TI E2E Community
Precision current measurement in industrial drives
Marc Royer, product marketing manager for our Precision Data Converter and
Linear businesses, and Arek Kacprzak, systems engineer in our Precision Data
Converter business, have written a joint article on “Precision
Current Measurement in Industrial Drives” for ECN’s Cutting Edge Blog,
which covers the latest in gadget and technology news.
In the article, Marc and Arek explore a recent trend for the premium
and servo drives market – using delta-sigma modulators rather than the traditional
SAR ADC approach, because delta-sigma modulation reduces overall system cost
while providing high performance. The article follows below. You can also read
it on ECN’s website: http://www.ecnmag.com/Blogs/2011/07/Cutting-Edge/Precision-Current-Measurement-in-Industrial-Drives/.
Precision Current Measurement in Industrial Drives
By Arek Kacprzak and Marc Royer, Texas InstrumentsGovernment regulations around the world are calling for higher
efficiency of industrial motor drives because they account for a considerable
amount of our total energy consumption. Higher efficiency requires optimization
of the torque and rotor speed, depending on the actual demand of the system,
which can be achieved in part by increasing the accuracy of the motor current
measurement. The industrial drives market includes five segments: DC, servo, compact AC,
standard AC, and premium AC. For the premium and servo drives segments,
designers tend to use discrete ADCs for current and position signal information
conversion, as shown in the block diagram below. Historically, the ADC
architecture used for the discrete ADCs has been SAR based.
This requires the use of expensive components such as Hall-effect
magnetic sensors for current sensing, and very precise, discrete,
simultaneous-sampling SAR converters for measurement of the load position
One industry trend that is gaining more and more traction is to use a different
ADC architecture, delta-sigma modulation, to perform current and position
measurement. The primary reason for this shift is that delta-sigma modulation
reduces overall system cost while providing high performance.
Although the primary function of the magnetic sensors is to measure current,
they also provide important electrical isolation. The magnetic sensor can
be replaced with a current shunt resistor and isolated delta-sigma modulator, a
more accurate and less expensive option, and provide direct measurement of
current. TI's latest isolated delta-sigma modulator, the AMC1204, is designed
specifically for direct connection to current shunt resistors and has a
galvanic isolation barrier. A block diagram of the new approach is shown below.
In the compact drives segment, cost is an even stronger consideration.
This results in designers using ADCs integrated in the host controller rather
than a discrete ADC solution. To further reduce costs, designers are able to
use current shunt resistors connected to isolated amplifiers, which are then
connected directly to the integrated ADCs on the host controller as an
alternative to more costly magnetic sensor architecture. TI’s latest isolated
amplifier, the AMC1200, is designed specifically for direct connection to
current shunt resistors and has a galvanic isolation barrier. A block diagram
of this solution is shown below.
Regardless of the class of drive, designers are always looking for ways
to reduce the overall cost of their system while maintaining performance.
Switching from a magnetic sensing to a current-sensing based system using an
isolated delta-sigma modulator or isolated amplifier can help achieve this.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.