 2019 Microchip Technology Inc. DS90003220A-page 1 TB3220 INTRODUCTION Many countries pursue standards which require increasing energy efficiency in domestic appliances, such as air conditioners, refrigerators, washing machines, fans and so on. Additionally, manufacturers and consumers prefer to reduce the size of such appliances. A Permanent Magnet Synchronous Motor (PMSM) is an ideal choice for such applications due to its high efficiency, energy density and robustness. PMSMs require sophisticated control schemes customized to suit the motor, load and the appliance system to achieve the best possible efficiency, durability and robustness. This document discusses the control scheme and some of the load-specific algorithms for control of PMSM-driven appliances, for example, compressors, washing machines and fans. PERMANENT MAGNET SYNCHRONOUS MOTOR (PMSM) The PMSM is made of a stationary part called the stator and a rotating part called the rotor. A stator consists of three phase windings, and when excited with a balanced three-phase voltage, it produces a rotating magnetic field. A rotor has permanent magnets, which produce their own magnetic field. The motor rotates due to torque produced when these two fields interact. PMSMs are classified into two categories depending on the rotor construction: 1. Surface Mount: The magnets are mounted on the surface of the rotor. They need special profiling to get a sinusoidal Back EMF (BEMF). This results in a symmetrical air gap reluctance for the magnetic flux path. Such a motor is called a Surface-Mounted Permanent Magnet Synchronous Motor (SPMSM). FIGURE 1: SPMSM INDUCTANCES (Ld = Lq) 2. Interior Mount: Magnets are embedded deep inside the rotor. This results in an asymmetrical air gap reluctance for the magnetic flux path. Such a motor is called an Interior-Permanent Magnet Synchronous Motor (IPMSM). FIGURE 2: IPMSM INDUCTANCES (Ld < Lq) Practically, even the surface-mounted PMSMs have slight asymmetry in their reluctance path due to manu- facturing processes and materials used. A measure of this asymmetry is called, ‘saliency’, which is calculated based on the inductance variation along the stator. Saliency produces its own torque, similar to a force pro- duced on an iron bar in a solenoid. This torque is called, ‘reluctance torque’, which is different and additional to the ‘permanent magnetic torque’ that is produced due to interaction of stator and rotor fields. Author: Prasad Kulkarni Microchip Technology Inc. Sensorless Field-Oriented Control of Permanent Magnet Synchronous Motor (Surface and Interior) for Appliances with Angle-Tracking Phase-Locked Loop Estimator