Energy Efficiency in Motor Systems

Table of Contents

1. Frontmatter

2. Electric Motors

   1. Frontmatter

   2. Technologies for High Efficiency Electric Motors

      Sebastião Lauro Nau, Carlos Eduardo Guarenti Martins, Claudio Schmitz, Edson Carlos Peres de Oliveira

      Abstract

      This chapter focuses on the main electric motor technologies to increase the efficiency of variable speed applications such as permanent magnet motor (interior PM, surface PM, hybrid PM), synchronous reluctance motor, line-start PM motor, switched reluctance motor, transverse flux motor, and axial flux motor. In order to understand the advantages of different motor technologies and their feasibility for variable speed application, a comparison between the main characteristics of permanent magnet motors (IPM, SPM, and HSM), synchronous reluctance motors, and induction motors are presented, considering the induction motor as reference.

   3. EASA AEMT Study of Motor Repair Impact on Efficiency of Premium Efficiency (IE3) Motors

      Thomas H. Bishop

      Abstract

      In response to various opinions about the feasibility of maintaining motor efficiency during repair, including replacement of the stator winding, the Electrical Apparatus Service Association (EASA) and the Association of Electrical and Mechanical Trades (AEMT) conducted two comprehensive rewind studies using third-party testing laboratories. The results of the first study, which were published in 2003 (The Effect of Repair/Rewinding on Motor Efficiency. Electrical Apparatus Service Association, 2003), clearly showed that the efficiency of energy efficient and IE2 motors ranging from 7.5 hp to 200 hp (5.5 kW to 150 kW) can be maintained (and sometimes improved) if the stator is rewound using established good practice procedures. The increasing use of premium efficient motors mandated by various countries led to a second rewind study in 2019, this time to determine if the efficiency of premium efficiency and IE3 motors can be maintained when they are rewound using the good practices described in the 2003 rewind study and ANSI/EASA AR100–2015 (Recommended Practice for the Repair of Rotating Electrical Apparatus. Electrical Apparatus Service Association (EASA), ANSI/EASA AR100, 2015). As with the 2003 study, the results of the 2019 rewind study of premium efficient and IE3 motors ranging from 40 hp to 100 hp (30 kW to 75 kW) clearly indicated that the answer was affirmative—with the average efficiency change for the entire test group falling within the range of accuracy for the test method (± 0.2%). This paper addresses the test methods, methodology, test results, and technical details of the 2019 rewind study.

   4. Assessment of PWM-Related Harmonic Losses in Three-Phase Induction Motors of Different Efficiency Classes

      Fernando J. T. E. Ferreira, José Alberto, Aníbal T. de Almeida

      Abstract

      In three-phase squirrel-cage induction motors (SCIMs) fed by variable-speed drives (VSDs), the no-load harmonic losses associated with the pulse-width modulated (PWM) voltage can have a significant impact on motor efficiency and temperature rise. Moreover, the PWM switching frequency selected in the VSD has a direct impact on SCIM PWM-related harmonic losses, VSD inverter losses, and power drive system (PDS) efficiency. In this chapter, the main results of an experimental assessment of PWM-related losses in a 7.5-kW PDS integrating a commercial VSD and a 4-pole SCIM of IE1, IE2, IE3, and IE4 efficiency classes are presented for 2-, 5-, 16-kHz switching frequency and 25- and 50-Hz fundamental frequency, at no-load and rated-torque operation. Based on experimental data, the coefficients of empirical equations to model VSD losses and SCIM PWM-related losses are found using an evolutionary solving method. These equations can be used to fairly predict the best switching frequency and expected efficiency of VSD, SCIM, and PDS for different operating conditions. Among all motors tested, the IE4-class SCIM showed the highest no-load loss percentage increase due to PWM-related harmonic losses.

   5. On the Selection of the Number of Poles of Three-Phase Induction Motors for Variable-Speed Power Drive Systems

      Fernando J. T. E. Ferreira, José Alberto, Aníbal T. de Almeida

      Abstract

      The selection of the number of poles of three-phase, squirrel-cage induction motors (SCIMs) for a given set of operating points of a variable-speed power drive system is not straightforward. In this chapter, the performance of 2-pole and 4-pole 50-Hz SCIMs for specific torque-speed operating points and optimized sinusoidal supply voltage in terms of frequency and amplitude is compared by means of simulations and experimental tests. For a given target torque, it is shown that the 4-pole SCIM has lower losses and absorbs less current at a target speed of 1500 r/min and the 2-pole SCIM has lower losses at a target speed of 3000 r/min but absorbs more current. The reduction of the motor current leads to lower conduction losses in the variable-speed drive, contributing to the increase of the power drive system efficiency. The conclusions presented in this paper contribute to a better decision regarding the selection of the number of poles and rated power of SCIMs for a given torque-speed range.

   6. Application Software for the Evaluation of Measurement Uncertainty in Induction Motors Efficiency Test According to IEC 60034-2-1

      Edoardo Fiorucci, Giovanni Bucci, Fabrizio Ciancetta

      Abstract

      The surveillance of the asynchronous motors market requires laboratories equipped with high-performance instrumentation, according to international regulations and state-of-the-art electrical power measurement devices. Moreover, ad hoc procedures and algorithms for estimating measurement uncertainties are also needed. In this paper, an accurate evaluation of the international standards have been performed, and application software for measuring indirect efficiency with its uncertainty has been presented.

   7. Operational Design Analysis of a Shaft Oil Spray Cooling in Electrical Machines

      Felix Hoffmann, Konrad Dubil, Jonas Bender, Thomas Wetzel, Martin Doppelbauer

      Abstract

      The design of electrical machines used in traction applications trends towards smaller and more efficient motors. Therefore, the thermal design aspect becomes more relevant. Conventional cooling methods may not have sufficient cooling capability and novel cooling concepts, like oil spray cooling of the end windings, are needed. However, no reliable correlations for the prediction of the cooling capability of oil spray cooling methods are available. This paper contributes with a design approach for the pressure difference of a shaft oil spray cooling system, which is essential for the regulation of the pumping system as well as the determination of the outlet pressure. Dimensionless numbers and analytical relationships are used to reduce the parameter space. The impact of the number of radial holes and the rotational speed can be approximated analytically. With the use of the non-dimensional Euler and Hagen number, the results are applicable to every Newtonian fluid at any temperature as long as the fluid properties are known. A sensitivity analysis is performed for the shaft geometries, showing that the diameter of the radial holes and the volumetric inlet flow have a major influence on the pressure difference, whereas the inner and outer diameter of the shaft exhibit a minor influence. The results of the above-mentioned approach are used to establish a series of tests to determine the heat transfer coefficients of liquid impingement jets on a plain surface using orifice-like nozzles at varying input pressures and volumetric inlet flow rates. The measurements showed that a smaller hole diameter of the nozzles and a higher volumetric inlet flow led to a higher heat transfer coefficient. The higher the temperature of the fluid, the higher the heat transfer coefficient. The nozzle distance, on the other hand, has no influence on the heat transfer coefficient and can therefore be neglected in the design process.

   8. Measurement of Detailed Efficiency Maps Minimizing Temperature Drifts

      André Krämer, Volkmar Reinhardt, Martin Doppelbauer

      Abstract

      Measurements of motor efficiency maps are an important aspect in the determination of motor characteristics. However, standardized efficiency classes are based on the losses of only one load point. An extension to efficiency maps is difficult due to transient effects like temperature drift during measurement. The scale of temperature change depends on aspects like measurement time and transient processes, which can vary between different measurements and thus may cause poor reproducibility. This chapter presents a new method that compensates this behavior without the need of control. By introducing compensation points, the average losses remain constant and therefore the temperature does too. Simulations with a detailed motor model as well as measurements on a test bench confirm this theory and show that measuring high-resolution efficiency maps with hardly any deviation from rated temperature is possible.

   9. Direct Calorimetric Test Bench for Power Drive Systems with Power Losses up to 20 kW

      Stan Caron, Pieter Defreyne, Steve Dereyne, Kurt Stockman

      Abstract

      A direct calorimetric test bench is presented, designed to test drives, motors and gearboxes with power losses up to 20 kW and a mechanical output power of 150 kW, up to 6000 rpm. The calorimeter setup is a direct type; therefore, it determines the power losses of a device under test (DUT) by measuring the coolant temperatures and flow rate. This type of measurement achieves an uncertainty below 1% on the power loss determination. The construction of the test bench, the required measurement equipment, the measurement procedure and especially measurement uncertainties and results are described in detail. The test case results of a measurement campaign with an electric axle drive, consisting of a liquid-cooled inverter, liquid-cooled high-speed permanent magnet synchronous motor and integrated slip-controlled clutch and gearbox, are presented. The calorimetric setup reaches an uncertainty of ±0.7% or ±25.9 W on the power loss at 25 kW mechanical output power.

   10. Impact of Stray Fields Due to the Structural Integration of a Linear Synchronous Machine for Hyperloop Technology

       J. Rens, S. Jacobs, E. Di Silvestro, G. Sellitto

       Abstract

       The hyperloop technology presents an opportunity for low-energy consumption high-speed transport, thanks to a reduction of air pressure within a tube-guided transport mode. This chapter focuses on the integration of a propulsion system in the tube, regarding its mechanical and electro-magnetic aspects. The structure for connecting the propulsion motor to the surrounding tube is designed for the loads that the machine needs to withstand, at all exploitation speeds up to 1000 km/h. The connection of the stator housing to the tube has a stray field impact linked to the position of the connecting ribs. When the rib is located behind a stator slot, some more flux penetration into the rib is noted, compared to when it is located behind a stator tooth. The impact of the structure on force development and losses in the motor are verified, comparing 2D with 3D Finite Element methods, implemented in JMAG. Regarding the prediction of magnetic flux in the stator and the generated propulsion force, excellent agreement is obtained. The 3D model predicts higher losses than 2D models, due to additional structural components and stray fields at the end of the stator stack. Losses in the structural components are significant but smaller than core losses in the stator yoke, due to the large lamination thickness used. At high speeds, the core losses in stator laminations were calculated using a 3D model of a single lamination, in order to model the skin effect. This results in a higher eddy-current level than the simplified 2D approach suggests.

   11. Rare Earth-Free Motors for Medium and High-Power Vehicles

       Fernando Nuño, Bruno de Wachter, André Nasr, Mircea Popescu, Giuseppe Fabri

       Abstract

       With the expected surge in electric vehicle (EV) sales over the next 10 years, there is growing concern that EV manufacturing will have a major negative environmental impact and suffer from disruptions in material supply. In particular, using rare-earth metals in the permanent magnets of the most ubiquitous EV motor could become increasingly controversial. Consequently, the European Commission funded the ReFreeDrive research project (grant agreement 770143), aiming to develop next-generation electric drivetrains entirely free of rare earth raw materials. The project developed eight different rare-earth-free motor prototypes based on three major technologies: copper rotor induction motors, synchronous reluctance motors with ferrite permanent magnets, and synchronous reluctance motors without permanent magnets. Through innovations at multiple levels (rotor design, stator using hairpin windings, advanced manufacturing techniques, use of advanced materials) the project demonstrated substantial improvements compared to state-of-the-art examples of these three motor types, achieving a 30% specific torque increase, a 50% reduction in motor losses, and lowering costs by between 15% and 35%. The proposed solutions are all suitable for mass production and eliminate the risks associated with critical rare earth material supply. Through performance optimization, the alternative motors developed as part of the project close the gap to rare-earth permanent magnet motors in terms of power density and total driving efficiency for a given powertrain cost. They also have significantly less negative environmental impact compared to the reference models.

   12. A Synchronous Reluctance Motor Solution for Electric Vehicles Traction

       Andrea Credo, Giuseppe Fabri, Francesco Parasiliti, Marco Villani

       Abstract

       The paper presents a high speed 200 kW synchronous reluctance (SynR) motor for a full electric vehicle. It is a low-cost magnet-free motor, also suitable for mass production and able to reach good performance and meet the demanding requirements typical of an electric car. An innovative asymmetric rotor with “fluid-shaped” barriers has been designed with multiple ribs that connect the rotor segments to each other axially and transversally. The motor performance has been evaluated over the full speed range by a finite element tool and for the Worldwide Light Vehicles Test Procedure (WLTP) Class 3 driving cycle.

   13. Estimation of Starting Characteristics of Three-Phase Induction Motors from No-Load Startup Tests

       Jacques R. Ruthes, Lucas Schons, Edson C. P. Oliveira, Luís A. Pereira, Matheus Perin

       Abstract

       This work addresses some aspects concerning the practical implementation of a method to estimate the steady-state performance of three-phase induction motors. The method requires only the acquisition of stator voltages and currents data during a no-load startup test taken at the final stage of the production line. The first step of the method implemented consists of estimating the parameters of the single-cage model considering both the rotor resistance and leakage inductance variable with slip. In the second step, the steady-state performance is determined using the equivalent circuit and the estimated parameters, thus allowing the motor manufacturer to check if the motor meets all the requirements stated by national and international norms. The main interest here resides in the starting characteristics such as locked-rotor torque and starting currents. Accordingly, to improve the accuracy of the results, some aspects related to the locked-rotor condition were investigated, namely (a) the influence of variations in the voltage amplitude, in particular the voltage drop during the first cycles, on the magnetizing and leakage inductances, (b) the influence of the mathematical expression chosen to model parameter variations with slip, and (c) the impact of the ratio considered between the stator and rotor leakage inductances. Finally, practical results obtained with estimated parameters are discussed and compared with results obtained with calculated parameters.

   14. Influence of the Machine Design on the Indirect Efficiency Determination of Permanent-Magnet Synchronous Machines

       B. Deusinger, A. Binder, H. Al-Khafaji

       Abstract

       For high-power permanent-magnet synchronous machines, the efficiency is usually in the range above 95%, where for a direct efficiency determination the measurement error gets too big. An alternative approach of indirect efficiency determination allows a bigger accuracy. It is done by the summation of individual losses, i.e., current-depending and additional load losses, iron losses, and additional losses caused by inverter feeding. These loss groups are determined at no-load and removed rotor operation. At power ratings below 200 kW the efficiency usually not exceeds 95%, so the proposed indirect method can be compared by the direct method experimentally. This comparison can be done also by numerical methods theoretically without an efficiency limit. In this context, five different permanent-magnet test machines, within the power range from 45 kW to 160 kW, were used to investigate the influence of the stator and rotor design on the losses and on the efficiency determination. For the test machine with a rated power of 160 kW and distributed fractional-slot stator winding, the indirect procedure is shown in detail via no-load, removed rotor, and load measurements for different rotor speeds. For this test machine, a quite good agreement between direct and indirect efficiency values was achieved for motor and generator operation, with deviations of less than 1 percentage point. For the other four test machines, measured loss and efficiency values were compared to simulation results at sinusoidal current feeding. Especially for those permanent-magnet synchronous machines with distributed stator winding without any sub-harmonic stator field waves, the proposed indirect efficiency determination method demonstrates to be a useful alternative to direct efficiency determination. For special machine designs with sub-harmonic stator field waves, caused by fractional slot windings, higher additional rotor losses may occur, which are not considered by the presented method. Therefore, the indirectly determined efficiency values for those machines show higher deviations up to 2 percentage points compared to the direct method.

   15. Voltage Variations Impacts on Electrical Motors: A Central America Study Case

       Jonathan M. Tabora, Lauro Correa dos Santos Junior, Thiago Mota Soares, Ubiratan Holanda Bezerra, Maria Emília de Lima Tostes, Edson Ortiz de Matos

       Abstract

       Most of the electric induction motors installed in Central America have been imported, due to not having manufacturing plants in this region, manufacturers prefer to import them from other neighboring countries such as Brazil, Mexico, etc. The main disadvantage of this situation is that the motors are manufactured with voltages different from those existing in the country or region where they will be installed. Although the motors have tolerances recommended by both the NEMA and IEC standards for power quality disturbances, voltage variations (VV) will have an impact on the efficiency and consumption of electric motors. Given this scenario, the present work aims to analyze four voltage variation conditions present in Central América on electric induction motor classes IE2, IE3, and IE4, the last being the line-start permanent magnet motor. This work addresses the influences of voltage variation on consumption, power factor, and temperature. Where a decrement in power factor, and an increment in consumption and temperature were observed for the overvoltage conditions, for the undervoltage, an increase in power factor and variations in consumption and temperature according to the motor class were observed.

   16. Line-Start Synchronous Reluctance Motors: Optimized Design for Both Starting Behaviour and Steady State Performances

       Antonio Scozzafava, Davide Pagliaro

       Abstract

       Line-start synchronous reluctance motors are hybrid motors that simultaneously have the advantages of synchronous reluctance motors (high performance, simple construction, low cost of materials, constant speed at variable load) and induction motors (IM) (mainly the ability to start if supplied directly from the mains).

       Scientific literature (Gamba et al., International Electric Machines & Drives Conference, Chicago, 648–655, 2013) has widely affirmed that these types of motors, although requiring less quantities of active material (magnetic lamination, copper wire, die-cast aluminium) to obtain the same efficiency class (for example IE3 or IE4) of induction motors, have reduced performance in the start-up phase, and especially in the critical synchronization phase. In particular, with the same load torque, the synchronization capability decreases with the increase in the load inertia. This new design is therefore focused on minimizing this weak point, thus obtaining a series of motors that can be usefully put on the market for most of the applications to replace induction motors. The presentation of the experimental test results on prototypes confirmed the very great potentials of the calculations, and they were strategic in the decision to place these motors in the market and start-up their series production.