Microchip Technology MA300015 Data Sheet

© 2008 Microchip Technology Inc.

DS01208A-page 1

In recent years, the motor control industry has been
focusing on designing power efficient motor control
drives for a wide variety of applications. The consumer
demand for improved power quality standards is driving
this trend. The power quality can be enhanced by
implementing Power Factor Correction (PFC), and
efficient control of a motor can be realized using
Sensorless Field Oriented Control (FOC) techniques.
The appliance industry often requires low-cost
implementation of these algorithms. This can be
achieved by integrating PFC and Sensorless FOC
algorithms on a single Digital Signal Controller (DSC). 

This application note describes the process of
integrating two complex applications: PFC and Sensor-
less FOC. These applications are implemented on a
Permanent Magnet Synchronous Motor (PMSM). In
addition, this application note also describes the inte-
gration of the algorithms, lists the necessary hardware
requirements, and provides the guidelines to optimize
the development procedure.

The integrated solution is based on these application
notes:

• AN1106, Power Factor Correction in Power 

• AN1078, Sensorless Field Oriented Control of 

The application note AN1106, describes the Power
Factor Correction (PFC) method. The application note
AN1078, describes the Sensorless Field Oriented
Control (FOC) method. The detailed digital design and
implementation techniques are provided in these
application notes. This application note is an
addendum to the above application notes. 

The integrated application is implemented on the
following families of dsPIC

®

 DSC devices:

• dsPIC30F 

• dsPIC33F

The low cost and high performance capabilities of the
DSC, combined with a wide variety of power electronic
peripherals such as the Analog-to-Digital Converter

(ADC) and the Pulse Width Modulator (PWM), enable
the digital design and the implementation of such a
complex application to be simpler and easier.

The majority of motor control systems often use PFC
as the first stage of the system. Without an input PFC
stage, the current drawn will have significant harmonic
content due to the presence of switching elements of
the inverter. In addition, since motor loads are highly
inductive, the input currents will induce significant
reactive power into the input system, thereby reducing
overall efficiency of the system. A PFC stage which is
a front-end converter of a motor control application,
provides better output voltage regulation and reduces
harmonic content of the input current drawn.The
standard boost converter topology with average current
mode control is the preferred method for implementing
digital PFC in these applications. 

The dual shunt Sensorless FOC method is a speed
control technique that drives the PMSM motor. The
Sensorless FOC technique overcomes restrictions
placed on some applications that cannot deploy
position or speed sensors. The speed and position of
the PMSM motor are estimated by measuring phase
currents. With a constant rotor magnetic field produced
by a permanent magnet on the rotor, the PMSM is very
efficient when used in appliances. When compared
with induction motors, PMSM motors are more
powerful for the same given size. They are also less
noisy than DC motors, since brushes are not involved.
Therefore, the PMSM motor is chosen for this
application. 

The dsPIC DSC devices are ideal for a variety of com-
plex applications running multiple algorithms at differ-
ent frequencies and using multiple peripherals to drive
the various circuits.  These applications (e.g., washing
machines, refrigerators, and air conditioners) use vari-
ous motor control peripherals to precisely control the
speed of the motor at various operating loads. The
integrated PFC and Sensorless FOC system uses the
following peripherals: 

• Pulse Width Modulator (PWM)

• Analog-to-Digital Converter (ADC)

• Quadrature Encoder Interface (QEI)