Practical aspects of direct bypass of boost converter in traction inverter applications

Direct bypass of DC-DC boost converter in traction inverter has many advantages including increased efficiency and pass-through capability. This paper explains different practical aspects of direct bypass of the boost stage of traction inverter using diode. Bypass diode enters into the linear operating region (DC Q-point) when the battery discharges through the bypass diode to drive the electric motors. Therefore, thermal stress of the DC-link capacitor is shared between the input and DC-link capacitors through the bypass diode. During battery charging operation, the inverters introduce voltage ripple in the DC-link terminal which results in unwanted energy circulation through the bypass diode. Both of these phenomena have been investigated in details. In addition, this paper proposes and validates a control strategy to eliminate the energy circulation during battery charging mode using minimum boosting at a reduced frequency to optimize the power loss of the boost converter.