Dead-Time Compensated Pulsewidth Modulator for a 3-Phase VSI Implemented with an AT89C52 Microcontroller

Modern microcontrollers are equipped with enhanced resources with built in huge flash program memory, increased RAM and EEPROM for data memory, timers, multi-channel ADCs and network controls. The enhanced on-chip resources make the microcontrollers a promising candidate for complex PWM implementations in embedded applications. In this paper a microcontroller based PWM implementation scheme is proposed that can produce high resolution PWM patterns for three phase inverters with dead-time compensation. An AT89C52 microcontroller computes the PWM pulse widths on carrier cycle basis based on the input frequency. The microcontroller send the pulse width information for the three phases to a memory minimized ROM lookup table, which is scanned by a binary counter to generate the real time PWM patterns. The on board timer of AT89C52 is utilized to generate programmed clock for the scanning binary counter. The ROM lookup table stores two types of PWM pattern for the same PWM duty in consecutive even and odd address locations. The even location stores the dead-time compensated PWM pattern for a leg for load current greater than zero. The immediate odd location contains the dead-time compensated pattern for current less than zero. A current feedback signal selects the appropriate PWM pattern for any duty and hence the resultant real time PWM pattern completely eliminates the dead-time effects resulting highly efficient PWM output.