Microchips doing more for motor, motion control

Advancing Technology: Sensorless vector control, power factor control, and higher temperature operation are among recent silicon developments.

By Frank J. Bartos, P.E. August 1, 2010
Microcontrollers—especially those intended for motor and motion control—continue to add capabilities and features. It’s happening via more onboard functions along with ability to implement added features through software tools, advanced algorithms, and libraries. Various manufacturers offer this technology in the form of digital signal processors and controllers (DSPs and DSCs), integrated circuits (ICs), field-programmable gate arrays (FPGAs), and other silicon devices.
An advocate of chip-level controls, Performance Motion Devices Inc. (PMD), offers its Magellan family of motion-control ICs and boards that work with several motor types, including brush dc, brushless dc (bldc), step, and microstepping motors. Four Magellan versions accommodate 1-4 motion axes, with loop closure times as low as 50 µs per axis. These programmable devices provide sinusoidal commutation and motion profiles such as S-curve, trapezoidal, electronic gearing, plus external profiles. Acceleration and deceleration values are independently programmable.
Another PMD product example—MC73110 motor control IC—provides digital current loop, velocity loop, and commutation for bldc motors. (See “motor” and “motion” control differences in an online extension.) This single-axis drive controller offers internal or external velocity profile mode (with external velocity command), or torque mode with an external torque command signal. MC73110 operates standalone, using preprogrammed parameters, or via microprocessor command. It’s suited for motors and drives in the 1-500 kW power range.
Open- or closed-loop
Recent developments from Microchip Technology Inc. include integration of sensorless field-oriented control (FOC) and power factor control (PFC) on a single chip—the company’s dsPIC33F line of DSC devices. Also known as flux vector control, FOC refers to high-performance motor torque and speed control obtained through either closed-loop (using rotor position feedback) or by sensorless methods. The latter methods derive rotor position by monitoring motor phase currents and voltages. PFC is a feature important for maintaining power quality and limiting motor harmonics.
A low-cost development board (dsPICDEM MCL, $150) works with Microchip’s DSC devices to evaluate bldc and permanent magnet synchronous (PMS) motors and develop applications for sensorless and closed-loop motion systems. Other development boards are available. Examples include closed-loop control of higher voltage (230 V) 3-phase ac induction motors, bldc motors, or PMS motors; also for unipolar/bipolar stepper motor applications.
STMicroelectronics Inc. (ST) also has extended its functions library that supports vector control of motors using ST’s 32-bit STM32 microcontroller (MCU). New algorithms focus on internal PM motors (used in high power density and highspeed applications), field-weakening control to extend the speed range of PMS motors, and singleshunt sensorless control. The latter is a patented technique developed by ST, said to cut system cost by eliminating two of three current-sense resistors used in conventional sensorless control. Sensorless vector control loop closure with STM32 MCUs is under 21 µs, according to STMicroelectronics.
In a related area, ST now offers motor speed control TRIACs rated for 150 °C maximum junction temperature. These “triodes for alternating current” come in several models with 4-10 A maximum rated current and low gate current of 10 mA, allowing direct logic-level switching. Benefits include savings from smaller heatsinks and component count and power supply size/cost, says the company.
Importantly, new generation microchips also are increasing their input-output capability and links with communication networks and sensor interfaces.
– Frank J. Bartos, P.E., is a Control Engineering consulting editor. Reach him at braunbart@sbcglobal.net. 

Author Bio: After researching and writing about motors, drives, motion control, embedded systems, PC-based control, and artificial intelligence topics for the past 20 years, Frank J. Bartos, P.E., retired as executive editor of Control Engineering as of Aug. 1, 2006. To present, he’s contributed multiple articles on these topics. Prior to his distinguished career as a technology journalist, Bartos held engineering positions of increasing responsibility in the design, development, and analysis of automation systems. His industry experience included heavy machinery, electric power plants, medical diagnostic equipment, and precision electromechanical systems.