Many industrial processes require precise and accurate control over system parameters such as flow, pressure, temperature, process speed, etc. The use of a variable frequency drive (VFD) to match the motor driven equipment’s speed and torque to the requirements of the process load can result in large energy savings, particularly in variable torque or centrifugal loads. It is estimated that 30 % of industrial motor systems may benefit from the application of a VFD to control motor speed and torque when the primary purpose is to achieve energy savings.
A VFD can be set up in many ways, each differently affecting operating efficiency, due to the infinite number of operating points between torque and speed. To establish a test procedure to measure efficiency, the Canadian Standards Association (CSA) has developed Standard CSA 838. This standard, published in 2010 and based on outcomes from the CEATI project: "Study To Establish A Test Protocol For Determining The Efficiency Of Variable Frequency Drives (VFDS)", has not yet received world-wide acceptance, but not because of its technical content. Other organizations, such as the European Committee for Electrotechnical Standardization (ENELEC), have decided to develop a new draft standard (not yet accepted) that includes a similar procedure as in the CSA, but adding a new approach using complex calculations to determine system efficiency. In addition, the International Electrotechnical Commission (IEC) will initiate a working group in 2014 to develop a new draft standard with references to the CSA Standard and others, since it is not in the IEC’s policy to adopt a specific national standard. VFD system efficiency remains an important issue for the industrial community, but no common test protocol has been yet been adopted.
Recently acquired VFD system testing results indicate a significant variation of 2 % to 8 % in VFD system efficiency between manufacturers and applications, particularly at low loads and low speeds. The potential energy savings in Canada alone for a 2 % efficiency improvement in VFD applications is estimated at over 1,000 GWh per year or 200 MW.
The aim of this work is to report a benchmark study of new VFD-motor technologies, such as Permanent Magnet (PM), Switch Reluctance (SR) and Synchronous Reluctance (SynR) systems of different sizes and from different manufacturers, and to evaluate potential gains in efficiency in these technologies compared to well established VFD-induction motor technology under the same test protocol – the CSA 838.
Keywords: Permanent Magnet, Switch Reluctance, Synchronous Reluctance, Efficiency, VFD, Motor, Test, Standard, Benchmark