Machine Losses Research Articles

Thermal Model Approach to the YASA Machine for In-Wheel Traction Applications

The axial-flux permanent magnet (AFPM) machines with yokeless and segmented armature (YASA) topology are suitable for in-wheel traction systems due to the high power density and efficiency. To guarantee the reliable operation of the YASA machines, an accurate thermal analysis should be undertaken in detail during the electrical machine design phase. The technical contribution of this paper is to establish a detailed thermal analysis model of the YASA machine by the lumped parameter thermal network (LPTN) method. Compared with the computational fluid dynamics (CFD) method and the finite element (FE) method, the LPTN method can obtain an accurate temperature distribution with low time consumption. Firstly, the LPTN model of each component of the YASA machine is constructed with technical details. Secondly, the losses of the YASA machine are obtained by the electromagnetic FE analysis. Then, the temperature distribution of the machine can be calculated by the LPTN model and loss information. Finally, a prototype of the YASA machine is manufactured and its temperature distribution under different operating conditions is tested by TT-K-30 thermocouple temperature sensors. The experimental data matches the LPTN results well.

An investigation into the influence of stator tooth and conductor geometry on AC winding losses in a 365kW permanent magnet machine equipped with rectangular bar conductors

Rectangular bar conductors located in parallel stator slots with a matched geometry offer a potentially attractive solution for permanent magnet machines as they can provide an improved slot fill factor with consequent reduced loss and enhanced heat transfer compared to random wound mush type coils. However, in addition to the manufacturing challenges posed by precisely forming coils from large cross-section bar conductors, the adoption of bar conductors is often constrained by consideration of additional AC losses which are a result of induced eddy currents in the conductors. These induced currents are a result of exposure to time varying fields both from armature reaction fields and incident permanent magnet flux passing through slot opening. In this paper, a 365kW 6000rpm 6-pole permanent magnet machine equipped with various arrangements of solid bar conductors is analysed to understand and illustrate the significance of AC losses in bar conductors and to quantitatively assess the influence of various design changes to the stator. The magnitude of AC losses in a baseline model with a single series wound bar is evaluated by 2D FEA simulations and shown to be prohibitive. In order to reduce AC losses, several design features including using multiple parallel transposed conductors and further optimization of tooth and conductor geometry are considered in this paper. Simulation results show that with optimized stator tooth geometry and multiple parallel transposed conductors, AC losses can be reduced by an order of magnitude compared to a machine designed on purely static considerations.

Alkyl-functionalized black phosphorus nanosheets triggers macroscale superlubricity on diamond-like carbon film

The mechanical components’ friction and wear are the main factors to reduce the lifetime and cause the energy loss of machine. In this work, the alkyl-functionalized black phosphorus (BP) nanosheets were synthetized and used as lubricating additives in poly alpha olefins (PAO), which could trigger macroscale superlubricity on the silicon doped diamond-like carbon (Si-DLC) film deposited on the engineering steel surfaces. The COF of the PAO with the alkyl-functionalized BP additives could reduce down to 0.006, which reduced by more than 90% in comparison to that in the absence of functionalized BP. It shows that the high contact pressure and shear action in the running-in process make PAO and functionalized BP recombine to form a composite tribofilm. This composite tribofilm mainly contained the phosphorus oxides and silicon oxides, providing an extremely low shear strength and thereby resulting in a superlubricity state. These findings provide a novel method to achieve oil-based superlubricity on the engineering steel surfaces through the synergistic lubrication effect between the BP and Si-DLC.

AC Losses in Form-Wound Coils of Surface Mounted Permanent Magnet Vernier Machines

Surface mounted permanent magnet Vernier (SPM-V) machines, because of their high torque density and multi-pole structure, are promising candidates for low-speed direct-drive applications. To achieve high torque density, the SPM-V machines are generally designed with high gear ratios. Therefore, their operating frequencies can be much higher than those of the conventional SPM machines. This potentially increases the alternating current (AC) winding losses, especially those with form-wound coils proposed for high-power applications. This article investigates the AC losses (including skin effect, proximity effect, rotor PM induced, and circulating current losses) in form-wound stator coils of a 3 MW direct-drive SPM-V machine with different slot/pole number combinations. The study reveals that the SPM-V machines have significantly higher AC winding losses than their conventional SPM counterparts for similar operating conditions. To reduce the AC winding losses in SPM-V machines, a novel flux shunt concept is proposed along with other conventional techniques such as increasing the number of turns/coil (with terminal voltage being kept constant) and parallel strands/turn, providing extra clearance at slot opening. With the loss reduction techniques implemented, the SPM-V machines can achieve comparable efficiency but much higher torque density than their conventional counterparts. Moreover, the proposed flux shunt was also found to be very effective in reducing the potential risk of permanent magnet (PM) irreversible demagnetization, a key issue for SPM-V machines at high power ratings.

Comparative Study of Switched Reluctance Generators With Separate Field Current and Circulating Current Excitations

In this paper, a circulating-current-excited switched reluctance generator system with the diode rectifier is comparatively studied with a field-current-separated switched reluctance generator. By using a DC power source connected in series with the winding to provide the circulating current, a controllable excitation field is established in the proposed generator. To highlight the influence of this DC voltage source, the injected field current of the field-current-separated generator is kept the same as the circulating current of the circulating-current-excited generator. Then, both advantages and disadvantages of the generators are summarized. The circulating-current-excited switched reluctance generator system inherits both the advantages of good reliability of the separated-winding generator by using the diode rectifier and low copper loss of the integrated-winding machine by combining the AC and DC current in one set of windings. Furthermore, two more practically conventional field-current-separated generators are also compared with the proposed generator in terms of the external characteristics. These two conventional generators have different winding configurations. At last, the analysis is verified by experiments.

Torque Ripple Suppression Based on Optimal Harmonic Current Injection in Dual Three-Phase PMSMs Under Magnetic Saturation

Dual three-phase permanent magnet synchronous machines (DTP-PMSMs) have received increasing attention from the industry and academia due to their advantages in lower burden on power inverters when operating in high power applications compared to the three-phase counterparts and low torque ripples. In this article, it reveals that the favorable low torque ripple characteristic of DTP-PMSM is undermined in the high power and overload operating mode. To solve this problem, this article proposes a novel torque ripple suppression strategy based on optimal harmonic current injection. A mathematical torque ripple model of DTP-PMSM considering the cross-coupling effects between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> axis is built. And based on this model, a detailed analysis is carried out to obtain the optimal harmonic current. The theoretical analysis also guarantees that the induced machine loss is minimum. Moreover, the proposed strategy has good dynamic performance since the algorithm involves no iterative computation and is computationally effective, which is proved on a laboratory DTP-PMSM system. The effect of parameter variation is also discussed and tested. The experiment results prove that the influence of magnetic saturation on torque ripple can be effectively suppressed.

Calculation of Rotor Harmonic Losses in Multiphase Induction Machines

The topic of this paper is the determination of rotor harmonic losses in multiphase machines. Specifically, harmonic losses occur in the rotor winding and core due to higher-order spatial harmonics of the flux density. This phenomenon influences machine parameters and overall performance and increases temperature rise in parts of the rotor. The flux density distribution is determined by the stator magnetomotive force harmonic content, which is directly related to the winding distribution. A cage-rotor asymmetrical six-phase induction machine is selected for this case study. An analysis of different stator winding topologies and their influence on harmonic losses is presented. A finite element-based method for calculating the contribution of individual stator magnetomotive force harmonics to the rotor losses is developed and described in the paper. The analysis includes scenarios with different phase current waveforms to emphasize the issues specific to the asymmetrical six-phase machine. It is found that the magnetomotive force components generated by non-torque-producing current components contribute significantly to harmonic losses. The obtained results can represent a foundation for optimal stator winding topology selection. This work is intended to motivate the development of new and the modification of existing models to properly include rotor harmonic losses during the design, performance prediction, and control of multiphase machines.

Minimization of Winding AC Losses Using Inhomogeneous Electrical Conductivity Enabled by Additive Manufacturing

The electrical conductivity (EC) of additively manufactured conductors can be purposely controlled by changing as-built orientation and postprocessing conditions. This feature can be leveraged to minimize winding alternate current (ac) losses in electrical machines adopting solid conductors. This article deals with the additive-manufacturing-based winding design of a high-specific-power permanent-magnet (PM) machine for aerospace applications. Specifically, conductors near slot opening are designed with low EC to reduce winding AC losses, while conductors near slot bottom adopt higher EC to reduce direct current (DC) losses. Parametric finite element models are developed for a thorough design parametric analysis targeting high-specific power as well as high efficiency. The implementation of the proposed coil concept with inhomogeneous EC is discussed and demonstrated. The EC measurements on rod and coil samples are conducted for material characterization.

Anatomization of the overall equipment effectiveness (OEE) for various machines in a tool and die shop

PurposeThe purpose of this research is to discover equipment losses and assess the accomplishment of overall equipment effectiveness (OEE) values.Design/methodology/approachIndustries specialized in die shops often have issues regarding their efficiencies, conferring to statistics further production line department procedure for various machines frequently suffered restrictions owing to excessive downtime and speed losses in machines thus, reducing their effectiveness and efficiency. OEE is a means of determining how effective a piece of equipment is when in working condition. Calculation of OEE finds the heart of the issue and the root cause for the underlying problem.FindingsThe dimensional outcomes suggest that the average machine effectiveness has not attained the norm of &gt;85%, but there is still room for progression.Originality/valueOne recommended procedure to reduce losses is to keep the actual pace of operation and downtime of equipment constant. Many such suggestions are provided to reduce the losses.

Transient stability and FRT technologies of different synchronous wind turbine

With the global energy transformation towards to a 100% renewable-based power system, the installed capacity of renewable energy generation has continued to grow rapidly in recent years. At the same time, due to the loss of synchronous machines, the grid-connected large-scale renewable energy bring great challenges to the safe and stable operation of power grid. In order to improve the stability of power grid, different synchronous wind turbine have widely attracted the attention of academia and industry. That is totally different on transient stability of vector synchronous wind turbine and self-synchronous wind turbine, and the fault ride through (FRT) control strategy is also different. Thus, the transient stability and FRT technologies of vector synchronous wind turbine and self-synchronous wind turbine are studied separately. There are many solutions for the FRT of vector synchronous wind turbine from different technical schemes. According to the different scope of application and implementation methods, it can be roughly divided into two categories: software improvement and hardware addition. Different FRT strategy of self-synchronous wind turbine are used under a smaller grid fault and serious grid fault, self-synchronous wind turbine recalculate the voltage and phase angle of the potential in the converter according to the PCC voltage, PCC phase angle, reactive power demand and residual active capacity under a smaller grid fault. When there is serious grid fault, the vector control and self-synchronous control modes switching FRT strategy is necessary.

Cage Losses in Induction Motors Considering Harmonics: A New Finite Element Procedure and Comparison With the Time-Domain Approach

The cage losses in induction machines due to spatial or time harmonics in the air-gap field are a crucial parameter for a precise estimation of the machine efficiency. Using finite element, the common approach to consider the overall cage losses, by performing complete time-domain analyses. Alternatively, a rough estimation is achieved introducing equivalent parameters in the circuital model. In this article, a methodology for cage losses computation due to air-gap spatial field harmonics is described. The proposed finite element procedure is faster than the time-domain analysis since it is based on magneto-static and linear time-harmonic simulations to carefully consider the iron saturation and compute the induced currents in a specific working point. In the article, a detailed procedure description and comparison with respect to the time-domain approach is reported.

Iron Loss Analysis in Axial Flux Permanent Magnet Synchronous Motors With Soft Magnetic Composite Core Material

Accurate calculation of iron losses in electric machines are essential for optimal machine design. This is especially important for axial flux permanent magnet motors with solid stator and rotor cores. This paper investigates iron losses in axial flux motor with soft magnetic composite material for the stator and the rotor. First, an analytical model is proposed to estimate iron losses under different operating conditions. The model is based on combining the Quasi 3-D computation approach and the magnetic equivalent circuit. The proposed model can be modified to account for different motor topologies and different stator and magnet designs. Then, The effect of torque ripple, on iron losses, is studied by comparing two motors: an optimized motor, with dummy pocket added to the stator tooth, and a non-optimized motor. Finally, the effect of the motor control scheme and the inverter switching frequency is studied by implementing two controllers: the Field Oriented Control and the Trapezoidal control. Simulations using 3-D finite element analysis and experimental tests are conducted, under different operating conditions, on two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{12}\,V$</tex-math></inline-formula> , 6 slots, 8 poles single stator single rotor fractional horsepower axial flux permanent magnet synchronous motor prototypes. Test results shows that motor optimization, the choice of the motor control scheme, and the selected switching frequency can significantly affect iron losses in the motor. Using an optimized motor with a smooth control scheme, such as Field Oriented Control, and a high switching frequency, can cause a variation in iron losses by around 14% compared to a non optimized motor with the Trapezoidal control and a low switching frequency.

Analytical Methodology for Modelling of Circulating Current Loss in Synchronous Electrical Machines With Permanent Magnets

This paper describes a novel analytical methodology for modelling winding copper losses as a result of circulating currents (CC) in permanent magnet synchronous machines (PMSM). CCs are important to be considered at an early design stage especially in high frequency and high performance machines where sub-optimal design choices can lead to significant alternating current (AC) losses. Nowadays mainly FEM method is used for precise calculation of circulating currents. However, it suffers on significant computational time required for building models and simulation of circulating current effect that makes it inapplicable for optimization purpose. The paper demonstrates the computationally efficient methodology through comparison with FEM based models for high power density PMSM with concentrated winding and validation against experimental results for a stator section at the fundamental frequency from 500 Hz to 2000 Hz. The methodology allows simulation of CC and AC Ohmic losses when machine supplied by any current waveforms, for arbitrary size and location of the conductors in the slots. A key novelty of the proposed method is the utilization of subdomain (SDM) approach in conjunction with solution of a system of ordinary differential equations (ODE) for an equivalent electrical circuit of machine windings. This approach is precise and fast but has never been used before for circulating current loss evaluation in windings of electrical machines. The model is intended to be used at the design stage of an electrical machine where multiple geometric dimensions, winding configurations and conductor placement in the slot are considered towards an optimal design.

Analysis of multi-field coupled air friction loss and temperature field of high-speed permanent magnet machine

The high-speed rotation of the high-speed permanent magnet machine (HSPMM) causes high air friction loss. The multi-field calculation of air friction loss is usually unidirectional coupling, so the interaction between temperature and air friction loss cannot be considered. By using the improved analytical model, the air friction loss considering the effect of temperature on air density and dynamic viscosity is calculated. The influence of this method on the temperature and air velocity of the machine is compared. The accuracy of this method is verified by comparing with the improved air friction loss numerical calculation model. The results show that the improved calculation model of air friction loss is more accurate.

Calculation and Decrease of Zigzag Leakage Flux Losses in a Wet Submersible Induction Machine by the Virtual Permanent Magnet Harmonic Machine Model

AbstractThe accurate estimation of the zigzag leakage flux losses (ZZLFL) caused by the slot harmonics and their interactions, which occupy a high proportion of stray losses, are of great significance in the efficiency calculation as well as the optimization design for the wet submersible induction machine (WSIM). In this paper, a two‐dimensional finite element method (FEM) is presented to separate ZZLFL into the iron losses and the eddy‐current losses. The air‐gap magnetic flux density is decomposed by the two‐dimensional fast Fourier transform at a sampling frequency of 5000 Hz. The hybrid excited virtual permanent magnet harmonic machine model is applied to reconstruct the air‐gap magnetic field and excite the stator and rotor separately. Each node harmonic iron losses are acquired through the modified Bertotti iron losses model with the consideration of high‐frequency power losses as a function of the magnetic flux density. The zigzag flux losses provided by different harmonics are obtained by subtracting the hybrid excitation losses. According to the different proportions of harmonic losses among zigzag flux losses, novel WSIM models are proposed in the paper to decrease zigzag flux losses and increase the efficiency. Adopting the same computation process, the novel models with different structures are explored and verified to improve the zigzag flux losses and power density. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Analysis of Rotor Losses in Permanent Magnet Vernier Machines

This article investigates rotor losses in permanent magnet Vernier machines. By analyzing air-gap field, the harmonic distribution and frequency of modulated open-circuit flux density and armature reaction flux density are obtained. Then, rotor losses production principle is revealed and the influence of each harmonic on the loss is analyzed. Meanwhile, the influence of each harmonic on torque is also studied. It is found that some harmonics have no contribution to torque but produce additional losses. On this basis, a new rotor structure is proposed to suppress the rotor losses. Comparison results indicate that by suppressing nonworking harmonics, the rotor losses can be reduced effectively without affecting the effective torque. Finally, the theoretical and finite-element analysis results are verified by prototype tests.

Pareto Optimal Weighting Factor Design of Predictive Current Controller of a Six-Phase Induction Machine Based on Particle Swarm Optimization Algorithm

Finite-set model predictive control (FS-MPC) as predictive current control (PCC) is considered an exciting option for the stator current control of multiphase machines due to their control flexibility and easy inclusion of constraints. The weighting factors (WFs) of PCC must be tuned for the variables of interest, such as the machine losses <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x-y$ </tex-math></inline-formula> currents, typically performed by trial-and-error procedure. Tuning methods based on artificial neural network (ANN) or the coefficient of variation were proposed for three-phase inverter and motor drive applications. However, the extension of this concept to the multiphase machine application is not straightforward, and only empirical procedures have been reported. In this context, this article proposes an optimal method to tune the WF of the PCC based on the multiobjective particle swarm optimization (MOPSO) algorithm. A Pareto dominance concept is used for the MOPSO to find the optimal WF values for the PCC, comparing parameters of root-mean-square error of the stator tracking currents. The proposed method offers a systematic approach to the WF selection, with an algorithm of easy implementation with direct control over the size of the search space and the speed of convergence. Simulation and experimental results in steady-state and transient conditions are provided to validate the proposed offline tuning procedure of the PCC of a six-phase induction machine. The improvements of RMSE can be more than 500% for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x-y$ </tex-math></inline-formula> subspace, with minor effect in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\beta $ </tex-math></inline-formula> subspace. Finally, the proposed method is extended to a more complex cost function, and the results are compared with an ANN approach.

Simulation of iron losses in induction machines using an iron loss model for rotating magnetization loci in no electrical steel

PurposeVarious iron loss models can be used for the simulation of electrical machines. In particular, the effect of rotating magnetic flux density at certain geometric locations in a machine is often neglected by conventional iron loss models. The purpose of this paper is to compare the adapted IEM loss model for rotational magnetization that is developed within the context of this work with other existing models in the framework of a finite element simulation of an exemplary induction machine.Design/methodology/approachIn this paper, an adapted IEM loss model for rotational magnetization, developed within the context of the paper, is implemented in a finite element method simulation and used to calculate the iron losses of an exemplary induction machine. The resulting iron losses are compared with the iron losses simulated using three other already existing iron loss models that do not consider the effects of rotational flux densities. The used iron loss models are the modified Bertotti model, the IEM-5 parameter model and a dynamic core loss model. For the analysis, different operating points and different locations within the machine are examined, leading to the analysis of different shapes and amplitudes of the flux density curves.FindingsThe modified Bertotti model, the IEM-5 parameter model and the dynamic core loss model underestimate the hysteresis and excess losses in locations of rotational magnetizations and low-flux densities, while they overestimate the losses for rotational magnetization and high-flux densities. The error is reduced by the adapted IEM loss model for rotational magnetization. Furthermore, it is shown that the dynamic core loss model results in significant higher hysteresis losses for magnetizations with a high amount of harmonics.Originality/valueThe simulation results show that the adapted IEM loss model for rotational magnetization provides very similar results to existing iron loss models in the case of unidirectional magnetization. Furthermore, it is able to reproduce the effects of rotational flux densities on iron losses within a machine simulation.

Online Diagnostic Method for the Detection of High-Resistance Connections and Open-Phase Faults in Six-Phase PMSM Drives

Even though multiphase machines have inherent fault-tolerant capabilities due to their additional degrees of freedom, fault diagnosis still plays an important role to continuously monitor these machines and, thus, prevent critical failures. High-resistance connection (HRC) is one of the most common electric faults in electrical machines and is caused by damaged power connections. These faults create a current unbalance, increasing both the machine losses and torque pulsations, and can eventually lead to open-phase faults (OPFs). This article proposes an online fault diagnostic method to detect HRCs and OPFs in six-phase permanent magnet machine drives. The proposed method is intended for application in electric drives controlled by a predictive current control strategy and does not require the installation of extra hardware. Two variants of the fault diagnostic algorithm are presented in this work: one based on the analysis of the secondary components of the reference current errors and the other variant based on the prediction current errors. Experimental results demonstrate the effectiveness and sensitivity of the proposed diagnostic method for the detection of these types of fault.

Power-balancing Coordinated Control of Wind Power and Demand-side Response Under Post-fault Condition

As the global energy transforms to renewable-based power system, the wind power generation has experienced a rapid increase. Due to the loss of synchronous machines and its frequency control mechanisms, the gradual evolution leads to critical challenges in maintaining the frequency stability. Under post-fault condition, the wind power generation has a slow recovery due to the fault ride-through (FRT) control strategy and may cause a larger frequency deviation due to the power imbalance between the supply and demand. Then, the impacts of the frequency deviations would further cause inaccuracy and instability in the control system for wind power generation. Considering the long parking time of electric vehicles (EVs), the demand-side response is provided to support the power grid via load-to-grid technology. Thus, a power-balancing coordinated control strategy of the wind power and the demand-side response is developed. It can significantly mitigate the power imbalance, thereby resulting in the enhanced frequency stability. Finally, the simulation results are provided to validate the power-balancing coordinated control strategy.