AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 2

• Manufacturer Part Number: AN1914
• Description: 3-Phase BLDC Motor Control with Sensorless Back EMF Zero Crossing Detection Using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

Motorola DSP Advantages and Features
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can perform the control tasks. Moreover, the necessary computing power can be minimized by using
dedicated on chip peripheral modules (such as A/D converter, dedicated PWM outputs, input capture
and output compare functions).
Three phase Brushless DC (BLDC) motors are good candidates because of their high efficiency
capability and easy to drive features. The disadvantage of this kind of motor is the fact that
commutation of motor phases relies on its rotor position. Although the rotor position is usually sensed
by sensors, there are applications that require sensorless control. Benefits of the sensorless solution are
elimination of the position sensor and its connections between the control unit and the motor.
The sensorless rotor position technique detects the zero crossing points of Back-EMF induced in the
motor windings. The phase Back-EMF Zero Crossing points are sensed while one of the three phase
windings is not powered. The obtained information is processed in order to commutate energized
phase pair and control the phase voltage, using Pulse Width Modulation.
This application note provides a fundamental mathematical method for modelling, torque calculation
and control concept of the presented drive. The drive was developed in order to address simple
applications (e.g. pumps, compressors, fans...) within certain ranges of speed and load. Results from
simulation show the drive behavior at different working conditions and better explain the drive
strategy.
The Motorola DSP56F80x family is well suited for digital motor control, combining the DSP’s
calculation capability with MCU’s controller features on a single chip. These DSPs offer many
dedicated peripherals like a Pulse Width Modulation (PWM) module, Analog-to-Digital Converter
(ADC), Timers, communication peripherals (SCI, SPI, CAN), on-chip Flash and RAM. Generally, all
family members are well suited for motor control application.
The DSP56F805 family member provides the following peripheral blocks:
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Motorola DSP Advantages and Features
Two Pulse Width Modulator modules (PWMA & PWMB), each with six PWM outputs, three
Current Status inputs, and four Fault inputs, fault tolerant design with deadtime insertion,
supports both Center- and Edge- aligned modes
Two twelve-bit, Analog-to-Digital Convertors (ADCs) that support simultaneous conversions
with dual 4-pin multiplexed inputs. ADC can be synchronized by PWM modules
Two Quadrature Decoders (Quad Dec0 & Quad Dec1), each with four inputs, or, alternatively,
two additional Quad Timers (A & B)
Two dedicated General Purpose Quad Timers totalling 6 pins: Timer C with 2 pins and Timer
D with 4 pins
CAN 2.0 A/B Module with 2-pin ports used to transmit and receive
Two Serial Communication Interfaces (SCI0 & SCI1), each with two pins, or four additional
GPIO lines
Serial Peripheral Interface (SPI), with configurable 4-pin port, or four additional GPIO lines
Computer Operating Properly (COP) timer
Two dedicated external interrupt pins
Fourteen dedicated General Purpose I/O (GPIO) pins, 18 multiplexed GPIO pins
External reset pin for hardware reset
External reset output pin for system reset
JTAG/On-Chip Emulation (OnCE)
DSP56F80x MC PWM Module in Motor Control Applications
Freescale Semiconductor, Inc.
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