Feature: Automotive
Design tips of using brushless DC motors in automotive applications
By Rolf Horn, Applications Engineer, Digi-Key Electronics B
rushless DC (BLDC) motors are increasingly used across many and varied applications, from remote IoT-controlled systems, to satellite
propulsion controllers. Te problem designers face with BLDC
motors is that the control algorithms necessary to drive them are complex and oſten specialised, making them difficult to get up and running in a reasonable amount of time. Developers are generally leſt to choose between a soſtware-based solution running on a microcontroller, which provides flexibility but also puts a computational burden on the microcontroller, or use a dedicated IC, which could encapsulate the full BLDC motor control function and move BLDC control away from the host.
BLDC motors BLDC motors provide efficient torque delivery over a wide range of speeds; they are also quiet and don’t suffer from mechanical friction like brush motors. BLDC motors are controlled by current, not voltage, making them suitable for a
18 April 2022
www.electronicsworld.co.uk
wide variety of applications and for which they come in many shapes, sizes and costs. For example, Trinamic Motion Control’s
QBL4208-41-04-006 is a 24V, 4000rpm motor that provides torque to 0.06Nm; see Figure 1. Te motor is lightweight (0.662lb) and offers several options for control, such as sensorless operation using back electromotive force (BEMF), or built-in sensors that report the position of the load. For more torque, designers can use the Trinamic QBL4208-41-04-025, also a 24V, 4000rpm BLDC motor but which delivers a little over 0.25Nm; see Figure 2. BLDC motors are driven via three-
phase lines that generate a magnetic field that pushes against permanent magnets to move the stator and spin the motor. In theory this sounds easy, but, in practice, driving a BLDC motor is fairly complicated, leaving developers to choose between a soſtware framework or a dedicated chip.
Software versus dedicated ICs Tere are several factors to choosing how to spin a BLDC motor: • Bill of materials (BOM) versus labour costs;
• Board versus soſtware complexity; • Maintenance time and costs. From a hardware perspective, it can be
very tempting to take the soſtware route, because a dedicated chip adds costs to the BOM. Instead, some consider spending a fraction more on a microcontroller, with the control algorithms already on it. Yet, despite appearances, this is not necessarily a winning approach, since there are some ramifications for this decision the design teams should consider. Although it decreases the overall BOM, this solution places an added burden on the microcontroller to process the BLDC state data and continuously drive the motor. If the microcontroller is also handling other sensors and controlling other devices, the soſtware development and maintenance costs could go through the roof if care is not taken. Tat said, a soſtware-based solution
does allow fine-tuning the motor control algorithms. As an example let’s consider moving
the motor control algorithm into the microcontroller, which could take up more RAM and flash memory. It does appear like it needs more consideration,
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