Sensorless Brushless DC Motor Control with PIC16

AN1175 Sensorless Brushless DC Motor Control with PIC16 MOTOR CONTROL Author: Joseph Julicher Dieter Peter BLDC motor control consists of two parts. Part 1 is Microchip Technology Inc. commutating the motor at the most efficient rate. Part 2 is regulating the speed of the motor within defined parameters. The purpose of this application note is to illustrate an elegant sensorless technique that can be INTRODUCTION implemented on low-cost microcontrollers. All demon- There is a lot of interest in using Brushless DC (BLDC) stration software will operate within an open loop with motors. Among the many advantages to a BLDC motor no speed regulation. over a brushed DC motor, we can enumerate the following: HARDWARE * The absence of the mechanical commutator The hardware for a BLDC system can be decomposedallows higher speeds into the following sections: * Brush performance limits the transient response in the DC motor - Motor Power Drivers, * With the DC motor you have to add the voltage - Rotor position detection using back EMF drop in the brushes among motor losses sensing * Brush restrictions on reactance voltage of the - Current Monitoring armature constrains the length of core reducing - Microcontroller the speed response and increasing the inertia for - Microcontroller Power Supply a specific torque - Speed Set-point Input * The source of heating in the BLDC motor is in the stator, while in the DC motor it is in the rotor, Motor Power Driver therefore it is easier to dissipate heat in the BLDC * Reduced audible and electromagnetic noise All BLDC motors require three half-bridge driver stages. Each stage controls one phase of the motor, as There are many different types of brushless motors, illustrated in Table 1 below: and the differences are: - The number of phases in the stator - The number of poles in the rotor - The position of the rotor and stator relative to each other (rotor spinning inside the stator vs. rotor spinning outside the stator) This application note will discuss the three-phase motors. Two-phase motors are discussed in AN1178, "Intelligent Fan Control" (DS01178) while one-phase motors are a degenerated form of two-phase motors. BACKGROUND For a full description of three-phase brushless motors,