Sensorless Field Oriented Control (FOC) of a Permanent ...

1 AN1078. Sensorless Field Oriented Control of a PMSM. This application note focuses on the PMSM-based Authors: Jorge Zambada and Debraj Deb Sensorless FOC Control of appliances because this Microchip Technology Inc. Control technique offers the greatest cost benefit in appliance motor Control . The Sensorless FOC. technique also overcomes restrictions placed on some INTRODUCTION applications that cannot deploy position or speed Designers can expect environmental demands to sensors because the motor is flooded, or because of continue to drive the need for advanced motor Control wire harness placement constraints. With a constant techniques that produce energy efficient air rotor magnetic Field produced by a Permanent magnet conditioners, washing machines and other home on the rotor, the PMSM is very efficient when used in an appliances.

2 Until now, sophisticated motor Control appliance. In addition, its stator magnetic Field is solutions have only been available from proprietary generated by sinusoidal distribution of windings. When sources. However, the implementation of advanced, compared to induction motors, a PMSM is powerful for cost-effective motor Control algorithms is now a reality, its size. It is also electrically less noisy than a DC motor, thanks to the new generation of Digital Signal since brushes are not used. Controllers (DSCs). Why Use Digital Signal Controllers for An air conditioner, for example, requires fast response for speed changes in the motor. Advanced motor Motor Control ? Control algorithms are needed to produce quieter units dsPIC DSCs are suitable for appliances like washing that are more energy efficient.

3 Field Oriented Control machines and air conditioner compressors because (FOC) has emerged as the leading method to achieve they incorporate peripherals that are ideally suited for these environmental demands. motor Control , such as: This application note discusses the implementation of Pulse-Width Modulation (PWM). a Sensorless FOC algorithm for a Permanent Magnet Analog-to-Digital Converter (ADC). Synchronous Motor (PMSM) using the Microchip dsPIC 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 code because MAC instructions and fractional The traditional Control method for BLDC motors drives operations can be executed in a single cycle.

4 Also, for the stator in a six-step process, which generates operations that require saturation capabilities, the oscillations on the produced torque. In six-step Control , dsPIC DSCs help avoid overflows by offering hardware a pair of windings is energized until the rotor reaches saturation protection. the next position, and then the motor is commutated to The dsPIC DSCs need fast and flexible the next step. Hall sensors determine the rotor position Analog-to-Digital (A/D) conversion for current to electronically commutate the motor. Advanced sensing a crucial function in motor Control . The dsPIC. Sensorless algorithms use the back-EMF generated in DSCs feature ADCs that can convert input samples at the stator winding to determine the rotor position.

5 1 Msps rates, and handle up to four inputs The dynamic response of six-step Control (also called simultaneously. Multiple trigger options on the ADCs trapezoidal Control ) is not suitable for washing enable use of inexpensive current sense resistors to machines because the load is changing dynamically measure winding currents. For example, the ability to within a wash cycle, and varies with different loads and trigger A/D conversions with the PWM module allows the selected wash cycle. Further, in a front load inexpensive current sensing circuitry to sense inputs at washing machine, the gravitational power works specific times (switching transistors allow current to against the motor load when the load is on the top side flow through sense resistors).

6 Of the drum. Only advanced algorithms such as FOC. can handle these dynamic load changes. 2010 Microchip Technology Inc. DS01078B-page 1. AN1078. MOTOR Control WITH DIGITAL Application Highlights SIGNAL CONTROLLERS The purpose of this application note is to illustrate a The dsPIC DSC Motor Control family is specifically software-based implementation of Sensorless , Field designed to Control the most popular types of motors, Oriented Control for PMSM using Microchip digital including: signal controllers. AC Induction Motor (ACIM) The Control software offers these features: Brushed DC Motor (BDC) Implements vector Control of a PMSM. Brushless DC Motor (BLDC) Position and speed estimation algorithm. Permanent Magnet Synchronous Motor (PMSM) eliminates the need for position sensors.

7 speed range tested from 500 to 17000 RPM. Several application notes have been published based on the dsPIC DSC motor Control family (see the With a 50 s Control loop period, the software References section). These application notes are requires approximately 21 MIPS of CPU overhead available on the Microchip web site (about 2/3 of the total available CPU). ( ). The application requires 450 bytes of data memory storage. With the user interface, This application note demonstrates how the dsPIC. approximately 6 Kbytes of program memory are DSC takes advantage of peripherals specifically suited required. The memory requirements of the for motor Control (motor Control PWM and high- speed application allow it to run on the ADC) to execute Sensorless Field Oriented Control of a dsPIC33FJ12MC202, which is the smallest and PMSM.

8 The DSP engine of the dsPIC DSC supports most cost-effective dsPIC33F device at the time the necessary fast mathematical operations. of this writing. An optional diagnostics mode can be enabled to Data Monitoring and Control Interface allow real-time observation of internal program The Data Monitor and Control Interface (DMCI) pro- variables on an oscilloscope. This feature vides quick dynamic integration with MPLAB IDE for facilitates Control loop adjustment. projects in which operational constraints of the applica- tion depend on variable Control of range values, on/off states or discrete values. If needed, application feed- back can be represented graphically. Examples include motor Control and audio processing applications.

9 The DMCI provides: Nine slider controls and nine boolean (on/off). controls (see Figure 1). 35 input controls (see Figure 2). Four graphs (see Figure 3). The interface provides project-aware navigation of program symbols (variables) that can be dynamically assigned to any combination of slider, direct input or boolean controls. The controls can then be used interactively to change values of program variables within MPLAB IDE. The graphs can be dynamically configured for viewing program generated data. Note: The characteristics of the DMCI tool are subject to change. This description of the DMCI tool is accurate at the date of publication. DS01078B-page 2 2010 Microchip Technology Inc. AN1078. FIGURE 1: DYNAMIC DATA Control INTERFACE.

10 FIGURE 2: USER-DEFINED DATA INPUT CONTROLS. 2010 Microchip Technology Inc. DS01078B-page 3. AN1078. FIGURE 3: GRAPHICAL DATA VIEW. DS01078B-page 4 2010 Microchip Technology Inc. AN1078. SYSTEM OVERVIEW Figure 5 illustrates how the 3-phase topology, as well as the current detection and fault generation circuitry, As shown in Figure 4, there are no position sensors are implemented. attached to the motor shaft. Instead, low-inductance The first transistor shown on the left side of the inverter shunt resistors, which are part of the inverter are used is used for Power Factor Correction (PFC), which is not for current measurements on the motor. A 3-phase part of this application note. inverter is used as the power stage to drive motor windings.