Field-Oriented Control of Brushless Motors without the Math

Field-Oriented Control of Brushless Motors without the Math

During their studies, engineers are confronted with much mathematics that forms the basis of electronics and electronic systems. However, once embedded in our selected industry segment, many of us never really have to contend with convolution, Laplace transforms, or the details of Fourier since we end up developing applications that use this mathematics, rather creating the algorithms themselves. Perhaps one area of exception has been motor control where, for everything but simple applications, a detailed understanding of the Clarke and Park transforms was required to implement field-oriented control (FOC) of brushless DC motors.

This has been a challenge, both to implementers and providers of silicon solutions that use FOC, to package the hardware and the software in such a manner that it is easy to use, configure, and optimize. On top, tools are needed to garner the insights into the state of the control algorithm and allow a “look inside” to support debugging during development. One significant area that causes challenges is the lack of determinism since the control algorithm can require significantly different amounts of time to execute the complex mathematics to calculate each commutation step. If the microprocessor is also handling other application tasks this can, in the worst case, lead to poor motor control or an unresponsive application.

To simplify the implementation and achieve more determinism, Toshiba has developed a series of microcontrollers (MCU) that implement the FOC algorithms in hardware. Known as the Advanced Vector Engine (A-VE), it integrates 3-phase to 2-phase conversion, space vector modulation, along with PI (proportional/integral) control blocks that are easily configured through hardware registers. It is also tightly coupled with the analog-to-digital converter (ADC) and pulse-width modulation (PWM) peripherals. As such, the A-VE can read in voltage and current values from the motor phases and directly prepare the PWM for the next commutation step with very little intervention from the microprocessor. Measurements and comparison undertaken by Toshiba show that, compared to a pure software implementation, this approach delivers a 70% reduction in processor load.

To assist in the tuning of the system, the “Motor Mind” tool can be used. It provides a graphical interface to edit all motor parameters and A-VE settings. Connecting over the serial interface of the MCU, it is possible to access settings in real time and even visualize information buried deep inside of the vector engine.

FOC provides a significant improvement over alternative motor-control approaches, delivering lower torque ripple and better control at low rotation speeds. One challenge is the upper end of the rotation speed spectrum that is limited by the controller’s ability to calculate the next commutation point in a timely manner. Toshiba’s A-VE capable MCUs can handle an electrical speed of over 4000Hz, which equates to a little more than 250,000 rpm for a single pole pair motor, ensuring that a wide range of motor applications can be supported.

If you’d like to read more about the A-VE peripheral integrated into Toshiba’s series of MCUs and learn about the tools and hardware that supports them, you can review our white paper on the topic available here:

Download the Whitepaper

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