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greenpowerZONE Products for the week of March 3, 2008
STMicroelectronics Says…
Sensorless Field-Oriented Motor-Control Solution for ARM Cortex Based Devices
STM32 implementation uses less than 30% of CPU resources for sensorless PMSM vector-control drive
STMicroelectronics has announced a complete three-phase motor-control development kit based on the breakthrough STM32 Flash microcontroller – launched mid-2007 – which provides all the necessary hardware and firmware to enable users to evaluate this 32-bit solution, and to begin development of their own sensorless motor-control application. The STM32 uses the powerful ARM Cortex-M3 core, developed specifically to address the requirements of cost-sensitive home-appliance and industrial applications that need high MCU performance with exceptional energy efficiency.
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.
EN-Genius Says…
Whether you’re a newbie to motor control or you’re a veteran in the process of converting your existing designs to more energy-efficient technologies, ST’s complete reference design for its STM32 processor should make your development efforts faster and less painful. The inclusion of a near-turnkey reference design that handles the trickier bits of sensorless PMSM applications is a great feature that is almost worth the cost of the kit itself. While this kit specifically addresses 3-phase ac permanent magnet motors (PMACs) and BLDC applications, ST says that it can also be used to drive 3-phase induction motors with a few software tweaks. ST has also hinted that we can expect to see some follow-on development kits that handle multiple motors and possibly other types of motors.
For those of you not familiar with the ST Coretex processor, it is a modified ARM-7 with DSP-like functions like single-clock multiply, 2-clock division that are oh-so-handy when calculating phase angles and pulse widths. Having an ARM-7 core at the heart of the STM32 means that you can build on the software provided by ST with a huge base of 3rd-party application code and development tools that will help you make the best use of the processor’s extra MIPS for running user interfaces, communication protocol stacks, or whatever else your heart desires.
This version of the Cortex has an I/O complement that’s specifically designed for motor control applications, including 16 analog channels that feed two integrated 12-bit ADCs that can take measurements in an interleaved or simultaneous fashion and can be read directly or via DMA to a memory-mapped location. The SMT32 also has three general-purpose, 16-bit, 36-MHz multi-event timers and a specialized 72-MHz timer that’s got the higher precision and custom features required for handling the PWM generation involved with controlling a 3-phase motor. Our thoughtful friends at ST have even given the timer an adjustable dead time output that saves lots of processor cycles. Speaking of saving clock cycles, the Cortex has a very efficient interrupt service mechanism that checks for pending interrupts to avoid some of the unnecessary stack pushes and pops that usually happen when multiple interrupts occur during high-speed real-time control operations.
ST has put some very aggressive pricing behind the STM32 series that lets it go head-to-head with some of the excellent DSP-based solutions from TI (reviewed here November 2005) and Microchip (reviewed here December 2007). We can expect it to be battling for sockets in all kinds of green power applications such as compressors in refrigerators and HVAC, drive motors in other white goods, and higher-power industrial motors where the power savings really add up.
The STM3210B-MCKIT is available now, priced at $1129 including a 24 V dc PMSM. An ac induction motor for use with the kit can be ordered separately.
Product Page STM3210B
Data Sheet STM32F103
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