Motor Types - Microchip Technology



Brushless DC (BLDC) Motor Control

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|This block diagram shows a system that could be used to drive a 3-phase brushless DC motor. Rotor feedback is required and is usually implemented as 3 |

|hall-effect sensors that detect the position of the rotor magnets. A ‘sensorless’ method can be used to remove mechanical sensors by measuring voltage /current |

|feedback. |

Find suitable Software, Tools & Training for BLDC Motor Control Application below

|[pic] | [pic] | [pic] | [pic] |

BLDC Motor Tutorial

|Overview: |

|Brushless DC motors are referred to by many aliases: Brushless Permanent Magnet, Permanent Magnet AC Motors, Permanent Magnet Synchronous Motors etc. The |

|confusion arises because 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. It is essentially a dc motor turned inside out. The brushes and commutator |

|have been eliminated and the windings are connected to the control electronics. The control electronics replace the function of the commutator and energize the |

|proper winding.The 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. |

|There are no sparks, which is one advantage of the brushless DC motor. The brushes of a dc motor have several limitations; brush life, brush residue, maximum |

|speed, and electrical noise. BLDC motors are potentially cleaner, faster, more efficient, less noisy and more reliable. However, BLDC motors require electronic |

|control. |

|Key characteristics of the BLDC Motor: |[pic] |

|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 | |

|How it works: |

|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 by 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 Control

|Input: | BLDC Motor Six Step Control: Back EMF method |

|Typically torque, speed, position, and/or direction |[pic] |

|Inputs can be analog voltage, potentiometer, switches, or digital | |

|communications | |

|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 Design Flowchart:

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|[pic] |

BLDC Motor Applications:

|BLDC Motor Applications include: |[pic] |

|Anti-lock Braking System | |

|Disk Drive Servo | |

|Throttle control | |

|Fuel pump | |

|Oil pump | |

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BLDC Motor Application Example: Sensorless BLDC

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|[pic] |

|Sensorless motors are lower cost due to the lack of the sensors, but they are more complicated to drive. A sensorless motor performs very well in |

|applications that don’t require the motor to start and stop. A sensor motor would be a better choice in applications that must periodically stop the motor. |

|Want to eliminate your Hall-Effect sensors and cabling cost by going sensorless? Take a look at Microchip’s PIC18F |

|The PIC18 MCU’s or dsPIC DSC’s 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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|[pic] |

|Need a highly integrated fan controller with a customizable speed/temperature profile? Take a look at Microchip’s PIC12HV and PIC16HV devices. The PIC12HV |

|and PIC16HV devices have a built-in 5V regulator and on-chip comparator to save system cost. The rotor position is determined by a Hall-Effect sensor |

|connected to the on-chip comparator. The Enhanced Capture Compare PWM (ECCP) Module uses this 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 profi le and the application can provide digital |

|status information to a host device. |

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