Wim Deprez

Improvement Potential for Energy Consumption in Discrete Part Production Machines

Industrial production inevitably results in an environmental impact. Energy consumption is responsible for a substantial part of this impact. Currently, machine designers spend little attention to minimising the energy consumption, since their primary focus is on the well-functioning of the machine.

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.

Energy related environmental impact reduction opportunities in machine design: case study of a laser cutting machine

Energy consumption is responsible for a substantial part of the environmental impact generated by industrial production (Gutowski et al., 2006). Currently, minimising the energy consumption is hardly a priority for many machine designers, since they concentrate primarily on improving functionality, accuracy and safety. Nevertheless, alternative machine designs with improved energy consumption are emerging. This paper investigates the case of a laser cutting machine as common sheet metal processing machine tool. This paper verifies the potential for energy improvement by means of a case study. The analysis covers both the energy consumption during productive and non-productive time. Energy consumption improvement opportunities are identified. For this purpose a conventional CO2 laser-cutting machine was investigated and compared with a possible fibre laser based machine configuration. The analysis shows that the CO2 laser source and the chiller unit are the largest energy consumers during productive time. During non-productive time, 12% of the yearly energy consumption is required to keep the chiller and other components active. For the alternative machine configuration it is assumed that no energy is needed during off-mode. The same scenario saves 16.6 MWh during productive time because of the improved efficiency of a fibre laser source.

Parameter Sensitivity and Measurement Uncertainty Propagation in Torque-Estimation Algorithms for Induction Machines

This paper studies error propagation and parameter sensitivity based on a torque estimation model for induction machines. The model is based on the equation describing the interaction of rotor flux linkage and rotor currents. Contrary to classical schemes for induction motor control this is an open loop scheme, however, the model still requires different machine parameters. Therefore the parameters sensitivity of the model is performed. For validation, the model is implemented in the real-time environment dSPACE and a test induction machine is subjected to different combinations of speed and torque profiles. The identified model can be used to replace mechanical torque measurement devices or as a backup of a cheap torque sensor

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.

Impact of steady-state voltage supply anomalies on three-phase squirrel-cage induction motors

In this paper, the consequences of steady-state voltage supply anomalies on the behavior, losses and operating limits of low-power, low-voltage, three-phase, squirrel-cage induction motors is presented. The study is mainly based on simulations and previously published works, but experimental results are also presented. The well-known motor derating curves proposed by NEMA are questioned. It is demonstrated that they are too general, and do not consider combined effects of voltage unbalance, magnitude deviation, and distortion. Additionally, the effects of ambient temperature and motor characteristics (e.g. rated power, frame type, rotor type and efficiency class) should also be considered. Another important issue discussed in this paper is the fact that voltage unbalance and voltage distortion definitions should be properly revised in order to eliminate ambiguities. A clear methodology to evaluate the impact of the referred power anomalies on motors is proposed. An artificial neural network-based approach for mathematical description of motor derating curves as a function of multiple variables is also proposed and validated. Several relevant considerations on motor simulation within power quality scope are presented.

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.

Reducing the computation time of nonlinear problems by an adaptive linear system tolerance

Within the finite-element framework, nonlinear magnetic problems are often solved by an iterative line search strategy. The efforts to achieve convergence concentrate on the selection of an adequate relaxation factor. The line search is performed along a direction obtained by solving a system of linear equations. However, it is not required to compute this intermediate solution with a high accuracy, to ensure convergence. This paper shows how the accuracy of the solver can be modified at each nonlinear iteration, in order to reduce the overall computation time.

Reliability analysis of a torque estimation model

In this paper a torque estimation model for induction machines is studied. The model requires several machine parameters as input. Since the input parameters are deduced from measurements burdened with inaccuracy, it is necessary to take into account uncertainty in the input of the model. A first order and second order reliability method are performed to evaluate the probability of failure of the system under the uncertain inputs. The system failure is defined through the limit state function and occurs when the calculated value of the torque differs significantly from the rated torque at rated conditions. Monte Carlo simulations are performed for validation and importance sampling is discussed to reduce the Monte Carlo simulation error. The probability of failure is also derived from the torque probability density function by means of a stochastic response surface method. The analysis includes current and speed measurement uncertainties as well.