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© 2009 Microchip Technology Inc. DS01292A-page 1
AN1292
INTRODUCTION
Current industry trends suggest the Permanent Magnet
Synchronous Motor (PMSM) as the first preference for
motor control application designers. Its strengths, such
as high power density, fast dynamic response and high
efficiency in comparison with other motors in its
category, coupled with decreased manufacturing costs
and improved magnetic properties, make the PMSM a
good recommendation for large-scale product
implementation.
Microchip Technology produces a wide range of Digital
Signal Controllers (DSCs) for enabling efficient, robust
and versatile control of all types of motors, along with
reference designs of the necessary tool sets, resulting
in a fast learning curve and a shortened development
cycle for new products.
FIELD ORIENTED CONTROL (FOC)
In case of the PMSM, the rotor field speed must be
equal to the stator (armature) field speed (i.e.,
synchronous). The loss of synchronization between the
rotor and stator fields causes the motor to halt.
Field Oriented Control (FOC) represents the method by
which one of the fluxes (rotor, stator or air gap) is
considered as a basis for creating a reference frame for
one of the other fluxes with the purpose of decoupling
the torque and flux-producing components of the stator
current. The decoupling assures the ease of control for
complex three-phase motors in the same manner as
DC motors with separate excitation. This means the
armature current is responsible for the torque
generation, and the excitation current is responsible for
the flux generation. In this application note, the rotor
flux is considered as a reference frame for the stator
and air gap flux.
Several application notes from Microchip explain the
principles behind FOC. Two such examples are:
AN1078 “Sensorless Field Oriented Control of PMSM
Motors using dsPIC30F or dsPIC33F Digital Signal
Controllers” and AN908 “Using the dsPIC30F for
Vector Control of an ACIM” (see “References”). It is
beyond the scope of this application note to explain the
FOC details; however, the particulars of the new
implementation will be covered with respect to the
previously indicated application notes.
The control scheme for FOC is presented in Figure 1.
This scheme was implemented and tested using the
dsPICDEM™ MCLV Development Board (DM330021),
which can drive a PMSM motor using different control
techniques without requiring any additional hardware.
The control scheme is similar to the one presented in
application note AN1162 “Sensorless Field Oriented
Control (FOC) of an AC Induction Motor (ACIM)” (see
“References”), except for the estimator particulars
and obviously the motor used – a PMSM instead of an
ACIM.
Author: Mihai Cheles
Microchip Technology Inc.
Sensorless Field Oriented Control (FOC) for a
Permanent Magnet Synchronous Motor (PMSM)
Using a PLL Estimator and Field Weakening (FW)
