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Due to the high-power density and compact structure, axial-flux permanent magnet (AFPM) machines have gradually received much attention with a view to researching breakthroughs in the next generation electric drive technology for electric vehicles in the recent decades. The AFPM machines with factional slot concentrated winding (FSCW) and yokeless stator, namely yokeless, and segmented armature (YASA) motors, have drawn much attention for its high-power density and potential manufacturability due to the concentrated winding and modular stator core configuration. However, the significant rotor loss resulting from the abundant armature reaction harmonics in FSCW machines imposes a great challenge to the rotor heat dissipation, especially when the pursuit of higher speed has become the trend for electric vehicle applications. On the other hand, distributed winding is widely used in high speed radial flux permanent magnet (PM) machines due to its low armature reaction harmonics. In order to figure out the advantages and disadvantages of various winding arrangement and rotor configuration of AFPM for electric vehicle applications, the comparative study of four AFPM machines with various winding configurations and rotor PM arrangements are comprehensively conducted in this article. First, the design and primary optimization of the four AFPM machines are conducted for the electric vehicle requirement specifications. Then, a comprehensive three-dimensional finite-element analysis (FEA) is employed to compare the electromagnetic performance including torque/power density, efficiency, and flux-weakening capacity. Furthermore, the guideline of winding selection of AFPM machines for electrical vehicle is given. Finally, a yokeless stator AFPM prototype with ISDW configuration is manufactured and tested to verify the validity of the FEA results, as well as confirm the comparison conclusion. [ABSTRACT FROM AUTHOR]

This article proposes a novel synchronous demodulation method of rotor position estimation for brushless synchronous starter/generator (BSSG) at zero and low speed based on self-harmonic signal injection. Instead of the conventional external voltage signal injection, second harmonic in the field winding of the main generator is employed as the indirectly injected high-frequency signal into the rotor winding. In order to achieve the synchronous demodulation scheme, a synchronous demodulation signal generated from the field current of the main exciter by specific second-order generalized integrators is proposed, and the corresponding synchronous demodulation method for the high-accuracy rotor position estimation has been improved based on the cascaded filters. Finally, the proposed rotor position estimation method for the sensorless starting control of BSSG is verified by simulation and experiment results, and a high-accuracy estimated rotor position could be obtained for the high-performance output of BSSG. [ABSTRACT FROM AUTHOR]

This article presents a new interior permanent magnet (IPM) rotor structure/ assembly, which inherits from the Halbach magnet configuration and spoke-type IPM rotor to achieve a high saliency ratio and high torque/ power density. With this rotor structure, the torque density and power density are improved obviously, while the rotor inner diameter can be maximized to reduce core material and increases internal space in the rotor. Accordingly, the electromagnetic performance of three motors consists of a unified stator but different rotors, namely flux-concentrating rotor, Halbach array permanent magnet (PM) rotor and spoke-type IPM rotor is compared by finite element analysis. Nevertheless, due to the segmented structure of flux-concentrating PM rotor without magnetic bridges, the mechanical challenges are analyzed in detail for electric vehicle application to hold the pole pieces validate the structural feasibility at 7200 r/min. Finally, a 72-slot/ 16-pole fractional-slot PM motor with new flux-concentrating rotor is manufactured and tested to verify its performance and feasibility. It can be concluded that the new rotor is superior to the spoke-type IPM and Halbach array PM rotor in terms of torque density and PM utilization. [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]

The field-winding-induced voltage pulsation in the doubly salient brushless dc (DSBLDC) generator leads to the field current ripple and challenges the dc power supply for the field winding. In this article, a new DSBLDC generator with stator-damper winding is proposed to reduce the induced voltage in the dc field winding. The stator-damper winding configuration is illustrated. The winding self-inductance and coupling characteristics are investigated. The influence of the allocation and dimension of the damper winding on the induced voltage suppression as well as the power generation performance is comparatively analyzed. A prototype of the stator-damper winding DSBLDC generator is designed and developed. The experimental results show that the induced voltage of the field winding is reduced by more than 90%, while the output power is nearly close to that of the conventional DSBLDC generator. [ABSTRACT FROM AUTHOR]

Doubly salient wound field machines exhibit the advantages of robust structure and controllable flux, and hence have been utilized as generators in applications of automobiles and renewable energy. However, the inherent unbalanced phase back-electromotive force (EMF) waveform caused by the asymmetric flux path brings difficulties for precise control and smooth operation. To solve the problem caused by unbalanced back-EMF waveform in conventional doubly salient machines, this paper presents a novel doubly salient wound field machine with balanced and symmetrical back-EMF waveform as starter generator in automobile application. The robust structure and the controllable flux are inherited, while the magnetless feature makes it promising for cost-sensitive applications. The proposed machine can be operated as an assistant motor for torque boosting at start-up stage, as well as a power recycling generator for battery charging at steady state. It is revealed that the proposed wound field machine exhibits similar cost, comparable torque density, improved torque ripple, and higher efficiency than the switched reluctance machine. Finally, the proposed prototype is fabricated, and dynamic experiment is conducted to validate the feasibility for automobile starter generator application. [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]

With the development of the transportation electrification, the demand for high-performance motor is growing rapidly. High torque density and wide constant power operating range are two key requirements of the electric vehicle (EV) traction applications. Considering the limited voltage and current, a successful EV traction machine should realize good linearity of torque–current characteristic and a proper characteristic current. In order to meet these strict demands, an optimized Fractional-Slot Concentrated-Winding(FSCW) permanent magnet (PM) machine with different rotor structures is proposed in this article based on the traditional spoke-type PM machine topology. The machine structures are introduced and optimized in the design procedure, and a magnetic equivalent circuit model is applied to illustrate its principle. The electromagnetic performances, including back electromotive force, output torque, and efficiency map, are compared between the original and optimized design to highlight the performance improvement of the optimized topology. Finally, a prototype machine has been built for the experimental validation. The experimental results, which agree well with the Finite Element (FE)-predicted results, confirm the validity of the analysis method used in predictions and the advantages of the optimized design. [ABSTRACT FROM AUTHOR]

In this article, a novel spoke-type permanent magnet (PM) machine with two types of PM materials is proposed to reduce the cost. In order to improve torque density and reduce torque ripple, the multi-objective optimization combined finite element method (FEM) and genetic algorithm (GA) are used. In addition, the electromagnetic performances of the novel spoke-type PM machine, including no-load air-gap flux density, electromagnetic torque, torque ripple, efficiency, and cost are compared with the conventional spoke-type PM machine. It is demonstrated that the novel spoke-type PM machine obtains a 1.5% lower torque ripple and 36% lower cost, and the torque density is 4.3% lower than the conventional spoke-type PM machine. Meanwhile, the novel spoke-type PM machine has lower core loss and higher efficiency. Finally, a 40 kW spoke-type PM machine is manufactured to verify the analyzing method. Experimental results demonstrate that the proposed machine exhibits high torque density and low cost in the application of electric vehicles (EVs). [ABSTRACT FROM AUTHOR]

Due to the larger diameter of effective air-gap for torque production, outer-rotor permanent magnet (PM) machines exhibit the distinctive advantages, such as high torque density and large rotor inertia. This article presents a compact outer-rotor permanent magnet starter/generator (OR-PM S/G) to match diesel engine for extended-range hybrid electric vehicle. In order to solve the serious temperature rise problem resulting from the copper losses under constrained slot space in the inner stator, a new winding indirect liquid cooling technique by inserting heat pipes in the center of slots is proposed. It facilitates a path from the center of the coils to the cooling medium with a higher thermal conductivity, thus increasing the tolerable current density of coils. By optimizing the geometry and dimensions of heat pipe and coil, the temperature rise in slots are achieved within an acceptable limit according to the computed results of FEA and computational fluid dynamics (CFD). In order to validate the cooling design, a 30kW OR-PM S/G prototype with rectangular-shaped PM and the proposed indirect liquid cooling windings is manufactured and experimented. The power capability and efficiency of the proposed OR-PMS/G are validated by the measured results with calculation results. A good agreement between the predicted and measured temperatures indicates the validity of indirect cooling method for concentrated winding with heat pipe. [ABSTRACT FROM AUTHOR]

A hybrid excitation brushless dc generator (HEBLDCG) system, consisting of a main generator (MG) and an integrated exciter, is proposed and developed in this article. The excitation sources types of the stand-alone generation system and corresponding characteristics of the sources types are summarized. In the target HEBLDCG system, the integrated exciter shares a flux path with the permanent magnet machine part (PMMP), which is a part of the MG, without extracting power from the output terminal or sacrificing the efficiency of the generation system. It is the reactive power in the PMMP that leads to these aforementioned advantages. Also, the basic design flowchart of the exciter is expounded upon, and the values of some parameters are discussed. The designed exciter meets the requirements of the field power of the MG for the whole speed range and under varying load conditions. Based on the well-designed exciter, the electromagnetic performance is analyzed in terms of its open-circuit and load performance. Furthermore, the reason why the output power of the MG is not reduced by the integrated exciter is analyzed. Finally, open-circuit and load experiments for the exciter are conducted, and the proposed excitation method is found appropriate for the HEBLDCG system. [ABSTRACT FROM AUTHOR]

In this article, the advanced angle control (AAC) for the active rectifier (AR) is proposed to improve the output power of doubly salient electromagnetic generator systems. The AAC AR is an optimization by turning on the switches in advance with an angle based on the angular position control (APC) and pulsewidth modulation (PWM) ARs. The operation principle of the AAC in ARs is different from that in the inverters. The phase inductance variation is analyzed. The inductance flat top at load condition is utilized to accelerate the commutation process and enlarge the phase current. The unified analysis is proposed by summarizing the four states of the conduction modes in the AR. The analysis of the proposed AAC strategies, the conventional APC, and PWM strategies are unified. The output power of AAC APC ARs is significantly improved compared with that of the conventional AR. The copper loss, iron loss, and torque ripple are reduced. The AAC strategies are compared with conventional strategies. The optimized performances of AAC strategies are verified by finite-element analysis and experimental results. [ABSTRACT FROM AUTHOR]

In order to solve the problems of poor capacity and unsatisfactory efficiency of flux-weakening control for the axial-flux permanent magnet (AFPM) machines with surface-mounted permanent magnet (PM) rotor structure, a new axial-flux hybrid-excitation machine (AFHEM) with double consequent-pole rotors is proposed, which combines the high torque density of the AFPM machine and the flexible flux regulation of the hybrid excitation machine. It meets the stringent requirements of the distributed in-wheel motor electric drive vehicle for high efficiency and high torque density. The topology, principle, and basic electromagnetic properties of the new axial-flux hybrid-excitation in-wheel motor are presented in this article. Based on the complex magnetic circuit of the AFHEM, a 3-D equivalent magnetic network (EMN) model is established. The air-gap flux density, flux linkage, back EMF, torque, and fault tolerance ability of the motor are solved through the EMN model and compared with the 3-D finite element analysis (FEA) to verify its validity and correctness. It is hoped to form a rapid design method for the new type of motor with the complex structure of 3-D magnetic flux path property. Finally, based on the EMN model, the influences of the magnetic saturation on the excitation regulation capability of the proposed AFHEM are analyzed, which provides a guideline for the optimization design of the new AFHE in-wheel motor. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of the rotor components were determined using a first-order modal model of the rotor components for various sump pump shaft lengths for actual working environments. By employing ANSYS-Workbench software, this paper uses a fluid-solid coupling analysis to calculate the reaction forces of the fluid on the rotor with results, which is then used in dry and wet modal analyses of the rotor parts to calculate the vibration modal characteristics with and without prestresses. The differences between the wet and dry modal characteristics were compared and investigated by ANSYS. The results show that increasing the sump pump shaft length reduces the first-order natural frequency of the prestressed rotor components. The structure also experiences stress stiffening, which is more obvious in the high-order modes. The natural frequency of the rotor in the wet mode is about 16% less than that in the dry mode for the various shaft lengths due to the added mass of the water on the surface which reduces the natural frequency. In the wet modal analysis, when the structure is in a different fluid medium, the influence of its modal distribution will also change, this is because the additional mass produced by the fluid medium of different density on the structure surface is different. Thus, the wet modal analysis of the rotor is important for more accurate dynamic analyses. [ABSTRACT FROM AUTHOR]

The magnetic field enhancement characteristic of an axially parallel hybrid excitation generator (APHEG) is revealed and analyzed in this article. The APHEG consists of a permanent magnet machine part (PMMP), a flux modulation machine part (FMMP), and a diode rectifier. The magnetic fields of the two parts are interactional despite the independent flux paths, which provides the possibility to enhance the FMMP field at the expense of weakening the PMMP field. By taking advantage of that, the combination of the PMMP and FMMP can effectively boost the output power in the defined voltage-boost region as the weakening of the PMMP field is negligible. In addition, the magnetic field of the FMMP can be further enhanced by regulating the rotor shift angle. Based on the analysis of the phasor diagrams, it is found that the flux amplitudes and phase displacement angles of the two parts are mutually restrictive and decide the optimized rotor shift angle range of the APHEG. Finally, a prototype APHEG has been developed, and the experiments verify the phasor diagrams and simulation analysis. [ABSTRACT FROM AUTHOR]

In this article, a high-speed Halbach-array permanent magnet (PM) rotor for ironless stator axial-flux permanent magnet (AFPM) machine is proposed and researched with consideration of the multiphysics constraints, including the electromagnetic characteristics, mechanical strength, and rotor dynamics. Considering the severity of attractive force between twin rotors, the complex repulsive force among PM segments of Halbach-array and centrifugal force, the new hybrid sleeve, and PM fixation method are proposed to improve the rotor mechanical strength. Then, the rotor stress is analyzed by numerical analysis and three-dimensional (3-D) finite-element analysis (FEA). Furtherly, the sleeve thickness and interference fit are optimized by 3-D FEA. The rotor dynamics and bearing arrangement are analyzed to validate the effectiveness of the high-speed Halbach-array PM rotor. A 50-kW, 9000 r/min ironless stator AFPM machine prototype with Halbach-array PM rotor is manufactured and tested. The measured results show that the output power is up to 53.8 kW at 9000 r/min. The feasibility of high-speed Halbach-array PM rotor and accuracy of analysis method are validated by both simulated and measured results. [ABSTRACT FROM AUTHOR]

Although hybrid excitation synchronous machines (HESMs) can provide an attractive flux-regulating capability, the fabrication and mechanical strength of the complex rotor are with significant challenges and need great efforts especially for high torque machines. In this article, a modular fabrication method of the dual-end magnetic-shunting rotor is proposed for high torque hybrid excitation synchronous machine. Then, by using numerical methods, the thermal stress of the rotor is calculated and compared with the 3-D FEA methods. To improve the mechanical strength of the rotor, the size of the screw, lug boss and filler is optimized, meanwhile, the rotor loss is optimized and thermal stress is evaluated. The results show that the proposed modular fabrication method demonstrates the improved mechanical strength and material utilization rate compared with the conventional fabrication process. Based on the three-dimensional finite-element analysis (3-D FEA) results, a 100 kW HESM prototype is successfully designed and manufactured using the proposed modular magnetic-shunting rotor. The experimental tests validate the effectiveness of the modular fabrication method and mechanical strength analysis. [ABSTRACT FROM AUTHOR]

This article proposed a sensorless starting control method for the brushless synchronous machine with the indirectly injected high-frequency signal, where the high-frequency signals are injected into the stator windings of the main exciter instead of the main generator. The impact of the nonlinear links of the rotary rectifier and various filters on the rotor position estimation error during the asynchronous demodulation method is analyzed in detail. Since the phase delay of the bandpass filter and the low-pass filter will deteriorate the zero-crossing points of the envelope curve, the signal restoration module could not restore the sinusoidal envelope curve accurately, then, the estimated rotor position error is expanded with the increasing of rotor speed in the starting process. Therefore, a novel mathematical analysis method with fewer filters for the rotor position demodulation is presented to improve the estimated rotor position error compared to the traditional method, and the feasibility and effectiveness of the proposed method are verified by the comparison of the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, the implementation of a single-stator double-rotor fractional-slot concentrated-winding (FSCW) axial-flux permanent-magnet machine is presented to verify a simple and reliable structure design and oil-immersed cooling of the stator with modular soft magnetic composites (SMC) core. Due to the yokeless and segmented stator, the process of embedding the windings into the stator teeth will probably become simpler. By preforming rectangular copper wire, the shorter end-winding length and higher fill factor can be achieved. In order to eliminate eddy current losses and manufacturing costs, the fiberglass epoxy is used for the supporting components of the fixation for modular SMC stator and PMs, which is a nonmagnetic and nonconductive material. Hence, the robustness of stator and rotor are taken into account due to the stator modularity weakening effect on strength. Meanwhile, a fully sealed stator with oil-immersed cooling is proposed to enable the current density of 20 A/mm2 in the armature windings for stable operation. The electromagnetic properties, including in magnetic field distribution, torque capacity, and flux-weakening ability, are performed based on the three-dimensional finite-element analysis, as well as the mechanical performance. The coupled thermal and computational fluid dynamics model is built to predict the flow and temperature distribution inside stator with oil-immersed forced cooling. The construction and experimental verification of a full-scale 30-kW prototype are elaborated to verify the predicted performances in terms of torque density, structural strength, and cooling. [ABSTRACT FROM AUTHOR]

In this article, a novel rotor position estimation method based on the second-order generated integrator (SOGI) is proposed for sensorless starting control of the brushless synchronous machine (BSM) with the indirect high-frequency signal injection method for the aircraft. The high-frequency signals are injected into the stator field windings of the main exciter, and the response signals coupled to armature windings and the rectifier are indirectly injected into the field windings of the main generator. The envelope demodulation method is proposed for the rotor position estimation, and the unitized filter design for the more accurate rotor position signal extraction is exploited instead of the traditional bandpass filter and low-phase filter based on the optimal parameters of SOGI. Finally, the feasibility and effectiveness of the proposed rotor position estimation method for BSM in the sensorless control are verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, a dual-pulse mode control of a high-speed doubly salient electromagnetic machine (DSEM) for efficiency improvement over a wide speed range is investigated and implemented. The dual-pulse mode control method and operation principle are introduced. The influence of excitation angles and field current on the operation performance is analyzed by finite-element method based on the back electromotive force (EMF) and inductance characteristics. The loss distribution for various speed and load torque requirement is attained, and the control parameters are optimized. The excitation angle can reduce the back EMF at high speed through transformer EMF and flux-weakening armature reaction. A prototype of 12/8-pole DSEM drive system is developed and dual-pulse mode control in high-speed operation under low dc-link voltage is implemented. Both the simulated and measured results show that the torque capacity of the DSEM is improved and the loss is reduced over a wide speed range. [ABSTRACT FROM AUTHOR]

Hybrid excitation synchronous machines (HESMs) are regarded as special permanent magnet synchronous machines (PMSMs), in which flux linkage, inductances, and characteristic current change with field current. The machine topology, optimized structure design, and modular fabrication method of an HESM with magnetic-shunting rotor are presented in this paper. To solve the thermal problems, an optimized cooling system considering the rotor losses is proposed. Then, the feature of adjustable d-axis inductance and flux linkage are theoretically analyzed and calculated. As a result, the characteristic current changes with the field current, which is significant to the constant power range. The adjustable d-axis inductance, flux linkage, and characteristic current are validated by finite-element analysis results. According to the feature of adjustable characteristic current, an optimized control strategy is proposed to improve the output power capacity of the HESM with modular magnetic-shunting rotor in the whole speed range by taking full advantage of the adjustable characteristic current feature, in which the characteristic current is adjusted close to the rated current at high speed. To validate the feasibility and superiority of the optimized design and control methods, a 100-kW HESM with modular magnetic-shunting rotor prototype is designed, manufactured, and tested. [ABSTRACT FROM AUTHOR]

A new hybrid excitation brushless dc generator (HEBLdcG) is comprised of the structure-paralleled permanent magnet machine part and flux modulation machine part (FMMP). The reactive power compensation effect of the HEBLdcG is illustrated and investigated in this paper. It is shown that the operation modes of the FMMP are influenced by both, the field current and armature current. Based on this, the three ranges in terms of the field current are divided. Three typical operation states representatively selected in the three ranges are defined as the power-balance state, compensator state, and short-circuit state, respectively. The short-circuit current can be diminished on account of the reactive power compensation effect. Furthermore, the analysis of the short-circuit characteristics shows that the short-circuit characteristic curve—short-circuit output current versus field current—is not a straight line, due to the saturation of the d-axis flux path of the FMMP. And the HEBLdcG at −8-A field current features the lowest total loss at the short-circuit state. At last, a prototype HEBLdcG is manufactured and the experiments validate the simulations. [ABSTRACT FROM AUTHOR]

Outer‐rotor permanent‐magnet (OR‐PM) machines provide several distinct advantages such as high torque density and large rotor inertia due to the large outer diameter of effective air gap for power conversion. The purpose of this study is to replace flywheel with the outer rotor by adopting OR‐PM machines since this topology is well‐suited for integration with diesel engines. This study specifically investigates a 16‐pole–18‐slot ring‐shaped PM motor with rectangular shaped PM rotor for integrated power generation application. At first, the pole arc, rotor yoke thickness and PM slot height of the OR‐PM machine with rectangular shaped PM are optimised. In addition, the no‐load magnetic field, cogging torque and back‐electromotive force of the OR‐PM machine with rectangular shaped PM and have been analysed and compared based on two‐dimensional finite element analysis. Additional comparison including torque characteristics, field weakening, cost and efficiency are also highlighted. The results show that the OR‐PM machine with rectangular shaped PM has better electromagnetic performances. Finally, a 25 kW OR‐PM machine prototype with rectangular shaped PM is manufactured and experimented. The predicted electromagnetic performance is validated by experimental results. [ABSTRACT FROM AUTHOR]

The Halbach‐array permanent magnet (PM) rotors can achieve higher air‐gap flux density due to magnetic flux gathering effect, which contributes to the higher‐torque density improvement of the ironless stator axial flux PM (AFPM) machine. However, the end leakage fluxes of the ironless stator AFPM machine are serious due to the large magnetic resistance of the main flux loop in ironless stator machines. Circular arc straight line permeance model is adopted to calculate magnet‐to‐magnet and magnet‐to‐rotor end leakage fluxes based on the analysis of the relationship between end leakage fluxes and coils. A magnetic equivalent circuit (MEC) model is established considering end leakage fluxes. The leakage coefficients representing the ratio of end leakage fluxes to main flux and radial coefficients representing effective radial lengths of end leakage fluxes are analysed via the MEC model. The coefficients vary with machine parameters including PM thickness, rotor yoke thickness and air‐gap length. On the basis of the analysis results, the influence factors of end leakage fluxes are summarised and the 50 kW ironless stator AFPM machine is optimised. Finally, a 50 kW ironless stator AFPM machine with Halbach‐array PM rotors is prototyped to verify the results of the finite element analysis and MEC model. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated method of three-phase ac excitation and high-frequency voltage signal injection (HFVSI) for sensorless controlled starting of brushless synchronous machines (BSM) used as starter/generator in variable frequency ac power systems of civil aircraft. Fixed 400 Hz of the three-phase ac power is adopted both for the ac excitation and HFVSI in the initial starting process to eliminate the bulky rotor position sensor for BSM. The resulting 6th sequence harmonic voltage determined by the rotating rectifier is utilized as the HFVSI into the field-winding of main generator without any extra high-frequency signal injection. The rotor position is estimated by the high-frequency response signals extracted from the armature windings of main generator. Due to the nonlinear rotating rectifier linked in the HFSI chain, a novel frequency-insensitive asynchronous demodulation strategy is proposed in this paper for rotor position estimation. Furthermore, the initial rotor position detection is calibrated by polarity decision of the induced currents of the armature windings within the establishment procedure of field current of the main generator at standstill. The effectiveness of the ac excitation and feasibility of rotor position estimation for sensorless starting control of BSM are validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

A new hybrid excitation brushless dc generator (HEBLDCG) consisting of structure-parallel permanent magnet machine part and flux modulation machine part is proposed in this paper. Based on the flux modulation effect, the permanent magnet machine and flux modulation machine parts, which have different operating principles, can be combined. In addition, the proposed HEBLDCG features a lower short-circuit current by regulating field current, which increases reliability. The operating modes of flux modulation machine part are fully analyzed under different conditions. Changes in the phase shift factor of the permanent magnet machine part caused by the operating modes of the flux modulation machine part are investigated. Further, the proposed HEBLDCG features constant voltage output at a wide range of speeds. Finally, a prototype HEBLDCG is designed and manufactured. The experimental data agree with the simulated data. Loss breakdown is analyzed and efficiency is measured. An HEBLDCG with a reliable diode rectifier is promising for application in on-board dc power generation systems. [ABSTRACT FROM AUTHOR]

Doubly salient brushless dc (DSBLDC) motor drive system has attracted increasing attention due to the rugged rotor structure, brushless operation and low cost. The switch open‐circuit (OC) fault increases the torque ripple and decreases the maximal output power of DSBLDC motor drive system. A fault‐tolerance control strategy for switch OC circuit is proposed in this study. The back electromotive force (BEMF) current would occur in a pulse‐width modulation (PWM) pattern. It severely degrades the proposed method's fault‐tolerant performance. So the cause of the BEMF current is analysed and BEMF current is suppressed by specific PWM pattern. Finally, the fault‐tolerance control strategy is verified by experiment results and the selection PWM pattern is proved to be correct and practical. [ABSTRACT FROM AUTHOR]

With the development of more electric aircraft, higher demand for electrical energy is put forward in generation systems. The constant speed drive is eliminated in variable frequency ac (VFAC) generation systems, which makes integrated starter-generator (SG) can be realized. Considering the inherent defects of wound rotor synchronous SG systems, such as the complex starting excitation methods and rotating rectifiers, this paper proposes a VFAC SG system based on hybrid excitation synchronous machines (HESMs) for aircraft applications. The key technology of HESM-based VFAC SG system is to regulate the field current in such a way that three major modes of VFAC SG system operation for aircraft applications, namely, engine starting operation, transition mode, and generating operation, can be realized effectively. The simulation model of HESM-based VFAC SG system is built and analyzed. A prototype HESM-based VFAC SG system has been designed and developed for experimental verification. The starting operation, transition mode, and generating operation of the prototype HESM-based VFAC SG system are implemented. The feasibility of HESMs to VFAC SG system for safety-critical aircraft applications has been validated. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes the design philosophies of the single-phase main exciter (ME) for an aircraft wound-rotor synchronous machine and investigates its operating characteristics in both generating and starting modes. The fundamental structure and starting–generating system are discussed. The load features of single-phase ME are summarized. The ME has the characteristics of linear current amplifier and approximately constant current source the generating mode, which can be used in the wide range of working temperature. Detailed waveforms and finite-element analysis verify that excitation current $I_{\mathrm {ef}}$ is almost irrelevant to speed but in direct proportion to frequency in the starting mode. Besides, simulated data indicate that the energy transferring efficiency between ME stator and rotor can reach about 55% by the single-phase ac excitation method. Finally, the experimental verification is carried out, and the simulated and experimental data and waveforms of single-phase ME agree well with each other. [ABSTRACT FROM AUTHOR]

The new bearingless doubly salient electro-magnetic machine has the advantages of the robust structure and reduced coupling between the suspension force and torque control due to the independent dc winding in stator. The angular position detection is eliminated for suspension force control which improves the reliability. The operation principle and air-gap flux density distribution are analyzed. The suspension force characteristics are investigated and verified both by the mathematical model and finite-element method in depth. The experimental results are given to verify the analysis. [ABSTRACT FROM AUTHOR]

This paper presents the integrated design and analysis of a new axial-flux permanent magnet (AFPM) machine, which consists of an ironless stator with double-layer concentrated nonoverlapping windings and twin external rotors with Halbach-array PMs. A general sizing equation based on fundamental theory, easily adjustable for ironless stator AFPM machine with concentrated windings, is derived to obtain preliminary parameters. Then, by using three-dimensional (3-D) finite element analysis (FEA), the optimization of a primary machine is implemented. A precise and fast calculation method based on a 3-D FEA model is proposed to confirm the eddy-current loss for ironless stator winding. By making a tradeoff between dc current loss and eddy-current loss of Litz wire for winding, the efficiency is further improved for a high frequency operation. Despite using Halbach-array PMs, a certain thickness of a rotor yoke is recommended to increase air-gap flux density. Finally, a prototype machine is developed, experimented, and evaluated. The test results reveal the strong overload and heat dispersal capacity of the proposed stator ironless AFPM machine with the maximum efficiency of 98.5%. Measured performances of the manufactured prototype verify the validity of the proposed analysis method and FEA results. [ABSTRACT FROM AUTHOR]

Doubly salient electromagnetic machines (DSEMs), which are characterised with fault tolerance, low cost, high reliability, and de‐excitation ability, are gaining more and more attention in safety‐critical and hash environment applications, such as the aircraft generation systems. Nevertheless, the non‐linear and strong coupled characteristics of the flux linkage is the obstruct crux in DSEM modelling. The DSEM model is the critical part of the system model, which is the foundation of theoretical analysis, control strategy developing, and stability analysis. This study is aimed to demonstrate the feasibility of indirect flux linkage measurement method, as well as the effectiveness of the extreme learning machine (ELM)‐based flux linkage modelling method. The basic principles of the indirect measurement are analysed and the measurement processes excluding rotor‐clamping devices are proposed. The ELM is employed to high‐precision flux linkage modelling with high efficiency. A three‐phase 12/8‐pole DSEM is tested to confirm the validity of the proposed modelling method. Both finite element analysis and experimental results are presented, verifying the effectiveness of the indirect flux linkage measurement and the ELM‐based modelling method. [ABSTRACT FROM AUTHOR]

Fractional‐slot concentrated‐winding (FSCW) permanent magnet synchronous machines, which are characterised with high power density, fault tolerance and wide constant‐power speed range, are gaining more and more attention in the aircraft starter generator (SG) systems. Nevertheless, the short‐circuit (SC) fault, especially the turn‐to‐turn SC fault, is the obstruct crux in aviation applications. This study is aimed to demonstrate the feasibility of FSCW permanent magnet SG (PMSG) in dealing with turn‐to‐turn SC fault. The law of FSCW‐PMSG SC fault is analysed and verified by finite‐element analysis (FEA), including the influence on turn‐to‐turn SC current by the number of the shorted turns and the coil position in the slot. The three‐phase current injection control is employed to mitigate the SC fault in PMSG when a turn‐to‐turn SC fault occurs. A 24‐slot, 16‐pole FSCW‐PMSG with spoke‐type rotor topology is designed to confirm the ability of inhibiting turn‐to‐turn SC current without the risk of irreversible demagnetisation. Both FEA and experimental results are presented, verifying the effectiveness of the three‐phase current injection control in restraining the turn‐to‐turn SC current for FSCW PMSG in an acceptable range. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is designed for electric vehicle traction applications with consideration of electromagnetic performance and mechanical strength. The HESM with magnetic shunting rotor is a topology of brushless HESM with extended magnetic bridge to embed field windings. The rotor core extends along the axial direction and the increase of rotor length is inevitable, which reduces torque density. In order to improve torque density, the excitation structure is optimized by built-in field windings and the HESM with one-end built-in field windings is presented. To improve the flux regulation capability and decrease the magnet consumption further, the HESM with dual-end built-in field windings is proposed and investigated. The comparative study of the performances of the original HESM and the HESMs with one/dual-end built-in field windings is carried out by three-dimensional finite element method (FEM). An original HESM prototype and a permanent magnet synchronous machine prototype have been developed and the experimental results, which agree well with the FE-predicted results, confirm the advantages of HESM and the validity of FEM used in predictions in this paper. [ABSTRACT FROM PUBLISHER]

In this paper, a new shaded-pole main exciter (ME) with additional short-circuited coils for aircraft three-stage starter–generator (SG) is proposed and investigated. The basic structure, winding configurations, operating principle, and start system structure of the presented shaded-pole ME are illustrated in detail. The comparative study between the original ME and the shaded-pole ME with respect to the starting mode performances is conducted by 2-D finite-element method (FEM). A prototype SG with original ME has been developed, and the experimental results are essentially consistent with the simulation results by the FEM utilized in the predictions in this paper. Simulation data and waveforms verify that the proposed shaded-pole ME is a good candidate for aircraft machines to satisfy the dual function of starter and generator. [ABSTRACT FROM AUTHOR]

In this paper, the electromagnetic torque (EM) performance analysis of a parallel hybrid excitation machine (PHEM) is investigated. It is composed of a permanent magnet (PM) part and variable reluctance part. The flux paths of the two parts are independent and the armature windings are connected in series. PHEM is an axial parallel coupling of two different types of brushless machine. The mechanisms of EM torque for the two parts are quite different and many problems of torque coupling still remain unsolved. A 2-D EM-circuit coupling simulation model is built to analyze the torque characteristics and coupling relationships. The simulation results indicate that the PM part plays a main role in the output torque of PHEM. The large inductance ripple of variable reluctance part would cause large torque ripple in PHEM. The target machine is experimentally tested to verify the output torque characteristics. Furthermore, the torque-angle characteristics are studied with different field current and it shows that the best load angle could be around 110° to get maximum output torque and relatively smaller torque ripple. [ABSTRACT FROM AUTHOR]

In this paper, a novel modeling method for hybrid excitation synchronous machines (HESMs) with radial/axial flux paths via magnetic equivalent circuit (MEC) is proposed. 3-D finite-element analysis (FEA) is essential when analyzing a machine with radial/axial flux paths due to the asymmetry in the axial direction. However, 3-D FEA is computationally expensive and time-consuming, especially during the preliminary design stage. The proposed modeling method is analyzed and validated based on an HESM with magnetic shunting rotor. The fundamental structure and working principle of the HESM with magnetic shunting rotor are introduced. On the basis of 3-D structure, an MEC considering saturation and leakage flux distribution is built and illustrated, as well as field analysis is performed. A 2-D equivalent finite-element model via MEC is built and illustrated. A prototype HESM with magnetic shunting rotor has been designed by the proposed modeling method and developed for experimental verification. With the proposed modeling method, the computational efficiency is significantly improved in the design stage. The proposed modeling method is verified by the good agreement between the predicted and measured results. [ABSTRACT FROM AUTHOR]

Hybrid excitation synchronous machines (HESMs) inherit the high‐torque density of permanent magnet synchronous machines and flux regulation capability of wound rotor synchronous machines. This makes HESMs attractive candidates for vehicle traction applications. To further improve torque density, an optimised HESM with magnet shunting rotor is proposed in this study. This study presents a maximum torque control strategy with zero d‐axis current. Furthermore, an optimised control strategy that utilises the coordinated operation between the field current and d‐axis current is proposed. The optimised control strategy exhibits advantages of low‐speed high‐torque, wide constant power range, and high efficiency in flux‐weakening (FW) region. A 100 kW drive system based on the optimised HESM with the proposed control strategy is developed, experimentally realised, and validated. The experimental results show that the FW range is 3.5–1, and the efficiency of the drive system is >92% in most operating region, which verify the superiority and effectiveness of the proposed HESM drive system. [ABSTRACT FROM AUTHOR]

Due to the introduction of field winding, the doubly salient electromagnetic (DSEM) machine is featured with good torque production capability. However, this capability is limited by the problems of the phase current reversal and excessive back- electromotive force with traditional control methods. In this paper, a new control method, namely asymmetric current control (ASCC), is proposed to further improve the output torque. Two control angles α and γ are introduced to implement the current-angle control. Simultaneously, the pulse width modulation control is utilized to shape the waveform of phase current. Consequently, the torque is increased drastically because of more effective phase current waveforms, which presents the asymmetry of positive and negative half period. Furthermore, the reluctance torque resulting from the interaction between self-inductance and asymmetric phase current exerts favorable effects on the torque output. By field-circuit-coupled analysis, the ASCC method for a 1.3 kW prototype is analyzed and compared with other traditional control methods. Laboratory testing of the 1.3 kW DSEM machine driven by the new control method confirms the validity of theoretical analysis and simulation improvement of torque. The simulation and experimental results show that the torque and power density can be improved to 1.5 times by the proposed control method. [ABSTRACT FROM AUTHOR]

In this paper, a variable-speed operating doubly salient electromagnetic generator (DSEG) for an automobile power system is proposed and investigated. Analysis and comparison between the 12/8-pole and the 18/12-pole configurations are given. The 18/12-pole DSEG is more suitable for the wide-speed range operation in terms of the capability of output power and efficiency due to the smaller reactance. The characteristic of flux regulation for the constant power operation in a wide speed range is analyzed, and the corresponding loss variation and efficiency is obtained as well. Finally, a prototype 18/12-pole DSEG has been designed. Both the simulation and the experimental results indicate that the proposed DSEG can offer a more desirable and stable power performance over a wide speed range with simple control for the automobile on-board generation application. [ABSTRACT FROM AUTHOR]

The doubly salient electromagnetic machine (DSEM) is a kind of variable reluctance machine, which is different from the conventional ac electric machines. A new 24/16-pole DSEM is presented, and the configuration and operation principle are discussed. Based on the comprehensive study of the field distribution feature, the DSEM is separated into eight sections to investigate the iron loss distribution. In order to predict the iron loss of the doubly salient electromagnetic generator (DSEG), the flux density variations of each section are resolved into radial and circumferential waveforms, and Fourier transform is utilized in consideration of harmonic components. A calculation model of iron loss is established, and the coefficients are determined by the measured data at different speeds. The iron loss distribution of the DSEG is investigated. The proportion of iron loss to copper loss is further analyzed under different load conditions. Moreover, the influences of speed, air-gap length, and field current on iron loss are analyzed and summarized. Finally, the calculation and analysis of iron loss are verified by experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a new topology of parallel hybrid excitation machine (PHEM), which integrates permanent-magnet synchronous motor (PMSM) and variable-reluctance machine, namely, doubly salient electromagnetic machine (DSEM), and provides a solution to better field-regulating capability. The configuration and the operation principle of the proposed PHEM are introduced. The combination criterion and design consideration are discussed. The performances of the two axial sections (PMSM and DSEM) are studied by 2-D finite-element analysis (FEA), respectively, to achieve reasonable integration. The field and voltage regulation capability of the PHEM is further investigated by 3-D FEA. A prototype PHEM is designed, manufactured, and tested. The measured results verify structural validity and finite-element predictions. The loss is predicted, and the measurement of short-circuit current illustrates the capacity of deexcitation at fault. The results confirm that the PHEM achieves effective power superposition of two different brushless machines. Bidirectional field-regulating capability facilitates a wide field regulating range of 6.5:1 under no load. [ABSTRACT FROM PUBLISHER]

The doubly salient brushless dc generator (DS-BLDCG) is constituted by a doubly salient electromagnetic generator (DSEG) and the associated rectifier circuit. The DS-BLDCG is suitable for the automobile auxiliary power unit (APU) application due to its merits of simplicity, high robustness, low cost, and flexible control. Since no constraint is imposed to the number of phases of the onboard brushless dc generator, the polyphase DSEG can be employed. In this paper, a 3-phase 12/8-pole DSEG and a 4-phase 16/12-pole DSEG with a rectifier circuit for the APU application are proposed. The taper stator pole and broadened rotor pole structure utilized to increase maximum output power is introduced in the four-phase DSEG design. Based on the two-dimensional (2-D) finite-element method (FEM) and field-circuit coupling analysis, a comprehensive comparison is presented. The 16/12-pole DS-BLDCG with broadened rotor pole exhibits lower peak value of the phase inductance yet larger negative phase current commutation overlapping angle. The rectifier circuit of the 16/12-pole DS-BLDCG is more complex and the copper consumption of the 12/8-pole DS-BLDCG is slightly less. A prototype 12/8-pole DS-BLDCG for the APU application is designed and developed. Both the simulation and experimental results indicate that the developed DS-BLDCG is a promising option for automobile APU application. [ABSTRACT FROM PUBLISHER]

The hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is a new topology of brushless HESM. To optimize the excitation construction, improve the flux control capability, and decrease the magnet consumption as well, two types of HESMs with different air-gap features are further proposed and investigated in this paper. First, configuration of the HESM with axial auxiliary air-gaps is presented. The comparative study of axial auxiliary air-gap scheme with respect to radial one is carried out. Three-dimensional (3-D) finite-element analysis (FEA) of the HESM is performed to achieve the field distribution, air-gap flux density and flux control characteristic, which indicates the HESM with axial auxiliary air-gaps also has good flux control capability and moreover enlarged excitation housing. Afterwards, construction and flux control principle of the new HESM with axial non-uniform air-gaps are introduced. A prototype HESM is developed, and the experimental results of open-circuit characteristic and terminal characteristic, which agree with the 3-D FEA results, verify the satisfactory field control performance, desirable power output capability, and the improved flux control capability of the HESM at negative excitation current as well. [ABSTRACT FROM PUBLISHER]

This paper investigates the design considerations of a new hybrid excitation synchronous machine (HESM), which is characterized by magnetic shunt rotor and brushless field excitation. First, the basic constraints of flux control capability are discussed and deduced. Then the influence of some key structural parameters on flux control capability of the HESM is investigated by using equivalent magnetic circuits. The influence of permanent magnet width is further studied and verified by 3-D finite element analysis. A prototype HESM with magnetic shunt rotor is designed and developed. The experimental results show the satisfactory output performance, especially the significant sinusoidal EMF waveforms of the machine, and also verify the influence of air-gap variation on flux control capability of the HESM. [ABSTRACT FROM PUBLISHER]

The unit machine of the traditional doubly salient electro-magnetic generator (DSEG) has a 6/4-pole structure, so it must have a large number of stator poles when used as a low speed wind turbine generator. The matching relationship between the stator pole number and the rotor pole number of a multi-poles-rotor DSEG is deduced, and a new 3N/4N-pole DSEG is proposed. The magnetostatic field distribution, excitation inductance characteristic, as well as output characteristic of the DSEG is investigated by 2-D and 3-D finite element analysis. Comparisons between the two different structures are presented in terms of power density, voltage ripple and efficiency. A low speed 24/32-pole prototype machine is developed, and the experimental results are given to verify the validity of the simulation analysis and the reasonable structure of 3N/4N-pole DSEG. [ABSTRACT FROM PUBLISHER]