Using the dsPIC30F & dsPIC33F DSCs for Sensorless BLDC Control

AN901 Using the dsPIC30F for Sensorless BLDC Control Known Limitations Author: Charlie Elliott Smart Power Solutions, LLP As delivered, the maximum output frequency at Co-author: Steve Bowling which the sensorless system works reliably is Microchip Technology Inc. approximately 150 Hz. However, this limitation allows very common 4-pole motors to run at up to 4500 RPM. INTRODUCTION The output frequency can be extended up to approximately 250 Hz (7500 RPM for a 4-pole This application note describes a fully working and motor) if phase advance is used. Higher speeds highly flexible software application for using the are possible with software modifications. dsPIC30F to control brushless DC (BLDC) motors Hard modulation of diagonally opposite inverter without position sensors. The software makes switches is supported. extensive use of dsPIC30F peripherals for motor control. The algorithm implemented for sensorless The system supports motoring in closed-loop control is particularly suitable for use on fans and commutation as would be required for a typical pumps. The program is written in C and has been fan or pump. specifically optimized and well annotated for ease of understanding and program modification. BACKGROUND The brushless DC (BLDC) motor is used for both Software Features consumer and industrial applications owing to its Back EMF zero-crossing routine precludes the compact size, controllability and high efficiency. need for position sensing components. Increasingly, it is also used in automotive applications Application includes adjustable parameters and as part of a strategy to eliminate belts and hydraulic two selectable starting methods to match the systems, to provide additional functionality and to particular load. improve fuel economy. The continuing reduction in cost of magnets and the electronics required for the control Detects if the sensorless algorithm gets lost. of BLDC motors has contributed to its use in an Restarts the sensorless control without stopping increasing number of applications and at higher power the motor. levels. Controls braking current to regulate DC bus The BLDC motor is usually operated with one or more voltage. rotor position sensors since the electrical excitation Commutation scheme allows up to 30° phase must be synchronous to the rotor position. For reasons advance to be linearly introduced as the speed of cost, reliability, mechanical packaging and especially increases for improved motor efficiency and if the rotor runs immersed in fluid, it is desirable to run extended speed range. the motor without position sensors - so called Four different ways of controlling the motor speed. sensorless operation. Simple user interface with LCD display and push Instead of elaborating on operation of the BLDC with buttons lets you adjust over 40 parameters. position sensors, it is assumed that the reader is Software consumes approximately 5 MIPS (worst already familiar with this technique. Microchip case) and requires approximately 16 Kbytes of Application Note AN857 contains a very useful program memory. introduction to BLDC motor control. Alternative Without the user interface and debug code, the