Sensorless Field-Oriented Motor-Control Solution for ARM Cortex Based Devices

ST is the first MCU supplier to offer a sensorless field-oriented motor-control solution based on the Cortex-M3 core. The kit demonstrates that the STM32 provides sufficient power, from the core and dedicated motor-control peripherals, to optimize the drive and to minimize the overall system cost. A complete sensorless vector-control algorithm for three-phase brushless PMSM (Permanent Magnet Synchronous Motor) motor is executed in less than 25 microseconds, using less than 30% of the CPU’s resources for most applications, and leaving plenty of processing power for other application tasks, if required. The code size for the PMSM solution is less than 16 Kbytes.

The hardware platform can be used for both PMSM and AC induction motors, operating at up to 48V; schematics are provided to minimize hardware design time. The kit allows real-time control and monitoring via an on-board color LCD and joystick, or standalone operation using on-board push buttons and trimmers. The Segger J-Link USB-powered JTAG emulator is included, and the Flash programming and real-time debugging capability allows the same hardware and firmware platform to be used from evaluation through to an advanced stage of development, removing the need for the user to build a platform before starting work on the target system. A debugger and programmer are also included.

Applications that can benefit from the cost-effective motor-control capability of the STM32 include washing machines, dishwasher pumps, refrigerators and air conditioners, in the appliance sector; and industrial applications such as electric vehicles, low-end and medium-range industrial drives, office automation, HVAC actuators and fans, and vending and cash machines.

Vector-control (or ‘field-oriented’) algorithms are widely used in high-performance drives, to provide precise and responsive speed control, and to guarantee optimized efficiency during transient operations. They also have the practical advantage of using the same framework to control both asynchronous and synchronous motors, a cost-saving feature for development teams dealing with a variety of applications and motor types. In addition, most sensorless drive algorithms are based on field-orientation methodology, leading to further opportunities to reduce the drive cost.

The easy-to-use kit enables engineers to run the included PMSM motor within minutes. Then, through the graphical display, users can familiarize themselves with all the sensorless controls (such as PID regulators) by re-tuning them during run-time, using the joystick and LCD. Finally, users can start developing their own applications, starting from the optimized C firmware libraries that have been used to build the demo application. The C library source code is provided on the supplied CD-ROM, with the exception of the sensorless algorithm, which is delivered as object code free upon request from ST, for both types of three-phase brushless motors (AC induction in sensor mode, and PMSM in sensor and sensorless modes). By using the industry-standard ARM architecture, the STM32 allows users to save time compared with developing their motor-control solution on a proprietary architecture.

The STM32 delivers impressive levels of performance and energy efficiency, while retaining the benefits of working with the open, industry-standard ARM architecture and development environment. The STM32F103 ‘Performance’ line, with 72MHz clock frequency, provides best-in-class 32-bit MCU performance, while the STM32F101 ‘Access’ line, with 36MHz clock frequency, offers users of 16-bit devices a significant increase in performance, but at 16-bit price levels.

The Cortex-M3 core was developed to target the low-cost requirements of a wide range of markets and applications where memory and processor size significantly impact the product cost. ST was a lead partner in this development, and was the first leading MCU supplier to introduce a product family based on the core. It is also one of the few manufacturers able to provide the full portfolio of motor control active components, from diodes to processors.