Light-Load and Cross-Load Control of Integrated OBC and APM for Electric Vehicle Applications

To achieve high power density, onboard charger (OBC) and the auxiliary power module (APM) are electrically integrated in electric vehicles (EVs). A key challenge of the integration is the light-load and cross-load operation in simultaneous power transfer modes, for example, in the charging mode. Specifically in [1], at light loads, the OBC operates at very high switching frequency and dc bus-side switches tend to lose zero-voltage switching (ZVS). Moreover, the operation at very high switching frequency limits the maximum power which can be delivered to the low voltage (LV) output. In this paper, a control for light-load and cross-load operation in the charging mode for integrated OBC and APM topology, proposed in [1], is presented. A smooth transition from variable frequency (VF) to fixed frequency (FF) control and vice versa is achieved with power hysteresis control. The detailed block-diagram of control is provided. Finally, the experimental waveforms at light-loads, cross-loads and during transition from VF to FF control and vice versa in charging mode of operation are provided. At light load operation of OBC, at V
Bus
= 400V, V
HV
= 370V, V
LV
= 13.8V, P
LY
= 240W, measured efficiencies of 96.4% and 94.4% are achieved at P
HV
= 2.67 kW and P
HV
≈ 550 W, respectively.