Kurt Stockman

Sensitivity of AC adjustable speed drives to voltage sags and short interruptions

This paper discusses the sensitivity of adjustable speed drives (ASDs) to voltage sags and short interruptions on the basis of extensive test results. Existing standards and previously published work are critically reviewed, and a description of test procedures needed for appropriate assessment of ASD sensitivity is presented. The following tests were performed: sensitivity to rectangular three-phase, two-phase, and single-phase voltage sags with ideal and nonideal supply characteristics, as well as sensitivity to nonrectangular-balanced three-phase voltage sags similar to those caused by the starting of large motors. The results show that although the behavior of this equipment has a rather complex pattern, a simple representation of ASD sensitivity to various types of voltage sags and short interruption can be established.

Sensitivity of personal computers to voltage sags and short interruptions

This paper discusses the sensitivity of personal computers (PCs) to voltage sags and short interruptions on the basis of the extensive test results. Existing standards and previously published works are reviewed, and a description of a used testing procedure is presented. The following tests were performed: sensitivity to rectangular voltage sags with ideal and nonideal supply characteristics, and sensitivity to voltage sags caused by the starting of large motors. The results obtained emphasize the importance of clear definition of the malfunction criteria for this equipment.

Distributed Generation for Mitigating Voltage Dips in Low-Voltage Distribution Grids

The presence of synchronous and induction generators has a positive effect on the retained voltage (the lowest rms voltage during the event) during voltage dips in high voltage networks. The impact of converter-connected distributed-generation (DG) units has been reported to be negligible, as most converters operate at unity power factor, and the currents injected in the grid are limited to the nominal current of the converter. However, the impact of DG units on the distorted grid voltage is strongly dependent on the voltage level, and thus the grid impedance, of the concerned grid. This paper investigates and compares the effects of converter-based DG units, synchronous and asynchronous generators on the retained voltage during voltage dips in low voltage distribution grids.

Analysis of the neutral conductor current in a three-phase supplied network with nonlinear single-phase loads

This paper describes what factors (i.e., load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affect the RMS value of the neutral conductor current.

A method to align a manufacturing execution system with Lean objectives

The application of information technology and Lean principles have long been seen as mutually exclusive, but both approaches are more and more claimed to be interdependent and complementary. Real-time production information is crucial to make important business decisions. A manufacturing execution system (MES) can provide the necessary support during the Lean journey. MES can trigger, feed or validate the Lean decision-making process by providing useful information. In addition, MES can maintain the process improvements by enforcing the standardised way of working. However, this is only possible when MES is aligned and is kept aligned to the Lean objectives. The MES processes must be included in the continuous improvement cycle to prevent them from becoming obsolete. In this work, a method is proposed to analyse this alignment between Lean and MES. The manufacturing operations management framework provided by ISA 95 is believed to deliver the necessary components to identify and structure this alignment. Mapping MES and Lean activities onto the same framework brings valuable insights about their dependency. The analysis is explored through a case example. Preventing the system from becoming obsolete, by proposing standard model changes, is an important direction for further research.

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.

Iso efficiency contour measurement results for variable speed drives

The efficiency of variable speed drives with induction motors and permanent magnet synchronous motors has received little attention so far in international standards. However the number of such applications is increasing rapidly and the potential energy savings are large. This paper is based on a measurement campaign of three collaborating research institutes and reports on the efficiency of motors up to 15 kW. The efficiency values are represented by means of iso efficiency contours. From these contours, the efficiency for IE1, IE2 and IE3 induction motors is compared with that of a permanent magnet machine for the entire torque - speed operation region. Also the impact of flux optimization with induction motors is analyzed. The required number of measurement points to construct accurate iso efficiency contours with minimum measurement effort is also discussed.

Iso efficiency contours as a concept to characterize variable speed drive efficiency

Despite recent revisions and harmonization efforts of international motor efficiency standards which has lead to the revised IEC Std 60034-2-1 and the efficiency classification of IEC Std 60034-30, there remains a lacuna in the context of motor systems efficiency. Although IEC is preparing a “Guide for the selection and application of energy-efficient motors including variable-speed applications” labeled IEC Std 60034-31, to date, there is no internationally accepted test protocol that allows the determination of drive system efficiency at different load points. As the first in a set of three by a joint research project of three research institutes, this paper introduces iso efficiency contours as a useful tool in this context. The concept of these contours as well as their mutual interaction with system specifications and losses are discussed. A first testing protocol for all types of motor drives is proposed. The concept is illustrated by first results of an extensive testing campaign.

Calculating energy consumption of motor systems with varying load using iso efficiency contours

Increasing awareness of ecological problems forces machine manufacturers to design greener machines. This implies amongst other things the selection of the most efficient electric motor system for their specific application. On the other hand, machine building applications evolve more and more from constant speed and load characteristics to varying speed and load applications. Therefore, the motor system that is used evolves more and more from direct online (DOL) to motors fed by a variable speed drive (VSD). However, current efficiency standardization focuses on DOL applications, and can by consequence not offer assistance to the machine builder to select the most efficient motor-VSD combination for his particular varying load application. The goal of this paper is to present a methodology that allows to predict the energy consumption for a specific motor-VSD combination and a specific varying speed-load application, using the fairly new concept of iso efficiency contours. By comparing the predicted energy consumption for a number of selected combinations, the most efficient one is revealed.

The Efficiency of Hybrid Stepping Motors: Analyzing the Impact of Control Algorithms

Stepping motors are used in numerous applications because of their low manufacturing cost and simple open-loop position control capabilities. It is well known that their energy efficiency is low, although the actual efficiency values are generally not available. Moreover, the bulk of the stepping motors are driven in a non-optimal way, e.g., in an open loop with a maximum current to avoid step loss and, thus, with low efficiency. In this article, the impact of the control algorithm on the efficiency of the motor is analyzed, measured, and discussed. The basic open-loop full-, half-, and microstepping algorithms are considered together with a more advanced vector control algorithm. For each algorithm, the torque/current optimization is discussed.