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This paper describes an adaptive method for compensating the reactive power with an active power filter (APF), which is initially rated for mitigation of only the harmonic currents given by a nonlinear industrial load. It is proven that, if the harmonic currents do not load the APF at the rated power, the available power can be used to provide a part of the required reactive power. Different indicators for designing such application are given, and it is proven that the proposed adaptive algorithm represents an added value to the APF. The algorithm is practically validated on a laboratory setup with a 7-kVA APF. Index Terms--Active filters, harmonics analysis, power-system harmonic, pulsewidth-modulated inverters, reactive power.

When permanent-magnet synchronous motors (PMSMs) are used for pump and fan applications, V/f control methods can be used to control them. The problem with open-loop V/f control of PMSMs without having damper windings in the rotor is the inherent instability after exceeding a certain applied frequency. In this paper, a new V/f control method is proposed for motor drives for stable operation in a wide frequency range. The magnitude of the voltage is controlled in order to maintain a constant stator flux linkage in the PMSM. The applied frequency is modulated proportional to the input power perturbations to stabilize the drive for a wide frequency range. No position sensor is required to implement this stabilizing technique. The small-signal analysis and the experimental results confirm the effectiveness of this stabilizing technique. The experimental results also indicate the satisfactory performance of the drive for pump and fan applications. Index Terms--Permanent-magnet synchronous motor (PMSM), sensorless control, synchronous motor stability, volts-per-hertz (V/f) control.

This paper contains an analysis of how the choice of energy optimal control of induction motors is influenced by motor construction, standard versus high-efficiency motor, and by application, constant torque (CT) and heating, ventilation, and air conditioning (HVAC) (interpreted as vector and scalar motor drives). The analysis is made with a 2.2-kW voltage-source-inverter-fed squirrel-cage motor drive as an example throughout the paper, but through statistics on the use of motors and their efficiencies, the conclusions are widened to a broader range (0-50 kW). Energy optimal control strategies are reviewed and cos([Psi]) control, a model-based control, and a search control are implemented in the laboratory in a vector and a scalar motor drive. The convergence speed for the strategies and their ability to reject disturbances are investigated by experiments. It is also shown experimentally that, for both standard and high-efficiency motors, motor energy-efficiency improvement is achievable by energy optimal control below 60% load torque. The energy savings using energy optimal control strategies are measured on a pump system with a certain load cycle. Model-based control is recommended for CT applications and cos([Psi]) control for HVAC applications. Index Terms - Efficiency, energy optimization, induction motor.

In 1997 Danfoss Drives A/S and the Institute of Energy Technology at Aalborg University in Denmark started an initial four-year collaboration called 'The Danfoss Professor Program.' The main goal of the program is to attract more students to the multidisciplinary area of power electronics and drives by offering a world-class curriculum taught by world-class teachers. During the four years of the program distinguished professors will visit the university, giving advanced courses in their specialty areas and interacting with postgraduate students. A new curriculum in power electronics and drives is also now being implemented at the university, based on courses developed together with professors from the program. Another goal is to strengthen the research team at the university in the area by fostering new contacts and research areas. Finally, training and education of engineers in industry is a major aim of the program. After 2 1/2 yr, the Danfoss Professor Program has resulted in a significant increase in the number of students and research output of Aalborg University in the power electronics and drives area. It is beginning to be recognized world wide as a model of successful Industry/University collaboration. This paper describes the major goals, implementation and an evaluation of the program. Index Terms--Education, power electronics and drives curriculum, research collaboration.