Sensorless Field Oriented Control of PMSM Motors using dsPIC30F or dsPIC33F Digital Signal Controllers

AN1078 Sensorless Field Oriented Control of PMSM Motors This application note focuses on the PMSM-based sen- Author: Jorge Zambada sorless FOC control of appliances because this control Microchip Technology Inc. technique offers the greatest cost benefit in appliance motor control. The sensorless FOC technique also overcomes restrictions placed on some applications INTRODUCTION that cannot deploy position or speed sensors because the motor is flooded, or because of wire harness place- Designers can expect environmental demands to con- ment constraints. With a constant rotor magnetic field tinue to drive the need for advanced motor control tech- produced by a permanent magnet on the rotor, the niques that produce energy efficient air conditioners, PMSM is very efficient when used in an appliance. In washing machines and other home appliances. Until addition, its stator magnetic field is generated by sinu- now, sophisticated motor control solutions have only soidal distribution of windings. When compared to been available from proprietary sources. However, the induction motors, PMSM motors are powerful for their implementation of advanced, cost-effective motor con- size. They are also electrically less noisy than DC trol algorithms is now a reality thanks to the new motors, since brushes are not used. generation of Digital Signal Controllers (DSCs). An air conditioner, for example, requires fast response Why Use Digital Signal Controllers for for speed changes in the motor. Advanced motor con- Motor Control? trol algorithms are needed to produce quieter units that are more energy efficient. Field Oriented Control (FOC) dsPIC DSCs are suitable for appliances like washing has emerged as the leading method to achieve these machines and air conditioner compressors because environmental demands. they incorporate peripherals that are ideally suited for motor control, such as: This application note discusses implementation of a sensorless FOC algorithm for Permanent Magnet Syn- * Pulse-Width Modulation (PWM) ® chronous Motors (PMSMs) using the Microchip dsPIC * Analog-to-Digital Converters (ADCs) DSC family. * Quadrature Encoder Interface (QEI) When performing controller routines and implementing Why Use the FOC Algorithm? digital filters, dsPIC DSCs enable designers to optimize The traditional control method for BLDC motors drives code because MAC instructions and fractional opera- the stator in a six-step process, which generates oscil- tions can be executed in a single cycle. Also, for oper- lations on the produced torque. In six-step control, a ations that require saturation capabilities, the dsPIC pair of windings is energized until the rotor reaches the DSCs help avoid overflows by offering hardware next position, then the motor is commutated to the next saturation protection. step. Hall sensors determine the rotor position to elec- DSCs need fast and flexible analog-to-digital (A/D) tronically commutate the motor. Advanced sensorless conversion for current sensing-a crucial function in algorithms use the back-EMF generated in the stator motor control. The dsPIC DSCs feature ADCs that can winding to determine the rotor position. convert input samples at 1 Msps rates, and handle up The dynamic response of six-step control (also called to four inputs simultaneously. Multiple trigger options trapezoidal control) is not suitable