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Most of the existing diagnosis techniques for interturn short circuits (ITSCs) in switched reluctance motors (SRMs) suffer from three major issues. 1) The problem of lower sensitivity where the system cannot detect an ITSC if a lower number of turns are short-circuited; 2) Interference of load variation on the detection reliability in which the fault index might initiate false alarm without any fault; 3) The dependency of the diagnosis system on the control strategy on which the motor is operating. This article proposes a novel method to diagnose ITSCs in SRMs independent of control schemes with better sensitivity and reliability using the signal injection technique. In SRMs, not all the phases take part in the torque production at any instant. The idle or inactive phase is injected with a high-frequency (HF) voltage signal for a preselected injection ratio within an electrical cycle. Any change in the winding parameters owing to an ITSC fault is deciphered by monitoring the HF currents generated in the phase windings. The results are validated experimentally for a four-phase 8/6 SRM employing two control strategies: 1) chopped current control and 2) angle position control. [ABSTRACT FROM AUTHOR]

In this article, a wireless resolver is proposed and implemented for wireless switched reluctance (SR) motors, which can detect the rotor position and transfer the information to the primary side without involving any battery storage or active components at the secondary side. The key is to integrate wireless power transfer (WPT) into a variable reluctance resolver to detect and transmit the rotor position. Compared with previous wireless SR motors adopting the Hall effect position encoder and Bluetooth communication, the robustness is highly improved, and the communication delay caused by the connection interval can be solved. Therefore, the proposed system takes the definite advantages of better dynamic performance and sealability. Besides, there is no need to specially design the SR motor, as all existing SR motors and other similar kinds of motors can readily employ this wireless resolver. An experimental prototype has been built for verification, which works well from 100 to 900 rpm with 20 mm WPT distance, and the additional power for position detection can be limited to 1.05 W while the motor consumes 54 W. [ABSTRACT FROM AUTHOR]

In this article, a simplified pulsewidth modulation (PWM) strategy is proposed for open-winding flux modulated doubly-salient reluctance motor (FMDRM) drives for switching action minimization and common-mode voltage (CMV) reduction. Conventionally, the open-winding converter topology is utilized to achieve the zero-sequence current flow path and dc-biased sinusoidal current excitation for the FMDRM, where the switching actions of power switches are doubled compared to the conventional modular three-phase converter, leading to higher switching losses. Different from the conventional space vector PWM scheme, the reference voltages of converter legs are directly calculated by the reference phase voltages in the proposed PWM scheme. In addition, a rotor-position-based sector division method is proposed to deal with the sector imbalance caused by the distorted back electromotive force (back EMF). Furthermore, different leg voltage clamping methods are respectively developed in odd and even sectors for switching action minimization, which can achieve voltage stress balance and CMV reduction. With the proposed scheme, the switching actions in each switching cycle can be reduced by half, which effectively increases the system efficiency of the FMDRM drive. Experiments are carried out on a three-phase 12/8 FMDRM prototype to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this article, a novel multiple three-phase PM assisted synchronous reluctance machine with delta windings is proposed for enhanced fault tolerance. The delta connected windings offer an additional degree of freedom of the phase currents. Hence, this machine drive could provide higher torque under phase open-circuit condition. More importantly, the delta windings inherently contain zero sequence current path and could help reducing the turn fault current in the event of the most challenging turn short-circuit fault. Owing to the zero sequence current, the residual flux linkage of the fault turn is more effectively nullified leading to lower fault current. The proposed machine performance together with fault tolerant capability under various fault scenarios are investigated and compared with the star connected winding machine by detailed finite element simulation and experimental tests. It shows that the two machines have the same performance under healthy condition whilst the delta winding machine exhibits higher fault tolerance. These advantages are achieved simply by changing the winding connections without any extra cost. Thus, it is more favorable for the fault tolerant applications. [ABSTRACT FROM AUTHOR]

This article proposes an online diagnosis scheme for transistor faults of asymmetric half-bridge converter (AHBC) in switched reluctance motor (SRM) drives. In order to extract more information from the phase current to identify faults, based on the conventional current measurement method, two novel current measurement methods are presented by reconstructing current sensors. According to the novel current measurement methods, a current prediction method is raised. The phase current at the kth sampling time is available so that the estimated current can be calculated. The fault can be detected and located by analyzing the given and actual switching states, which are deduced by comparing the measured and estimated currents. Compared with existing methods, the proposed scheme can be applied to diagnosis of multiple faults in n-phase AHBC, which can operate at various control strategies and chopping modes. With a single current sensor in each phase, the scheme will not increase the cost and complexity of the SRM drive. Furthermore, the scheme does not require complicated computation, making it easy to implement online. The experimental results confirm the effectiveness and flexibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this article, we deal with design considerations of a new ac hybrid-excitation permanent-magnet machine with axial stator. Due to the presence of an axial stator, the machine features a typical three-dimensional geometric structure and field distribution. A simplified reluctance-based network is developed to capture the main design features of the machine. The analytical equations are deduced relating the main geometric dimensions to the machine design criteria: speed, power, and flux regulation capability. The influence of key machine geometric parameters, i.e., radial/axial air-gap length, stack length, and bore diameter, on output power, flux density, and flux regulation capability is investigated. It is found that there is a design tradeoff between the machine power density and flux regulation capability. The d/q-axis inductance and its ratio, which has an influence on flux weakening capability and operation performance, is examined. Finally, a 6-pole/36-slot prototype is built. Intensive experimental tests are carried out to verify the machine characteristics. [ABSTRACT FROM AUTHOR]

Vehicle to vehicle (V2V) energy sharing is emerging as an alternate solution to range anxiety and limited charging infrastructure challenges associated with electric vehicles (EVs). The existing off-board dc fast charging options for V2V application found in the literature are not effective due to the additional weight, size and cost of the external charger or interface. In this article, a new V2V interface is proposed in which both EV’s motor winding neutrals and negative rails of on-board drivetrains are directly connected to each other. This further helps in forming an integrated dual bidirectional dc–dc converter to control the direction of power flow. The proposed approach does not require reconfiguration of motor winding or mechanical clutch to arrest the motor from rotating and/or the reconfiguration of drivetrain inverter connections. The major hardware requirement for the proposed approach is, access to the already existing neutral connection of the EV motor phase windings. To achieve dc fast charging, all three-legs of voltage source inverter of energy Provider-EV are switched using interleaved pulsewidth modulation. Furthermore, finite element analysis is presented for 150 kW EV motor model and its performance validation with the high frequency dc current flowing in the motor windings during the V2V operation. A scaled lab prototype is developed to demonstrate the energy sharing between two Lithium-ion battery banks through the proposed direct V2V power transfer concept. [ABSTRACT FROM AUTHOR]

Dc-field excited modular variable flux reluctance machines (VFRM) are passive salient-pole rotor and independent stator winding, which makes it suitable for aerospace applications. Fault-tolerant operation is commonly required to improve its reliability. Hence, the performance under winding open-circuit faults is analyzed and the fault-tolerant control strategy is presented to increase the output capacity in this article. First, the dc-rectified output voltages and power of the VFRM under both normal and open-circuit faults are derived. Then, phase angle control strategy of the fault-tolerant operation for a 12-slot-14-rotor-pole (12s14r) modular VFRM is proposed, where the control sequence is optimized to achieve the maximum output power of the generation system. Compared with the classical fault-tolerant method, a higher applicability of the proposed method in terms of the types of fault-tolerant operations can be achieved. The electromagnetic properties, including the armature current and the capacity of electrical power output, are analyzed with finite-element analysis. The effectiveness and feasibility of the proposed fault-topology and control strategy are verified by the 12s14r VFRM prototype in normal, fault, and fault-tolerant operation. [ABSTRACT FROM AUTHOR]

This article reveals the flux leakage design and modeling principle of a flux leakage controllable permanent magnet (FLC-PM) machine by considering driving cycles. The key is to obtain the relationship between flux leakage characteristics and multiple operating conditions. Based on the flux leakage controllable concept, an FLC-PM machine with an artfully designed flux leakage region is proposed. The design principle of the machine is investigated by analyzing the magnetic circuit of the machine in multiple operating conditions. The flux leakage factor is introduced to characterize the variable magnetic field in multiple operating conditions. On this basis, the mathematical model of the FLC-PM machine is deduced, and the driving characteristics of the machine are studied in detail. In order to evaluate the presented principle of the FLC-PM machine, a prototype is manufactured for experiments. Through the theoretical analysis and experimental testing, it is verified that the proposed principle is feasible and effective. [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]

Multiphase machines with a prime number of phases (five and seven) have shown better torque density than machines with other phase numbers. Unfortunately, these machines require a special stator design. Hence, this article proposes general rewinding techniques to obtain a five-phase winding from the existing standard three-phase stator frames. The proposed rewinding techniques are applied to construct a five-phase star-connected synchronous reluctance machine (SynRM 1) and a novel combined star-pentagon winding (SynRM 2). Simple mathematical formulations are introduced to compute the equivalent winding factor. The performance of five-phase SynRMs is analyzed using two-dimensional Ansys Maxwell transient simulations under the same copper volume for both healthy and faulty cases. SynRM 1 and 2 provide 6.56% and 13.35% higher torque compared to the three-phase SynRM at rated current and at optimal current angle. The torque ripple is decreased by 17% and 30%, respectively. Moreover, SynRM 1 and 2 offer a better performance at the faulty case; e.g., at one phase opened, the average torque of SynRM 1 and 2 is 82% and 108% higher compared to the three-phase SynRM. In addition, the torque ripple is reduced by about 63% and 81%. Finally, experimental results are done to validate the proposed winding techniques. [ABSTRACT FROM AUTHOR]

Vernier reluctance machine (VRM) with dc field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this article proposes a new armature winding design method for VRM with dc field coils across two stator teeth. The key is to break the traditional winding design principle based on the flux modulation effect of fundamental dc field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order dc field harmonics arising from the unique magnetomotive force distribution of dc field coils across two stator teeth. By this means, the torque density can be improved by 75.6% against the existing poor counterpart. In this article, the machine structure and operation principle are introduced, with emphasis on the high-order dc field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the electromagnetic performance of VRMs using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method. [ABSTRACT FROM AUTHOR]

This article proposes an accurate harmonic current suppression strategy for direct current (dc)-biased VRMs based on adaptive notch filter (ANF) to reduce torque ripple and power loss. A new harmonic reference frame is proposed in dq-axis and combined with ANF, thus harmonic currents are accurately extracted and analyzed. Furthermore, a phase-shift strategy is proposed for dc-biased VRMs, realizing precise compensation of harmonic voltages. The proposed ANF-based harmonic currents suppression strategy has a better performance in harmonic suppression and dynamic response and is suitable for a wider speed range in comparison with traditional harmonic suppression control strategy. What is more, the parameter design of the proposed method is easier compared with traditional method. Finally, the conclusions are verified by experimental results. [ABSTRACT FROM AUTHOR]

In this article, a phase-shifting fault-tolerant control (PS-FTC) method with single-phase current sensor is proposed for primary permanent-magnet linear motor traction system. The phase with healthy sensor is defined as the first phase, while the other two phases without healthy sensors are, respectively, defined as the second and third phases. In PS-FTC, hysteresis current control is adopted. The actual currents of the second and third phases are replaced by the estimated values, while the reference values are obtained by phase shifting of the estimated first-phase current. Although the linear motor parameters have been used in the calculation of the estimated currents, the parameter variations do not affect the performances of PS-FTC. Compared with the conventional fault-tolerant control (C-FTC) method and the existing fault-tolerant control schemes with single-phase current sensor, PS-FTC is robust and shows better steady-state performances. Furthermore, a hybrid strategy combining PS-FTC and C-FTC is adopted to improve the transient-state performances. The effectiveness of PS-FTC and the hybrid strategy are verified by the theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

The interturn short-circuit fault of stator winding is a common failure mode in switched reluctance motors (SRMs), which can severely harm the operation of the motor. In this article, a novel method for diagnosing the interturn short-circuit fault in the current chopping mode is proposed, which is suitable for online monitoring and protection of SRMs. The proposed method achieves a fast response and high sensitivity and can mitigate the interference of load conditions on detection reliability. Moreover, this method is based on phase currents, which does not require additional sensor or detection circuits. Meanwhile, the effects of interturn fault location in the stator winding on the motor flux and motor parameters are analyzed in detail through finite-element analysis, which is helpful to establish a reliable diagnostics technique for various fault conditions. Experimentations based on an 8/6 four-phase SRM with special windings designed to simulate interturn short circuit conditions are conducted, and the results have verified the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article investigates the design methods and performance optimization of segmented-double-stator switched reluctance machine (SDS-SRM). First, two segmented U-shaped single-stator SRMs are introduced, including inner-rotor and outer-rotor constructions. In order to enhance the torque and power density, these two kinds of single-stator SRMs are combined together to constitute an SDS-SRM. Then, the relationships of torque ripple coefficient with the mechanical offset angles of the inner and outer rotor teeth are investigated to obtain the optimal rotor structure, and the corresponding conduction phase sequences for double-stator excitation mode are also analyzed. Furthermore, the flux distributions of the inner and outer stators with different coil magnetic polarities configurations are researched, and it reveals that the phase windings both on inner and outer stators with NSSNNSSN polarities have better magnetic field decoupling characteristics. To evaluate the final topology of the proposed SDS-SRM, the static magnetic characteristics and dynamic performances are presented. Finally, the SDS-SRM prototype is manufactured and tested to validate the theory and simulation analyses. [ABSTRACT FROM AUTHOR]

Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor. On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive. Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information. Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability. The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC. By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates. Experimental results are provided to validate the proposed sensorless FOC philosophy. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method (AM) based on the air-gap magnetomotive force (MMF) permeance model is proposed to predict the nonlinear instantaneous torque of switched reluctance machines (SRMs). The analytical expression of the air-gap MMF is first obtained from the winding function and current profile, while the air-gap magnetic permeance considering the double-sided slotting effects is also derived. Then, the nonsaturated field distribution along the air-gap circumference is presented based on which the instantaneous torque can be calculated from the Lorentz force law. Furthermore, the model is enhanced with a saturation distribution factor to include the nonlinear characteristics. The proposed method is free from preliminary data or empirical coefficient and benefits from the simplified model and solution. The AM will be validated by the two-dimensional finite-element method based on four SRMs with different structures. Moreover, an SRM prototype is manufactured for experimental verification. [ABSTRACT FROM AUTHOR]

For traditional 12/8 bearingless switched reluctance motors (BSRMs), the coupling between torque and levitation increases the complexity of control. For the turbomachinery application, 2 degrees of freedom (DOF) BSRMs stabilized by extra 3-DOF active magnetic bearings are required. In this article, an improved BSRM with 4 rotor poles and 12 stator poles is proposed to realize 4-DOF radial levitation, and the torque dead zone is compensated because that two rotors and these poles are assemble with 15 mechanical degree shifted. The decoupling of torque and radial levitation is realized simultaneously. Moreover, the operation principle of axial reluctance force is analyzed for passive levitation in the axial direction. Various experiments were completed to verify the performance of the proposed BSRM, and the prototype achieved stable levitation of the rotor in 10 000 r/min. [ABSTRACT FROM AUTHOR]

In order to improve the performance (low torque ripple, low suspension ripple, and high power factor) of the permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM), the multiobjective optimal design based on fast nondominated sorting genetic algorithm (NSGA-Ⅱ) of PMa-BSynRM rotor topology is investigated in this article. First, the structure and operation principle of the PMa-BSynRM are introduced. Second, the initial rotor design that gives optimizer the ability to produce a variety of barrier shapes and the comprehensive sensitive analysis that evaluates the influence of each design variable on optimization objectives are presented. Third, the optimal design is selected from the Pareto front, which is generated by NSGA-Ⅱ, and validated by finite-element analysis. The simulation results confirm that the torque and suspension force capacity of optimal motor are improved significantly in comparison with initial design, whereas the value of power factor reaches 0.81. Finally, the optimal prototype motor is manufactured, and experimental results confirm the validity and superiority of the optimized design. [ABSTRACT FROM AUTHOR]

Based on the characteristic of doubly salient electromagnetic machines (DSEMs) that the incremental inductance varies with the rotor position, a sensorless startup strategy is proposed in this article. First, the pulse injection based method is adopted to estimate the initial rotor sector. The influence of the field current on the position estimation error is analyzed. Second, the startup method with no test pulse is introduced to start DSEM. Two key strategies are proposed: the commutation strategy based on the series incremental inductance detection and the anti-out-of-step control strategy based on the circulating current detection. The series incremental inductance is estimated in a chopping period and is compared with a preset threshold to obtain the commutation signal. The circulating current of the nonconducting phase is detected to monitor whether the DSEM is out of step. Furthermore, the current chopping mode is optimized, which has influence on the circulating current of the nonconducting phase. The proposed strategy can avoid the discontinuity of phase current caused by the test pulse in the existing technique. Finally, the effectiveness and the feasibility of the proposed method are verified by a series of experiments on the 9-kW 12/8 pole DSEM prototype. [ABSTRACT FROM AUTHOR]

A drive topology composed of a T-type single-phase three-level voltage source rectifier (VSR) and a four-level switched reluctance motor (SRM) converter is proposed in this article. The commonly used diode bridge rectifier presenting degraded power quality is replaced by the VSR to drive the SRM converter. Compared with the conventional split-dc converter, the four-level SRM converter of the proposed drive topology adopts one more switch and one more diode for each phase, but two more operation modes are formed. With the double-voltage demagnetization mode of the four-level SRM converter, the tailing time of demagnetization current is significantly reduced, which increases the utilization of inductance increasing region. All the operation modes of this converter can be implemented successfully, even in the multiphase excitation region. Moreover, a centralized control strategy is proposed to regulate the VSR and SRM together, within which the speed and grid-side power factor are regulated by the d-axis and q-axis component of grid-side current in VSR, respectively. Most importantly, the bidirectional energy flow is realized. An idea-proofed testbench is constructed. The results obtained from the comparative experiments confirm the validity of the proposed drive topology and its control strategy. [ABSTRACT FROM AUTHOR]

In order to combine the advantages of modularity and hybrid-excitation for motor torque and power density enhancement, this article proposes a 12/4 modular-topology, permanent magnet (PM) assist, hybrid-excitation switched reluctance machine (HESRM) with both segmented-stator and -rotor. The machine topology and basic operating principle are presented. Three key parameters of the machine are optimized for assessment on the torque production. The three-dimensional finite-element analysis is employed to consider the effects of end winding and core saturation. The static magnetic characteristics and dynamic performances are simulated and compared with a 12/4 segmented SRM (SSRM) without PM and a 12/10 segmented-stator HESRM. Two prototypes of the proposed 12/4 HESRM and a 12/10 segmented-stator HESRM with the same size are manufactured and developed for experimental verification. Both results show that the proposed motor can achieve higher dynamic average torque and higher power/torque density at high-speed operation. It also has a stronger starting capability, more rapid response for command changes, as well as better stability and tracking features. [ABSTRACT FROM AUTHOR]

In this article, a partial parallel dual active bridge (PPDAB) converter is proposed to lower the current stress over the switching devices on the low-voltage side. Gallium Nitride (GaN) transistors are used to improve efficiency and power density at 1 MHz switching frequency. Moreover, in order to reduce the number of magnetic components and achieve more compact design, with a unique three-leg core geometry, a new method of integrating three transformers and their associated interfacing inductors is proposed. The integration is able to shorten winding length and therefore reduces winding dc resistance. Moreover, wounding the secondary windings on each outer leg in the core enlarges leakage inductance, which can serve as the interfacing inductor Lac in the PPDAB converter. Given that, a reluctance model to analyze coupling effect of the secondary windings as well as their current balance is derived and validated by finite element simulations. Based on both calculations and simulations, the proposed integrated transformer is found to be functionally equivalent to three discrete transformers, in which their primary windings are connected in series, and the additional Lac inductor. Additionally, given the same number of the turns of the windings in each parallel module, the ac currents in these three secondary windings can inherently balance. Finally, a fully GaN-based 1.2-kW 1-MHz 400V/50V prototype with a peak efficiency of 97.51% is built and tested to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this article, a variable flux reluctance machine (VFRM) with dc field excitation and modular structure is proposed and it exhibits controllable flux, simplified manufacture, better fault tolerant capability, and potentially reduced material consumption. Its operational theory is illustrated by using flux modulation principles, and the working harmonics considering the modular structure are analyzed. Besides, the winding factors of modular VFRM are derived considering the flux gap width. The parameters are optimized by two-dimensional finite element method to maximize the back electromotive force (back-EMF) and the ratio of phase self-inductance to mutual inductance. Moreover, the electromagnetic performance including open circuit air-gap flux distributions, open circuit air-gap flux densities, flux linkage, back-EMF, inductance of armature windings, output characteristics, loss, power factor, and efficiency-map are compared for 12s10r and 12s14r nonmodular and modular VFRM. Additionally, the fault including short circuit and open circuit fault are analyzed. Finally, a modular 12s14r VFRM prototype is manufactured and tested to validate the theoretical and finite-element analyses. [ABSTRACT FROM AUTHOR]