4.4. Field-Oriented Control (FOC)

FOC consists of a velocity controller, a current controller, and commutation and estmation subcomponents. A high-level block diagram of the FOC components is shown in Figure 4.3.

Figure 4.3 Block diagram of MCAF Field Oriented Control

This diagram shows a number of features that are described in the test harness.

4.4.1. Velocity Control

The velocity control loop is a straightforward, scalar PI controller, with managed saturation features to prevent integrator windup when either the velocity or current controller saturates.

It is preceded by a rate limiter, to provide more gentle trajectory shaping and reduce transient overshoot.

Saturation and antiwindup features are present and covered in a separate document.

4.4.2. Current Control

The current control loop is a vector control loop that operates in the dq reference frame, with reference transforms to convert to/from the ABC stationary reference frame in which currents are measured and duty cycles are commanded. The vector control loop itself is a straightforward pair of PI controllers, with managed saturation features to prevent integrator windup when the current controller saturates. (Saturation and antiwindup features are covered in more detail in a separate document.)

Figure 4.3 shows a filter block preceding the current controller. It is intended to slow down incoming commands from the velocity loop, which typically executes at a slower rate. This filter is unimplemented for MCAF v1.0, but is reserved for a future version.

Figure 4.3 also shows DC link voltage compensation prior to the Inverse Park Transform. This is also not implemented for MCAF v1.0, but is reserved for MCAF v2.0.

4.4.3. Position and Velocity Estimator

The sensorless estimator used to estimate position and velocity is essentially the one used in AN1292.

4.4.4. Implementation Notes

4.4.4.1. Modules

4.4.4.1.1. Core FOC

Module	Files	Description	Comments
parameters/foc_params	parameters/foc_params.h	FOC control parameters
parameters/init_params	parameters/init_params.c parameters/init_params.h	Initialization of FOC control parameters
parameters/sat_PI_params	parameters/sat_PI_params.h	PI Saturation parameters
foc	foc.c foc.h foc_types.h	Top-level FOC	These functions are called from the state machine modules, as described in the implementation notes.
sat_PI	sat_PI.c sat_PI.h sat_PI_types.h	PI loop saturation management

The field_weak module, covering flux weakening and not included in the above table, is presently disabled in MCAF v1.0, and is being redesigned for a future version. In MCAF v1.0, the velocity controller sets the d-axis current command to zero.

4.4.4.1.2. Commutation

Module	Files	Description	Comments
parameters/pll_params	parameters/pll_params.h	PLL estimator parameters
commutation	commutation.c commutation.h commutation_types.h	Top-level commutation / estimation
pll	pll.c pll.h	PLL (AN1292 sensorless estimator)
qei	qei.c qei.h	Quadrature encoder estimator	The quadrature encoder is used to obtain a reference position for testing estimator performance.