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Since the introduction of mica paper and synthetic resin-based taping insulation for rotating-machines in 1950s, only evolutional improvements in their properties and processing have been made. Due to its challenging nature, much of recent insulation research has been focused on the aspect of reliability rather than performance enhancement. This paper presents the development and performance evaluation of a revolutionary nanostructured insulation in the manufacturing of large propulsion motors with game-changing torque density and payload efficiency for marine Next Generation Integrated Power System. It is demonstrated that nanostructured insulation based on 2D-platelet fillers could offer significant improvement over conventional insulation system in electrical, dielectric, thermal and mechanical properties. Optimal nanostructured insulation formation identified through a Design of Experiment study exhibits high thermal conductivity of $>0.8$ W/( $\text{m}\cdot \text{K}$ ), high breakdown strength of >40 kV/mm, low dielectric constant of less than 5.5 and low dielectric loss factor of less than 2.5% at 155°C. Voltage endurance tests on coupons with optimal formulation, in accordance with IEC 60343 standard, demonstrate satisfactory endurance life. Furthermore, a multi-physics finite-element-analysis model of the winding in a medium-voltage electric motor is established to perform electromagnetic and thermal analyses in ANSYS under various temperature boundary conditions. The study indicates a remarkable increase of 14% in torque handling capacity of a motor wound with proposed nanostructured insulation material when compared to an identical motor wound with conventional micaceous insulation.

Common-mode voltage (CMV) is of great concern in voltage source inverter (VSI)-fed motor drive systems. The pulsating CMV introduced by the VSI contributes to significant common-mode and bearing currents, which may lead to electromagnetic interference (EMI) problems and bearing failure. The presence of highest CMV occurs in a two-level VSI when zero voltage vectors are engaged. To combat the adverse effect by CMV, an integrated active zero-state switch (IAZS) can be adopted for the VSI to achieve reduced CMV when zero voltage vectors are desired. In this paper, an optimized pulse-width modulation (PWM) scheme is proposed to fully exploit the IAZS. The new zero voltage vector initiated by IAZS plays an important role in minimizing both amplitude and frequency in CMV. Simulation as well as experimental results have validated the effectiveness of the proposed modulation scheme with IAZS.

This paper investigates the dielectric stress and leakage current density as seen by medium-voltage motor stator ground-wall insulation when the stator winding is excited by 3-, 5-, and 7-level multilevel inverter output waveforms. Effect of firing angle on insulation stress is also studied for a 3-level multilevel inverter. Results show that in addition to the number of output voltage levels, PWM wave shape is also important. Both these factors work together to aid or inhibit the effect on the insulation health. Strong correlation is shown between the increase in the voltage RMS value and increase in dielectric stress when ignoring the dv/dt impact for a fixed DC input voltage and operating frequency of the inverter. Similarly, the dielectric stress in the stator insulation increased with an increase in firing angle, since larger firing angles led to higher RMS voltage values.

Advent of Wide band-gap (WBG) SiC and GaN devices has revolutionized the All Electric Ship (AES) technology as they provided a major push to move from conventional 2-level inverters towards multilevel inverters. WBG multilevel inverters facilitate high voltage, high-frequency operation and improve the performance of shipboard electric systems. However, their effect on insulation systems needs to be explored to better plan and design electric drives for longer durability and reliability. This paper investigates the effect of a 7-level active neutral point clamped (ANPC) SiC multilevel inverter on medium voltage cable insulation and motor stator ground-wall insulation. The simulation of ANPC is done in ANSYS Twin Builder. The dielectric stress and leakage currents in the cable and motor stator-insulation system have been analyzed in ANSYS Maxwell.

Health of insulation systems has been a critical concern for the electric power industry for line-frequency applications. The use of wide bandgap (WBG) semiconductors in power converters has led to more interest in studying high switching frequency effects on insulation material, especially in medium-voltage (MV) applications. Higher voltages and switching frequencies used in inverters subject insulation material in a motor drive to higher dielectric stress and cause premature failure. There have been many studies which address this aspect of insulation health and breakdown in inverter-fed machines. However, no literature investigates the impact of inverter topology on insulation. This paper aims at investigating the effect of inverter topology on motor stator ground-wall insulation. In addition to the output voltage waveform of different topologies, impedance of each topology is characterized over frequency to evaluate the system’s performance. Additionally, multi-physics simulations of an MV induction machine fed by two different inverter topologies are simulated in ANSYS to illustrate the impact of each topology on the electric field across the insulation material.

Reliability assessment of power semiconductor devices requires accelerated stress tests. Different test methods might produce different results. In this paper, two different test methods are used for on-state resistance degradation for Si MOSFETs: High frequency cycling and low frequency cycling. Presented results indicate that the degradation of on-state resistance occurs irrespective of which method is used. Additionally, gate-to-source capacitance degradation is shown where results show that the gate-to-source impedance degrades over time.

The theory of switched systems which focuses on stability and control synthesis of systems with multiple modes or different dynamics, has gained significant attention from control theorists, computer scientists, and practicing engineers. Switching between motor controllers due to sensor faults, faster response, or targeted dynamics, open a new dimension of shaping a motor drive's performance. There are three main types of control strategies for induction motor drives: constant volts per hertz (V/f) control, field-oriented control (FOC), and direct torque control (DTC). Multi-mode-controlled induction motor drive can be modelled as a switched system where each control mode results in different motor dynamics. In this paper, a comprehensive state-space model of an induction motor drive under different control mode is developed11This work is supported by the National Science Foundation under Award 1752297.. Detailed analysis as well as simulation results are included to demonstrate the validity of the state-space representation for induction motor under different mode.

Modeling faulty behavior of systems has benefits in diagnosis and control. In this paper a data-driven method, dynamic mode decomposition with control (DMDc), is employed for modeling an inverter-fed induction machine. Results are shown and compared for two scenarios: A step input change and an inverter fault. For both cases, the algorithm can correctly predict behavior of the system. The advantage of this model is its independence from the system parameters. The results show promise for data-drivenfault diagnostics and system modeling.

Wide bandgap (WBG) power semiconductor devices, such as SiC and GaN, have broadened the applications of motor drives in medium- and high-voltage regimes by pushing the limits of voltage, frequency, and power. These advantages of WBG inverters are being leveraged in aircraft and ship industries as they move towards next generation more- and all-electric designs. While the superiority of WBG technology in terms of faster switching, greater voltage breakdown strength, and short recovery time are known, its effect on the motor drive insulation is relatively unknown. This paper focuses on high-voltage high-frequency WBG inverters and analyses their effect on medium-voltage machine insulation. Specifically, analysis of dielectric stress and leakage current density is carried out on a 3-phase medium voltage motor's stator ground-wall insulation excited by a 2 level hex-bridge WBG inverter and a 3 level multilevel inverter in Ansys Maxwell and the results are presented.

Recently, electric utilities have been scrutinized worldwide for their environmental impact, depletion of resources, and the consistently rising cost of electricity to customers. All these issues could be reduced if residential customers changed their demand patterns. This research focuses on one of the most common demand-side management programs, which consists of time-of-use (TOU) tariffs. This tariff system has the potential to reduce peak energy demand, which will decrease costs and carbon dioxide emissions from utilities. Also, this system will allow more efficient use of existing electricity generation and network capacity. In this paper, an optimal TOU tariff system is proposed, and its impact is assessed on a dataset of residential users in a town where smart meters are installed. Changes in the electricity demand profile and ability of the electrical supply to support loads with no or minimal load shedding are studied.

This paper presents a system-level fault tolerant method for microgrid inverters. It is applied by adding a controlled bidirectional switch between parallel inverters to allow for rerouting power during faults. The method is simulated and verified on PV inverters as well as grid-interfaced batteries. Results show that it is possible to recover significant amounts of curtailed power lost from distributed energy resources when their power electronics interfaces suffer from faults.

This paper presents open-circuit fault analysis and diagnosis of a four-phase interleaved dc-dc power converter. The converter operation mode is first discussed in healthy condition. All fault cases are analyzed and discussed. A reconfiguration method is proposed for fault mitigation at level of the interleaved converter. Results are shown to validate the proposed reconfiguration method, where the converter’s output voltage is maintained at the desired value irrespective of which switch fails.

Conducted electromagnetic interference (EMI) has been a major concern in designing power converters, requiring additional filtering components. Passive EMI filters, which are composed of inductors and capacitors, usually occupy a great portion of the volume and weight in power converters. Active EMI filters (AEF) or hybrid EMI filters (HEF) are best candidates over traditional passive EMI filters to achieve higher power density in power converters. In this paper, a novel design of transformer-less AEF is proposed with the application in AC-DC power converters. The proposed design features feedforward control and is based on the concept of virtual impedance enhancement. A prototype of proposed AEF is built and tested with a commercial power adapter in the lab. The effectiveness of the proposed AEF in conducted EMI reduction is validated through simulation and experiment.

DC-link capacitors are at the heart of every power electronic inverter. A major drawback of DC-link capacitors is their aging factor which is due to various thermal and electrical stresses. This results in reduced system efficiency and complete system failure if left untreated. This paper proposes a data-driven condition monitoring system for the DC-link capacitor in grid-tied solar inverters. Compared to the literature, the condition of a DC-link capacitor is estimated without directly predicting the value of its capacitance or ESR. By treating the solar inverter system as a black box and by using the existing system sensors, the proposed condition monitoring method outputs the condition of the capacitor and classifies it as healthy, half-degraded or fully degraded. The proposed method is non-invasive and low-cost, where no additional sensors are required. By relying on classification techniques, this work addresses the difficulty of collecting real-world datasets with small incremental capacitance steps used in training regression models that predict capacitance values. Features not previously used in the literature are explored and result in very high classification accuracy. The proposed method is tested on a single-stage, single-phase grid tied PV inverter simulation model. The proposed method achieves 99% accuracy, a value similar to that found in the state of the art. The feasibility of the proposed method is tested on a low-cost microcontroller.

Medium Voltage DC (MVDC) power systems have become more prevalent in industry, specifically marine distribution systems due in part to improved power density among the topology’s components. One drawback to MVDC systems is the ripple generated from the MVDC active rectifier, which can affect downstream loads (e.g., propulsion loads) which are fed by the MVDC bus. This paper explores an MVDC series DC active filter (SDAF) which is designed to attenuate unwanted harmonics present on the MVDC bus, leading to improved power quality of the system with tight and rapid control over the DC bus voltage. The addition of representative loads such as an AC permanent magnet synchronous motor (PMSM) is also explored.

This paper presents control design for a multi-input single-output dc-dc power converter, which is proposed to interface two battery sub-modules, or one battery and one fuel cell with the dc rail in an electric vehicle. Using an advanced control method, the system should ensure that the output voltage remains constant even when the load changes. The advantage of these types of converters is the high voltage gain and the reduction in the capacitor size on the output, while maintaining two channels to support the dc rail. A fair comparison between LQI and conventional control scenarios is done. The modeling of the converter, the LQI controller dynamics and the comparison results are presented in this paper.

Multi-level inverters (MLIs) have shown popularity among medium voltage marine drives, especially as they allow for increased reliability through reconfiguration. Many of today’s voltage source inverters (VSI) utilize space vector pulse width modulation (SVPWM) compared to sinusoidal PWM (SPWM) due to the advantages of SVPWM in providing increased modulation index. Today’s MLIs are limited in the number of levels for various reasons. This includes the ability to stack a large number of switches and coordinate their turn on/off transients, availability of control platforms that provide enough PWM channels, and ability to produce large space vector maps. This paper’s main focus is to create a method for direct calculation of the switching sequence for neutral point clamped (NPC) inverters, for any Nlevel inverter, which is essential when MLIs are reconfigured for different levels to mitigate semiconductor switch faults. Calculation of the desired vertices to achieve a certain voltage vector is purposed through a novel projection and mapping of the reference vector in the space vector diagram.

1Common-mode voltage produced by voltage source inverters is of great concern in motor drives because significant amount of common-mode conducted/bearing current is induced and interferes with system operation. As an alternative to inserting bulky passive filters to attenuate common-mode current, a new topology "active zero-state switch (AZS)" is proposed. Minor adjustment to standard space vector pulse width modulation is also made to realize the proposed scheme and achieve reduced common-mode voltage. The new topology and adjusted modulation scheme are shown to effectively reduce common-mode voltage in a standard commercial voltage source inverter.

This paper presents a new approach for maximum power point tracking, namely, adaptive ripple correlation control (ARCC). Finding the proper value of the control law gain for traditional ripple correlation control (RCC) is not straightforward and does not adapt to significant changes in the solar irradiance and temperature. This paper presents a fast and robust method that adapts the control law gain k in order to achieve maximum power point tracking with small power ripple content p. The paper starts with a review of the basic concepts of ripple correlation control. We then propose an adaptation technique with three variants: Two fixed gain values, one fixed gain value and another dynamic value, and two dynamic gain values. Afterwards we present simulation results that validate the quick and robust response of our proposed methods compared to P&O and INCO. Next, a comparison to traditional RCC and a comparison between control gain of various methods are presented. Finally, we conclude by presenting tips on setting up the fixed and varying gain values.

This paper presents a novel method for obtaining the control gain for the integral control law of Ripple Correlation Control (RCC) for Maximum Power Point Tracking. The control gain in the standard RCC is not straightforward to obtain and does not adapt to significant changes in irradiance and temperature. Our proposed method is based on estimating the maximum power point (MPP) value for a given solar panel model as a function of irradiance and temperature. We then uses a PID controller to set the control gain such that MPP is attained. The paper starts with a review of basic concepts of ripple correlation control. Next, we present a curve fitting approach for estimating the maximum power point. The set point is then used along with the measured value of power to obtain an error signal for the PID which generates our adaptive/corrective control gain k. We then present simulation results for several irradiance settings. A sensitivity analysis and an analysis on the number of points required for the MPP fit are then presented. Finally we compare the proposed model based RCC to the traditional RCC.

This paper investigates the effect of impact factors (IFs) to harmonic content of an electric machine drive circuit, post-fault reconfigured multilevel inverters (MLIs) by using an accurate mathematical model, and impact of reconfiguration methods on THD. Due to the difficulty of analyzing harmonic content of MLIs mathematically, software tools are typically used to simply calculate the value of THD as metric. In this paper, an accurate mathematical model including both low- and high-frequency contents of harmonics in MLIs is utilized to derive the general expression of their output voltage THD. The effect of IFs on harmonic content are analyzed based on the general expression. Simulations and experiments are performed to validate the proposed mathematical model. The impacts of the reconfiguration methods on THD are analyzed. The impact of THD and other essential metrics on power quality are analyzed, and an minimal degradation of power quality caused by reconfiguration methods is proposed.

This article models an all-electric ship as a multidrive marine propulsion system from an electromechanical perspective and evaluates the overall losses in the system at various inverter faults. The model can be divided into electric drive controls modelling and the actual ship model. The electrical drive part of the model consists of the supervisory controller and electrical motor drives along with all its losses, while the ship model accounts for the hull resistance loss, thrust power calculations and the propeller losses for a YP yard patrol craft. Losses of the multi-drive propulsion system are evaluated under normal-mode and limp-mode operation and the impact of faults and reconfiguration of load on system losses are studied.

In electric drives, semiconductor devices are susceptible to faults due to high switching stresses. An unsupervised principal component analysis (PCA) approach that utilizes the on-state median values of voltage and current signals as features is proposed; it is computationally efficient for realtime operation. A key innovation is handling variations of the operating point in the feature space using exponentially weighted samples to recursively compute the time evolution of means of on-state features used in a PCA-based anomaly detector. Data from accelerated tests on commercial SiC devices are used to validate the effectiveness of the proposed approach in predicting incipient semiconductor faults. An experimental setup is also used to demonstrate real-time implementation of the proposed method.

In this paper, a new sensorless scalar control capable of enhancing torque capability for induction motor drives at low speeds is proposed. The proposed control addressed the problem that the conventional volt-per-hertz (V/f)control suffers from: torque capability is significantly impaired at low speeds due to stator flux weakening. A simple, encoder-free, but robust voltage compensation scheme for stator flux strengthening is therefore developed based on the dynamic model of an induction machine. Both simulation and experimental results are provided to demonstrate the superiority of proposed sensorless scalar control in torque capability enhancement and speed regulation over open-loop V/f, as well as stator resistive voltage compensated V/f control, especially at low speeds.

Rapid growing demand in higher power/torque density and payload efficiency of marine electrical propulsion can be addressed by a high heat transfer, indirect cooled stator insulation system. A novel nanocomposite insulation has been developed for high torque density machine through proper dispersion of 2D nanoclay in epoxy resin matrix to obtain improvement in both thermal and electrical performance. The voltage endurance testing shows that while neat epoxy resin failed within 500 hours, the nanocomposite survived for more than 3000 hours. The erosion rate, evaluated by the depth and volume, of nanocomposite was also significantly slower than the neat epoxy resin. The layered structure of clay is attributed to benefit the discharge resistance.

This paper proposes a fault prognostic method of multilevel inverters based on logic combinations that track the evolution of on-state resistance of semiconductor switches during their degradation. The proposed method utilizes the decreasing trend of semiconductor's on-state resistance when its degradation starts. The changed electrical properties and quantities in the circuit due to the change of the on-state resistance are used as indicators to prognose the failure of the semiconductor. Existing fault diagnosis and prognosis methods are first overviewed, and the limitations of these methods are highlighted. The advantages of the proposed prognostic method are 1) Need for a small amount of data for training and 2) Its computational requirements are simpler and faster than existing methods. A 5-level neutral-point-clamped inverter is simulated in MATLAB/Simulink and the simulation results indicate the effectiveness of the proposed prognostic method.

Most of the present high-voltage high-frequency insulation material testing focuses on the thermal and electrical properties of transformer oil and cable insulation. This paper elucidates the methodology and the experimental setup for high-voltage high-frequency testing of motor winding insulation. The experimental setup gives a pulsed output of voltages ranging from 2 kV till 10 kV peak-to-peak. The experimental setup is used to test the insulation material Kapton HN at different thicknesses [1mil, 2mil, 3mil and 5 mil) at a frequency of 3kHz. Results of the breakdown tests as well as the experimental setup are discussed in this paper.

Permanent magnet synchronous machines (PMSM) and induction machines (IM) have been the primary choice for propulsion system of electric vehicles (EV) and hybrid electric vehicles (HEV). However, other propulsion motor alternatives would be of interest due to the cost of rare-earth materials and simpler construction and manufacturing of these alternatives. Switched reluctance motors (SRMs) tend to be a good candidate with their high torque capability, robust structure, simple manufacturing, and independence from rare-earth materials. One prominent issue with SRMs is the acoustic noise initiated from stator vibration which can be reduced by controlling the radial force within the machine. This paper aims at developing and implementing a novel PWM-control-based noise and vibration reduction technique for switched reluctance motor drives. Experimental results have shown the effectiveness of the proposed technique.

The main focus of this paper is to propose a reconfiguration method to mitigate short circuit faults in neutral point clamped (NPC) multilevel inverters. Existing reconfiguration methods use either a redundant strategy or need additional devices pre-installed in the circuit which will increase the bulk and complexity of the system. Different from these methods, control-strategy-based reconfiguration is the most robust one since it does not require any change in the circuit configuration. However, most existing control-strategy-based methods distort the phase-to-neutral voltage which results in a degradation of power quality. To maintain control-strategy-based reconfiguration and avoid phase voltage distortion, a new and practical reconfiguration method is proposed in this paper. The proposed method is applicable to any NPC multilevel inverter. MATLAB/Simulink is used to simulate a five-level NPC inverter with non-idealities to verify the proposed reconfiguration method. A single-phase five-level NPC has been built in hardware, tested in healthy condition, and the proposed method has been validated in a low voltage condition.

The main focus of this paper is to investigate the effect of post-fault reconfiguration on the inverter voltage total harmonic distortion in multilevel inverters (MLI). Three different operating conditions are compared: 1) Healthy, 2) Faulty, and 3) Reconfigured using different methods that utilize inherent inverter redundancy. Literature mostly addresses balancing line-to-line voltage RMS when reconfiguring the inverter after fault occurrence, and line-to-neutral voltage and harmonic content after reconfiguration is ignored. However, line-to-neutral voltage quality is essential for per-phase analysis of Y-connected three-phase loads, neutral point power conditioning when the neutral exists, unbalanced loading conditions, and harmonic content analysis required by some grid interconnection standards such as AS4777 and IEEE1547. This paper first introduces an accurate analytical model to analyze the harmonic content of the line-to-neutral voltage. Then, two fault conditions are introduced into the model and verified in experiments. Three popular reconfiguration methods to mitigate these faults are then evaluated to analyze and compare harmonic content and RMS values of the achieved line-to-neutral voltages. Simulation and experimental results of healthy, faulty, and reconfigured conditions show that the predicted RMS and total harmonic distortion of the line-to-neutral voltage using the proposed model are accurate. Results also show that the line-to-neutral voltage is severely impacted by existing reconfiguration methods.

In this paper, a novel topology and control scheme for active electromagnetic interference (EMI) filter based on the idea of virtual impedance enhancement is proposed. To ease analysis, a general and simplified equivalent circuit is introduced to predict the conducted emissions incurred from switched-mode power converters. In addition, theoretical analysis is given to show how the proposed active EMI filter (AEF) should be designed along with simulation validation. A prototype of proposed AEF is implemented and tested to verify its effectiveness on proof-of-concept test setup. It is shown that the proposed AEF is capable of attenuating conducted emissions.

This article investigates the efficiency of a propulsion motor drive system due to load sharing. Two 2250HP-rated induction motor drives controlled via indirect field oriented control are simulated. Load sharing with different configurations is studied to analyze the impact of individual drive loads on the multi-drive system efficiency. Motor losses, Inverter losses and propeller losses are accounted for in efficiency calculations. For each load torque shared, the individual drive efficiency is calculated to determine which load sharing scheme provides maximum system efficiency. The approach for load sharing and system efficiency maximization is applicable to ship propulsion motor drives for maximum efficiency beyond rated load torques, and to other multi-drive systems.

This paper presents comprehensive validation tests of a recent qd0-frame core-loss model of three-phase induction machines at different load conditions. The machine is run at different frequencies/speeds and flux levels. These tests reinforce the model at different operating conditions before further model-based analysis and control design. Moreover, to properly use the model, a series of model parameter adaptation tests are applied under different frequencies (while the flux is constant) and different flux levels (while the frequency is constant). The effects of frequency and flux level on the model parameters as well as the copper and core losses are discussed. The simulated/estimated machine copper and core losses in the qd0-frame, which are calculated based on the core-loss model, are compared with the experimental counterparts at different testing conditions. Results show that the proposed core-loss model has excellent accuracy in estimating machine copper and core losses at different frequencies, loads, and flux levels with proper parameter adaptation of the model for each condition.

This paper presents a multi-physics finite-element-analysis (FEA) model that is used to study the impacts of a new nano-structured stator winding insulation material in large propulsion electric machines. Electromagnetic and thermal simulations are performed in ANSYS Maxwell and Steady-state Thermal respectively, and then linked in ANSYS Workbench interface. Detailed construction of the multi-physics FEA model is provided. Moreover, comparison of the proposed insulation material and the conventional micaceous insulation on machine's electrical, magnetic, mechanical and thermal performances is given, which indicates the superiority of the proposed insulation material as well as the possibility of re-rating the machine to higher current, torque and power ratings.

This paper proposes a generalized logic-based method for fault diagnosis in multilevel inverters that can be integrated with reconfiguration methods. Thus, both effective fault diagnosis and fault tolerance can be accomplished. To validate such integration, the proposed fault diagnosis method is applied to a five-level neutral point clamped inverter with three reconfiguration methods proposed in the technical literature. The effectiveness of the fault diagnosis method is verified with simulation and experimental results, while the integration of this method with the reconfiguration techniques is validated with MATLAB/Simulink simulations. Several simulation and experimental results under healthy and faulty conditions are presented to demonstrate the satisfactory performance of the proposed integrated fault diagnosis and recovery.

It has been identified in ONR Next Generation Integrated Power System (NGIPS) Roadmap that fundamental research in dielectric insulation research enables payload efficiency and affordable high power density of integrated electric propulsion motors. The objective of this study is to revolutionize electrical insulation in the manufacturing of NGIPS motors for military electric propulsion with game-changing torque density and payload efficiency through the development of nanostructured insulation with significant improvements in both electrical and thermal performance. This paper presents the progress of nanostructured insulation innovation, high field characterization, performance and insulation integrity validation under high voltage, high frequency multi-stresses. The thermal, dielectric and voltage endurance properties of novel nanocomposite insulation based on 2D-nanostructured platelet fillers were investigated. It was demonstrated that nanostructured insulation could offer significant improvement over conventional insulation system in electrical, dielectric, thermal and mechanical properties. A Design of Experiment was employed to study the effects of various 2D fillers and their interplay, and more importantly to identify the optimal nanostructured formulation with high thermal conductivity of >0.8 W/mK, low dielectric constant of less than 5, low dissipation factor of less than 3% at 150°C and high breakdown strength of >1000V/mil. Furthermore, disk samples with optimal formulation from Design of Experiment were fabricated for voltage endurance tests in accordance with IEC 60343 standard for evaluation of their long-term endurance life.

Conventional Maximum Torque-Per-Ampere (MTPA) control was derived from the three-phase induction machine model ignoring iron loss. A new MTPA control is proposed in this digest, whose accuracy is improved by considering machine iron loss using a newly published induction machine iron-loss model. The detailed derivation of the proposed MTPA control and possible enhancement of torque-per-ampere capability are provided. Moreover, a new MTPA controller is designed and implemented in MATLAB/Simulink. The proposed MTPA control is compared with the conventional MTPA control and the indirect field-oriented control (IFOC) of rated flux in simulation. It shows that the proposed MTPA control can provide significantly higher torque than the conventional MTPA control and IFOC at the same current level before saturation, or require significantly less current to support the same load torque. At low-load conditions, the proposed MTPA control shows higher efficiency with minor extra cost of dynamic performance compared to the IFOC. Since the advantages of the proposed MTPA control are more significant for certain combination of machine's iron-loss resistance and the operating frequency, possible targets of the proposed MTPA control are high-speed induction machines and induction machines of relatively large iron loss.

Scalar control has been the most popular control method implemented in induction machine drive systems. This paper presents an enhanced open-loop Volts-per-Hertz (V/f) controller aimed at strengthening the magnetizing flux of an induction machine when operated below its rated frequency. Instead of using the traditional constant V/f based on the idealized approximate steady-state machine model and/or simple stator voltage drop compensation, this method derives a new V/f ratio from a more accurate steady-state model which takes core loss into consideration as well as the stator voltage drop. In addition, a frequency boost strategy is introduced with the proposed V/f ratio for slip compensation. The analytically derived V/f ratio under different frequencies at rated load is then compared to experimentally obtained data to verify its effectiveness.

This paper compares two main topologies used for capacitive-coupled consumer wireless charging which has several advantages over inductive coupling including lower cost and no shielding requirements. There has been minimal data in the literature on preferred transmitter topologies. Two types of transmission systems are compared in simulations and experiments. An experimental charging system was built and tested with the evaluation of efficiency of h-bridge and half bridge transmitters. Preliminary experimental results indicate that the h-bridge is both economically and efficiency-wise advantageous over the half bridge in this application. The overall results show that the H-bridge is more efficient even though it has more semiconductor switching devices causing it to have a slightly higher cost. Immediate future work is implementation of closed-loop control for receiver-side voltage regulation.

This paper presents a real-time integrated model of a micro-grid to simulate its electrical energy infrastructure. This infrastructure includes two PV arrays, a fuel cell, and a diesel generator that support building loads when islanded from the utility grid. The paper reviews existing models, which are usually available either as 1) low-level dynamic models, along with power electronics for specific components, e.g. PV system or fuel cell, or 2) high-level such as with conventional power systems where power electronics are ignored due to their faster dynamics. The proposed modeling strategy for sustainable power generation is emphasized for both grid-connected and islanding modes and combines slow and fast dynamics where both a micro-grid and related power electronics dynamics are simulated to show how a high-fidelity model can be used in a dynamic micro-grid environment. A synchronized regulator for islanded mode is presented. The PV arrays and fuel cell are assumed to be always available and variable irradiance conditions (e.g. nighttime) and the change of hydrogen and oxygen densities of fuel cell are shown in the paper. The diesel generator is used for black start or when the utility grid voltage or frequency drop below a threshold during which potential grid collapse could occur and the micro-grid goes into the island mode. The micro-grid model is simulated using a real-time simulator so that longer case studies and scenarios can be studied without ignoring fast dynamics. The main contribution of this paper is that both these time scales (slow and fast) are integrated in this real-time simulation platform for more realistic performance analysis. The results show the ability of the integrated micro-grid simulation to function in both grid-tied and islanded modes.

In this paper, a comprehensive behavioral efficiency model of an electric motor drive system is proposed. The proposed model includes all possible motor drive losses without ignoring, approximating or assuming any of the inverter or machine losses, which are usually done for other efficiency models, hence the model is comprehensive. The input (DC electrical) and the output (mechanical) power of the motor drive system were measured and recorded for different drive operating points. These data were used to build the behavioral model through surface fitting using MATLAB. Different kinds of surface fits were used and discussed, and their effectiveness was evaluated. Moreover, a mathematical expression extracted from polynomial surface fit was used to derive the maximum efficiency point. The accuracy of this approach was verified with an additional experimental dataset not used for surface fitting. The proposed model can be easily integrated when designing, manufacturing and commissioning electric drives using rapid prototyping tools, and when designing maximum efficiency or minimum power loss control algorithms.

This paper provides a comprehensive analysis and comparison of different rotor bar material in squirrel-cage induction machine from electrical, physical and economic perspectives in order to explore the impacts of rotor bar material on machine efficiency with physical and economic considerations. Specifically, aluminum, copper and silver are selected in this work and studied on three machines of different ratings, where silver is proposed as a hypothetical rotor bar material to open discussion and to explore potential possibilities. To provide an overall analysis, an analytical model and a finite-element model of an induction machine are used in this work with their focus on machine efficiency and magnetic flux distribution, respectively. It shows that a silver rotor can provide the highest efficiency under all tested loads and machines with efficiency enhancement of 0.20 to 1.55 percentage points compared to the aluminum counterpart depending on the machine rating and load. Moreover, better performance, such as larger output power, smaller starting torque, more concentrated magnetic flux distribution, etc., are observed with the increase of rotor bar conductivity. However, the significantly high price of silver could impede its usage in most applications currently and copper rotor bar is believed to have the overall superiority among the three kinds of material, although it suffers from casting issues due to its high melting points. Silver rotor bars or silver alloys may be used in energy-limited areas where high efficiency is needed to compete with certain magnetic material.

This paper proposes reliability block diagrams for various photovoltaic (PV) system topologies and evaluates their reliability functions and mean time to failure (MTTF). The paper presents sensitivity analysis of the system MTTF with respect to individual failure rates of power electronic converters. The proposed approach can be used to determine reliability specifications of required converters in terms of desired MTTFs based on a desired PV system MTTF. This creates a reliability feedback loop to refine the PV system topology leading to a “design for reliability” approach. Results and reliability models proposed in this paper can be used for further comparing the reliability of different power electronic topologies in PV applications, and can extend to a wide range of energy systems utilizing power electronic converters.