Enhanced Stray-Load Loss Measurements Through a Zig-Zag Variable Load Test Approach

This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consistsofalternativelyapplyingloadlevelshigherandlowerthan the rated load, so that the stator winding temperature zigzags aroundtheratedvalue.Hence,multiplereadingscanbeperformed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizesandpolecounts,applyingboththestandardvariableloadtest procedure and the proposed approach. The experimental results show that theproposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure

Simplified Thermal Model of Disk-Shaped Automotive Smart Braking Actuators

This paper articulates the challenges in the thermal modelling of surface-mounted permanent magnet motors for automotive brake-by-wire systems, which operate by injecting high dc currents in two of the three phases for short time intervals. This unconventional operation requires dedicated thermal models for the prediction of uneven heat distributions inside the machine. This study extends a previous work conducted on slender-shaped motors to a disk-shaped machine where the edge effects could compromise the model accuracy. Additionally, here efforts have been made to minimize the number of experimental tests needed for the correct calibration of the proposed phase-split lumped-parameters thermal models

Electrical Machine Topologies: Hottest Topics in the Electrical Machine Research Community

In this article, the state of the art in electrical machine design is outlined underlining the problems and challenges to be solved by engineers. As highlighted in this article, even if electrical machine design is often considered a mature issue from the technical and technological point of view, every year, new progresses and steps forward are made. New and more sophisticated design tools can be used worldwide, and innovative manufacturing processes, new insulation materials, and higher performance magnetic materials are available on the market. In addition, the evolution of the hardware used in digital control and new powerful power electronic devices represents a constant stimulus to improve the performance of electrical machines and reintroduce electrical machine structures that were not adopted in the past due to technological and technical constraints. As shown in this article, electrical machine design is an evergreen topic, and its importance is rising more each year under the push of more energy-saving requirements and higher-efficiency systems for electromechanical conversion. A green world will not be possible without electrical machines

A direct-drive wave energy converter with contactless force transmission system

Commonly proposed ocean wave energy converters (OWEC) use inefficient and maintenance demanding intermediate hydraulic and pneumatic systems. We propose a novel rotary direct-drive OWEC that eliminates these intermediate stages. The new device employs a contactless force transmission system (CFTS) comprising a “piston” and a “cylinder” and a ball screw to spin a conventional rotary generator. We present an analytical model of the OWEC and also propose a numerical technique that performs a coupled fluid-structure interaction simulation of the wave energy device in a 3-D numerical wave flume using a computational fluids dynamics (CFD) code. In previous investigations, the motion of floating bodies was prescribed rather than determined. The current method represents a significant advancement in that it determines the motion of the buoy from the dynamic solution of the fluid flow problem and the dynamic buoy motion problem. The technique was extended to assess the performance of two neighboring buoys and their interference effects.Keywords: direct-drive, ocean wave energy, fluid-structure interactio

Accurate determination of induction machine torque and current versus speed characteristics

The determination of induction machine torque and current speed characteristics relies on methods based on either direct testing or calculation, using machine equivalent circuit. Both methods may lead to significant errors. The paper discusses the challenges encountered using these methods and an approach is presented in the paper to overcome the inherent challenges. The proposed approach considers saturation and compensates for skin effect and machine temperature to improve accuracy. Five induction motors of different pole pairs were analyzed and tested to provide understanding of the underlying issues of predicting torque and current characteristics of induction machines. The findings indicate that, for direct testing, multiple data points closer to nominal voltage are required. In the case of equivalent circuit modeling, proper correction of the model for temperature and saturation leads to improved prediction of the torque characteristics of general purpose induction machines

Impact of number of poles on the steady-state performance of induction motors

A simplified analysis of influence of pole pairs on the steady-state behavior of induction motors is presented. The analysis makes simplifying assumptions to express relationship between key steady-state performance parameters of 2-pole reference motor compared to its multiple pole counterparts. The analysis is performed using considerations of fixed geometrical dimensions on one hand and fixed output power on the other hand. Available manufacturer catalog data of medium voltage (MV) induction machines from one manufacturer are used to evaluate the soundness of the analysis. Also test and catalog data analyses of commercially manufactured low-voltage (LV) machines from different manufacturers are evaluated to determine extent to which they conform to the theoretical considerations of the analyses. The preliminary findings indicate more agreement with the MV motors than the LV motors

An Overview of Electric Machine Trends in Modern Electric Vehicles

Electric machines are critical components of the drivetrains of electric vehicles. Over the past few years the majority of traction drive systems have converged toward containing some form of a permanent magnet machine. There is increasing tendency toward the improvement of power density and efficiency of traction machines, thereby giving rise to innovative designs and improvements of basic machine topologies and the emergence of new classes of machines. This paper provides an overview of present trends toward high specific power density machines for traction drive systems. The focus will be on current technology and the trends that are likely to be pursued in the near future to achieve the high specific power goals set for the industry. The paper discusses machines that are applied in both hybrid and battery electric drivetrains without distinction and does not discuss the associated power electronic inverters. Future electric machine trends that are likely to occur are also projected

Impact of Number of Poles on the Steady-State Performance of Induction Motors

A simplified analysis of influence of pole pairs on the steady-state behavior of induction motors is presented. The analysis makes simplifying assumptions to express relationship between key steady-state performance parameters of 2-pole reference motor compared to its multiple pole counterparts. The analysis is performed using considerations of fixed geometrical dimensions on one hand and fixed output power on the other hand. Available manufacturer catalog data of medium voltage (MV) induction machines from one manufacturer are used to evaluate the soundness of the analysis. Also test and catalog data analyses of commercially manufactured low-voltage (LV) machines from different manufacturers are evaluated to determine extent to which they conform to the theoretical considerations of the analyses. The preliminary findings indicate more agreement with the MV motors than the LV motors