Enhanced Gate Driver with Variable Turn On and Turn Off Speeds

Insulated Gate Bipolar Transistors (IGBT) are widely used for the vehicle traction inverter. Switching characteristics of these devices contribute to the inverter total loss and inverter efficiency is affected by the energy loss during each switching event. Traditional gate driver circuits are usually designed to meet the worst-case scenario and result is high switching loss of the IGBTs. Gate driver turn on and turn off resistances are selected accordingly for the worst-case scenario and their purpose is to protect the device from overshoot voltage that can cause the avalanche breakdown of the device. The gate charge and discharge circuit is usually composed of one or two resistors and the loss during turn-on and turn-off time is not optimized for all of the vehicle-operating conditions. Since microprocessor (μP) monitors the dc-bus voltage, output current and torque command, it can also determine if the device switching speed needs to be changed under different operating conditions. In order to reduce the switching losses during all operating conditions, the gate charge and discharge resistance has to vary. Enhanced gate driver control proposed in this paper employs two sets of push-pull device drivers that have different resistor values. This method of gate drive ensures that the device switching speed is optimized for all vehicle-operating conditions and the total inverter efficiency is increased.

Furthermore, conventional gate drive has large gate resistance that increases the power module switching losses and it affects the vehicle fuel economy. This work proposes the enhanced gate drive circuit that optimizes the device switching turn-on, turn-off speeds and minimizes the device switching losses. This paper will show the detailed gate-drive-circuit design that utilizes multiple paths for gate charge and gate discharge.