Soft Start-Up Control Strategy for Dual Active Bridge Converter with a Supercapacitor

Min-Soo Kim, Do-Hyun Kim, Dong-Keun Jeong, Jang-Mok Kim and Hee-Je Kim
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Min-Soo Kim: Department of Electrical Engineering, Pusan National University, Pusan 46241, Korea
Do-Hyun Kim: Department of Electrical Engineering, Pusan National University, Pusan 46241, Korea
Dong-Keun Jeong: Power Conversion and Control Research Center, HVDC Research Division, KERI, Changwon 51543, Korea
Jang-Mok Kim: Department of Electrical Engineering, Pusan National University, Pusan 46241, Korea
Hee-Je Kim: Department of Electrical Engineering, Pusan National University, Pusan 46241, Korea

Energies, 2020, vol. 13, issue 16, 1-19

Abstract: Renewable energy needs are steadily on the rise. Bidirectional DC/DC converters are essential in charging and discharging various storage batteries, such as PV/ESS (photovoltaic/energy storage system). A dual active bridge (DAB) converter, in particular, transfers power in both directions by phase shift using a soiled state transformer (SST). To reduce switching inrush current in batteries under high voltages, a soft start-up is demonstrated during the initial switching operation. When a supercapacitor (SC) is used as a battery, the reverse power caused by the inrush current appears under high voltage at the DC-link side. This causes serious electrical damage to the PV/ESS’ boost converter and inverter. To suppress peak overshoot voltage and stabilize soft start-up transients, we propose a three-step soft start-up controller and algorithm for bidirectional DAB converter implementation at virtual ESS and UPS. The step-by-step control strategy by OLDC (open loop duty control), OLPSC (open loop phase shift control), and OLFC (open loop frequency control) provides a stable soft start-up operation. In the initial stage of the OLDC, the duty ratio is gradually increased by the PWM (Pulse width modulation) signal. In the middle stage, a phase difference is seen as per the voltage of the SC. The OLPSC is performed to reduce the phase difference. In the final stage, the OLFC is performed to smoothly control the small phase difference. The overshoot or inrush current is drastically suppressed toward the DC-link and SC module. Consequently, we demonstrate a proposed controller and algorithm with prototype 5 kW DAB converter.

Keywords: 3-step soft start-up operation; dual active bridge (DAB) converter; photovoltaic/energy storage system (PV/ESS); supercapacitor (SC); phase shift (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
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