So as to keep down the overall component count and lower the costs involved, as well as saving valuable space, sensor-less control of BLDC motors is proving to be increasingly appealing to today’s design engineers. This approach is used in household appliances, industrial hardware and various other scenarios. Accurately determining the back EMF induced allows the position of the rotor to be calculated so that the BLDC can be driven more effectively, with the need for inclusion of Hall sensor devices being circumvented.
Over the years field oriented control (FOC) has emerged as the preferred method via which to undertake sensor-less motor control, providing the high precision data needed for elevated levels of operational efficiency. It must be acknowledged though that there are situations where it is not necessarily ideal.
When running at low speeds, after the motor’s operation has been initiated for instance, getting accurate positioning data is difficult. Consequently, the use of a high-frequency test signal is needed in order for the rotor’s position to be derived. This, however, will result in torque ripple being generated - which subsequently leads to electro-magnetic interference, acoustic noise and energy losses.
The latest additions to the game-changing TXZ+ series of 32-bit MCUs available from Toshiba offer a way of dealing with this problem. These Arm Cortex-M based devices leverage the company’s unique Advanced Programmable Motor Driver (A-PMD) technology. Using this, individual pulse-width modulated (PWM) carriers are assigned to each motor phase. Common triggers are generated for the MCU ADCs synchronously monitoring the current on the applicable motor phases. The upshot of this is that high-frequency test signals no longer need to be applied when the motor is operating at lower speeds - thereby enabling less noisy motor performance with heightened degrees of efficiency.
To download the whitepaper that Toshiba has published on how A-PMD is making BLDC motor control more effective at low speeds, please click below: