The impact of supervision and management on motor efficiency

Governments around the world have provided regulatory pressure to use electric motors more efficiently. First came the Environmental Protection Act of 1992, which mandated motor efficiency standards, and since 1997, the U.S. government has been steadily increasing regulations. There are other voluntary measures as well, such as the National Electrical Manufacturers Association (NEMA) Advanced Efficiency Labeling Standard (2001). Australia implemented standards for motors ranging from 0.73 kW to 185 kW in 2001 and tightened efficiency requirements in 2006. More recently (March 2009), the European Union adopted mandatory minimum energy efficiency performance standards (MEPs) that will be phased in between 2011 and 2017. Brazil (2002) and China (starting in 2010) also have existing or planned mandatory standards. See the figure below for a comparison of efficiency requirements for motors of various sizes in several jurisdictions, including voluntary NEMA and the Coalition for Energy Efficiency (CEE) standards, versus existing efficiency standards for various motors. The line depicts several mandatory and voluntary automotive efficiency standards around the world and focuses on representative commercial vehicles.

Efficiency range of a 1800 rpm car

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Motor Controller

Motor savings are achieved in several ways. The first is in the motor design itself, through better materials used, design, and construction. Another is by optimizing the relationship between the internal motor magnetic field and the angle of rotation of the machine. This is accomplished using a new family of motor control algorithms, generally referred to together as space vector control, flux vector control, or field oriented control. By keeping the rotor and stator magnetic fields oriented at the optimum angle between them under varying speed and torque conditions (usually nearly 90 degrees), the motor is always maintained at peak efficiency. As a side benefit, other features can also be optimized, such as fast and stable dynamic response to changes in load, speed, or torque, precise control of soft starting and braking at low speeds, start-up torque drag, and fault detection; often without sacrificing much in the way of overall energy efficiency. Some of these features were once available only on more expensive motor types, but can be achieved with the now ubiquitous, low-cost, and reliable AC induction motors, including 90 percent of all U.S. automobiles sold on the market. One of the most important advantages of the newer control algorithms is efficient variable-speed operation.