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Embedded Software and Motor Control Libraries for PXR40xx

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4.102.4 Description<br />

The quadrature phase model of a PMSM motor, in a synchronous reference frame, is very<br />

popular <strong>for</strong> field oriented control structures because both controllable quantities, current<br />

<strong>and</strong> voltage, are DC values. This allows employing only simple controllers to <strong>for</strong>ce the<br />

machine currents into the defined states.<br />

The voltage equations of this model can be obtained by trans<strong>for</strong>ming the motor three<br />

phase voltage equations into a quadrature phase rotational frame, which is aligned <strong>and</strong><br />

rotates synchronously with the rotor. Such a trans<strong>for</strong>mation, after some mathematical<br />

corrections, yields the following set of equations, describing the quadrature phase model<br />

of a PMSM motor, in a synchronous reference frame:<br />

Equation GMCLIB_DecouplingPMSM_Eq1<br />

It can be seen that GMCLIB_DecouplingPMSM_Eq1 represents a non-linear cross<br />

dependent system. The linear voltage components cover the model of the phase winding,<br />

which is simplified to a resistance in series with inductance (R-L circuit). The crosscoupling<br />

components represent the mutual coupling between the two phases of the<br />

quadrature phase model, <strong>and</strong> the back-EMF component (visible only in q-axis voltage)<br />

represents the generated back EMF voltage caused by rotor rotation.<br />

In order to achieve dynamic torque, speed <strong>and</strong> positional control, the non-linear <strong>and</strong><br />

back-EMF components from GMCLIB_DecouplingPMSM_Eq1 must be compensated<br />

<strong>for</strong>. This will result in a fully decoupled flux <strong>and</strong> torque control of the machine <strong>and</strong><br />

simplifies the PMSM motor model into two independent R-L circuit models as follows:<br />

Equation GMCLIB_DecouplingPMSM_Eq2<br />

Chapter 4 API References<br />

Such a simplification of the PMSM model also greatly simplifies the design of both the<br />

d-q current controllers.<br />

There<strong>for</strong>e, it is advantageous to compensate <strong>for</strong> the cross-coupling terms in<br />

GMCLIB_DecouplingPMSM_Eq1, using the feed-<strong>for</strong>ward voltages u_dq_comp given<br />

from GMCLIB_DecouplingPMSM_Eq1 as follows:<br />

<strong>Embedded</strong> <strong>Software</strong> <strong>and</strong> <strong>Motor</strong> <strong>Control</strong> <strong>Libraries</strong> <strong>for</strong> <strong>PXR40xx</strong>, Rev. 1.0<br />

Freescale Semiconductor, Inc. 473

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