MULTIPHASE BRUSHLESS DC MOTOR

Introduction A BLDC motor accomplishes commutation electronically using rotor position feedback to determine when to switch the current unlike brushed dc motor which uses carbon brush to provide unidirectional current. STATOR= Stator windings of a BLDC motor are connected to a control circuit (an integrated switching circuit).It is wound with a specific number of poles. ROTOR=Permanent magnets are mounted on the rotor of a BLDC motor.The permanent-magnet rotor is typically made either of rare earth magnets (Sm-Co) or of ceramic magnets (ferrites).

continued.. There are two types of stator windings: trapezoidal and sinusoidal, which refers to the shape of the back electromotive force (BEMF) signal. The shape of the BEMF is determined by different coil interconnections. A sinusoidal motor produces smoother electromagnetic torque than a trapezoidal motor.

Operational Theory Motor operation is based on the attraction or repulsion between magnetic poles. Using the three-phase motor shown in figure , the process starts when current flows through one of the three stator windings and generates a magnetic pole that attracts the closest permanent magnet of the opposite pole. Sequentially charging each winding will cause the rotor to follow in a rotating field

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Brushless DC Motor Control The essence of BDCL lies in controlling the polarity of the stator which in turns control the rotation of the rotor. Brushless DC motors use electric switches(connected in H- bridge structure) to realize current commutation, and thus continuously rotate the motor.

Single Phase BLDC commutation relies on feedback on the rotor position to decide when to energize the corresponding switches to generate the biggest torque. Hall sensor is used to detect the correct position of the rotor when the change in polarity of stator is required. A Hall position sensor (“a”) is mounted to the outside stator, which induces an output voltage proportional to the magnetic intensity. the sensor goes HIGH when the rotor’s North Pole passes by, and goes LOW when the rotor’s South Pole passes by.

3-Phase A three-phase BLDC motor requires three Hall sensors to detect the rotor’s position. Three Hall sensors are mounted on the stator at 120° intervals. For every 60° rotation, one of the Hall sensors changes its state; it takes six steps to complete a whole electrical cycle

Advantages of Brushless DC Motor

continued.. Minimized torque ripple Reduced Noise Increased Power density Improve fault- tolerance w.r.t open circuit lags

High Efficiency High Torque to Weight Ratio Longer Life Time Compact and Light weight Improve fault-tolerance w.r.t open circuit

Speed Control

Speed Control Method One can control speed of motor using two methods: No. of stator poles per phase. Frequency.

Speed Control Method We can find the speed of motor by formula: S= 120 x f P S= Speed of motor in rpm f= Frequency P= No. of Stator Poles per phase

Torque Comparison

Torque Comparison 2 wire motor is not smoothly started. Multi Phase motor is smoothly started and rotated with high torque at low speed and high power at high speed.

Torque Comparison The BLDC is controlled by two types of waveforms produced by inverters: Trapezoid Sinusoidal

Torque Comparison Trapezoid Waveform: Motors powered by trapezoid waveform produced 10% more torque than sinusoidal. But motors are not smooth and have ripples in torque.

Torque Comparison Sinusoidal Waveform: Used for low speed but it is smooth and have less ripple in torque.

Torque Comparison With the increase in phases ,the torque becomes less rippled because of smoother rotation of rotor

Torque Comparison Torque also depends upon the configuration of stator windings. For Y-configuration, motor gives high torque at low speed but not as high as at top speed. For Delta-configuration, motor gives low torque at low speed but can give high torque at top speed.

Torque Comparison Furthermore, Torque can be increased by increasing no. of rotor poles.

Applications

Applications Multiphase Brushless DC motors are used in: In Electric Vehicles (Evs) PC fans , DVD players Aero modeling Heating and Vantilation Radio Controlled Cars

BLDC in Electric Cars Windings on stator Permanent magnets are on the rotor Side. BLDC used in Evs due to following advantages : Low maintenance 80-90% efficiency High operating speeds No brush sparking Compact size

continued.. Quick response Zero tailpipe emissions Charge itself on applying brakes Cheap to drive

continued.. Pc fans and DVDs for more efficient and less noisy … In Heating , Ventillation and Air conditioning industries (HVAC) Used in aero modeling like aircrafts and helicpters … Radio controlled cars having less input power and more torque