What is ‘Field Oriented Control’ and What Good Is It?

Using brushless servo motors and drives in your next new product? You have probably seen the buzzwords: 'Trapezoidal', 'Sinusoidal', and 'Field Oriented Control'. You will need to understand what they mean so that you can make the right choice for your design. During the last decade or two, servomotors have evolved from largely brush types to brushless. This has been driven by lower maintenance and higher reliability of brushless motors. As brushless motors have become more prevalent during this period, the circuit and system techniques used to drive them have evolved as well. The variety of control schemes has lead to a similar variety of buzzwords that describe them. Most high performance servo systems employ an inner control loop that regulates torque. This inner torque loop will then be enclosed in outer velocity and position loops to attain the desired type of control. While the designs of the outer loops are largely independent of motor type, the design of the torque loop is inherently specific to the motor being controlled.