Dual Sensorless PMSM Field-Oriented Control With Power Factor Correction on MC56F84789 DSC,
Rev.0, 05/2013
Freescale Semiconductor, Inc.
very similar to the trapezoidal BLDC (Electronically-Commuted) motor. There are two main
differences:
• Motor construction
o The shape of BEMF inducted voltage — sinusoidal (PM synchronous motor)
versus trapezoidal (BLDC) motor.
• Control — shape of the control voltage
o 3-phase sinusoidal (all three phases connected at one time) versus rectangular six-
step commutation (one phase is non-conducting at any time).
Generally, the performance of sinusoidal PMSM is better due to constant torque, while the
trapezoidal BLDC motor can be more easily controlled. The trapezoidal BLDC motors are used
mainly for historical reasons. It was easier to create a six-step commutation and estimate the
rotor position with simpler algorithms, since one phase is non-conducting. The sinusoidal PM
synchronous motors require more sophisticated control, but provide some benefits such as
smoother torque, lower acoustic noise, and so on. As shown in this document, the MC56F84789
provides all the necessary functionality for dual 3-phase sinusoidal PM synchronous motor
vector control.
Using Freescale MC56F84789 gives a valid reason to replace the trapezoidal BLDC
(electronically-commuted) motors with the 3-phase sinusoidal PMSM with almost no system
cost increase. The application described here is a speed vector control. The speed-control
algorithms can be sorted into following two general groups.
• Scalar control: The constant Volt per Hertz control is a very popular technique
representing scalar control.
• Vector- or field-oriented control (FOC): The field-oriented techniques bring overall
improvements to drive performance over scalar control such as higher efficiency, full
torque control, decoupled control of flux and torque, improved dynamics, and so on.
For the PM synchronous motor control, it is necessary to know the exact rotor position. This
application uses special algorithms to estimate the speed and position instead of using a physical
position sensor. This design reference manual describes the basic motor theory, the system
design concept, hardware implementation, and the software design, including the FreeMASTER
software visualization tool.
1.4 Freescale DSC advantages and features
The Freescale’s MC56F84789 is well-suited for digital motor control, combining the calculation
capability with the features of the MCU on a single chip. These controllers offer many dedicated
peripherals such as pulse width modulation (PWM) modules, analog-to-digital converters
(ADC), timers, direct memory access (DMA), cross bar units (XBAR), communication
peripherals (SCI, SPI, I
2
C), and onboard Flash and RAM.
MC56F84789 provides the following blocks:
• Core operating at a frequency of 100 MHz
o Single-cycle 32 × 32-bit multiplier-accumulator (MAC) with 32- or 64-bit result
with an optional 32-bit parallel move