Isolated single stage bidirectional AC-DC converter with power decoupling and reactive power control to interface battery with the single phase grid

Abstract

An isolated single stage bidirectional AC-DC converter with a series-connected buffer to power decoupling is proposed to interface battery with the single phase grid. None electrolytic capacitor is used in the proposed structure. The converter is a modified AC-DC DAB series-resonant single phase converter where a third active bridge is used to power decoupling and it is series-connected with the rectified grid voltage active bridge. A very practical bidirectional power decoupling technique which controls the voltage amplitude in the series-connected buffer (SCB) is proposed. Unlike existing structures, two independent time-variant duty ratios is applied on both AC active bridges (rectified grid and the series-connected buffer) and fixed duty ratio on DC side (battery). The proposed modulation allows the power decoupling of the low frequency AC grid voltage variations in the series-resonant circuit. As a result, the steady-state response of the proposed AC-DC converter with SCB is equivalent of a DC-DC DAB with a series-resonant circuit. Decoupled close loop control for the grid current and for the SCB voltage are implemented. Furthermore, reactive power in the grid is compensated in the tank circuit with fixed duty ratio on DC side. Bidirectional power flow is controlled with phase shift modulation. High efficiency is obtained due to Zero Voltage Switching (ZVS) in all MOSFETs. Finally, the 1kW prototype is validated experimentally.