Improved energy efficiency and reduced system costs are the driving factors in modern motor control designs used in fans, pumps, compressors or geared motors. The implementation of sophisticated motor control concepts with sensor less Field Oriented Control (FOC) and Power Factor Correction (PFC) help to fulfill these demands. To demonstrate the capabilities of these powerful concepts Infineon has built a reference design for the motor control of air conditioners using dual sensor less FOC and active PFC based on the 16-bit microcontroller XE164. This innovative approach leads to a significant improvement of the energy efficiency and to a reduction of the Bill of Materials (BoM).
FOC is a method to generate a three phase sinusoidal signal which can easily be controlled in frequency and amplitude in order to minimize the current which means to maximize the efficiency. The related vector control is a math technique for controlling brushless DC and AC induction motors that reduces motor size, cost and power consumption. With FOC the efficiency of a motor can be improved significantly and raised up to 95%. This has a big impact on power consumption, motor dynamics, heat dissipation and noise. A sensor less FOC (figure 1) on BLDC (Brushless DC motor) or PMSM (Permanent Magnet Synchronous Motors) provides additional cost benefits compared to sensor based motor control.
Fig 1: Block diagram of sensorless FOC
- For higher resolution, click here
A BLDC has a permanent magnet rotor and a wound stator. The position of the coils (phases), with respect to the permanent magnet field, are sensed and the current switched electronically (commutated) to the appropriate phases. To sense the rotor position typically Hall Effect sensors are used. But the costs for an encoder or other position sensor can be saved, with sensor less approaches using the back EMF (Electromagnetic Force) of the motor to calculate the rotation angle and rotor position. The back EMF is calculated in the flux estimator, which is based on the voltage model of the system in the two phase reference frame. A single shunt is enough to reconstruct the phase currents.
System manufacturers are looking for cost-effective implementations of these advanced algorithms. This can be achieved by integrating both the sensor less FOC and PFC on a single microcontroller. With this powerful combination the system behavior can be exactly adapted and optimized to the application needs.
In the following application example a dual sensor less FOC with active PFC was implemented with the XE164 MCU (figure 2). The three PWM units, several timer and two very fast and powerful ADCs make the XE164 a perfect fit for a variety of motor control applications. This application software runs on the XE164, which is part of the drive card of the Dual Motor Drive Application Kit from Infineon.
Fig 2: Block Diagram XE164- For higher resolution, click here
Power Factor Correction
The EN-61000-3-2 sets the harmonic regulation standard on any off-line application with power consumption over 75W. This essentially demands Power Factor Correction. Power Factor Correction is a specific filter, used in power supplies from a higher load on like in PC power supplies or modern inverters, to increase the ratio of the real power and apparent power flowing to the load.
