SM Field-Oriented Control

Synchronous machine field-oriented control

Libraries:
Simscape / Electrical / Control / SM Control

Description

The SM Field-Oriented Control block implements a synchronous machine (SM) field-oriented control structure. Field Oriented Control (FOC) is a performant AC motor control strategy that decouples torque and flux by transforming the stationary phase currents to a rotating frame. Use FOC when rotor speed and position are known and your application requires:

High torque and low current at startup
High efficiency

Equations

The SM FOC is made up of several control blocks from the Control library. To see and modify these blocks and the FOC's internal structure, right-click the block in Simulink and select Mask > Look Under Mask. The overall control structure is made up of several parts:

The outer loop controller converts the reference signal you supply to the reference d-axis, q-axis, and field currents.
You can choose the type of reference signal you provide using the Control mode parameter:
- Velocity control — Control or regulate the rotation speed of the synchronous machine. An internal Velocity Controller block generates a reference torque from the rotor speed error.
- Torque control — Control or regulate the mechanical torque of the SM.
An internal SM Current Reference Generator block generates the reference currents using a proportional-integral (PI) controller, minimizing the torque error.
The inner loop controller converts the current references into voltage references. An internal SM Current Controller generates the voltage references using a PI controller minimizing the current error, and the feedforward terms:

$\begin{array}{l} v_{d_F F} = - ω_{e} L_{q} {_{i}}_{q} \\ v_{q_F F} = ω_{e} (L_{d} i_{d} + L_{m f} i_{f}) \\ v_{f_F F} = 0 \end{array}$
where:
- ω_e is the rotor electrical angular velocity.
- L_d and L_q are the d- and q-axis stator inductances.
- L_mf is the mutual field armature inductance.
- i_d, i_q, and i_f, are the stator d-q and field excitation currents, respectively.
The PWM Generator converts the reference stator voltages into gate pulses to be passed to a Power Converter that is powering the stator windings of the synchronous machine.
The Excitation PWM Generator converts the reference field voltage into gate pulses to be passed to a DC-DC Chopper powering the SM field winding.

This diagram shows the overall architecture of the block.

In the diagram:

ω and ω_ref are the measured and reference angular velocities, respectively.
T_ref is the reference electromagnetic torque. If you configure the block for speed control, a Velocity Controller generates this reference torque.
i and v are stator currents and voltages. Subscripts d, q, and f, represent the d-axis, q-axis, and field winding. Subscripts a, b, and c, represent the three stator windings.
θ_e is the rotor electrical angle.
G is a gate pulse, subscripts H and L represent high and low, and subscripts a, b, and c, represent the three stator windings. Subscript ex represents the field excitation pulses.

You can choose to implement either velocity or torque control with the Control mode parameter. The block implements velocity control exactly as shown in the diagram. The block implements torque control by removing the Velocity Controller block and accepting the reference torque directly.

Assumptions

The machine parameters are known.

Limitations

The control structure is implemented with a single sample rate.

Examples

Three-Phase Synchronous Machine Drive

Control the rotor speed in a Synchronous Machine (SM) based electrical drive. A high-voltage battery feeds the SM through a controlled three-phase converter for the stator windings and through a controlled two-quadrant chopper for the rotor winding. Use the model to design the SM controller, selecting architecture and gains to achieve desired performance. The Scopes subsystem contains scopes that allow you to see the simulation results.

Open Model

Ports

Input

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Reference — System reference
scalar

System reference specified as torque reference in N*m or velocity reference in rad/s, depending on the control mode selected.