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:
| |
|[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
| |
|[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
| |
|[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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