STMicroelectronics (NYSE: STM), a world leader in microcontrollers, has extended its library of functions supporting vector control of electric motors using the 32-bit STM32 microcontroller (MCU), with new turnkey algorithms supporting single-shunt sensorless control, control of IPM (Internal Permanent Magnet) motors, and field-weakening controls for PMSM motors. ST’s Cortex-M3 based STM32 MCU has already been designed into approximately 40 customer motor-control applications.
The additional library functions, now available in the STM32 Motor Control Library Version 2.0, will allow faster time-to-market, lower BOM costs, optimal motor selection and a larger operating envelope in future generations of appliances, industrial drives, pumps, HVAC systems, vending and cash machines, and electric vehicles.
At the same time, ST has extended access to the motor-control library from third-party tool chains, by adding support for the Keil, IAR and Green Hills STM32 design environments. The STM32 Motor Control Library Version 2.0 is available free-of-charge upon request, and can be used directly with the STM3210B-MCKIT hardware evaluation and development kit for motor-control applications based on the STM32.
Among the new algorithms now available to designers, support for single-shunt current sensing saves system cost by eliminating two of the three current-sense resistors from conventional sensorless control schemes. Single-shunt sensing is a patented technique developed by ST, which delivers additional benefits of high DC-bus voltage use, minimum current distortion, and low audible noise. By also adding a Maximum Torque Per Ampere (MTPA) algorithm, the extended library gives designers extra freedom to specify brushless IPM motors in applications requiring the high power density and very high-speed capabilities of these devices. Moreover, ST has also added stator-voltage closed-loop field-weakening control. This reduces sensitivity to motor parameter and environmental variations, thereby expanding the operating limits of all types of PMSM motors. On top of this, feed-forward control compensates bus-voltage ripple and improves current regulation during high-speed flux-weakening operations. A code generator tool that saves time and accelerates development will be available upon request from mid-October.
With these additional algorithms available, developers can take advantage of the STM32′s rich motor-control peripherals, which include up to two integrated three-phase PWM timers allowing one MCU to control up to two brushless motors simultaneously. By breaking the one MCU-per-motor convention, designers can use the STM32 to save cost, size and power without sacrificing performance. There are also up to three integrated ADCs capable of supporting triple sample-and-hold current acquisition for high-accuracy motor drives. Also, by using the industry-standard architecture of the advanced ARM Cortex-M3 CPU, the STM32 allows users to save time compared with developing their motor-control solution on a proprietary architecture.
STM32 MCU variants include the ‘Performance’ line, with 72MHz clock frequency, and the ‘Access’ line with 36MHz clock frequency. Within both lines, ST will eventually offer integrated Flash densities from 16Kbyte to 512Kbyte, and package options ranging from 36-pin QFN to 144-pin LQFP or BGA outlines. Example prices are $1.80 for 32Kbyte, 48-pin LQFP ‘Access’ line MCUs, and $3.60 for 128Kbyte, 100-pin LQFP ‘Performance’ line devices, in quantities over 10,000 units.
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