Comprehensive design of an isolated AC-DC converter to emulate on-road current of electrical scooter for testing lithium battery

This paper develops a fast response, bidirectional, and single-phase isolated AC-DC converter for testing the battery of electric scooter. The converter which is based on fast current control can simulate the on-road power flow by controlling the current of battery in laboratory. The current command is recorded from the battery in electrical scooter when is running on road. The proposed converter should provide bi-directional power flow control for testing battery to simulate driving and braking conditions. Moreover, the discharging energy can be sent back to grid to achieve energy saving. The proposed converter consists of two bidirectional stages. The front end is a single-phase AC-DC converter under charging operation. It becomes a DC-AC converter to recover discharging energy from battery to grid. The second stage is an isolated DC-DC converter which provides charging and discharging behavior for battery. In order to reduce the influence of voltage ripple yielded by the AC-DC converter in charging mode, a high cutoff frequency LC filer is added in front of battery. Then, a careful design of current controller with 2 kHz bandwidth is applied to reduce the ripple current on battery. A current-fed full-bridge control topology is used to boost voltage and send the energy from battery to grid through the DC-AC converter in discharging mode. For improving the control range under discharging mode, an auxiliary switch is used to achieve 0.1A current control. Therefore, the on-road current behavior of battery used in electrical scooter can be truly reflected by the presented battery emulator. A DSP-based converter which is connected between 110V/60Hz/single phase grid and 1kW/48V/Lithium polymer battery is established to confirm the good performance of the proposed battery testing system.