Analysis of Bootstrap Circuit Operation With an Inverted PWM Drive Scheme for a Three-Phase Inverter for a Brushless DC Motor Drive

A bootstrap circuit for operating the high-side insulated-gate bipolar transistor of a three-phase inverter for a brushless dc motor drive is analyzed theoretically to avoid under voltage lockout by minimizing the discharge of a bootstrap capacitor (BSC). Unlike various methods of reducing the discharge of BSCs, which limits the controllability of the motor speed/torque, a proposed inverted PWM driving scheme has no limit to the controllability while maintaining the proper voltage level for a BSC. This method is verified experimentally in this paper.