Vector control offers further advantages, in terms of motor efficiency when the load changes, such as with a washing machine where the load is rapidly changing. It also offers faster response times in controlling the speed of the motor.
Depending on the application, this can result in as much as a 20 percent improvement in efficiency, but it comes at a price in terms of complexity: "Vector control is a mathematical technique to separate the control of the torque and the flux of three-phase permanent magnetic motors. It is a compute-intensive function, which is why it typically requires at least a 16bit or 32bit microcontroller."
Although its use in low power motor control is only now being explored, it isn't a new innovation: "Vector control itself isn't new; I would say it's about 20 years old. What is new is the implementation of vector control in low cost applications, such as home appliances. It is really enabled by powerful microcontrollers that are only now available at a reasonable price that is compatible with the final application."
With a vector control algorithm running at 10kHz, Bille believes it takes about 15 percent of the STM32's available processing bandwidth, allowing additional computations to be carried out that can further improve the application: "Usually, for vector control, some form of feedback is required. This feedback can be an encoder or sensor, but it can also be a complex algorithm based on the current flowing in to the motor, to estimate the motor position. Thanks to the power of these new microcontrollers, we can also add, for permanent magnet motors, an algorithm for sensorless reconstruction of the motor position, which is required for vector control."
Bille also explained that the development of affordable vector control coincides with the increased popularity of more advanced motors, such as internal permanent magnet motors: "Internal permanent magnet motors have become more popular in recent years; they combine the advantages of both a reluctance motor and permanent magnet motor. This makes it possible, for a given power, to reduce the size of the motor. This is the trend we are now seeing." A trend that Bille believes is helped by the availability of affordable vector control solutions.
Bille admits that vector control is more difficult to develop than traditional motor control methods: "It is more difficult to develop vector control, which is why ST and most of our competitors offer a vector control firmware library. Of course, the quality of the control itself will depend on the performance of the microcontroller you are using and the quality of the firmware." Inherent in that statement is the need for the appropriate peripherals to complement the cpu core. Bille stated that vector control performance could also be limited by the bit width and conversion time of the ADC used for sensorless motor position measurement, as well as the PWM module.