07-11-2012, 11:24 AM
PMSM Field Oriented Control
1PMSM Field Oriented.pdf (Size: 98.93 KB / Downloads: 32)
Introduction
Is controlling Permanent Magnet Synchronous Motor (PMSM) mysterious to you? PMSM is essentially a
three-phase AC motor with sinusoidal back EMF driven by a DC source, which is converted to three-phase
alternating currents supplying to the three stator windings of a PMSM by an Electronic Control Unit (ECU). In
order to drive a PMSM smoothly, an ECU shall be designed such that the stator current space vector, which
is the sum of the three phase currents, shall be always in the quadrature direction with respect to the rotor
and has constant magnitude, irrespective of rotation speed and back EMF frequency. This results in maximum
torque and minimum torque ripple. Field Oriented Control (FOC) technology can be used to achieve this
goal. In FOC, motor stator currents and voltages are manipulated in the direct-quadrature (d-q) reference
frame of the rotor, which means that the stator current feedback must be mathematically transformed from
the three-phase static reference frame of the stator windings to the two axis rotating d-q reference frame of
the rotor, by using Clarke transform and Park transform, prior to PI processing. Figure 1 shows the stator
space vector and its projections on α – β axis and d – q axis respectively.
On the contrary, the voltages to be applied to the stator windings must be mathematically transformed from
the d-q frame of the rotor to the three-phase reference frame of the stator, by using inverse Park transform
and inverse Clarke transform, before they can be used for PWM output. The update frequency of the control
loops must be high enough and the PWM should be properly configured to ensure sinusoidal currents applied
to the stator windings. Figure 2 is the diagram of velocity/current control loop using FOC technology.