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This letter gives the correction to a few mistakes in the illustrations of a paper published by the authors in the IEEE Transactions on Energy Conversion, vol.17, p.90-4, Mar. 2002.

During a session of the first Intersociety Energy Conversion Engineering Conference, a panel discussion dealt with approaches to nonconventional energy conversion education. This short paper covers the contribution of this author. It is realized that these topics should be covered during university studies; however, the question of where in a curriculum, or when during a student's university career formal courses should be offered, has not yet been answered. The author suggests that only a small number of engineers are needed in this area, and that there is really no space in any undergraduate curriculum to give these topics the amount of time they require. Accordingly, the place for such studies is on the graduate level, at the very few universities which can expect to interest a sufficiently large number of students in order to develop and carry on a specialized program in an economical way.

Dual-active-bridge (DAB) based DC-DC converter is usually chosen for energy conversion. In this paper, there exists many coupled relationships such as the controversy between local minimum current stress and transmission power, which influence efficiency promotion greatly. To analyze complicated coupled relationship and obtain the global minimum values, after unifying backflow power and transmission power into one integral function, a novel extended-phase-shift (EPS) control based on complete differential algorithm is proposed, which can not only eliminate the backflow power completely, but can realize a type of multi-objective optimizations including improvement of transmission power and decrease of current stress. Through the proposed method in this paper, the efficiency can be improved gradually. Moreover, the coupled relationships among variables are clarified clearly, which can avoid power loss increase during optimization. A DAB-based prototype is established and the experimental results verify the correctness and effectiveness of the proposed method.

After decades of operations, the first batches of offshore wind farms (OWF) are approaching the end of service lifetimes, while the demand for energy transformation is continuously pushing countries around the globe to construct larger OWFs. Therefore, the old OWF's repowering and scale-expansion becomes a possibly-feasible plan which deserves more researches. This paper firstly analyzes the potential benefits of combining the repowering and expansion parts in collector system topology design, which is followed by further analysis and mathematical verifications of economy and reliability advantages for applying cross-substation incorporation (CSI) to the collector system. To achieve the optimal topology design for OWF repowering and expansion, this paper also proposes a multi-layer optimization framework that consists of an offshore substation (OS) refinement layer, an OWF partition layer, and an intra-zone cable connection layer. The whole optimization concerns the wind turbine (WT) capacity deviation between the repowered part and the expanded part, and the final output is generated with the aim of achieving optimal economy and reliability. The proposed topology is tested and compared with traditional radial and ring topologies on a benchmark collector system, and the results verify the high performance in the economy (both short-term and long-term) and reliability.

The individual-machine-equal-area-criterion method already shows potential in the transient stability assessment of multimachine systems. This two-paper series systematically analyzes the transient characteristics of the system trajectory from a genuine individual-machine transient energy perspective. In the first paper, the stability property that characterizes a critical machine is investigated by defining the residual kinetic energy, which only occurs at the maximum individual-machine potential energy point. We indicate that the transient energy conversion inside a critical machine can delineate the trajectory stability of the machine. In this way, the mapping between individual-machine kinetic energy and individual-machine trajectory can hence be established. Simulation results show that the individual-machine transient energy describes the system trajectory more precisely than the superimposed global transient energy in terms of transient stability analysis, and we also demonstrate that the conjecture in early individual-machine studies might fail in special simulation cases.

Electromechanical coupling in kinetic energy harvesters is the key aspect of these devices that ensures an effective energy conversion process. When modelling and designing such devices, it is necessary to incorporate electromechanical coupling correctly since it will determine the amount of energy that will be converted during its operation. As the engineering community prefers compact (lumped) models of such devices, the conventional choice of the lumped model for the electromagnetic type of electromechanical coupling is linear damping, proportional to the velocity of the mechanical resonator in a harvester, leading to the idea of maximizing the velocity in order to improve the energy conversion process. In this paper, we show that electromechanical coupling in electromagnetic kinetic energy harvesters is inherently nonlinear and requires a number of aspects to be taken into account if one wants to optimize a device. We show that the proposed model, which is based on first principles of electromagnetics, can be reduced to a nonlinear lumped model that is particularly convenient for analysis and design. The modelling approach and the resulting lumped model are verified using two MEMS electromagnetic harvesters operating over a range of frequencies from 300 to 500 Hz (Harvester A) and from 50 to 70 Hz (Harvester B) generating from mV (Harvester A) to few volts (Harvester B) of RMS voltage, respectively. The proposed modelling approach is not limited to energy harvesters but can also be applied to magnetic sensors or other MEMS devices that utilise electromagnetic transduction. Science Foundation Ireland Author states that this is a template - AC

Recently, electrical engineers are paying great attention to develop oceanic wave energy conversion technologies based on the piezoelectric materials because of their excellent conveniences. Piezoelectric oceanic wave energy converters (OWECs) have several benefits over the others such as its small size, lightweight, no requirement of using intermediate device as well as having less negative impacts on the oceanic environment. Various review and research papers focus on the piezoelectric devices, their operation and application for oceanic energy conversion. But, to the best of the authors' knowledge, none of the existing research or review papers present detailed scheme of piezoelectric device based power generation covering all the relevant topics as depicted in this review. This article focuses different aspects of piezoelectric device based oceanic wave energy conversion technology including prospect, historical development, classification, operating principle, configuration, arrangement, model, processing, post-processing, and their test setups. In addition, technical challenges, future direction of research and critical review are also illustrated. It is assumed that, this article would play a significant role for the future development of piezoelectric OWECs and the researcher working in this field.

The presence of harmonics in solar Photo Voltaic (PV) energy conversion system results in deterioration of power quality. To address such issue, this paper aims to investigate the elimination of harmonics in a solar fed cascaded fifteen level inverter with aid of Proportional Integral (PI), Artificial Neural Network (ANN) and Fuzzy Logic (FL) based controllers. Unlike other techniques, the proposed FLC based approach helps in obtaining reduced harmonic distortions that intend to an enhancement in power quality. In addition to the power quality improvement, this paper also proposed to provide output voltage regulation in terms of maintaining voltage and frequency at the inverter output end in compatible with the grid connection requirements. The simulations are performed in the MATLAB / Simulink environment for solar fed cascaded 15 level inverter incorporating PI, ANN and FL based controllers. To exhibit the proposed technique, a 3 kWp photovoltaic plant coupled to multilevel inverter is designed and hardware is demonstrated. All the three techniques are experimentally investigated with the measurement of power quality metrics along with establishing output voltage regulation.

In this paper we present a solution for real-time multi-FPGA simulation of energy conversion systems based on the Latency-Based Linear Multistep Compound (LB-LMC) simulation approach. The approach relies on a nodal decomposition approach derived from multiport network analysis, and fast parallel communication between Field Programmable Gate Array (FPGA) devices. The results presented in this paper –using a microgrid example– demonstrate how the developed real-time platform overcame the resource scalability limit of single FPGA solvers while achieving a time step size of 100 nanoseconds.

This paper proposes an analytical model to calculate the airgap function and inductance, which can be used to get an optimal design during the initial design phase. It investigates the relationship between the design parameters of the rotor and the motor performance.This paper is under review in IEEE Transactions on Energy Conversion.

Marine wave energy is characterized by high power density and worldwide distribution, thus being an important renewable energy source. To better utilize the power, a novel dual-stator high-temperature-superconducting linear vernier generator (DS-HTS-LVG) is proposed in this paper. A special excitation winding arrangement with different pole pitches is presented in this paper to increase the thrust density and power factor. The configuration and operation principle of the presented machine are demonstrated. Some key parameters of the machine are optimized to achieve better electro-magnetic performance. Moreover, by using the finite-element method, the performance of the proposed DS-HTS-LVG is compared with a conventional DS-HTS-LVG. The results show that the proposed generator has ~36% higher power density and increases the power factor from 0.38 to 0.57, verifying the superiority of the proposed machine and the effectiveness of the novel winding arrangement.

The dimensioning of the prime mover of a wave energy converter (WEC) is a key step in the entire WEC design process. This paper presents an automatic optimization methodology that focuses on the preliminary dimensioning of a point absorber WEC. By means of the proposed methodology, the engineering problem of dimensioning a WEC becomes a mathematical optimization problem. The methodology is based on a multi-objective differential evolutionary algorithm that optimizes the geometry of a heaving two-body point absorber WEC where the power take-off (PTO), its control, and location are preselected. The algorithm considers two cost functions (WEC surface and annual energy extraction) and several constraints related to PTO characteristics or wave climate. This paper proposes a case study based on a real WEC development project in order to present the methodology. In addition, the impact on the results of the definition of the optimization problem is evaluated. The changes in cost functions and constraints evaluated have led to different geometry solutions. This automatic methodology could be easily integrated in the entire WEC design process, providing a set of properly selected base cases to focus on the detail engineering, among other potential applications.

Maximum power point tracking (MPPT) algorithms have become key elements in improving solar photovoltaic (PV) energy conversion systems. Numerous algorithms have been developed and implemented successfully in recent technology. This paper intended to introduce an improved incremental conductance (IC) algorithm based on the mathematical residue theorem. The major difference introduced in this paper is in considering the residual value of the IC to ensure MPPT achievement. Ensuring the minimal residue in IC improves the operation and eliminates the fluctuation around the operation points. Improved energy conversion efficiency has been achieved and the system has been proved mathematically and by simulations. One of the advantages that the system is free of parameters affect and atmospheric condition data are not required. The controller gain is based on sliding mode compensator to improve the uncertainty handling ability of the developed control approach.

The need for lighter and smaller railway traction drives and recent advances in power semiconductor technology have resulted in a new energy conversion paradigm, one without the classical heavy and bulky line-frequency transformer. Several multilevel topologies have been introduced over the past years, all having in common the use of medium-frequency (MF) energy conversion to reduce the weight and volume of the magnetic components. This paper is concerned with the design of the input filter for an MF traction converter, focusing on a solution that minimizes the filter's overall mass. Two filter topologies are investigated, namely a single-pole filter (inductor) and a passively damped $LCL$ filter. The paper first describes the requirements to be fulfilled, establishes the spectrum to consider for the design, and proposes a method to determine the initial parameters of the filter's components. The results show that an $LCL$ -type filter achieves considerable weight savings in comparison to the single-pole solution.

To maximize energy conversion, real-time control of a wave energy converter (WEC) requires knowledge of the present and future excitation force ( $F_{\rm{ex}}$ ) acting on the device, which is a nonmeasurable quantity. The problem of estimation and forecasting of $F_{\rm{ex}}$ becomes more challenging when arrays of WECs are considered, due to the hydrodynamic interactions in the array. In this paper, a global $F_{\rm{ex}}$ estimator for a complete WEC array is developed and compared to a set of independent estimators, which utilize information local only to each device. A significant question is whether the array of measurements is sufficient to compensate for the greater complexity of the wave field, compared to the isolated body case. The paper shows that the global estimator is always more accurate than the independent estimator, improving up to $\text{45}\%$ the estimation accuracy of the independent estimator. Regarding prediction, two different $F_{\rm{ex}}$ forecasters for a WEC array are compared: a global forecaster, utilizing $F_{\rm{ex}}$ estimates from the full set of array devices, and an independent forecaster, utilizing only a local $F_{\rm{ex}}$ estimate. We demonstrate that the global forecaster achieves more accurate results, not only compared to the independent forecaster, but also compared to the isolated body case.

This paper proposes a new family of electric motors based on the concept of an airgapless device. In this type of device, the rotor is allowed to touch the stator at a contact point, which maximizes the internal flux and, therefore, the electromagnetic torque. A higher torque density motor is proposed in this paper due to a reduced reluctance caused by zero airgap situation. A comparison with other high-torque-density electric motors demonstrates the advantages of the proposed airgapless motors. The proposed motor will maximize the generated torque, allowing these types of motors to be competitive in applications where hydraulic motors are prevalent, i.e., low-speed and high-torque requirements. Hydraulic motor systems face two major problems with their braking system and with low efficiency due to a large number of energy conversion stages (i.e., a motor pump, hydraulic connections, and the hydraulic motor itself). The proposed electric motor, unlike hydraulic motors, converts electrical energy directly to mechanical energy with no extra braking system necessary and with higher efficiency. The modeling of this machine with a minimum number of poles is discussed before a generalization is presented. A proof-of-concept electric motor with nine magnetic bipoles is built to validate the theoretical assumptions proposed in this paper.

The three phases of brushless dc motor (BLDCM) are involved in energy conversion during the commutation interval. A novel commutation analysis method of the BLDCM based on coordinate transformation theory is proposed in this paper, though this coordinate transformation theory is popular in the control of three-phase sinusoidal motors, such as induction motors and permanent magnet synchronous motors. The method is intuitive and easy to understand compared with the method based on circuit solving. Combined with the voltage vector diagram of the inverter, commutation control to reduce commutation torque ripple under low speed (LS_RCTR) and high speed (HS_RCTR) is deduced. However, under a heavy load and high-speed condition, long commutation time may result in commutation failure if these commutation controls to RCTR is adopted. To avoid that, commutation time must be controlled. Then, commutation control to reduce commutation time under low-speed (LS_RCT) and high-speed (two cases, named HS_RCT1 and HS_RCT2) are proposed. The improved control of BLDCM presented in this paper can coordinate commutation torque ripple and commutation time in full speed range. Finally, the feasibility and effectiveness of these methods are verified by experiment.

At present, most of the linear generators contain a heavy translator for converting wave power from the ocean into electrical power. As the translator is connected to the buoy, the buoy dynamic performance is reduced by the large mass and, as a result, low velocity of the translator would degrade the electricity generation of the linear generator. This problem has been minimized by the new design in this paper, where the translator is clipped off at first and split into two separate portions to minimize its weight. The secondary stator is magnetically coupled with a special m-shaped main stator which is used to flow the necessary magnetic flux. The weight of the proposed translator is 21.82% lower than that of conventional one and 49.1% by using a recently available permanent magnet with higher specifications. The finite-element method is applied in ANSYS simulation environment for the analysis and comparison between the proposed and conventional designs. Different parameters of the conventional and the proposed linear generator have been discussed in this paper. The simulation results show that the proposed design can generate the same amount of electricity as the existing one with almost half of the translator size. According to the mathematical model, it is understood that the dynamics of the translator would be higher for its lower mass and vice versa. Therefore, minimizing the translator size would result in decrease of mass, which increases the dynamics of the buoy connected to the translator.

The ever increasing need to extend battery life in IoT devices, self-powered sensors, and autonomous nodes highlights the need to reduce energy consumption as much as possible. One of the main issues still not fully addressed is the reduction of power consumption of sensors and measurement systems in standby mode, which represents a significant amount of the total power dissipation. In fact, nowadays, despite the continuous efforts, standby power is still far from being negligible. This paper exploits a new approach named “zero-current standby” to tackle this issue; moreover, due to the fact that the transducer implements kinetic-to-electrical energy conversion, a sensor that performs kinetic energy measurements is obtained and characterized. The proposed solution goes beyond the concept of the standby state itself, as it can actually be applied to appliances turned OFF. The design of a piezoelectric-based sensor able to measure kinetic energy is discussed in this paper. The proposed device will also allow zero-energy standby operation, with vibrations acting as trigger for sensor activation and data transmission via Wi-Fi. Numerical analysis, laboratory characterization, and experimental results of a complete working prototype are presented here, demonstrating both the suitability of the approach proposed and the improvement with respect to conventional strategies.

This paper addresses the issue of real-time control for applications, subject to physical constraints, involving an energy maximization objective. Typical application areas include renewable energy systems where, in spite of the fact that the raw energy resource is free, the capital and operational costs associated with the energy conversion process are not. In addition, economic energy delivery can only be achieved if the conversion device is operated efficiently. Previous approaches to this problem include model predictive control (MPC), but the computational cost associated with MPC can be high. Pseudospectral solutions show considerable promise in achieving a good balance between performance and computation, but currently available solutions deal with fixed-period optimization. In this paper, a receding horizon real-time pseudospectral control is developed, based on half-range Chebyshev Fourier basis functions, which can accurately represent harmonic signals in the application domain, while also efficiently dealing with the signal truncation effects associated with a receding horizon formulation. An application example, based on a wave energy converter, is used to illustrate the new control algorithm.

Along with the ever-increasing requirement of power and energy density in the electromagnetic launch field, the air-core compulsator has been the research focus for the last two decades. However, when considering the multiphase air-core compulsators designed for railguns, no existing published papers have investigated the different discharge processes and different performances caused by different phase numbers. This paper has investigated the different performances influenced by the phase number of the air-core compulsator. The current commutation is of great importance especially in the fast electromechanical energy conversion. The current commutation and pulse regulation in the discharge process of the multiphase air-core compulsator have been studied in detail. Three different railgun systems have been discussed in which a three-phase, a four-phase, and a novel five-phase compulsator are adopted. Besides, three sets of corresponding parameters have been designed and proposed for simulation under the premise that all compulsators have the same volume and weight. Different from the traditional applications in which the current commutation is always avoided, the key point in this paper is the utilization of the current commutation process. A new idea for the design of the phase number of the air-core compulsator is presented. The conclusion is pioneering and instructive to the design of the multiphase compulsator for railgun systems.

This paper presents a novel switched reluctance motor incorporating a new design methodology. The proposed structure is designed using distinct concepts including design considerations of salient poles and the motor energy conversion capacity. First, multiple techniques to increase the motor torque using these concepts are discussed. Then, the new design is introduced. Based on the concepts of maximum energy conversion and also providing a topology change process, a novel stator-segmented structure is proposed. The three-phase form of the proposed motor has six segments in the stator with four poles and a solid rotor with 22 poles. The novel motor's characteristics are initially obtained using finite-element analysis and shown to exhibit higher torque density when compared to the conventional structure. Finally, the performance of the new design and analysis methods described in the paper are verified by experimental results obtained by a built prototype.

Maximum power point tracking (MPPT) is an integral part of a system of energy conversion using photovoltaic (PV) arrays. The power-voltage characteristic of PV arrays operating under partial shading conditions exhibits multiple local maximum power points (LMPPs). In this paper, a new method has been presented to track the global maximum power point (GMPP) of PV. Compared with the past proposed global MPPT techniques, the method proposed in this paper has the advantages of determining whether partial shading is present, calculating the number of peaks on P – V curves, and predicting the locations of GMPP and LMPP. The new method can quickly find GMPP, and avoid much energy loss due to blind scan. The experimental results verify that the proposed method guarantees convergence to the global MPP under partial shading conditions.

With the wave energy conversion system (WECS) integrated to grid, the lack of satisfactory ability to ride through transient voltage faults will reduce the stability and reliability of the grid. In this paper, in order to enhance the low-voltage-ride-through (LVRT) capability of the WECS, the structure and the mathematical model of a magnetic-gear permanent magnet synchronous generator (MG_PMSG) and a float-type wave energy converter (WEC) are introduced firstly. The output power characteristic of the WECS is analyzed. Then, a novel coordinative LVRT control scheme based on supercapacitor energy storage system (SC_ESS) is proposed. The control scheme includes four modes which are determined by the severity of voltage sags and active power deviation of the WECS. Machine-side converter (MSC) control, grid-side converter (GSC) control and SC_ESS control are used coordinately in the four operation modes. The results of simulation and experiment have verified the effectiveness of the proposed control scheme in normal running conditions.

The double-sided tubular linear machine (DSTLM) has a more compact structure than general single-sided motors, resulting in a higher power density, typically at the cost of a higher cogging force. To reduce this aspect and make it more suitable for applications in wave energy conversion systems or elevator driver systems, a new tooth-cutting topology is proposed in this paper. The Schwarz-Christoffel (SC) mapping method is used to model and analyze the magnetic field and cogging force of the DSTLM. Based on the analytical model and the relationships between the cutting dimensions and the force performances, optimization is carried out by using a differential evolution algorithm (DEA). The optimization and the experiment results show that the proposed tooth-cutting topology can effectively reduce the cogging force at the small cost of weakening average thrust.

Digital control implementation is crucial in modern power electronic converters and energy conversion systems, as more complex control and friendly user interface are required. The fuel cell (FC) is a promising clean energy source and a reliable technology for niche applications providing high conversion efficiency. In this paper, a digitally controlled FC system is documented based on the boost-inverter topology that achieves both boosting and inversion functions in a single-stage. A digital signal processor TMS320F28335 is used to implement the control of the FC system in order to provide a number of benefits including low-cost, good performance, an easy implementation of a relatively complicated algorithm, and user friendly interface. The control design, analysis, simulation and experimental results are presented in the paper to confirm the performance of the digitally controlled FC system.

This paper presents the analysis of a performance-oriented electric motors diagnostics in modern energy conversion system. With increased demand for electrical energy in world industries, the population of energy conversion devices such as generators/motors has greatly increased. As emerging and not being a mature enough technology in the application of renewable energy conversion or electric-drive transportation, the protection and diagnosis of electric motors have been extensively studied for safety and reliability. Meanwhile, motor phase currents commonly involve random noise components generated by harsh energy system environments, low- and high-order harmonics interferences caused by power inverters and fast switching devices, and various other design imperfections. Therefore, it is quite challenging to model the overall noise content and eliminate the disturbance while detecting motor fault signatures. Due to the inherent random variation of motor noise statistics, the noise model and elimination strategy should also be adaptively updated according to instantaneous noise conditions through which detection can be done with predefined performance expectation. Several successful solutions in the literature have managed to perform a diagnosis under certain noise conditions; however, a detailed performance and adaptability analysis covering arbitrary noise variation has not been satisfactorily addressed. This paper mainly deals with performance oriented threshold design strategies for fault signature detection utilizing the noise statistics of the motor phase current signal. The proposed solution is generalized to cover arbitrary Gaussian noise variations and derive the optimal form of the threshold that satisfies user's prior detection quality expectations. The mathematical derivations are proved through statistical theory and the experimental verifications are performed by using a 3-hp motor setup.

The papers in this special section focus on energy conversion in next generation electric ships. These papers bring together papers focused on the recent advancements in energy conversion techniques used in electric ship technologies.

In this paper, a financial valuation method for energy hubs with conversion, storage, and demand-side management (DSM) capabilities is proposed. An energy hub is an integrated system of units, e.g., a combined heat and power plant and a heat storage, which allows the conversion and storage of multiple energy carriers. In this paper, an extended energy hub model is presented which additionally takes into account the possibility of performing DSM with the load(s) connected to the hub output. Taking into account the energy hub's flexibility to change its output power(s), its economic value is determined with a method based on Monte Carlo simulation. This method calculates an optimal dispatch of the hub for a large amount of possible price paths of the input and output energy carriers. By means of the proposed energy hub Monte Carlo valuation model, integrated systems of multi-energy conversion and storage devices can be valued together with load management schemes. In doing so, the energy hub's ability to flexibly adapt its output to uncertain and volatile market prices is explicitly considered.

In many modern energy conversion systems, a dc voltage, which is provided from a sustainable energy source or energy storage device, must be boosted and converted to an ac voltage with a fixed amplitude and frequency. In this paper, a switching pattern based on the concept of the conventional space-vector pulsewidth-modulated (SVPWM) technique is developed for single-stage, three-phase boost-inverters using the topology of current-source inverters. The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three-charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the dc input voltage. The developed switching pattern was experimentally verified through a laboratory-scaled three-phase 500-W boost inverter and the results are presented in this paper.

A scroll air motor, also known as a scroll expander, is a relatively new concept to pneumatic actuators. Its unique structure leads to its feature of high ability in energy conversion. In recent years, scroll air motors have been adopted by combined heat and power boilers, uninterrupted power supplies, and some other energy storage systems as a new mechatronic device for energy conversion. The paper aims to present the work in developing a complete mathematical model of the scroll air motor for analysis of scroll energy efficiency and the factors affecting energy efficiency. The work will be reported in two parts of the paper. The paper describes the derivation of spiral equations, chamber volume calculations, and the driving torque of the scroll air motor. The dynamic process modeling and energy efficiency analysis will be presented in Part II of the paper.

The growing penetration of hydrogen vehicles and modern energy conversion technologies strengthen the coupling of transportation and energy networks. This paper proposes a hydrogen supply infrastructure planning model for the integration of hydrogen vehicles and renewable energy. To flexibly meet the energy demand of hydrogen vehicles, the proposed model makes investment decisions for various facilities, including hydrogen pipelines, hydrogen refueling stations, power to gas devices, and renewable energy generators. Besides, with the pipeline transportation method applied, the hydrogen network is constructed and coordinated with the electricity and transportation networks. The multi-network synergistic effect is thus fully utilized, and brings higher operational flexibility and investment economy. Furthermore, a two-stage stochastic planning model is provided to accommodate the variability of renewable energy and traffic loads. To reduce the computational complexity of the proposed stochastic planning model, both linearization techniques and Benders decomposition algorithm are applied. Simulation results of the 8-node system and the 24-node system demonstrate the effectiveness of the proposed model and algorithm. Compared to the uncoordinated model, the proposed model saves by 11% of the total cost for the 24-node test system. Also, the computational performance of the Benders decomposition algorithm surpasses that of the basic algorithm by more than 24.6% in the two test systems.

At present, based on the piecewise linear inductance model, the main method for analytic calculation of phase current on switched reluctance generators is flux-linkage divided by inductance, and there is no analysis and deduction in detail on base of the obtained expressions of phase current. Expressions of phase current are solved by the separation variable method, and then the characteristics of current curve and the energy conversion relations are analysed in the paper. Also expressions of phase current are applied to the decision condition of current tendency and the analysis on magnetic field energy in the freewheeling mode. And a method to optimize the firing angle is proposed to get the most average electromagnetic torque. The results of simulation validate the theory in the paper and show that the theory is also applicable to the non-linear inductance model.

Power-electronics interface and the technique of pulsewidth modulation have been the heart of controlling the illumination intensity of lighting devices. It is, however, observed that for some lighting devices, the use of such a methodology leads to a lower energy-conversion efficiency (with a lower light intensity for the same amount of electrical input power) than potentially possible. The main problem is related to the saturable characteristic of the electrical-to-optical energy conversion, which follows that of an exponential characteristic, and the fast nature of this reaction in these lighting devices. This paper presents an in-depth discussion on the phenomenon and offers a solution to the problem. Specifically, it is proposed that an n -level type of driving approach to be adopted in the design and construction of power-electronic drivers for fast-response saturable lighting devices to achieve a quasi-optimal lighting efficacy. The result is energy saving for the same required light illumination. Theoretical proofs and experimental results are provided for verification. The topic of discussion in this paper and the proposed approach are not only applicable to the area of electronic circuits and lighting devices, but also to general controlled systems which comprise components that inherit a saturable and fast-reactive energy conversion characteristic.

A new electromagnetic-launcher (EML) performance parameter called the specific force is presented and analyzed in this paper. The specific force is the second derivative of the EML's force equation with respect to current and represents the force generated by the EML per unit square ampere, i.e., the EML's current efficiency. The specific force is independent of operating current and is defined for EMLs utilizing linear and nonlinear magnetic materials. The second derivative is termed as the specific force, since it unifies the various EML geometries so that only one force equation is required. The specific force, together with the energy-conversion efficiency, can be used as criterion to evaluate and compare EML geometries for various applications. The specific force for conventional railguns, augmented railguns, conventional helical launchers, and high-efficiency helical launchers is derived in this paper. The experimental performance of conventional railguns, augmented railguns, and conventional helical launchers are also analyzed in terms of their specific-force parameters.

In order to improve the efficiency of energy conversion for a photovoltaic (PV) system, a soft-switching boost converter using a simple auxiliary resonant circuit, which is composed of an auxiliary switch, a diode, a resonant inductor, and a resonant capacitor, is adopted in this paper. The conventional boost converter decreases the efficiency because of hard switching, which generates losses when the switches are turned on/off. During this interval, all switches in the adopted circuit perform zero-current switching by the resonant inductor at turn-on, and zero-voltage switching by the resonant capacitor at turn-off. This switching pattern can reduce the switching losses, voltage and current stress of the switching device. Moreover, it is very easy to control. In this paper, we have analyzed the operational principles of the adopted soft-switching boost converter, and it is designed for PV generation system. Simulation and experimental results are presented to confirm the theoretical analysis.

Population growth in the world along with rapid technological expansion of the society demand efficient, economically viable, and environment-friendly energy conversion systems. The previous theoretical and simulation works have demonstrated that a 500-Hz single-phase high-frequency ac (HFAC) microgrid is a novel step toward integrating renewable energy sources in a distributed generation system. This paper goes one step further in describing the practical implementation of HFAC microgrid with active filters for a small 1-kW system. The protection issues for both the source and series converters are also addressed in this paper by developing a new but simple protection scheme. In the experimental microgrid system, a universal active power line conditioner (UPLC) and a unified power quality conditioner (UPQC) are incorporated to control the power flow and power quality, respectively. Controllers for both the UPQC and UPLC are developed based on the instantaneous single-phase p-q theory, and controlled pulsewidth modulated inverters are then implemented to synthesize the desired compensating waveforms. The experimental results obtained confirm that the HFAC microgrid is a practical and useful step toward successfully integrating distributed renewable energy sources ensuring the improved system utilization.

This paper presents experimental results from a wave energy converter (WEC) that is based on a linear generator connected to a rectifier and filter components. The converter-filter system is installed onshore, while the linear wave generator operates offshore a few kilometers from the Swedish west coast. The power from the generator has been rectified with a diode bridge and then filtered using a capacitive filter. Performance of the whole conversion system was studied using resistive loads connected across the filter. The aim was to investigate the operational characteristics of the generator while supplying a nonlinear load. By changing the value of the resistive component of the load, the speed of the translator can be changed and so also the damping of the generator. The power absorbed by the generator was studied at different sea states as well. The observations presented in this paper could be beneficial for the design of efficient wave energy conversion systems.

Ocean energy conversion systems have recently seen renewed interest, stimulated mostly by today's increasing energy discussions. In addition to ocean current energy converters, several commercial ocean wave energy projects have already been undertaken; however, no clear economic model exists for developers to follow. Therefore, this paper focuses on U.S. economic factors that affect the use of wave power for generation of electric energy. These are addressed with regard to economic and business incentives for renewables and wave energy. This paper also investigates incentive programs needed to promote wave energy conversion technology.

In the framework of microgenerators, we present in this paper the key points for energy harvesting from temperature using ferroelectric materials. Thermoelectric devices profit from temperature spatial gradients, whereas ferroelectric materials require temporal fluctuation of temperature, thus leading to different applications targets. Ferroelectric materials may harvest perfectly the available thermal energy whatever the materials properties (limited by Carnot conversion efficiency) whereas thermoelectric material's efficiency is limited by materials properties (ZT figure of merit). However, it is shown that the necessary electric fields for Carnot cycles are far beyond the breakdown limit of bulk ferroelectric materials. Thin films may be an excellent solution for rising up to ultra-high electric fields and outstanding efficiency. Different thermodynamic cycles are presented in the paper: principles, advantages, and drawbacks. Using the Carnot cycle, the harvested energy would be independent of materials properties. However, using more realistic cycles, the energy conversion effectiveness remains dependent on the materials properties as discussed in the paper. A particular coupling factor is defined to quantify and check the effectiveness of pyroelectric energy harvesting. It is defined similarly to an electromechanical coupling factor as k2 = p2thetas0/(epsivthetas 33 CE), where p, thetas0, epsivthetas 33, Ce are pyroelectric coefficient, maximum working temperature, dielectric permittivity, and specific heat, respectively. The importance of the electrothermal coupling factor is shown and discussed as an energy harvesting figure of merit. It gives the effectiveness of all techniques of energy harvesting (except the Carnot cycle). It is finally shown that we could reach very high efficiency using lang111rang0.75Pb(Mg1/3Nb2/3)-0.25PbTiO3 single crystals and synchronized switch harvesting on inductor (almost 50% of Carnot efficiency). Finally, practical implementation key points of pyroelectric energy harvesting are presented showing that the different thermodynamic cycles are feasible and potentially effective, even compared to thermoelectric devices.

A multilevel DC-DC power conversion system with multiple DC sources is proposed in this paper. With this conversion system, the output voltage can be changed almost continuously without any magnetic components. With this magnetic-less system, very high temperature operation is possible. Power loss and efficiency analysis is provided in the paper. Comparison results show that the system does not require more semiconductors or capacitance than the traditional boost converter. Experimental results are provided to confirm the analysis and control concept.

For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications: rise time of 10-25 ns, pulsewidth of 50-150 ns, pulse repetition rate of up to 1000 pulses per second, peak voltage pulse of 70 kV, peak current of 3.5 kA, dc bias voltage of 10-35 kV, and energy per pulse of up to 30 J. Sixteen parallel wire cylinder reactors are used to match the source. Gas and reactor temperatures can be controlled individually with water flow around the outside of those cylinders. The system is designed for gaseous oxidation and electrostatic dust precipitation. The system has been used for up to 17 kW in average power. This paper reports the system in detail, discusses issues related to the matching between the source and the reactor, and presents an example of industrial demonstrations on odor abatement at 1000 m3/h. Finally, this paper also gives a general guideline for design of corona plasma systems

Voltage source inverters (VSI) have been widely used in uninterruptible power supplies, unified power flow controllers or unified power quality conditioners, and distributed generation systems (DGS). VSIs are inherently efficient, compact, and economical devices used to control power flow and provide quality supply. VSIs can be classified as voltage-controlled VSIs (VCVSIs) and current-controlled VSIs (CCVSIs), depending on their control mechanism. In this paper, a detailed comparison of VCVSIs and CCVSIs for DGS applications is presented. This paper examines the advantages and limitations of each control technique in a single-phase DGS, without incorporating additional hardware and/or extra complex control techniques. Discussions on the concepts, hypotheses, and computer simulations of different VSIs in the presence of different loads and conditions are presented. The experimental results confirm the validity of the analysis and simulations outlined. The paper provides design recommendations for the use of VCVSIs and CCVSIs in various applications

This paper illustrates the operation of a tubular-machine drive as a linear generator for a heave-buoy wave energy conversion. Linear generators, which are adopted in marine power plants, offer the advantage of generating without introducing any conversion crank gear or hydraulic system. The use of a tubular-machine topology allows the electromagnetic thrust density to be improved. This paper briefly summarizes the principles of marine wave buoy interaction and reports the design analysis and control of a permanent-magnet (PM) synchronous tubular linear machine based on a scaled generator prototype and on a rotating simulation test bench

Hybrid excited synchronous machines (HESM) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and wound field synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review papers. The principle of hybrid excitation allows solving many drawbacks related to permanent magnet electric machines operation: flux weakening, energy efficiency, and permanent magnets price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources, PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous structures (FSHESM).

Direct drive wave energy conversion (DD-WEC) is a typical low-speed long-stroke application. Harvesting wave energy presents enormous challenges, because wave energy naturally exists in the form of extremely low speed, high force, or torque motion. However, the frequency of flux linkage in field-modulated machine can be increased by the magnetic gear effect, and the output voltage and power density can also be effectively enhanced. In this paper, based on the field modulated principle, a field-modulated transverse flux linear generator (FM-TFLG) is proposed. Different combinations of permanent magnet number, slot number and translator number are selected and their performances are compared and analyzed. Results show that the electric frequency is enhanced as the modulation ratio increases. Compared with 18/12/17 (permanent magnet number/slot number/translator number) topology, 12/12/11 FM-TFLG has advantages of lower thrust ripple and total harmonic distortion (THD) of back-EMF, higher thrust/power density and efficiency. The proposed 12/12/11 FM-TFLG is a good candidate for DD-WEC.

The archimedes wave swing (AWS) is a system that converts ocean wave energy into electric energy. The goal of the research described in this paper is to identify the most suitable generator type for this application. Of the conventional generator types, the three-phase permanent-magnet synchronous generator with iron in both stator and translator is most suitable, because it is cheaper and more efficient than the induction generator, the switched reluctance generator, and the permanent-magnet (PM) generator with an air-gap winding. The paper also proposes a new transverse-flux PM (TFPM) generator topology that could be suitable for this application. This new double-sided moving-iron TFPM generator has flux concentrators, magnets, and conductors on the stator, while the translator only consists of iron.

This paper discusses how the switched reluctance generator (SRG) converts energy as directed by a controller. Beginning with a review of the electromechanics of generation, the paper identifies the implications of the energy conversion process on how the SRG is controlled. The structure of the SRG controller for speed-control and power-control applications is discussed. Practical implementation details for commutation of the SRG are reviewed. Concepts are illustrated with a 6-kW SRG designed to serve as a starter/alternator in automotive applications.

DC distribution system (DCDS) has many preferable advantages to integrate renewable energy sources and native-DC loads than AC distribution system (ACDS), and the benefits of higher power density, greater energy conversion and wider supply radius can be obtained. In this paper, a methodology of sizing the techno-economic of a medium-low voltage DCDS is proposed. Firstly, the system framework and its equipment composition are stated. Then, considering the distribution capacity, supply ability, operation loss and reliability, the technical indicators of the demonstrated DCDS are analyzed and quantified. In regards to the DCDS's distribution-level and consumer-level, the calculation models of the annual costs are presented. Further, different scenarios are imitated to verify the efficacy of the proposed sizing approach, and the techno-economic comparison is implemented in the DCDS and ACDS with similar structure configurations. The calculation results reveal that the DCDS shows a visible economic performance at the consumer-level, and for the scenario of accessing high proportion DC loads, it is more cost-effective than the ACDS. Finally, the correctness of the cost models is proven, and this study can offer a reliable reference for building the medium-low voltage DCDS.

Multi-energy systems (MESs) make it possible to satisfy consumer’s energy demand using multiple coupled energy infrastructures, thus increasing the reliability of the energy supply compared to separate energy systems (SESs). To accurately and efficiently assess and improve the reliability of MESs, this paper proposes a MES reliability and vulnerability assessment method using energy hub (EH) model. The energy conversion, transmission and storage in MESs are compactly and linearly described by EH model, making reliability and vulnerability assessment of MESs tractable. Indices for MES vulnerability assessment are proposed to find the key components for improving MES reliability. Multi-parametric linear programming (MPLP) with a self-adaptive critical region set is proposed to reduce the computational burden caused by iteratively solving LP problems for a large number of samples during the assessment process. The results of a case study show that the proposed reliability and vulnerability assessment method is able to effectively evaluate the energy supply reliability of different energy sectors in MES as well as find the critical component of an MES from reliability perspective to support its planning. The proposed algorithm, i.e., MPLP with a self-adaptive critical region set, can improve the computational efficiency by an order of magnitude compared to the traditional LP method.