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Brushless DC (BLDC) Motor Overview

A Brushless DC (BLDC) motor is a Permanent Magnet Synchronous Motor with unique back EMF waveform that allows them to behave similarly to a brushed DC motor. Some confusion can arise from the name, as a brushless DC motor does not directly operate off a DC voltage source. However, the basic principle of operation is similar to a DC motor.

A Brushless DC Motor has:

  • A rotor with permanent magnets and a stator with windings
  • A BLDC motor is essentially a DC motor turned inside out
  • Brushes and commutator have been eliminated and the windings are connected to the control electronics
  • Control electronics replace the function of the commutator and energize the proper winding
  • Windings are energized in a pattern which rotates around the stator
  • The energized stator winding leads the rotor magnet and switches just as the rotor aligns with the stator
BrushedDC_Block_640x480v2
Recommended Products for BLDC Motor Control
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Microchip offers a complete line of single chip three-phase brushless drivers and three-phase brushless motor MOSFET gate drivers for a broad range of motor applications. These products are designed to interface to any microcontroller or be used in a standalone configuration.

  • For Single-Chip Drivers for BLDC Motor Control Start with the: MTD6501
  • For MOSFET Gate Drivers for BLDC Motor Control Start with the: MCP8024

Microchip’s award winning 8-bit PIC® MCUs are an excellent solution for simple trapezoidal sensored or sensorless control.

  • For 8-bit PIC MCUs for BLDC Motor Control Start with the: PIC16F917

For advanced closed loop sensorless or sensored BLDC motor control Microchip’s dsPIC® family of digital signal controllers (DSCs) offer DSP performance and advanced motor control peripherals.

Microchip offers both MIPS and ARM Cortex MCU's for high performance, 32-bit motor control. These devices feature high performance peripherals tailored for high speed, closed loop motor control.

BLDC Motor Control Application Notes and Software
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Motor control application notes on control algorithms include example software and source code.

Sinusoidal and FOC control application notes are listed under the PMSM motor type.

BLDC Motor Control Development Tools
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For Microchip's three-phase brushless gate driver and dsPIC33 solution - MCP8025 TQFP BLDC Motor Driver Evaluation Board (ADM00557)

For Microchip single-chip BLDC drivers - MTD6505 3-Phase BLDC Sensorless Fan Controller Demonstration Board

For 8-bit PIC MCUs - F1 BLDC Motor Add On for F1 LVEval Platform

For 16-bit dsPIC DSCs - MCSK Motor Control Starter Kit (DM330015)
MCLV-2 Low Voltage Motor Control Development Board (DM330021-2)
Low Voltage Motor Control Development Bundle (DV330100)

For 32-bit ARM Cortex and MIPS MCU’s – PIC32MK Motor Control PIM for use with MCLV-2 Low Voltage Board(MA320024)
SAMD21 Low Voltage Motor Control Kit (compatible with SAM D2x and SAM C2x plug-in-modules)

Key Characteristics of the BLDC Motor
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  • There are no sparks
  • Potentially cleaner, faster, more efficient, less noisy
    and more reliable
  • Heat is generated in the stator: easier to remove and maintain
  • Rotor has permanent magnets vs. coils thus lighter less inertia:
    easier to start/stop
  • Linear torque/current relationship smooth acceleration
    or constant torque
  • Higher torque ripple due to lack of information between sectors
  • Low cost to manufacture
  • Simple, low-cost design for fixed-speed applications
  • Clean, fast and efficient
  • Speed proportionate to line frequency (50 or 60 Hz)
  • Complex control for variable speed and torque
  • Require electronic control
BrushedDCMotorDesignFlowchart
How it Works
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The Brushless DC Motor does not operate directly off a DC voltage source. The brushless DC motor has a rotor with permanent magnets, a stator with windings and commutation that is performed electronically. Typically three Hall sensors are used to detect the rotor position and commutation is performed based on Hall sensor inputs.

The motor is driven b rectangular or trapezoidal voltage strokes coupled with the given rotor position. The voltage strokes must be properly applied between the phases, so that the angle between the stator flux and the rotor flux is kept close to 90° to get the maximum generated torque. The position sensor required for the commutation can be very simple, since only six pulses per revolution (in a three-phase machine) are required. Typically, the position feedback is comprised using three Hall effect sensors aligned with the back-EMF of the motor. In sensorless control, back-EMF zero crossing is used for commutation.

BLDC Motor Control
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Input:

  • Typically torque, speed, position and/or direction
  • Inputs can be analog voltage, potentiometer, switches 
    or digital communications

BLDC Motor Control:

  • Basic I/O for firmware bit-bang for 6-step #3 phase PWMs
    for hardware PWM
  • Comparators for speed sensing in sensorless control,
    over-current detection
  • Capture/Compare/PWM or input captures for speed sensing

Feedback:

  • Hall effect sensors, optical encoder or back-EMF voltage
BLDC_6step_large
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BLDC Motor Design Flow Chart
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StepperMotorFlowChartLarge
Motor Application Example: Scenarios BLDC
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microstepping
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BLDC sensorless motor key points of interest:

  • Lower cost due to the lack of the sensors
  • More complicated to drive
  • Performs very well in applications that don't require the motor to start and stop
  • Would be a better choice in applications that must periodically stop the motor

The PIC18 MCUs or dsPIC® DSCs A/D samples the motor phase voltages. From the voltages, the CPU determines the rotor position and drives the motor control PWM module to generate trapezoidal output signals for the 3-phase inverter circuit.

Brushless DC Motor Application: Brushless Fan Control
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BrushlessFanControl
Click image to enlarge
Need a highly integrated fan controller with a customizable speed/temperature profile?
Take a look at Microchip's PIC12HV and  PIC16HV devices. 
  • Built-in 5V regulator and on-chip comparator to save system cost
  • Rotor position is determined by a Hall effect sensor connected to the on-chip comparator
  • Enhanced Capture Compare PWM (ECCP) module uses feedback information to drive the motor by steering the PWM signal to the appropriate motor phase
  • Temperature sensor inputs can be used to create a unique fan speed profile
  • Application can provide digital status information to a host device
Applications
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  • Anti-lock braking system
  • Disk drive servo
  • Throttle control
  • Fuel Pump
  • Oil Pump