Rajib Mikail | North Carolina State University (original) (raw)

Patents by Rajib Mikail

Technologies for providing DC arc protection in a DC socket include an electromagnet positioned i... more Technologies for providing DC arc protection in a DC socket include an electromagnet positioned in the DC socket configured to produce a magnetic field. The electromagnet is positioned to be adjacent to a contact region between one or more supply terminals of a DC socket and one or more prongs of a DC plug. As the DC plug is disconnected from the DC socket, a DC arc might form between one or more of the supply terminals and one or more of the prongs. The magnetic field produced by the electromagnet reduces the energy of the DC arc and reduces the time duration of the DC arc.

A motor control system is provided. The motor control system includes a motor, a position sensor,... more A motor control system is provided. The motor control system includes a motor, a position sensor, a current sensor, and a control module. The motor has a rotor and a stator. The motor generates an output torque based on a phase current applied to the motor. The output torque generated by the motor creates a torque ripple that is within a predefined range. The position sensor monitors the motor to determine a rotor position. The current sensor monitors the motor to determine the phase current. The control module is in communication with the motor, the position sensor, and the current sensor. The control module includes a lookup table that stores values of phase current commands. The control module determines a phase current command from the lookup table based on the rotor position and the phase current.

Thesis by Rajib Mikail

The dissertation presents the design, control and implementation of a high performance switched ... more The dissertation presents the design, control and implementation of a high performance
switched reluctance motor (SRM) drive with very low torque ripple requirements over a wide speed range. The developed design and control methodologies have been verified with system level high fidelity simulation models, finite element analysis (FEA) and experiments.

A highly accurate mathematical machine model incorporating the mutual coupling effects has been developed which can be configured based on FEA based characteristics or built machine characteristics. The model accuracy is similar to what has been achieved through FEA. The model is useful in system level simulation based analysis and controller performance evaluation for high performance applications such as electric power steering, precision tooling, robotic automation, trajectory tracking and actuator control. The performance of the motor drive has been verified first before fabrication using a coupled simulation of the FEA software and a dynamic simulation model. The control algorithm has also been tuned using the same approach.

A novel current profiling method in addition to machine structural design steps have been developed for high performance applications where torque ripple and acoustic noise specifications are challenging for the reluctance type machines. The method delivers smooth operation and high performance in all four quadrants over the entire speed range of operation. The torque ripple has been minimized to below 3% in the specified operation range. The relative acoustic noise analysis through structural FEA shows that the circumferential displacement is within acceptable limits.

Following a reference current accurately is critical to achieve the control objectives in torque ripple sensitive applications. A novel fixed switching frequency predictive current controller has been developed to better follow the SRM reference phase current with a fixed PWM frequency over the entire speed range in all the four quadrants of operation.

The SR machine and controller hardware has been built according to the design. Torque output data at a higher bandwidth and phase current waveforms have been collected from an experimental setup to evaluate and verify the motor drive system performance. A detailed error analysis has also been done to analyze the sensor errors and manufacturing build variations.

Papers by Rajib Mikail

2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019

This paper introduces direct online electric machines to achieve high torque at low speeds while ... more This paper introduces direct online electric machines to achieve high torque at low speeds while maintaining a low number of poles. The proposed concept integrates line-start motor with a magnetic gear into a single housing with improved starting performance and rated operation torque density. Magnetic gears can scale the torque and speed of rotary systems, while avoiding problems associated with transferring torque through physical contact. The high speed PM rotor of the magnetic gear has Halbach structure and is physically integrated to the line-start rotor. The Halbach design restricts field interference between line-start and PM rotor, which helps with maintaining reliable and smooth starting performance with high locked rotor and breakdown torque capabilities. With Halbach design, the starting and steady state torque are smoother. Moreover, the Halbach design enhances magnetic field towards pole modulators of the magnetic gear, which enhances the power density of the proposed concept compared to the existing low speed, high torque solutions. Compared to the conventional mechanically geared system, the proposed solution is more compact with potentially increased mechanical reliability due to the reduction of mechanical contacts and does not require maintenance. When compared to the VSD fed direct drive systems the proposed solution provides improved torque density with cost saving potential.

2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018

Thermal management is crucial in the development of electrical machine technologies. This paper p... more Thermal management is crucial in the development of electrical machine technologies. This paper presents a concept of using lamination to design cooling channels embedded in the stators. Additionally, a process of modeling is presented by an analytical model for initial screening purposes.

ABSTRACT The dissertation presents the design, control and implementation of a high performance s... more ABSTRACT The dissertation presents the design, control and implementation of a high performance switched reluctance motor (SRM) drive with very low torque ripple requirements over a wide speed range. The developed design and control methodologies have been verified with system level high fidelity simulation models, finite element analysis (FEA) and experiments. A highly accurate mathematical machine model incorporating the mutual coupling effects has been developed which can be configured based on FEA based characteristics or built machine characteristics. The model accuracy is similar to what has been achieved through FEA. The model is useful in system level simulation based analysis and controller performance evaluation for high performance applications such as electric power steering, precision tooling, robotic automation, trajectory tracking and actuator control. The performance of the motor drive has been verified first before fabrication using a coupled simulation of the FEA software and a dynamic simulation model. The control algorithm has also been tuned using the same approach. A novel current profiling method in addition to machine structural design steps have been developed for high performance applications where torque ripple and acoustic noise specifications are challenging for the reluctance type machines. The method delivers smooth operation and high performance in all four quadrants over the entire speed range of operation. The torque ripple has been minimized to below 3% in the specified operation range. The relative acoustic noise analysis through structural FEA shows that the circumferential displacement is within acceptable limits. Following a reference current accurately is critical to achieve the control objectives in torque ripple sensitive applications. A novel fixed switching frequency predictive current controller has been developed to better follow the SRM reference phase current with a fixed PWM frequency over the entire speed range in all the four quadrants of operation. The SR machine and controller hardware has been built according to the design. Torque output data at a higher bandwidth and phase current waveforms have been collected from an experimental setup to evaluate and verify the motor drive system performance. A detailed error analysis has also been done to analyze the sensor errors and manufacturing build variations.

2020 IEEE Energy Conversion Congress and Exposition (ECCE)

A novel 3D-airgap electric machine concept with multiple torque producing planes within the same ... more A novel 3D-airgap electric machine concept with multiple torque producing planes within the same structure is proposed to enhance the torque density of conventional machine topologies. The airgap of conventional machine topologies is limited to one fixed plane. The 3D-airgap configuration can be conceived in several different ways. In this research, one planar axial airgap and one cylindrical airgap is electromagnetically integrated into one 3D-airgap machine which increases mass utilization by integrating structural components into torque producing components. Moreover, the 3D-airgap concept maximizes the use of the end-winding section of the radial flux portion by converting it into a torque producing component. The 3D-airgap machine concept is validated through 3D-finite element analysis (FEA). It is found that the 3D-airgap concept can have more than double torque density compared to the 2D-airgap machine within the same active volume. It also helps to increase the torque per unit conductor loss; thus, it will have a better thermal performance for the same output torque. Resulting power density (kW/liter and kW/kg) also improves substantially. Additionally, a simulation method is proposed to predict 3D-airgap machines’ performances using the superposition principle. The proposed simulation method significantly reduces the computational time required for 3D-FEA.

2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019

This paper presents a ripple minimization strategy through interactive space harmonic minimizatio... more This paper presents a ripple minimization strategy through interactive space harmonic minimization of fractional slot permanent magnet (PM) machines for high-performance applications. This method uses a space-shifted wye-delta configuration of its stator winding and avoids the need for magnet shaping or skewing of the rotor. The proposed strategy reduces the onload cogging torque and utilizes the space harmonics interaction of stator and rotor. The effectiveness of the proposed method is shown by analyzing the performances of two fractional slot; 12-slot/10-pole (q=2/5)(q=2/5)(q=2/5) and 12-slot/8-pole($q=1/2)$ PM machines. Application to a 12-slot/10-pole PM machine shows a torque-density improvement along with very low ripple performance compared to the existing techniques. Moreover, in comparison with the existing ripple minimization techniques, this strategy can achieve either the same or better ripple performance with either the same or higher average torque depending on the slot/pole combination. The effect on loaded and open-circuit cogging torque is also presented and compared with existing techniques.

2018 IEEE Transportation Electrification Conference and Expo (ITEC), 2018

A new winding concept for fractional slot concentrated winding (FSCW) is proposed that can simult... more A new winding concept for fractional slot concentrated winding (FSCW) is proposed that can simultaneously cancel both sub and higher order harmonics of stator MMF. The new winding concept proposes two sets of three-phase windings by doubling the number of stator slots connected in wye-delta configuration. These two winding sets are shifted in space with respect to each other and are connected in series. The wye-delta configuration eliminates sub-harmonics and enhances the torque-producing component whereas their relative shifting angle eliminates the dominant higher order harmonics to provide a cleaner and enhanced spectrum. This concept is effective when the stator slot number is multiple of twelve. The application of the proposed winding to a PM machine demonstrated dominant sub and higher order harmonics cancellation, THD reduction, torque ripple reduction, and magnetic loss reduction along with torque density and power factor improvements.

IEEE Transactions on Transportation Electrification, 2021

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

This paper proposes a 90% HRE-free hybrid rotor concept to enhance the demagnetization performanc... more This paper proposes a 90% HRE-free hybrid rotor concept to enhance the demagnetization performance of a 100 kW motor for traction applications. The demagnetization analysis is presented for three cases- for a motor with 100% HRE-free, 90% HRE-free, and finally with a 100%-HRE magnet. The proposed concept divides each magnet into several segments, and use HRE magnets at the most demagnetization prone top corners of a rectangular magnet. For the proposed hybrid rotor, magnets can be safe from irreversible demagnetization up to 150°C even at 100% negative d–axis current and three-phase short-circuit fault. The hybrid rotor uses approximately 90% HRE-free PM content. Moreover, the hybrid rotor reduces the magnet loss by 90%, which helps alleviate the challenging thermal management problem in a rotary environment.

2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018

A winding method for AC Machines is presented to eliminate both the sub and super space harmonics... more A winding method for AC Machines is presented to eliminate both the sub and super space harmonics of fractional slot concentrated windings where the stator slot numbers are integer multiples of six. The proposed method is based on three single-layer concentrated windings where the number of turns in one layer is optimized whereas the other layers are shifted to cancel the sub-harmonics. The cancellation of super-harmonics is achieved through series connection of two space shifted layers which effectively doubles the number of slots. The proposed method has been successfully validated in widely used 12-slot/10-pole and 18-slot/14-pole machine configurations. Applying the proposed winding concept to a Permanent Magnet Synchronous Machine (PMSM) demonstrates the cancellation of dominant sub and super harmonics, THD reduction, torque ripple reduction, and core loss minimization.

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

A novel winding embedded liquid cooling (WELC) concept is proposed to improve thermal management ... more A novel winding embedded liquid cooling (WELC) concept is proposed to improve thermal management of high power density slotless motor. This concept introduces thermal plastic based liquid cooling channels through the non-magnetic thermal plastic winding support for slotless motor. A comprehensive analysis on key thermal paths from all thermal sources to the ambient for the proposed WELC concept is presented. This paper demonstrates the efficacy of the WELC concept for a 120 kW slotless motor using computational fluid dynamics (CFD). A lumped parameter thermal network (LPTN) has also been developed for the WELC concept which has been validated using CFD analysis. It is found that the WELC concept can achieve a continuous current density of 23.3 A(rms)/mm2, which is 50% higher than that of a conventional axial water jacket cooling.

2017 IEEE Energy Conversion Congress and Exposition (ECCE), 2017

This paper proposes a slotless, lightweight permanent magnet (PM) motor for drone applications. T... more This paper proposes a slotless, lightweight permanent magnet (PM) motor for drone applications. This research analyzes the steps through FEA to achieve the torque speed profile required for drone applications with optimum pole count for the base speed. A comparison on slotless vs slotted stators is presented. In addition, an optimization using halbach configuration proves to give a superior design over conventional rotor designs. Finally, the analysis leads to a slotless stator with halbach PM configuration in the rotor for a 4 kW system achieving high power density, very low cogging torque and torque ripple, sinusoidal BEMF, and good system efficiency. The resulting low inductance (μH range) of the proposed machine opens up the opportunity of using wide band gap devices as the enabling technology.

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper presents a comprehensive design methodology to achieve wide field weakening operation ... more This paper presents a comprehensive design methodology to achieve wide field weakening operation in low inductance slotless or coreless Permanent Magnet Synchronous Machines (PMSMs). Design constraints and steps are presented to achieve wide constant power speed range (CPSR) and desired torque-speed characteristics. Extended Field weakening Range is achieved through a stator-embedded inductor integrated with the torque producing machine windings. System efficiency and power factor maps over the speed range are summarized with and without the embedded inductor. The concept helps to achieve the desirable extended torque speed range beyond the base speed. In addition to desired CPSR, this method also helps to reduce PWM induced current ripple, and core losses while improving high-speed efficiency for a slotless machine.

IEEE Transactions on Industry Applications, 2021

This article presents a comprehensive design methodology to improve the field weakening (FW) oper... more This article presents a comprehensive design methodology to improve the field weakening (FW) operation of low inductance slotless permanent magnet synchronous machines (PMSMs). The proposed concept of using a stator embedded inductor integrated with the torque producing machine windings helps achieve a wide constant power speed range (CPSR) and a desired torque/speed characteristics. Key performance parameters including system efficiency and PWM induced current ripple are summarized for scenarios with and without the embedded inductor in the entire operating range using 2-D finite element analysis. The concept helps to achieve the desirable extended torque/speed range. It also helps to improve the efficiency beyond the base speed operation for a high speed, high power machine. In addition to achieving desired CPSR, this method also helps to reduce the PWM induced current ripple, short circuit current, and current ripple induced core losses. A slotless machine with the integrated embedded inductor has been designed following the proposed design guidelines to extend the CPSR, and a prototype motor has been built to validate the simulation results with the experimental results.

IEEE Transactions on Industry Applications, 2020

A systematic approach based on a novel space-shifted three-layer winding (SSTLW) to eliminate bot... more A systematic approach based on a novel space-shifted three-layer winding (SSTLW) to eliminate both the sub- and superharmonics of fractional slot concentrated winding ac machines is presented. In this proposed three-layer fractional slot winding, the number of turns in one layer and the relative positions of other two layers are optimized to cancel subharmonics. The cancellation of superharmonics is achieved through series connection of two SSTLWs through effective doubling of the number of slots. The cancellation of the dominant sub- and superharmonics using this approach leads to reducing the total harmonic distortion, torque ripple, PM eddy current loss, and rotor core loss, while simultaneously improving power factor and saliency ratio. The proposed design methodology and ensuring improvements have been validated through finite element analysis for the widely used 12-slot/10-pole and 18-slot/14-pole permanent magnet synchronous machine (PMSM) configurations. A prototype three-layer winding is built for a 10-pole PMSM to validate the simulation results experimentally.

IEEE Transactions on Industry Applications, 2020

Tunnel FETs (TFETs) have been identified as the most promising steep slope devices for ultralow p... more Tunnel FETs (TFETs) have been identified as the most promising steep slope devices for ultralow power logic circuits. In this paper, we demonstrate in-plane InAs/Si TFETs monolithically integrated on Si, using our recently developed template-assisted selective epitaxy approach. These devices represent some of the most scaled TFETs with dimensions of less than 30 nm, combined with excellent aggregate performance with average subthreshold swing (SS), of around 70 mV/decade combined with I ON of a few µA/µm for |V DS | = |V GS | = 0.5 V. Here, we will discuss the device fabrication as well as the experimental electrical data. Extensive low temperature characterization and activation energy analysis is used to gain insights into the factors limiting device performance. Combined with the simulation study presented in part 2 of this paper, this will elucidate how traps are ultimately limiting the SS.

IEEE Transactions on Industry Applications, 2019

A slotless, lightweight permanent magnet (PM) motor with high pole count is designed and analyzed... more A slotless, lightweight permanent magnet (PM) motor with high pole count is designed and analyzed for a drone system that requires four motors of 0.5 kW each for a 2kW propulsion power to attain the required torque-speed profile. The design optimization was carried out using finite element analysis (FEA) which lead to a slotless stator with outer rotor Halbach PM configuration achieving high power density, zero cogging torque, low torque ripple, sinusoidal BEMF, and good system efficiency. The Halbach configuration is found to have superior power density, and torque ripple over conventional concepts for the aerial applications. The power density and efficiency of the slotless motor can be enhanced through the use of nonconventional thermoplastic material, and Halbach segmentation. The resulting low inductance of the slotless machine introduces a controls challenge, but it can be overcome with today's enabling technology of wide bandgap devices. A comprehensive analysis and comparison of the slotless design with an equivalent slottedradial version showed the superiority of the former. An optimum slotless design has been prototyped and test results along with analysis are presented.

2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019

2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018

2020 IEEE Energy Conversion Congress and Exposition (ECCE)

2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019

2018 IEEE Transportation Electrification Conference and Expo (ITEC), 2018

IEEE Transactions on Transportation Electrification, 2021

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

2017 IEEE Energy Conversion Congress and Exposition (ECCE), 2017

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

IEEE Transactions on Industry Applications, 2021

IEEE Transactions on Industry Applications, 2020

IEEE Transactions on Industry Applications, 2019

2015 IEEE Applied Power Electronics Conference and Exposition (APEC), 2015

ABSTRACT An accurate rotor resistance estimation model of squirrel cage induction motors (SCIMs) ... more ABSTRACT An accurate rotor resistance estimation model of squirrel cage induction motors (SCIMs) is developed in 3D FEA. 2D transient analysis was utilized for excitations in the 3D model to improve its accuracy over previous 2D and analytical methods. Rated and starting performance from the FEA model match with the nominal and locked-rotor performance of a 3-phase, 460 V, 1 hp test machine. A modified ring model has been proposed and machine torque-slip characteristics and nominal performance have been analyzed. The effect of slot opening and 4 classes of SCIM bar geometry have been investigated to analyze their relative performance. Finally, four different ring and bar combinations are suggested, with the modified rotor structure presenting gain in starting and rated performance compared to the test machine. Results present the design tradeoffs and performance analysis, first for a 1 hp SCIM and then extended for a higher power (10 hp) machine.

ABSTRACT A motor control system is provided. The motor control system includes a motor, a positio... more ABSTRACT A motor control system is provided. The motor control system includes a motor, a position sensor, a current sensor, and a control module. The motor has a rotor and a stator. The motor generates an output torque based on a phase current applied to the motor. The output torque generated by the motor creates a torque ripple that is within a predefined range. The position sensor monitors the motor to determine a rotor position. The current sensor monitors the motor to determine the phase current. The control module is in communication with the motor, the position sensor, and the current sensor. The control module includes a lookup table that stores values of phase current commands. The control module determines a phase current command from the lookup table based on the rotor position and the phase current.

IEEE Transactions on Industry Applications, 2015

ABSTRACT The paper presents a method of profiling the phase currents to minimize the torque rippl... more ABSTRACT The paper presents a method of profiling the phase currents to minimize the torque ripple of switched reluctance machines (SRM) operating in four quadrant mode over the entire speed range of operation. The method is based on machine and controller design through coupled simulation of the finite element based machine model and the dynamic controller model. The method considers the mutual coupling effect between conducting phases. The research quantifies the effect of sensor error and manufacturing build variations on the level of torque ripple minimization. The mitigation processes to address the issues in mass production are also presented.