Field Oriented Control of PMSM Drive

Field Oriented Control of PMSM Drive

Introduction to Field Oriented Control (FOC)

Field Oriented Control (FOC) is a technique used to control the speed of PMSM drives. PMSM stands for Permanent Magnet Synchronous Motor. The FOC method measures the rotor angle and speed, processes these measurements through a control algorithm, and generates reference currents to control the motor.

FOC Control Logic

The block diagram for the FOC of PMSM is as follows:

1. Angle Measurement: Measure the rotor angle in mechanical form and convert it to electrical form using a conversion factor.

2. Speed Measurement: Measure the motor speed and compare it with the reference speed.

3. Speed Controller: Process the speed error using a PI controller to generate the reference current (iq*).

4. Current Reference Generation: Set the direct axis current (id) to zero and generate the reference currents (ia*, ib*, ic*) using a dq to abc conversion.

5. Current Regulation: Compare the reference currents with the actual currents and process the error using a hysteresis band current controller to generate the PWM pulses for the inverter.

Simulink Model of FOC Control of PMSM

We will implement the FOC control logic in Simulink. The model includes:

• Universal Bridge: Connects to the PMSM motor.

• Measurement Blocks: Measure stator currents (ia, ib, ic), speed, electromagnetic torque, and rotor angle in radians.

• Speed Control Loop: Compare actual speed with reference speed, process the error through a PI controller, and generate iq*.

• Current Reference Generation: Set id* to zero and generate abc reference currents using dq to abc conversion.

• PWM Generation: Use a hysteresis band current controller to generate PWM pulses for the inverter.

Simulation Setup

• Reference Speed: Use a step signal to provide the reference speed command.

• Load Torque: Set initial load torque to 6 Nm and change it to 3 Nm.

Simulation Results and Discussion

The simulation results show the performance of the FOC control of PMSM. The key observations are:

• Speed Response: The motor speed tracks the reference speed command, reaching the desired speed with minimal overshoot and steady-state error.

• Voltage and Current Response: The output voltage of the inverter and the stator currents change according to the speed command. The voltage and current responses exhibit steady-state behavior after reaching the reference speed.

• Electromagnetic Torque: The electromagnetic torque shows high starting torque and steady-state torque after reaching the reference speed. During speed command changes, the torque exhibits some disturbances before stabilizing.

Conclusion

Field Oriented Control of PMSM drive allows precise speed control by generating appropriate reference currents and regulating the motor's voltage and current. The Simulink model demonstrates the effectiveness of FOC in controlling the PMSM drive.