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Design Challenges and Considerations for Brushless DC Motors and Their Drives

Design Challenges and Considerations for Brushless DC Motors and Their Drives

Introduction:
Generating rotary motion was one of the first experiments carried out with electricity in the 18th century – an ‘electric whirl’ was invented, actually an electrostatic reaction motor. When the long view of capital expense payback, operating costs and environmental loading is considered, there is therefore every incentive to update to, and build-in the best performing motors with smart control

Motor Types:
The dominant motor in the overall market including industrial is the AC brushless induction type with around 70% share. Single-phase types are versatile but not very efficient, three-phase types are more powerful, efficient and self-start. AC induction motors are very reliable and low cost. Truly synchronous motors without ‘slip’ are an option such as the wound-rotor synchronous motor (WRSM) or the synchronous reluctance motor (SyRM) which can be efficient but are more costly and not very widely used.

BLDC Motors:

BLDC motor and particularly the electronics required to generate the multiphase AC for the stator windings and how control is implemented for optimum performance. The BLDC motor has a sequence of applied voltage to the three coils for ‘trapezoidal’ drive. The drive is normally generated by an arrangement of six semiconductor switches, typically MOSFETs, or increasingly wide band-gap devices such as SiC-FETs in a bridge configuration, providing the six voltage combinations, with appropriate ‘dead’ time between each phase to avoid ‘shoot through.

Controlling the BLDC Motor:
There is a choice of commutation style – the way that the stator coils are driven to ensure continuous rotation.

Vector or Field Oriented Control:

A technique for controlling sinusoidally commutated BLDC motors is vector or field-oriented control (FOC) [3]. FOC provides smooth operation over the whole speed range and superior dynamic performance with fast acceleration and deceleration.

Qorvo BLDC Motor Control Solutions Providing the optimum drive for a BLDC motor is difficult with a multitude of parameters to sense and complex algorithms required to generate the appropriate multiphase PWM waveforms. Fortunately, all of the drive and control functions can now be integrated into a Power Application ControllerTM (PAC) such as the range offered by Qorvo in their PAC5xxx series.

Reference Designs Make Design-in Easy:

Reference designs are available and an example is the RD5556, which showcases the PAC5556 motor controller and silicon carbide SiC FET cascode power switches from Qorvo. The design can be used for three-phase motor control up to 600VDC and 3kW, as is found for example, in AC appliances. In industry, the design suits applications including motor control for pumps, compressors and fans.

Conclusion:

The efficiency of brushless DC motors has made them the ideal choice for applications where small size, low weight, controllability and high torque are also desirable, such as in appliances, power tools and a wide range of industrial and consumer uses. The complexity and cost of advanced control and drives has in the past been a barrier to the widespread adoption of BLDC motors, but now, the integrated drive solutions from Qorvo in their PAC series controllers and SiC FET switches from Qorvo are an integrated, versatile and cost-effective solution.

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