Frederik D'Hulster

Ride-through of adjustable speed drives during voltage dips

Abstract Adjustable speed drives are reported to be very susceptible to voltage dips. This paper investigates the behaviour of standard induction motor drives in the power range from 2.2 up to 7.5 kW for different types of voltage dips. Voltage tolerance curves are presented and an optimal selection of the under-voltage protection is proposed in order to maintain operation without loss of performance. The opportunities, provided by an active front end and a boost converter, to improve the ride-through of standard drives are investigated and their effect on the voltage tolerance curves is considered.

Thermal analysis of the influence of nonlinear, unbalanced and asymmetric loads on current conducting capacity of LV-cables

Asymmetry, unbalance and nonlinearity of loads affect the current distribution in both phase and neutral conductor cores in three phase power supply systems. Consequently, temperature distribution in the cable section which is directly related to the power dissipation is influenced. Applying a maximum insulation temperature as boundary condition, the power conducting capacity of LV-cables will substantially be affected by asymmetry, unbalance and especially nonlinearity of loads. The most relevant combinations of asymmetry, unbalance, and nonlinearity were analyzed. The temperature distribution in the cable section is thermally calculated and is subsequently simulated, using 2D finite element modelling. Finally, measurements of the cable temperature arc performed verifying the simulation results.

Bag the sags

This article describes the vulnerability of variable speed drives (VSD) to voltage sags on a theoretical basis. Then, three embedded mitigation methods are addressed in theory which protect textile processes against voltage sags, and practical measurements with a sag generator are shown. The use of embedded solutions such as kinetic buffering and boost convertor or an active front end will increase the voltage sag immunity of the process. Finally, two processes in the textile industry are described, and a brief cost-benefit analysis of the solutions is made. Experiments with a sag generator show that the voltage sag behaviour can be well described by theoretical models.

Embedded solutions to protect textile processes against voltage sags

Variable speed drives (VSD) are reported to be very susceptible to voltage sags. In textile industry processes, such as extrusion and weaving, many synchronised VSDs are installed, reducing the reliability of the processes under voltage sag conditions. This paper evaluates the influence of embedded mitigation methods on the voltage tolerance curves of extrusion and weaving units using theoretical considerations as well as practical measurements. A brief cost-benefit analysis of the installation in these two textile processes is given.

Cost effective solutions to increase the immunity of AC drives against voltage dips

This paper describes cost effective solutions to increase the immunity of standard field oriented AC drives against voltage dips. The solutions are based on the classification of dips into three types and an experimental analysis of protection mechanisms applied in commercial drives. For asymmetric diptypes, complete ride-through is obtained by selecting the correct amount of dc link capacitance. For symmetric dips however, field weakening is required to maintain torque control. The performances of field weakening techniques are analyzed with respect to voltage dips. Control of an induction machine is shown to be more difficult compared to a permanent magnet synchronous machine. The methods proposed to reduce the sensitivity of AC drives against voltage dips are verified experimentally