Looking at electric drive efficiency

variable-frequency drives (VFDs) provide dramatic energy savings in myriad applications with varying loads and speeds. While power and energy savings are key benefits, VFD efficiency is also of interest because drives can experience significant efficiency losses at partial load operation-much like electric motors.

07/01/2009


Five makes of VFDs tested had efficiency variations (bands) as shown for 50 hp (37 kW) units running at different speeds - along with larger characteristic efficiency drop-off at reduced torque and speed.

Few will dispute that variable-frequency drives (VFDs) provide dramatic energy savings in myriad applications with varying loads and speeds. While power and energy savings are key benefits, VFD efficiency is also of interest because drives can experience significant efficiency losses at partial load operation—much like electric motors. Yet motors have received predominant attention for energy efficiency, including development of recognized test procedures and standards. A broader look at “motor system” efficiency must recognize the effect of VFDs.

Recent progress in this area includes work done at the energy technology labs of Hydro-Quebec's (Canada) Research Institute. Findings of the underlying study, “Variable Frequency Drive Testing,” have been presented at Motor Summit 2008 (Zurich, Switzerland), MEPSA 2009 (Sydney, Australia), and 2009 Motor, Drive & Automation Systems Conference (Orlando, FL) by Pierre Angers, an engineer at Hydro-Quebec.

“Published VFD efficiencies at other than full rated power are scarce,” says Angers. “There is no recognized VFD efficiency standard for comparing different makes of drives.” Efficiency is the highest around 100% speed, which is just where you don't want to use variable-speed drives, hence most available efficiency values are virtually “useless,” Angers explains.

Goals of the project were to establish an efficiency testing procedure for VFDs, motors, and VFD-motor combinations—as well as to enable efficiency comparison between various VFD systems. Angers has tested five major makes of VFDs, which powered three sizes of induction motors (10, 50, and 100 hp/7.5, 37, 75 kW) at various loads and speeds. For each test run a series of 20 test points ranged widely over “% speed” and “% nominal torque” values (25-100% speed and 10-100% torque). Drive manufacturers' names remain proprietary. Test setup measured efficiency as a ratio of output to input power.

Preliminary results show 2-8% variation in VFD system efficiency, especially at low loads and speeds. Efficiency variation between different brands of VFDs was substantially less (see diagram). However, variability of VFD efficiency is further impacted by factors such as drive temperature, supply voltage (and voltage unbalance), switching frequency, and drive options like active front-end, reactors, or output filters.

One novel aspect of Angers' research is presentation of motor system efficiency results as a contour map, with percent nominal speed and percent torque serving as other variables. A typical conveyor application plots as a horizontal line (constant torque) across the efficiency contours, while a pump/fan application plots as a cubic system curve.

The work described here is the basis of a protocol for testing VFD efficiency. Two proposed standards are in draft status: Canadian standard (CSA C838) Variable Frequency Drives and International Electrotechnical Commission standard IEC 60034-2-3.

Users of VFDs obtain energy savings from matching motor speed to load requirements; in addition, they need to be able to compare efficiency of different electric drive brands for their applications.


Author Information
Frank J. Bartos, P.E., is a Control Engineering consulting editor. Reach him at braunbart@sbcglobal.net .




Engineers' Choice Awards
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
System Integrator Giants
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
How to Maximize Factory Automation Efficiency with Low Cost Machine Vision
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Wireless Reliability in Harsh Environments
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Human Factors and the Impact on Plant Safety
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
July 2018
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
June 2018
Discrete and process sensor fundamentals, autotuning controls, system integrator roundtable
May 2018
Salary and Career Survey, IT and OT convergence, robotic standards and safety, secure circuit protection
Edge Computing
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data Center Design
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
PLCs
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SIDB

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

June 2018
Machine learning, produced water benefits, progressive cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
John O. Ayuk, PE, CFSE, PMP, CAP
Automation Engineer; Wood Group
Doug Baker
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Engineers' Choice Awards
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
System Integrator Giants
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
How to Maximize Factory Automation Efficiency with Low Cost Machine Vision
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Wireless Reliability in Harsh Environments
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Human Factors and the Impact on Plant Safety
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
July 2018
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
June 2018
Discrete and process sensor fundamentals, autotuning controls, system integrator roundtable
May 2018
Salary and Career Survey, IT and OT convergence, robotic standards and safety, secure circuit protection
Edge Computing
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data Center Design
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
PLCs
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SIDB

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

June 2018
Machine learning, produced water benefits, progressive cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
John O. Ayuk, PE, CFSE, PMP, CAP
Automation Engineer; Wood Group
Doug Baker
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Engineers' Choice Awards
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers.
System Integrator Giants
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
How to Maximize Factory Automation Efficiency with Low Cost Machine Vision
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Wireless Reliability in Harsh Environments
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
Human Factors and the Impact on Plant Safety
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
July 2018
Ladder logic best practices and object-oriented programming, safety instrumented systems, enclosure design issues and challenges, process control advice
June 2018
Discrete and process sensor fundamentals, autotuning controls, system integrator roundtable
May 2018
Salary and Career Survey, IT and OT convergence, robotic standards and safety, secure circuit protection
Edge Computing
This article collection contains several articles on how today's technologies heap benefits onto an edge-computing architecture such as faster computing, better networking, more memory, smarter analytics, cloud-based intelligence, and lower costs.
Data Center Design
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
PLCs
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. Featured articles in this digital report compare PLCs and programmable automation controllers (PACs), industrial PCs, and robotic controllers.
SIDB

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

June 2018
Machine learning, produced water benefits, progressive cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
John O. Ayuk, PE, CFSE, PMP, CAP
Automation Engineer; Wood Group
Doug Baker
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me