04-08-2012, 01:47 PM
Battery Charging during the braking of a brushless dc motor
Battery Charging.pptx (Size: 372.41 KB / Downloads: 49)
INTRODUCTION
The brushless motors are becoming more and more widespread in the fields of industrial electronics, home appliances, automotive and robotics.
This is due to their higher efficiency and lower maintenance compared to conventional brushed DC motors.
What is commutator and brush ?
Commutator is a cylindrical structure, made of copper or carbon with high conductivity. Mounted on the rotor part of the brushed motor. Helps to conduct current through conductor when the brushes comes to contact during rotation.
The electrical contacts to the rotating ring called brushes.
Brushless DC Motors
The stator (or stationary part of the motor) consists of a frame and copper wire windings . In a brushless DC motor the rotor (or rotating part of the motor) is a shaft with one or more permanent magnets.
The rotor may be located inside or outside the stator. Internal rotors use magnets with one or more pairs of poles (north and south). External rotors often have radial-mounted magnets which allow a higher number of poles and proportionally greater torque.
BLDC motors are a type of synchronous motors: the magnetic field generated by the stator and the magnetic field generated by the rotor rotate at the same frequency.
BLDC motors can be built in single-phase, two-phase or three-phase configurations. The last type is the most widely used .
Typical back EMF waveforms for a three-phase BLDC motor with trapezoidal flux distribution are shown in Fig below.
ADVANTAGES OF BLDC MOTOR OVER PMSM
In BLDC motor PM are on the rotor & electromagnets are on the stator controlled by software. Thus the advantages are:
Because of computer control it is more precise & more efficient.
There is no sparking & less electrical noise.
Voltage and current rating is high.
High speed can be achieved.
Motor During Braking
When braking, the brushless DC motor generates a trapezoidal back emf across its terminals. The rectifying bridge rectifies this AC voltage to a DC voltage to be controlled by the MOSFET that follows.
A high current, high voltage MOSFET is placed between the battery and the rectifier which turned on and off depending on the throttle level signal provided to the PWM generator.
CONCLUSION
The need for improved fuel economy is generating a large need for cost effect and reliable solutions to drive electric motors under very challenging conditions. With its smaller raw material cost and its inherent higher reliability brushless motors are the obvious way of the future. The today’s capabilities of sensorless control bring the future already a significant step closer. New developments in hard- and software will continue to increase performance and reduce cost.