3 System Overview

Figure 3-1 shows a block diagram of the integrated PFC and Sensorless FOC system.

The first stage is a rectifier stage that converts the input line voltage into a rectified AC voltage. The rectified AC voltage is the input to the second stage, which is the boost converter stage.

During the second stage, the boost converter boosts the input voltage and shapes the inductor current similar to that of the rectified AC voltage. This is achieved by implementing digital power factor correction. The Average Current Mode Control method is used to implement PFC. In this control method, the output DC voltage is controlled by varying the average value of the current amplitude signal reference, which is calculated digitally.

The third and the final stage of the integrated system is a three-phase inverter stage that inverts the DC voltage into a three-phase AC voltage. The inverted three-phase AC voltage is the input to the PMSM. This stage is controlled by implementing the Sensorless FOC strategy on the device. The Sensorless FOC controls the stator currents flowing into the PMSM to meet the desired speed and torque requirements of the system. The position and speed information is estimated from the stator currents. Please refer to AN2520, Sensorless Field Oriented Control (FOC) for a Permanent Magnet Synchronous Motor (PMSM) Using a PLL Estimator and Equation-based Flux Weakening (FW), for details on the rotor position estimation using stator currents.

The integrated system uses five compensators to implement PFC and Sensorless FOC technique. The PFC technique uses two compensators to control the voltage and current control loops, and the Sensorless FOC technique uses three compensators to control the speed control loop, torque control loop, and flux control loop. All of the compensators are realized by implementing Proportional-Integral (PI) controllers.

Figure 3-1. Integrated PFC and Sensorless FOC System Block Diagram