Single-Stage LLC Charger with PFC Functionality and Wide Input Voltage Range

We present a compact battery charger topology for weight and cost sensitive applications with an average output current of 9 A targeted for 36 V batteries commonly found in electric bicycles. Instead of using a conventional boost converter with large DC-link capacitors, we accomplish PFC-functionality by shaping the charging current into a sin2-shape. In addition, a novel control scheme without input-current sensing is introduced. A-priori knowledge is used to implement a feed-forward control in combination with a closed-loop output current control to maintain the target current. The use of a full-bridge/half-bridge LLC converter enables operation in a wide input-voltage range.A fully featured prototype has been built with a peak output power of 1050 W. An average output power of 400 W was measured, resulting in a power density of 1.8 kW/dm3. At 9 A charging current, a power factor of 0.96 was measured and the efficiency exceeds 93% on average with passive rectification.The impact of pulse charging has been evaluated on a 400 Wh battery which was charged with the proposed converter as well as CC-CV-charging for reference. Both charging schemes show similar battery surface temperatures.