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Refereed/Peer-reviewed This article proposes a two-stage optimization algorithm to effectively determine the system configuration at one stage, as well as the capacity of components at the other stage in the middle of the former. This algorithm fits in best with the hybrid systems with more possible types of components. The studied system, in this article, includes diesel generators, wind turbines, photovoltaic arrays, and tidal generators as the power generation components, as well as battery banks and flywheels as the energy storage components. It also includes fuel cells and electrolyzers that either work as batteries or generate electricity in the presence of biomass. When the number of components (decision variables) increases, it becomes difficult to find an optimal solution by the conventional methods. Therefore, in this study, a two-stage multiobjective optimization algorithm is applied to design a cost effective and environmental friendly ac minigrid hybrid power system. In each iteration of the proposed algorithm, first, renewable energy sources and energy storage components are selected to form a hybrid power system along with the diesel generator. Then, the capacities of the components are optimized based on the two objective functions, including levelized cost of electricity and emissions. The optimization model uses real annual data in hourly time intervals for the load, solar insolation, ambient temperature, and wind speed. It is found that the proposed algorithm decreases the susceptibility of the solutions to multiple runs compared with the conventional algorithms and achieves a better optimized power system design.

Refereed/Peer-reviewed This paper proposes two structures of dual-stator permanent-magnet vernier machines (VMs) for high-torque low-speed applications. The proposed structures consist of dual-sided rotor which is sandwiched by inner and outer stators. These topologies include 22 and 46 consequent-pole magnets in the rotor and 24 and 48 stator slots for Design A and Design B, respectively. Design A is an improved structure of dual stator VM and Design B is a novel topology of a dual stator VM that can deliver considerably higher back-EMF and torque than Design A. The only drawback in Design B is lower power factor. The characteristics and performance parameters of the proposed VMs are evaluated using FEA. Sensitivity analysis is used to figure out the optimum dimensions of the magnets. In fact, two combinations of slot/pole number of the vernier machines are investigated as Design A and Design B. The capabilities of the proposed vernier machines are presented in a fair comparison with other VMs namely as consequent pole dual rotor VM (CPDRVM), consequent pole dual stator VM (CPDSVM) and dual stator spoke array VM (DSSAVM). In this regard, the key machine features considered for comparison are back-EMF, torque, torque per magnet volume (TPMV), power factor, loss, and efficiency profiles. The proposed structure (Design B) generates higher torque and TPMV compared to the other studied machines while Design A can achieve a higher power factor.

Efficiency maps (EffMs) illustrate the maximum efficiencies of electric machines over a range of torque-speed operating points. This paper reviews the available techniques for efficiency map calculation and gives a general understanding of EffM modelling and interpretation for traction motors. It shows the accuracy versus calculation effort trade-off for different methods. The process of efficiency map calculation for sample induction motor and permanent magnet synchronous machines is explained. Calculation of EffMs using commercial software is also covered. Finally, possible future research opportunities in this field are suggested. Refereed/Peer-reviewed

Refereed/Peer-reviewed In this article, the analysis of induction machines using five separated subdomains including the rotor slot, rotor slot opening, airgap, stator slot opening, and stator slot regions is considered. The Maxwell equations of each region are solved considering the boundary conditions. Uniform distributions of the current density in the rectangular slots of both the rotor and stator are considered to find the energy of the winding and to calculate the machine inductances using the energy equation. The calculated flux density of each subdomain is used to find the flux distribution. The calculated magnetic flux intensities are required to estimate the saturation level of the motor cores and correct the saturation-related values such as the leakage and magnetizing inductances. The machine core losses are calculated based on the Steinmetz equation at the no-load condition. The calculated inductances and resistances are used in the equivalent circuit of the squirrel-cage induction machine (SCIM) for the performance prediction. The results demonstrate the reliability of the saturation model in the prediction of the saturation influence in a wide range of magnetization levels. The accuracy of the proposed model in the prediction of the performance of the SCIM is validated using two-dimensional (2-D) and 3-D finite-element analysis results. A sensitivity analysis with 75 different geometries was conducted to show the capability of the model for the performance prediction of a wide range of induction machines.

The bond-graph (BG) enables to model multi-physics systems in the energy domains. This paper shows that BG models are an alternative, more intuitive and simpler to interpret, graphical tool as compared to existing dynamic models for performance prediction of the line-start permanent-magnet synchronous motors (LSPMSMs). It includes electrical, magnetic, and mechanical energy domains where the stator windings, rotor bars, and permanent magnets are the main components of the model. The dynamical equations of the proposed BG are extracted and solved using the MATLAB ordinary differential equation solver for a sample LSPMSM. The dynamics of the studied LSPMSM is investigated under two operating conditions (1) a healthy motor and (2) a motor with broken rotor bars. The simulation results are compared with the finite-element analysis (FEA) as the most accurate method to simulate the electric motor behaviour. It is shown that the proposed BG model accurately predicts the performance parameters of the motor such as current, torque, and speed under various operating conditions. In addition to the modelling validation, the transient behavior of the LSPMSM are discussed to describe the possible reasons for its behaviour during transient and steady-state operating conditions.

Refereed/Peer-reviewed This paper proposes a quasi-resonant step-up DC-DC converter to provide the DC-link voltage for piezoelectric transmitters (PZETs). The resonance not only provides a soft-switching condition for the converter switches, but also helps to decrease the converter element sizes for marine applications. Operation modes of the proposed converter are discussed. The current and voltage of the converter components are derived analytically, and hence the converter gain is obtained. The performance of the proposed high-step-up, high-power density converter is examined through a comprehensive simulation study. The simulation results demonstrate the soft-switching operation and short transient time required for the converter to reach the reference output voltage. The converter output voltage remains unchanged when an inverter with a passive filter is placed at its output while supplying the PZET. The proposed DC-DC converter is prototyped to validate the converter gain and soft-switching operation experimentally. The converter gain and soft-switching results in simulation are well matched with those of the experimental tests. The converter efficiency in three different switching frequencies is obtained experimentally. The power density of the proposed topology is determined via the designing of a printed circuit board. The experimental results demonstrate the appropriate gain and efficiency of the converter in the tested power range.

Refereed/Peer-reviewed This paper proposes an optimization model to address the generator preventive maintenance scheduling (GPMS) in large power systems with high penetration of renewable energy resources (RERs). The dynamic programming (DP) technique is modified to reduce the required computational effort. A step for system inertia calculation and a constraint of minimum system inertia requirement are integrated into the GPMS model to address the inertia reduction issue linked with the proliferation of RERs in power networks. This study also considers the energy reserve requirement of the power system. The efficacy of the developed model is evaluated based on the operational data of an actual large power system including 41GW of conventional generators (400 units), and 14GW of wind and solar photovoltaics (PVs). The proposed algorithm is validated against the original DP method and the GPMS technique currently used by the Vietnamese system operator (SO). It is shown that the proposed simplified DP, while being much faster than the full DP, still guarantees an optimal solution as good as the full DP's solution. The proposed method outperforms the technique currently used by the Vietnamese SO, generating significant improvements in the system capacity reserve profile and reliability indexes with less adjustment effort required. The proposed algorithm is validated against the original DP method and the GPMS technique currently used by the Vietnamese system operator (SO). It is shown that the proposed simplified DP, while being much faster than the full DP, still guarantees an optimal solution as good as the full DP's solution. The proposed method outperforms the technique currently used by the Vietnamese SO, generating significant improvements in the system capacity reserve profile and reliability indexes with less adjustment effort required.

Refereed/Peer-reviewed Electrical motors are one of the key building blocks in power systems and an important load type in industry and residential buildings. The concept of axial-flux induction machines (AFIM) is drawing particular attention since it shows performance characteristics that are superior to the conventional radial flux induction machine (RFIM). This paper gives a state-of-the-art overview of AFIMs in the aspects of its history, construction, design, modelling, simulation, analysis, features, electromagnetics, and manufacturing. Especially, the review focus is given on the design, performance analysis, and features. Moreover, comparative studies among different induction machines are provided. Research gaps and possible trends are identified and discussed in this paper.

Refereed/Peer-reviewed Electric motors are one of the key building blocks of electric vehicles (EVs). The electric motor is drawing particular attention due to the variety of topologies that can be chosen as candidates for EV applications. Through the proper motor type selection and design, the performance of EVs can be enhanced, such as efficiency and stability. This paper presents a state-of-the-art overview of alternative electric motors for EV applications. Firstly, the classification and performance of alternative electric motors is described. Then, research gaps and possible future trends are introduced and identified in this review paper.

Refereed/Peer-reviewed Decaying DC (DDC) offset current mitigation is a vital challenge in phasor current estimation since it causes malfunctioning/maloperation of measurements and protection systems. Due to the inductive nature of electric power systems, the current during fault inception cannot change immediately and it contains a transient oscillation. The oscillatory component acts similar to an exponential DC signal and its characteristics depend on the X/R ratio of the system, fault location, and fault impedance. DDC attenuates accurate phasor estimation, which is pivotal in protection systems. Therefore, the DDC must be eliminated from the fault current (FC) signal. This paper presents an overview of DDC mitigation methods by considering different groups—before the discrete Fourier transform (pre-DFT), after the discrete Fourier transform (post-DFT), the least square-based (LS-based), and other methods. Through a comprehensive review of the existing schemes, the effects of noise, harmonics, multiple DDCs (MDDCs), and off-nominal frequency (ONF) on the accuracy of DDC estimation, were recognized. A detailed discussion (along with some simulation results) are presented to address the main advantages/disadvantages of the past studies. Finally, this paper presents a few suggestions for future researchers, for researchers to investigate more implementable solutions in this field.