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 Tech of the Week

Multi-vector electronic control of an AC motor drive reduces torque ripple and improves efficiency

Nissan Motor Co., Ltd.

By suppressing or controlling harmonic currents and voltages of the motor to overcome torque ripple, this system improves the efficiency and torque performance of an AC motor, especially permanent magnet synchronous motors (PMSM), which are very popular in industry due to high efficiency and small volume compared to other types of motors. Many PMSMs use a concentrated winding for the benefit of simple manufacturing and low cost, and they have a large spatial harmonics. PMSMs are controlled by conventional vector control drives, but voltages and current harmonics present in the motor can deteriorate accuracy and efficiency. Compared to conventional vector control, this technique further improves efficiency and torque performance by reducing the harmonics. This technique can be used in many types of equipment, including trucks and other vehicles, elevators, washing machines, air conditioners, machine tools, robotics, and industrial equipment where quick response and accuracy in speed or position control are required. The technique is simple to implement, and may be applied to existing equipment.

Less expensive motors perform as well as expensive ones; expensive motors perform at or near theoretical optimum.

The technology improves efficiency in PMSM electric motors in such a way that two potential outcomes can be realized.

  • Less expensive motors that do not use complex windings can be made to perform as well as more expensive equipment, or
  • More expensive motors already optimized for conventional controllers can be made to perform at peak efficiency approaching their theoretical best performance. Such performance is not achievable using conventional controllers.

A wide variety of appliances and equipment can thus be made more efficient, or can be operated electrically at even high RPMs with utmost efficiency and with minimal heat loss. Factory tugs, trucks, industrial machine tools, air conditioners, refrigerators, and even aircraft can benefit from the increase in efficiency, showing improved range, reduced power draw, and extended equipment life cycles.

For battery-powered or hybrid equipment (such as industrial tugs) the controller improvement extends equipment range, extends equipment life, and reduces maintenance costs. Heat loss from the motor is minimized. For equipment that uses small, high-RPM electric motors (machine tools, for example), the technology offers high efficiency and better accuracy.

The technology controls harmonic currents even at high RPMs. It may be implemented in circuitry or software, and applied to existing equipment.

The technology is available for non-automobile applications; however, it is available for truck, construction, and industrial vehicles other than forklifts.

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