Embedded Software IP & Technology Transfer in Power Electronics Applications

Archives for October 2009

Motor Energy Efficiency, Power Factor and Actel mixed-signal FPGAs

Here’s a very extensive article written in two parts (part 1 here, part 2 here) by John Smitty of Actel Corporation.

According to Smitty, “the potential energy savings are staggering. Over 40 million electric motors are used in manufacturing operations in the United States alone. Electric motors account for 65 to 70 percent of industrial electrical energy consumption and approximately 57 percent of all electrical consumption worldwide. Saving even a few percent of the world’s estimated 16,000-plus terawatt-hours (TWh) annual consumption of electricity amounts to several hundreds of trillions of watt-hours per year.”

High-performance motor control design is one way to achieve those energy savings and this may be done using DSP chips but those rapidly limited because “they are sequential state machines that can only do a very limited amount of computation in a single clock cycle“. Here’s how the author explains why mixed-signal FPGAs can overcome this situation:

Unlike DSPs, the mixed-signal FPGA can do many computations in parallel, and can do certain specialized computations such as computing sines and cosines (which are generally required by these algorithms) much faster than most any DSP microcontroller, at a lower cost per computation. As a bonus, FPGAs invariably consume less power than any type of microcontroller doing the same function“.

Also, “FPGAs offer much flexibility. For instance, if your algorithm requires an extra PWM, it can easily be added to an FPGA solution. PWMs pre-built into a DSP or ASSP integrated circuit may or may not perform the PWM algorithm you want, or take into consideration the needs of your power circuitry. With an FPGA, the PWM can be customized exactly to your specifications. An FPGA can be adapted to accept most any type of feedback sensor (encoder, Hall effect, or tachometer, for example) or a sensorless algorithm based upon motor back-EMF measurements can be implemented“.

Using NI CompactRIO for FPGA-based motor control in Factory Automation

Here’s a recent article written by Greg Crouch, Embedded Systems Business Director at National Instrument., on the topic of FPGA-based motor control for Factory Automation.

Embedded-machine builder EUROelectronics reduced power use with FPGA-based field-oriented control (Source : National Instruments)

FPGA-based algorithm control delivers better efficiency than microprocessors can achieve. A wide range of control-system algorithms are available, including trapezoidal, sinusoidal and field-oriented.

Trapezoidal, or six-step, control is the simplest but lowest-performance method. For each of the six commutation steps, the motor drive provides a current path between two windings while leaving the third motor phase disconnected. However, torque ripple causes vibration, noise, mechanical wear and greatly reduced servo performance.

Sinusoidal control, also known as voltage-over-frequency commutation, addresses many of these issues. A sinusoidal controller drives the three motor windings with currents that vary smoothly. This eliminates torque ripple issues and offers smooth rotation.

More information on NI CompactRIO can be found directly on their website.