3-Phase BLDC Motor Sensorless Control Using MC56F8013

System Concept3.3 System Blocks Concept3.3.1 PWM Voltage Generation for BLDC MotorsA 3-phase voltage system as described in 2.1 The Brushless DC Motor must be created to run the BLDCmotor. It is provided by a 3-phase power stage with six power switches (IGBTs or MOSFETs) controlledby the hybrid controller’s on-chip PWM module.When generating PWM signals for this BLDC motor control application, the bottom and top powerswitches of the non-fed phase must be switched off (see Figure 3-2 and Figure 3-3).For the application, PWM signals can be created in two ways: independent PWM mode andcomplementary PWM mode. Thanks to the MC56F8013 PWM module and its Mask/Swap feature, bothmodes can be used with minor software overhead.Complementary PWM ModeIn complementary PWM mode, the top and bottom switch of a phase operate in a complementary way.This mode enables regenerative braking, where the DC-bus voltage may increase during deceleration orstop. In this mode, Swap and Mask features of PWM module are used together.commutation commutation commutationcommutationcommutationcommutationPWMA +A offA swapA offA -B +B swapB offB offB swapB -C +C offC swapC offC -60120 180 240 300 360Electrical AngletFigure 3-2. Complementary PWM Mode Patterns for BLDC MotorIndependent PWM ModeIn independent PWM mode, the top and bottom switch of a phase operate independent over acommutation period, if the top switch is performing PWM, the bottom switch is off, and vice versa. In thismode, regenerative braking is not enabled. Only the Mask feature of the PWM module is required.3-Phase BLDC Motor Sensorless Control using MC56F8013, Rev. 028 Freescale Semiconductor