Low Resource Microcontroller 3 Phase BLDC Motor Speed Controller

Posted on Feb 6, 2014

This article focuses on a minimal resource microcontroller implementation for a 3 phase BLDC motor, closed loop speed motor controller application based on a Microchip PIC12 device. It shows how minimisation techniques can reduce the number of I/O pins to just 6 for this type of application. It assumes the reader understands the commutation sequen

Low Resource Microcontroller 3 Phase BLDC Motor Speed Controller
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ce for the aforementioned type of motor. Just how small a microcontroller can control a 3 phase BLDC motor Well to answer that question requires the chip resources to be identified which align with the external BLDC motor control topology and functionality for the intended application. If at the outset we address the low cost volume market for speed control applications used in fans and pumps the problem narrows down. In relation to this type of system there are those with sensor and sensor-less configurations (for determining rotor position) which both offer pros and cons but in terms of I/O count if the rotor position sensing can be done on one pin we are off to a good start. Also if multi function pins can be deployed for a simple user interface and logic minimization techniques can reduce the pin count further then the minimal resource map for a suitable device can be approached. In Figure 1, the block diagram illustrates a system using a single Hall sensor for rotor position feedback (many systems use 3 for this purpose), a potentiometer for speed setting, a start and stop switch, a motor over current trip and a 3 phase power bridge to drive the motor. The resulting amount of independent connections to the microcontroller shown between the system sub components is 11 (5 inputs and 6 outputs). However, minimisation can be accomplished if the microcontroller supports multi function pins and ubiquitous peripherals....

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