lightings,", Power Electronics, IEEE Transactions on, vol.24, no.5, pp.1399-1408, May 2009

[5] W. Beibei, R. Xinbo, Y. Kai, and X. Ming, "A Method of Reducing the Peak-to-Average Ratio of LED Current for Electrolytic Capacitor-Less AC-DC Drivers," Power Electronics, IEEE Transactions on, vol. 25, pp. 592-601, 2010.