BRUSHLESS MOTOR COMMUTATION PRESENTATION BY SWAPNA.M

PRESENTATION OUTLINE OBJECTIVE THE BRUSHLESS DC (BLDC) MOTOR COMPARISON OF BLDC MOTOR & BRUSHED MOTOR ADVANTAGES OF BLDC MOTOR METHODS OF COMMUTATION TRAPEZOIDAL COMMUTATION SINUSOIDAL COMMUTATION

OBJECTIVE To investigate different methods of commutation of BLDC motor-Trapezoidal & Sinusoidal

The Brushless DC (BLDC) Motor A modern, much improved, version of the traditional brushed DC motor. An inside out DC motor with electronic commutation Field- permanent magnets- is on the rotor. Armature- is on the stator which has good cooling. Two types of motor sinusoidal trapezoidal

Sinusoidal motor Sinusoidal distribution of magnetic flux 2. Sinusoidal current waveforms 3. Sinusoidal distribution of stator conductors. Trapezoidal motor Rectangular distribution of magnetic flux 2. Rectangular current waveform 3. Concentrated stator windings. Mechanical commutator of brushed motor replaced by electronic switching of the phases. Switching - synchronised to absolute rotor position – smooth torque production.

Comparison of BLDC Motor & Brushed Motor Feature BLDC Motor Brushed Motor Commutation Electronic Commutation based on Hall Sensors Brushed Commutation Maintenance Less Periodic Life Longer Shorter Speed/Torque Characteristics Flat Moderately Flat Efficiency High Moderate Output Power Low Rotor inertia Higher Speed Range Lower Electric Noise Arcs in brushes-generate noise Cost of Building Control Complex & Expensive Simple & inexpensive Control Requirements Controller is always required No controller is required

Advantages of BLDC Motor Better speed versus torque characteristics High dynamic response High efficiency Long operating life Noiseless operation Higher speed ranges Ratio of torque to size of the motor is higher Applications Appliances, Automotive, Aerospace, Consumer, Medical, Industrial Automation Equipment and Instrumentation.

Commutation of BLDC Motor Commutation – to energize the appropriate windings in the stator to provide optimum torque generation depending on the rotor position. Methods of Commutation Trapezoidal Commutation Sinusoidal Commutation

Trapezoidal Commutation Simplest method of control for dc brushless motors Only two phase coils are active at any instant Commutation –every 60 degree Hall effect sensors are used

Merits 1. Simple control circuits 2. Switching loss is less 3 Merits 1. Simple control circuits 2. Switching loss is less 3. Only one current at a time needs to be controlled. 4. Only one current sensor is necessary. Demerits 1. Overall system efficiency is poor 2. Torque ripple is present at each 60 degree phase commutation 3. Inadequate to provide smooth and precise motor control

Sinusoidal Commutation All three phases are active at any moment. Attempt to drive - three currents that vary smoothly and sinusoidally as the motor turns Smooth torque control & accurate position control is required. An encoder is required