Single-stage ZETA-SEPIC-based multifunctional integrated converter for plugin electric vehicles


A single-stage-based integrated power electronic converter has been proposed for plug-in electric vehicles (PEVs). The proposed converter achieves all modes of vehicle operation, i.e. plug-in charging, propulsion and regenerative braking modes with wide voltage conversion ratio (M) [M < 1 as well as M > 1] in each mode. Therefore, a wide variation of battery voltage can be charged from the universal input voltage (90–260 V) and allowing more flexible control for capturing regenerative braking energy and dc-link voltage. The proposed converter has least components compared to those existing converters which have stepping up and stepping down capability in all modes. Moreover, a single switch operates in pulse width modulation in each mode of converter operation hence control system design becomes simpler and easy to implement. To correctly select the power stage switches, a loss analysis of the proposed converter has been investigated in ac/dc and dc/dc stages. Both simulation and experimental results are presented to validate the operation of the converter.





Fig. 1 Block diagram and proposed structure of the integrated converter

(a) Block diagram of PEV with on-board integrated battery charger, (b) Proposed ZETA-SEPIC-based integrated converter for PEVs



Fig. 2 Simulation results

(a) Simulation waveforms during plug-in charging mode with 220 VRMS of grid voltage, (b) Waveforms of propulsion mode, (c) Dynamic operation of propulsion mode with step load variations, (d) Closed loop verification of regenerative braking mode by varying the dc-link voltage

 Fig. 3 Simulation results during plug-in charging mode with 100 V (peak) grid voltage and 60 V battery voltage (a) Waveforms of vg, ig, VCf and ILf , (b) Waveforms of VC and Vb, (c) Simulation results with grid voltage of 90 V

Fig. 4 Simulation waveforms during propulsion and regenerative braking with 60 V battery and 100 V dc link (a) Waveforms in propulsion mode with 400 W load, (b) Dynamic operation of  propulsion mode with load variations, (c) Closed loop verification of regenerative braking mode by varying the dc-link voltage



A bridge modular switched-capacitor-based multilevel inverter with optimized UFD-SPWM control method is proposed in the paper. The switched-capacitor-based stage can obtain high conversion efficiency and multiple voltage levels. Meanwhile, it functions as an active energy buffer, enhancing the power decoupling ability and conducing to cut the total size of the twice-line energy buffering capacitance. Furthermore, voltage multi-level in DC-link reduces the switching loss of inversion stage because turn-off voltage stress of switches changes with phase of output voltage rather than always suffers from one relatively high DC voltage. Most importantly, the control method of UFD-SPWM, doubling equivalent witching frequency, is employed in the inversion stage for a high quality output waveform with reduced harmonic. In addition, the optimized voltage level phase maximizes the fundamental component in output voltage pulses to reduce harmonic backflow as possible. Hence, the comprehensive system efficiency has been promoted and up to peak value of 97.6%. Finally, two conversion stages are controlled independently for promoting reliability and decreasing complexity. In future work, detailed loss discussion, including theoretic calculation and validation of loss breakdown, will be presented.



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