Field Oriented Control Using High-Quality Low-Cost 8-Bit µC

Full benefits of sinusoidal commutation at a minimum system cost.
Infineon is the world’s first microcontroller supplier to offer optimized 8-bit MCUs capable of supporting Sensorless Field Oriented Control (FOC). FOC is a powerful technique for operating electric motors resulting in smooth and energy efficient operation at all speeds. Increasingly being used in consumer and industrial motor control applications, typically a 16-, 32-bit MCU or DSP is required to handle the complex trigonometric FOC equations. Achieving this efficient method of control with a low-cost but highly optimized 8-bit microcontroller redefines the economic models for developers of home appliances and other motor-controlled products such as fans and HVAC control.

The FOC feature is implemented on the 8-bit XC886/8 MCU by combining a high-performance 8051 core and a “Vector Computer” coprocessor core, which performs 16-bit arithmetic operations. This vector computer is build by two parallel operating units: MDU, a 16-bit multiply and divide unit, and CORDIC, a 16-bit coprocessor dedicated for vector rotation and angular calculations. In order to implement a sensorless solution, the PWM pattern generation and the triggering of the ADC for single shunt current measurement must be very fast and accurate. The XC886/888C(L)M perfectly implements the above requirement using an event based hardware trigger from the PWM unit CapCom6E towards the ADC.

Compared to current solutions on the market, in which FOC execution engages the whole central processing unit (CPU) load, FOC execution on the Infineon XC886/XC888 microcontrollers only requires 58 percent of the CPU’s performance, providing additional resources for functions such as system control and communications. One of the key benefits of the solution is the software reprogrammability which enables an optimized startup phase of the motor by programming a controlled ramp using any signal of the algorithm. 

 
Key Features of XC886/888 which enables Field Oriented Control:

• High performance 16-bit vector computer (CORDIC + MDU)
• Fully programmable co-processor

• Key functions

  • Vector rotation and transformations like Park transform
  • Normalizing and scaling
• Interrupt based operation with minimum CPU load
   

• PWM unit for advanced motor control (CapCom6E)

  • 16-bit resolution for high precision space vector PWM generation
  • Dead time control for minimum hardware effort (direct control of MOSFET/IGBT)
  • CTRAP provides hardware overload protection
     

• Fast 10-bit A/D Converter (sample time of 0.25 µs)

  • Enables single shunt current measurement
  • Reduced torque ripple due to minimized blind angle
  • Hardware synchronization to PWM unit reduce CPU load
  • Two result registers to maximize sampling performance
    

Applications

• Home appliances
• Industrial and automotive motor control Applications

XC886/888 Block Diagram

Implementation of Field Oriented Control