Abstract
This paper presents a soft switching direct current (DC) converter, with the benefits of bidirectional power conversion and wide-ranging voltage operation for battery charging and discharging capability. A series resonant circuit with variable switching frequency modulation is used to achieve the advantages of soft switching turn-on or turn-off of semiconductor devices. Therefore, the switching power losses in power devices can be reduced. A symmetric resonant circuit topology with a capacitor–inductor–inductor–capacitor (CLLC) structure is adopted to achieve a bidirectional power conversion capability for battery storage units in electric vehicle applications. Due to the symmetric circuit structure on both input and output sides, the converter has similar voltage gains for each power flow operation. In order to overcome the drawback of narrow voltage range operation in conventional resonant converters, a variable transformer turns ratio is adopted in the circuit, to achieve wide output voltage operation (150–450 V) for battery charging applications. To demonstrate the converter performance, a 1-kW laboratory prototype was constructed and tested. Experimental results are provided, to verify the effectiveness of the studied circuit.
Highlights
Power converters with bidirectional power flow have been widely utilized betweenAC and direct current (DC) grid systems and battery storage systems
The same circuit structures can be used for electric vehicle (EV) systems, to achieve vehicleto-grid (V2G) and grid-to-vehicle (G2V) operations
The basic circuit topologies of a bidirectional AC/DC converter are based on four or six three-leg active switches. These AC/DC converters can be controlled in power factor correctors (PFC) operation under forward power flow, or inverter operation under reverse power flow
Summary
Power converters with bidirectional power flow have been widely utilized between. AC and DC grid systems and battery storage systems. In references [10,11], symmetric PWM converters with two full bridge circuit structures were studied, to accomplish bidirectional power flow with PWM modulation and phase-shift angle control between two full bridge circuits with a load voltage range. In references [12–14], resonant converters with a capacitor–inductor–inductor–capacitor (CLLC) circuit structure were studied, to realize bidirectional power operation with pulse frequency modulation for electric EV or energy storage unit applications. In order to overcome the drawbacks of the above circuit topologies, a new DC converter is provided, to implement soft switching operation, a wide voltage output capability (150~450 V), and bidirectional power flow for energy storage units, bidirectional DC nanogrid systems, and battery charge/discharge systems. A laboratory prototype (1 kW power) was implemented to demonstrate the effectiveness of the proposed bidirectional resonant converter with the features of soft switching operation, bidirectional power flow, and wide voltage output.
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