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A modular motor drive (MMD) is composed of multiple identical pole drive units (PDUs), which consist of a concentrated stator winding fed by a dedicated power electronic converter module. To exploit the full flexibility and reliability of these MMDs, they are equipped with multiple controllers, operating as synchronized peers, and each driving only a limited set of PDUs. An MMD can hence be considered as a multiagent system, in which all the agents cooperate to deliver a certain torque demand. The goal of this work is to distribute this torque demand among the agents of a modular drive in a completely decentralized way, in order to comply with the flexibility and reliability of the hardware, while still taking into account the present condition of each agent. A deterministic consensus algorithm is used for this purpose, in combination with decentralized proportional integral (PI) current controllers. Communication is only allowed between neighboring agents, to limit the communication load. It is shown in this article that the total torque demand is delivered, under healthy conditions as well as during agent malfunctions and with nonidentical agents. The concept is demonstrated on a modular axial-flux permanent magnet synchronous machine with 15 PDUs that are assigned to five agents. [ABSTRACT FROM AUTHOR]

Thanks to the absence of rotor windings and permanent magnets, switched reluctance motors have a small weight construction. The integration of a modular power converter in a switched reluctance motor leads to a highly compact and fault-tolerant motor drive with small weight and high power density. In this article, a polygon-retrofitted integration topology is proposed for switched reluctance motors. Both the switched reluctance motor and the power converter are cooled with one shared cooling circuit. The power converter is designed and implemented using silicon carbide technology for its low losses and small thermal resistance. The proposed integration topology is extensively studied using multiphysics modeling and experimental measurements on a fully integrated rotating setup. A highly compact and power dense drive of 3.1 kW/L is obtained. [ABSTRACT FROM AUTHOR]

The electric drive power density and fault tolerance capability are of fundamental importance in many applications such as aerospace and traction applications. The modularization and the physical integration of the electric motor and the power converter components can lead to a high power density and a high fault tolerance drive system. The power density of a highly modular and integrated drive based on an axial flux permanent magnet synchronous machine and GaN converter is investigated in this paper. Several power density boosting techniques are provided and investigated using CFD simulations. These techniques incorporate optimization of the converter topology, the geometry of the shared cooling structure of the electric machine and the power converter and optimal selection of the materials in the path of heat transfer from the machine and the power converter to the cooling ambient. The power density of the reference integrated design is increased from 1.12 kW/ $l$ to 2.14 kW/ $l$. The CFD computations are validated by extensive measurements on a modular integrated setup. [ABSTRACT FROM AUTHOR]

In this article, a circulating-current-excited switched reluctance generator system using a standard diode rectifier is proposed and examined. It features a dc power source connected in series with the ring-connected windings, which provides the dc-bias current as the excitation current in the windings. Using a series-connected dc power source, a dc-bias current is easily realized in the ac winding. Compared with the existing machine having dc-bias in the ac winding, the proposed generator can provide dc power with a standard diode rectifier. Less active legs and no rotor position sensor are needed for the control of the circulating current of the proposed generator, which increases the reliability of the generation system. The system configuration and the operation principle are introduced in detail. Then, the electromagnetic performance of the proposed generation system is analyzed at both open-circuit and load conditions. The asymmetric current distributions are deduced and verified by the simulations. At last, the prototype is tested under varied operation conditions and the experiments agree well with the analysis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this article, a dc-link structure feasible for integration with the circumscribing polygon modular integrated drives is proposed. The proposed dc-link structure combines both the dc-link capacitors and the bus-bar together and integrates them with the machine and the converter modules without increasing the outer diameter of the integrated machine/converter structure. A generic design methodology for the proposed dc-link structure is provided and applied on a reconfigurable 15 stator coils concentrated winding axial flux machine for all its possible phase configurations. The design methodology presented in this article involves the determination of the required dc-link capacitance and the multiphysics design of the bus-bar. The parasitics of the bus-bar part of the proposed dc-link structure are evaluated using electromagnetic finite element method (FEM) models and their influence on the dc-link waveforms is evaluated. Due to the expected high ambient temperature inside an integrated drive, electromagnetic and computational fluid dynamics (CFD) models are developed for the proposed dc-link structure to evaluate the loss density and the temperature distribution of the bus-bar to ensure reliable operation. An experimental setup is built to validate the design methodology. [ABSTRACT FROM AUTHOR]

This article proposes a real-time control strategy for induction motor drives, harmonizing accurate torque, and flux tracking with energy efficiency. Common problems related to lengthy control horizons and the associated computational burden are dealt with by introducing a value function approximation in the model-predictive structure to quantify the impact of instantaneous decisions on future states. An augmented model of the drive is introduced to determine this value function approximation offline. The resulting optimization problem is implemented in a real-time environment and its effectiveness is established on an experimental setup for both steady state and dynamic load conditions. Experiments show that the proposed approach outperforms default model-based methods by up to 89.7%, thus making it a promising real-time optimal control strategy in the domain of electric drives. [ABSTRACT FROM AUTHOR]

In this article, a circumscribing polygon integrated modular motor drive topology with shared cooling for the power converter and the electrical machine is proposed and benchmarked with the nonintegrated version. The proposed topology is applied on an axial flux permanent magnet synchronous machine. The topology is capable of mechanically mounting the power converter, sufficiently cooling both the power converter and the electrical machine, and combining both of them into the same housing. The mechanical and the thermal design are done to ensure thermal decoupling between the power converter and the motor winding, and to provide a low thermal resistance from the power converter and the electrical machine to the ambient. Due to the limited space available for the power converter module, wide bandgap semiconductor technology is chosen for the implementation of the converter module, thanks to their small package size and low power losses. A highly modular, integrated, and compact drive is achieved compared to the nonintegrated one. A computational fluid dynamics (CFD) model is developed for one module of the proposed integrated drive to evaluate the maximum current that can be injected by one converter module without exceeding the junction temperature limit of the switches and the maximum winding temperature. An experimental setup is built to validate the results of the introduced multiphysics models. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the induction machine rotor temperature is important for both condition monitoring and motor performance. Lumped-parameter thermal networks allow to flexibly model the temperature distribution with low computational effort. However, their accuracy highly depends on the accuracy of their thermal parameters. Moreover, these parameters are determined offline and held constant during operation. In this article, a rotor temperature virtual sensing strategy is proposed, combining a lumped-parameter thermal network with stator windings temperature measurements. The latter measurement data can be easily collected and together with the thermal network serve as input to a dual Kalman filter to estimate both the rotor temperature evolutions and the thermal model parameters. The advantage of the presented approach is that the thermal model does not need exact identification for the considered motor. One can start from a thermal model identified from intrusive rotor measurement data on a comparable motor that is subsequently transferred to the motor to be monitored. This results in a fast and convenient way to estimate the rotor temperature in real-time. Experimental results on a 4-pole 5.5 kW induction machine demonstrate the validity of the presented strategy to accurately monitor the rotor temperature within an error range of approximately $\pm 6^{\;\circ }{\rm C}$. [ABSTRACT FROM AUTHOR]

To meet the demand for increasingly high power density in electric drives, the concept of a so-called integrated modular motor drive has emerged. The machine is composed of multiple identical modules, which receive individual control signals for multiphase control, to reduce unwanted stator current harmonics. Each module is equipped with its own power electronic converter, which is integrated in the machine housing. This integration imposes strict constraints on the dc-link capacitor design. To reduce the dc-link current ripple, and hence relax the design constraints on the dc-link capacitor, without compromising the possibility to eliminate unwanted stator current harmonics by means of multiphase control, a new interleaving strategy is proposed in this article. The n modules of the machine are split into p subgroups of m modules for interleaving, while the n-phase control is preserved. An analytical model, simulations and experimental results are provided for a 4 kW test setup, confirming that multiphase control can be combined with interleaving. As a result, both the stator current harmonic distortion and the dc-link current ripple can be reduced simultaneously. [ABSTRACT FROM AUTHOR]

Concentrated windings are favourable in electric motors with a high torque density because of the achievable high winding filling factor and their short end-windings. Nevertheless, the performance of the cooling system has the biggest impact on the reachable torque density limits. This article introduces a thermally conductive insert piece that encloses the stator end-windings with extensions in the stator slots. This results in an extended contact surface between the stator windings and the machine housing, which is advantageous for the conductive heat transfer. The introduced indirect cooling concept is compatible with traditional cooling techniques such as forced air and water jacket cooling. The concept is illustrated with 3D thermal finite element simulations, including the anisotropic thermal material properties, as well as ad hoc measurements on a stator pole unit mock-up of a 6-4 switched reluctance machine. Where the stator with reference cooling system was only able to handle a continuous current density of 19.0 A/mm $^2$ , 26.5 A/mm $^2$ could be obtained in the winding of the stator with the extended end-winding cooling inserts. [ABSTRACT FROM AUTHOR]

In this article, a fault tolerant deadbeat controller is proposed, which is able to compensate for both partial and uniform demagnetization faults in axial flux permanent-magnet synchronous machines with double rotor, even with asymmetric defects in both rotors. For this purpose, the system model used by the deadbeat controller is equipped with a look-up table of the back-emf, in function of the mechanical rotor position. This look-up table is generated by means of an analytical model based on the magnetic vector potential. With this information, the deadbeat controller can eliminate both the additional bias and ripple in the stator current components caused by demagnetization faults. The proposed control strategy is validated on a 4 kW test set-up of an axial flux permanent-magnet synchronous machine with yokeless and segmented armature topology fed by a three-phase two-level voltage source inverter, both by simulations and experiments. Key performance indicators concerning bias and ripple of the current components illustrate the superior performance of the proposed control strategy in comparison to a standard deadbeat controller without an up-to-date look-up table of the back-emf. [ABSTRACT FROM AUTHOR]

This paper proposes a method to design an electrical variable transmission (EVT) of which the stator and inner rotor contain a distributed three-phase winding, and the outer rotor is equipped with permanent magnets and a dc-field winding. The main problem with the design of EVTs is that the modeling relies on time-consuming finite-element (FE) calculations. Studying the effect of design changes is, therefore, a cumbersome task. To minimize the need for FE calculations, scaling laws are applied, which reduce the computational effort to a matter of milliseconds per design. Therefore, the losses of multiple scaled designs can be analyzed for a given load cycle while taking constraints into account such as maximum torque. By presenting this data in a performance map, the optimal design regarding the losses is easily deduced. To validate the presented methodology, FE calculations, measurements, and available literature are used. [ABSTRACT FROM AUTHOR]

This paper presents a simple and efficient magnetic equivalent circuit (MEC) model for surface axial flux permanent magnet synchronous machines. The MEC model is used to solve all the electromagnetic properties of the machine including the no load, full load voltages, cogging torque, torque ripple, and stator iron core losses. Moreover, this approach can be extended for all surface permanent magnet synchronous machines. The main novelty of this approach is the development of a static system, which accounts for the rotation. The model takes into account the rotor rotation via time-dependent permanent magnet magnetization sources. The static system matrix facilitates a very fast solving. In addition, to take into account the three-dimensional (3-D) effect, a multislicing of the machine in the radial direction is done. This boosts the simulation time to only 60 s for six slices and 50 time steps including the nonlinear behavior of the stator elements with a great accuracy. Additionally, the number of elements in the MEC can be adjusted to reduce the computational time. This model is verified by means of 3-D and two-dimensional (2-D) multislice finite-element models. In addition, experimental validations are also provided at the end. [ABSTRACT FROM AUTHOR]

Control topologies in electric drive applications commonly aim at minimizing the dissipated power in the system to guarantee energy-efficient operation. Especially in vehicle electrification, loss minimization is the main objective in the supervisory control loops as this is directly related to the range of the vehicle. Advanced drive systems are characterized by an elevated complexity but require nevertheless a real-time control strategy to be implemented. Appropriate model abstraction, enabling real-time viability with a reliable system representation, is found in convex mapping procedures of the dissipated power in the drive components. These reduced-order models are generally obtained based on model information solely. This paper proposes a methodology to recursively enhance the reliability of the convex loss approximations. An instantaneous power flow estimation is assessed based on a unification of model expectations and sensor data. Using this information, a proper adaptation to the underlying convex loss coefficients is then determined. The methodology is validated in simulation for an electric drive on three different case studies. The algorithm is furthermore applied on actual experimental data of an asynchronous drive for validation purposes. Preliminary results demonstrate that the error on the loss assessment is reduced by 55.7%–89.0%. Adaptive convex loss mappings can, therefore, be consulted in practical control structures to ameliorate the reliability of loss minimization control schemes, while still maintaining a computationally efficient format. [ABSTRACT FROM AUTHOR]

Despite the use of state-of-the-art thermal modeling tools in the design stage, the measured thermal behavior of prototype electrical machines can differ significantly from the modeled ones. This paper shows how a thermal model, based on the finite-element method, of an electric machine can be improved using inverse modeling techniques. In a thorough study, a forward high fidelity finite-element thermal model of a 4-kW axial flux permanent magnet (PM) machine is introduced and improved using inverse modeling techniques via noncollocated thermal sensors. Parametric model order reduction of the high fidelity finite-element thermal model based on the moment matching method is performed to make the recovery of the actual thermal parameters characterizing the thermal behavior of the axial flux PM machine tractable. Furthermore, the same reduced order model is used to identify the different power loss components in the machine. Experimental results confirm that the presented two-stage approach is capable of identifying the thermal parameters and losses with high accuracy. [ABSTRACT FROM AUTHOR]

Increasing performance requirements for electrical machines such as energy efficiency and torque density require a multiphysics design approach. In these designs, many machine parts very often combine multiple functions, such as electromagnetic, thermal, and mechanical, to keep the design compact and reduce the overall weight, or introduce nonconventional materials in electrical machines. In this paper, epoxy potting techniques are used to keep the different stator parts of a yokeless and segmented armature axial flux PM machine together, and it focuses mainly on the multiphysics aspects of the epoxy resins as well as on their implications on the overall stator design. In this multiphysics design approach, the effect of specific epoxy resin parameters such as maximum service temperature, thermal conductivity, Brookfield viscosity, tensile strength, and coefficient of thermal expansion, on the electromagnetic, thermal and mechanical behavior of the stator are examined. Epoxy resin parameters are evaluated in detailed experiments on small test samples, and finally, measurements on a full prototype 4 kW, 2500 rpm stator are performed. [ABSTRACT FROM AUTHOR]

This paper describes how an electrical variable transmission (EVT) can be used as an alternative for mechanical continuously variable transmission (CVT) systems. An EVT is an electromagnetic power split device having two mechanical and two electrical ports. The speed ratio between both mechanical ports (rotors) can be varied in a continuously variable way, so that this machine can be used as an electromagnetic alternative for the mechanical push-belt and half-toroidal CVT. Its operating principle is based on splitting the power into an electromagnetic direct path and an electrical path involving two inverters connected back to back. Its potential use as a CVT is investigated by comparing experimental data against toroidal and belt CVT data from literature having comparable power ratings. To this end, measurements are performed on a prototype \text120-kW permanent magnet EVT. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electromagnetic power-split device with two mechanical and two electrical ports. It can be used in hybrid electric vehicles to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. Although crucial for the EVT design and evaluation, no papers are found to give a detailed overview of the different loss components in such a machine and how they can be calculated and measured. In contrast to conventional electrical machines, this machine has more degrees of freedom, which can be exploited to measure the different loss contributions separately. This paper proposes a methodology to identify and measure the different loss components in this kind of machines. The proposed method is able to identify the iron losses in stator and inner rotor, the copper losses, bearing losses, and slip ring friction losses separately. To this end, measurements of both torque and speed sensors in different operating points are combined. The methods are applied to identify the different loss contributions in a prototype permanent magnet assisted EVT, both in no-load operation as under load where its functionality as power-split device is evaluated. [ABSTRACT FROM PUBLISHER]

A time-harmonic analytical model is presented for a combined study of demagnetization and rotor eccentricity in single-stator double-rotor axial flux permanent magnet synchronous machines (AFPMSM). Demagnetization defects are modeled by scaling the magnetization “square wave” by magnetization factors for each individual magnet on both rotors. Static, dynamic, and mixed rotor eccentricities are modeled using a permeance function. The original contribution of the model is that asymmetrical defects in the two air gaps of the machine can be described with acceptable accuracy and limited additional calculation time. The model is validated with a finite element method and experiments in both healthy and defected operations. Because the model has a short computation time, it is useful for real-time condition monitoring of any AFPMSM with double air gap and either concentrated or distributed windings. [ABSTRACT FROM PUBLISHER]

The paper studies demagnetization detection in axial flux permanent magnet synchronous machines of the yokeless and segmented armature (YASA) type. In YASA machines, asymmetrical defects can occur: the demagnetization defects in the permanent magnets of both rotors differ from each other. Many techniques can indicate that there is a defect, even if it is an asymmetrical defect, but cannot detect which rotor has the defect, i.e., exactly locate the asymmetrical defect. In this paper, a method is proposed to detect and locate asymmetrical demagnetization defects in AFPMSMs. The method is useful for real-time condition monitoring of demagnetization defects, or as virtual temperature sensor for the magnets. A sensing coil is placed in each air gap. An analytical model is constructed, which uses the demagnetization defect and the three-phase current as input and calculates the sensing coil back-EMF. Sensing coils back-EMF data are combined with the data from the analytical model to solve an electromagnetic inverse problem. The results are the demagnetization amount and location of the demagnetization defect. The method is validated with the experimental data. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electrical machine consisting of a stator and two concentric rotors. It is a competitive alternative for power split devices used in current series–parallel hybrid electric vehicles (HEVs). Although tending to have high power densities, permanent magnet (PM) machines suffer from no-load iron losses. Since the torque interaction between stator and outer rotor is low during large time intervals, the EVT in this paper possesses a flux bridge with dc-field winding to modulate the stator field, while maintaining the inner rotor flux linkage. In this paper, a torque controller is proposed that optimally combines the stator, dc-field, and inner rotor currents in order to minimize the copper and iron losses in every operating point of torque and speed on both rotors. Also the electromagnetic coupling between both rotors is considered. It turns out that there are two optimal load angles for the stator currents, of which one of the two is dominant depending on speed and torque. The control is tested on a 120 kW prototype EVT, and measurement results are given to illustrate the optimal performance obtained with the proposed torque control. In addition, efficiencies are measured in order to support the statements made concerning the proposed method. [ABSTRACT FROM PUBLISHER]

In this paper, a complete sensitivity analysis of the optimal parameters for the axial flux permanent magnet synchronous machines working in the field weakening region is implemented. Thanks to the presence of a parameterized accurate analytical model, it is possible to obtain all the required parameters of the machine. The two goals of the ideal design are to maximize the power density: P\text{density} and the ratio of maximal to rated speed: n\max/n_r, which is an inductance related parameter keeping the efficiency at the target speed above 90$\%$. Different slots/poles/phases combinations are studied to reveal the optimum combination for each phase. This paper has studied the effect of the ratio of number of stator slots to number of rotor poles on the P\text{density} and n\max/n_r. It is shown that a low value of this parameter results in a better P\text{density} and n\max/n_r. The effect of the outer diameter, and the inner to outer diameter ratio are studied with respect to the two design goals. In addition, a comparison between the finite and the theoretical infinite speed designs is implemented. A complete 3D finite element validation has proven the robustness of the analytical model. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q- and d-axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d-axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d-axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine. [ABSTRACT FROM PUBLISHER]