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Vector control of a 3-Phase PMSM using Z16FMC MCU

This article presents the vector control of a 3-phase PMSM using the ZNEO Z16FMC microcontroller. It discusses the implementation of field oriented control scheme for PMSM, and summarizes the difference between AC induction machines and permanent magnet synchronous machines.

Zilog's Z16FMC Series Flash MCUs are based on Zilog's advanced Z16FMC 16-bit ZNEO CPU core and are optimized for such motor control applications. These MCUs sup- port the control of single and multiphase variable speed motors. Target applications include consumer appliances, HVAC, factory automation, refrigeration, and automotive applications. To rotate a 3-phase motor, three AC voltage signals must be supplied and phase shifted 120 degrees from each other. To do so, the
Z16FMC Series Flash MCUs feature a flexible PWM module with three complementary pairs, or six independent PWM outputs, supporting dead-band operation and fault protection trip inputs. These features provide multiphase control capability for various motor types and ensure safe operation of the motor by providing immediate shutdown of the PWM pins during a fault condition. The duty cycle of each microcontroller PWM output is varied to control the period and amplitude of the generated AC signal, which in turn determines the speed and torque of the motor.

Field Oriented Control Theory of Operation
Field oriented control consists of space vector control and space vector modulation. The space vector control term refers to the independent control of the flux and torque currents, i.e., the d-q components and the necessary ninety-degree alignment between the rotor flux and the stator flux. The space vector modulation term refers to the sinusoidal pulse width modulation pattern to rotate the reference vector Is within the hexagon with a magnitude and angle adjustment based on the field oriented control corrections, as shown in Figure 1.

Figure 1: Vector-Control-of-a-3-Phase-PMSM-Using-Z16FMC-MCU-2-1470639070.

Generally, all field oriented control algorithms are contained within the PWM service interrupt routine, referred to as inner loop in this application note. These algorithms consists of:

Phase current measurements. § Clarke transform (3-2 axis transformation). § Flux estimator (flux speed integrator to estimate rotor angle). § Park transform. § PI current controllers. § Inverse Park transformation. § Inverse Clarke transformation. § Applying resulting PWM signals to the inverter bridge. § Hardware Setup.

Figure 2: Shows the Linix DC brushless motor, the opto-isolated USB Smart Cable and Zilog's MultiMotor Development Kit.

Using the test setup, three oscilloscope probes were connected to the BEMF voltage dividers of Phase A, Phase B, and Phase C of the MultiMotor Series Devel- opment Board to show the three phase voltages. A current probe was connected to one of the phases to show the current waveform. The speed control potentiometer was set to the middle of the entire range to start at full speed. The potentiometer was then adjusted to any position between the lowest speed (all the way down from the middle position) and up to with no load:

PI loop action (minimum of over or undershoot and time to ramp to full speed).
PI loop stability (waveforms and power supply currents should show no fluctuations).
Closed loop performance (must maintain speed when applying more or less voltage to the motor, i.e., constant power).
Current consumption during ramp up (avoiding excessive currents).

Shape of phase voltage and currents (currents in all three phases must be approximately sinusoidal).

The control of a PMSM consists of two parts, Field Oriented Control to align the rotor flux and stator flux at an angle of 90 degrees to each other, and the Space Vector Modulation scheme to apply control voltages to the three phases of the motor to achieve this alignment under torque control.

IXYS in profile
Headquartered in Milpitas, CA, and Leiden, Netherlands, IXYS has gained a worldwide reputation as a premier power semiconductor manufacturer. Its diversified product base of specialized power semiconductors, integrated circuits and RF power is utilized by more than 2500 customers worldwide, ranging across industrial, transportation, telecommunications, computer, medical, consumer and clean tech markets. Learn more about IXYS' 30-year history, its founder Dr. Nathan Zommer, its divisions and current growth.

Acknowledgement to IXYS for the article.

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