Detailed Switching Research Articles

The digital twin of complex shipboard DC microgrids: The high‐performing synergy of compiled models and HIL platform in the dynamics emulation of zonal power electronic power distribution systems

AbstractNowadays, resilience is a crucial attribute to be pursued in advanced shipboard DC microgrids. When the power distribution is zonal, the presence of autonomous‐controlled converters guarantees both power use and resiliency improvement. The adoption of bidirectional controlled devices ensures power routing among generating units, storage, and loads. Moreover, zonal electrical distribution systems are effective in applying the optimization algorithms for green, safe, and high‐performing ship operation. In zonal DC microgrids, real‐time cooperation among controlled converters through properly set communication protocols enables the ship mission achievement. To this aim, functional tests are to be done on such complex power infrastructure. The digital twin approach provides the de‐risking step before the onboard deployment for controlled systems and communication. A zonal DC shipboard microgrid is the case study to test the synergy between compiled models and power converters on two hardware in the loop platforms, then verified by experiment in this paper. The first platform exploits the Linux real time application interface on the average value models of converters. This solution is then compared with a platform that utilizes the Typhoon hardware in the loop environment, proposing a combination of average value models and detailed switching models for the real‐time emulation of controlled grid.

Enhanced resistive switching performance and structural evolution of NiO/Nb2O5−x bilayer memristive device

The development of bilayer models is crucial for enhancing the performance and enabling multifunctionality of next-generation resistive random-access memory (RRAM). However, detailed switching information is still insufficient for multilayer RRAM, necessitating direct observation of the microstructural evolution to clarify its switching mechanism. In this study, the electrical properties of Pt/Nb2O5−x/Pt monolayer devices were improved by introducing a polycrystalline NiO layer, and the resulting Pt/NiO/Nb2O5−x/Pt bilayer devices exhibited a doubling of the endurance and a reduction of the set voltage. The bilayer device also exhibited a long retention time (>104 s) and high on/off ratio of 104. Transmission electron microscopy, X-ray photoelectron spectroscopy, and electron energy-loss spectroscopy revealed that the conductive filament (CF) contained oxygen vacancies. In addition, a funnel-shaped CF was observed in the Pt/NiO/Nb2O5−x/Pt system, with the neck at the NiO/Nb2O5−x interface. This study provides a distinctive viewpoint and an innovative strategy for improving RRAM devices and exploring new applications in electronics.

Detailed Analysis of Classic Z-source Topology for Protection in DC Power Systems

This paper presents an in-depth analysis of the classic Z-source topology for DC power system protection, an area previously unexplored in such detail. Using OpenModelica simulations, the study offers valuable insights into the Z-source topology’s behavior, protection mechanisms, and energy dissipation processes. It includes detailed diagrams, switching states, and explanations of operating principles, supported by waveforms illustrating energy flow through the Z-source components. The findings demonstrate that the Z-source breaker effectively handles fault conditions by disconnecting the source from the load almost instantaneously, within tens of microseconds. The simulations confirm the theoretical models, showing that the Z-source topology efficiently dissipates fault energy through inductors, capacitors, and resistors, thereby protecting sensitive equipment. This thorough analysis enhances understanding of the Z-source topology in DC power systems and establishes a solid foundation for future research and practical applications.

Analysis of Data-Driven Modeling of Cycloconverters for Efficient Electromagnetic Transient Simulations of Electrified Ship Propulsion Systems

Simulation studies of modern electrified ship propulsion systems using the discrete switching models of cycloconverters are very time-consuming and require expertise and accuracy in modeling all the details of the ship’s electric power system. Alternatively, data-driven models of cycloconverter-based Variable-Frequency-Drive (VFD) systems are proposed, which may simplify the modeling and improve simulation efficiency and speed. The data-driven models can be established based on several measurements or a few runs of the detailed simulations, but their subsequent use enables very fast and efficient systemlevel studies. In this paper, the data-driven models of cycloconverter-based VFDs are analyzed in terms of their accuracy and numerical efficiency with respect to their detailed switching model counterparts for harmonic studies of an example ship propulsion system. The advantages and drawbacks of both modeling techniques are demonstrated through time-domain and frequency-domain electromagnetic transient simulations conducted in MATLAB/Simulink using the Simscape Electrical toolbox.

Harmonic elimination of a fifteen‐level inverter with reduced number of switches using genetic algorithm

AbstractMultilevel inverters play a crucial role in high‐power renewable energy applications and medium voltage drives. However, existing solutions such as capacitor‐clamped and diode‐clamped multilevel inverters are not suitable for these applications due to their dependence on isolated DC sources, complex control techniques, and potential reliability issues. Here, a novel fifteen‐level inverter topology is proposed which addresses these limitations. The proposed multilevel inverters utilize a topology with reduced number of switches, which can effectively accommodate isolated DC sources. It consists of eight switches for level generation and four switches for polarity generation (H‐bridge). One of the key advantages of this topology is that it significantly reduces the Total Harmonic Distortion (THD) in accordance with the IEEE 519 standards. Genetic algorithm‐based selective harmonic elimination technique was employed for THD minimization. A detailed switching loss calculation and harmonic analysis were performed to support the effectiveness of the proposed topology and the control used. The implementation of the proposed topology is simple and straightforward. Furthermore, to validate the results, insulated gate bipolar transistor based hardware model was developed. The optimized firing pulses were generated using the dSPACE 1104 controller. The results were compared with the existing recent literature and was found to address the limitations of existing topology.

Analytical Dual-Sequence Current Injections Feasible Region of Weak-Grid Connected VSC Under Asymmetric Grid Faults

For phase-locked-loop synchronization (PLL-Syn) based Weak-Grid connected Voltage Source Converter (WG-VSC) system under asymmetric grid faults, published works mainly focus on existing of equilibrium point and small signal stability, which cannot address PLL-Syn transient stability problems. For the first time, we have proposed an analytical solution to the question of “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Whether the WG-VSC system can reach to a new available equilibrium point (EP) of fault-on state from original EP of pre-fault state without loss of PLL-Syn transient stability under asymmetric faults?</i> ”. Dual-sequence current injections feasible region (CIFR) of WG-VSCs in positive and negative sequence current injection space is defined firstly. Then, by considering <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PLL-Syn transient stability constraint, Maximum available current constraint, and PCC Voltage constraint</i> , an analytical expression of CIFR has been obtained. Finally, experiments results based on detailed switching model in RT-BOX hardware-in-loop platform have been provided to verify the CIFR constructed in this paper. It should be noted that the work of this paper can not only address PLL-Syn transient stability problems of WG-VSC system under asymmetric faults, but also can pave the way for asymmetric fault ride-through control considering transient stability constraints.

Using Dynamic Phasors To Model and Analyze Selective Harmonic Compensated Single-Phase Grid-Forming Inverter Connected to Nonlinear and Resistive Loads

In an islanded microgrid, a grid-forming inverter (GFMI) is required to maintain a stable sinusoidal voltage at nominal frequency and amplitude with minimal distortion regardless of loading conditions. As a result, the accurate design of GFMI control schemes in an islanded microgrid requires accurate understanding of the converter dynamics and system harmonics. Electromagnetic transient (EMT) simulations based on detailed switching models give an accurate picture of the GFMI's behaviour. However, EMT simulations take a relatively long time to produce accurate results in large-scale systems. On the other hand, conventional phasor models are unsuitable for harmonic studies. To address this limitation, this article leverages the dynamic phasor (DP) method to develop a new model of a single-phase GFMI connected to single-phase nonlinear (diode-bridge rectifier) and resistive loads. The benefit of the DP method lies in its inherent feature of transforming time-domain signals into slow-varying or DC signals, thereby enabling faster simulations. In this article, the relationship between the control gains of the proposed DP model and the conventional detailed model is established for the first time through small-signal and frequency-domain-based comparative analyses. User-written codes of the proposed DP model are scripted in MATLAB, and simulations on MATLAB/Simulink show that the proposed DP model results have a high degree of correlation with the detailed switching model results. A significant savings in computation time is exhibited by the proposed DP models. The simulation results are validated against experimental results to confirm the accuracy of the proposed DP model.

Real-Time Transient Simulation and Studies of Offshore Wind Turbines

The real-time models of offshore wind turbine generators complied with industry standards are presented in this paper. The developed models provide essential capabilities for future electromagnetic transient controls and testing offshore wind farms, such as low-voltage ride-through, active/reactive power support, transient current limiting. Furthermore, the proposed models provide an additional capability of controlling negative sequence current, which meets the future requirements for protecting wind farm systems. This paper presents average-value and detailed switching real-time models in the Opal-RT real-time simulator. The efficacy of the proposed real-time models in terms of computational efficiency is demonstrated by comparing them with the non-real-time models. Extensive case studies are performed to demonstrate the control functions of the proposed models, such as dynamic-wind condition, power curtailment, low-voltage and fault ride-through, negative sequence current control, etc. The wind turbine model validation against the generic model presented by the Western Electricity Coordinating Council (WECC) is conducted to show their compliance with industry standards utilized by WECC. A real-time model of a 450 MW offshore wind farm is developed to show the feasibility of large-scale wind farm modeling.

Pricing Variance Swaps under MRG Model with Regime-Switching: Discrete Observations Case

In this paper, we creatively price the discretely sampled variance swaps under the mean-reverting Gaussian model (MRG model in short) with regime-switching asymmetric double exponential jump diffusion. We extend the traditional MRG model by further considering the trend of the financial market as well as a sudden and unexpected event of the market. This new model is meaningful because it uses observable Markov chains that represent market states to adjust its parameters, which helps capture the movement of the market and fluctuations in asset prices. By utilizing the characteristic function and the conditional transition characteristic function, we obtain analytical solutions for pricing formulae. Note that this is our first effort to provide the analytical solution for the ordinary differential equations satisfied by the Feynman–Kac theorem. To achieve this, we have developed a new methodology in Proposition 2 that involves dividing the sampling interval into more detailed switching and non-switching intervals. One significant advantage of our closed-form solution is its high computational accuracy and efficiency. Subsequent semi-Monte Carlo simulations will provide specific validation results.

Dynamic Phasor-Based Modeling and Simulation of a Single-Phase Diode-Bridge Rectifier

This paper presents dynamic phasor (DP) models of a single-phase diode-bridge rectifier (DBR). Single-phase DBRs serve as a primary building block of consumer electronics, whether with a simple filter or coupled with additional circuitry to produce unity power factor rectification. Four DP models are proposed, two models (DP-SF and DP-AW) suitable for systems with negligible line inductance and two models (DP-Full and DP-Fund) which can be used when the line inductance causes significant commutation overlap. The proposed models are implemented in MATLAB and simulation results are compared against a detailed switching model simulation. A significant reduction in simulation time is demonstrated by the proposed DP models. The simulation results are validated against experimental data, confirming the accuracy of the proposed modeling approaches.

Reconfigurable Rectifier-Based Detuned Series-Series Compensated IPT System for Anti-Misalignment and Efficiency Improvement

For an inductive power transfer (IPT) system, mobility is one of the most attractive features, but coupling variations can dramatically affect the system's output. In this article, a reconfigurable rectifier-based detuned series-series (SS) compensated IPT system is proposed to tolerate an extensive coupling range and improve the system efficiency simultaneously. The reconfigurable rectifier, which can operate in a full-bridge rectifier mode or a half-bridge rectifier mode, is used to alter the equivalent ac load from one value to the other so the expected coupling range of the detuned SS topology can be extended. At the same time, the system efficiency is also partly improved because the ac load is changed to get closer to the optimal load of the IPT system. First, a detuned SS IPT system with the reconfigurable rectifier is presented and followed by the analysis of the working modes. Then, a detailed parameter design process and switching control of the reconfigurable rectifier are introduced. Finally, a 400-W prototype was constructed to verify the validity of the proposed method. The experimental results demonstrate that the output power fluctuation of the proposed IPT system is less than 17.5% and the lowest efficiency can be improved from 68.6% to 87.5% with the coupling coefficient varying from 0.1 to 0.4. The proposed method can implement significant antimisalignment and efficiency improvement simultaneously, and it is regarded as a potential solution for low-power IPT applications with high spatial mobility.

Impacts of Current Limiting on the Transient Stability of the Virtual Synchronous Generator

This article investigates the impacts of different current limiting strategies on the transient stability of the virtual synchronous generator (VSG). The power–angle curve of the VSG under different operating conditions is theoretically characterized in detail and experimentally verified through tests conducted on hardware-implemented lab-scale VSGs. It is shown that the reference current saturation approaches prioritizing the current vector angle, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current, and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current reshape the VSG power–angle curve in different ways. The resulting impacts on the VSG transient stability are comprehensively investigated through time-domain simulation of a battery energy storage system that is operated as a VSG and connected to a medium-voltage Canadian distribution feeder. The transient stability margin of the VSG is evaluated by determining the critical clearing time (CCT) of various fault scenarios. The studies conducted in the PSCAD/EMTDC software environment utilizing a detailed switching model of the VSG indicate that 1) the current limit of the VSG significantly impacts its power output during and after faults; and 2) the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis priority current limiting strategy provides a larger transient stability margin (CCT) as compared with the current vector angle and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current priority approaches.

Full-Order and Simplified Dynamic Phasor Models of a Single-Phase Two-Stage Grid-Connected PV System

The dynamic phasor (DP) method is a useful tool for developing simulation-efficient models suitable for system-level analysis. In this paper, two DP models of a single-phase two-stage grid-connected photovoltaic (PV) system are proposed. In the first DP model (DP-Full), the PV array, PV capacitor, boost converter, DC-link, and MPPT (maximum power point tracking) control are modeled. In the second DP model (DP-Simp), the DC-side model is simplified by aggregating the PV capacitor- and boost inductor dynamics into a first-order function while calculating the MPP voltage and current analytically. The accuracy and execution speed of the two DP models are verified by comparing their performance with those of a detailed switching model simulated in an electromagnetic transient program. Simulation and error calculation results show that there is a good agreement between results from the proposed DP models and the switching model. Simulation studies of a two-bus power system demonstrate the computational advantage of the DP-Simp and DP-Full models over the detailed switching model in a multi-converter scenario. The proposed DP models can be used for the fast-paced transient analysis of distribution grids with high PV penetrations.

Efficient Phasor-Based Dynamic Volt/VAr and Volt/Watt Analysis of Large Distribution Grid With High Penetration of Smart Inverters

As the penetration of power-electronics based smart inverters (SIs) is increasing in distribution grids, it adds computational challenges in solving dynamic models of large-scale distribution feeders. Voltage and reactive power (Volt/VAr), and voltage and active power (Volt/Watt) dynamics have been analyzed at slower time scales akin to the control of legacy grid devices. However, smart inverters, being power-electronics based devices, can provide dynamic active/reactive power support at a faster time scale, which necessitates Volt/VAr and Volt/Watt dynamics to be analyzed at a faster time scale. The existing dynamic models are overly detailed and computationally intractable for distribution feeders with a large number of inverters. In this context, this proposed work aims towards developing a computationally tractable, scalable, and accurate phasor-based model for dynamic Volt/VAr and Volt/Watt analyses of large distribution systems with high penetration of smart inverters. Case studies demonstrate that the proposed phasor-based model sufficiently captures the Volt/VAr and Volt/Watt dynamics, and is computationally faster by one order of magnitude compared to the average model and by two orders of magnitude compared to the detailed switching model. Case studies also demonstrate the efficacy and scalability of the proposed model in analyzing Volt/VAr and Volt/Watt dynamics of large-scale power networks with hundreds of SIs.

Average-Value Modeling of Line-Commutated Inverter Systems With Commutation Failure

Line-commutated converters are extensively used as the interface between ac grids and classic HVDC systems. At the inverter side, commutation failure of switches is one of the most common faults that can pose threats to the system operation. Practical and reliable study of such phenomena relies on accurate and efficient converter models for simulations. Recently, a parametric average-value model (PAVM) has been presented for ac–dc rectifiers, which considers the internal faults of the converter. In this paper, the PAVM methodology is extended to the dc–ac inverter systems, including the commutation failure of switches. The proposed PAVM also augments an automatic fault detection technique to determine the faulty switches. Using comprehensive simulation studies, the developed model is verified to accurately predict the commutation failure of switches and reconstruct the waveforms consistent with the detailed switching models of inverters while being computationally more efficient. The proposed PAVM is envisioned to be an efficient and accurate asset for simulation of HVDC systems and inevitable when faults of switches need to be considered.

Autonomous Power Management of Distributed Energy Storage Systems in Islanded Microgrids

In this paper, an autonomous power management strategy is proposed for distributed energy storage units deployed in islanded microgrids with photovoltaic (PV) and droop controlled units. The proposed strategy offers controlled and selective prioritization of the charging/discharging actions while coordinating with PV and droop units to maintain power balance in the microgrid. The selective priority allows battery units with low state-of-charge (SOC) to keep charging, at a reduced or a full rate, while other battery units meet the demand. This is in contrast to the autonomous techniques in the literature where all units can only charge/discharge simultaneously. This is achieved by employing the proposed adaptive piecewise <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P/f</i> characteristics, with breakpoints that enable seamless transition between power control and frequency regulation. The charging/discharging decisions and the amount of power exchanged with the microgrid, is determined autonomously at each unit using local measurements only. Also, the strategy offers a unidirectional shutdown mechanism where, below a certain SOC limit, it modifies the structure of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P/f</i> characteristics so the unit cannot discharge, yet it can still charge anytime surplus generation becomes available. Simulation results from a detailed switching model, and also an averaged model, for prolonged simulation times, are used to validate the proposed strategy.

Switching characteristics analysis and power loss minimization of SiC BJT based on dual power supply RC driving circuit

As a current driven power device, SiC BJT needs effective driving scheme, but the present schemes are either complicated or not parameter optimized. In this paper we give an optimized parameter design method based on dual power supply RC driving circuit. First, the detailed switching process of SiC BJT considering the loop parasitic parameters is presented. Then, the influence of the accelerating capacitor on the switching loss and driving loss of SiC BJT is analyzed. The theoretical and simulation analysis shows that as the accelerating capacitor increases, the driving loss of SiC BJT increases proportionally, while the switching loss decreases less. Finally, the switching process of SiC BJT was investigated experimentally at various accelerating capacitor values from 3.3 nF to 94 nF. It was found that with the increase of the accelerating capacitor, the total loss during the switching process first decreases and then increases. The total loss minimization during the switching process of SiC BJT can be achieved through properly selecting the accelerating capacitor.

Intermediate-state imaging of electrical switching and quantum coupling of molybdenum disulfide monolayer

SignificanceThin transparent semiconductors of two-dimensional materials are attractive for the practical applications in next-generation nanoelectronic and optoelectronic devices. Probing the electron states and electrical switching mechanisms of a molybdenum disulphide monolayer with atomic-scale thickness (6.5 Å) allows us to unlock the full technological potential of this nanomaterial. We introduced a plasmonic phase imaging method to uncover the underlying mechanism and detailed switching dynamics of an electrical-state switching event. This dramatic phase change can be attributed to the reversible switching of classical electromagnetic coupling and quantum coupling effects interplaying between a single metal nanoparticle and molybdenum disulphide monolayer, and the transient intermediate states during the switching event can be directly imaged by a plasmonic technique.

Current source gate drivers for 3-phase VSI operated in small-scale wind turbine systems

The paper is dedicated to the improvement of efficiency of small-scale wind turbines’ (SSWT) power electronic converters. An efficiency of the 3-phase voltage source inverter that operates with low output voltage (<60 V) and high grid-side input voltage (380 V) is investigated. Such a solution allows skipping the intermediate DC/DC boost converter and thus reducing conversion losses and complexity of a system. The inverter has to oaperate with low duty cycles, which, in turn, demands increasing of switching speed and thus requires application of advanced transistors. To evaluate the switching performance, studies were carried out with various types of switches, namely Si IGBT, Si MOSFET, Cascode SiC JFET, SiC MOSFET using classic gate drivers and proposed current source drivers. Detailed switching waveforms were obtained using the double pulse method and analyzed for each type of the switch. The switching speed was assessed and losses were evaluated. Two types of transistors were selected for testing in the VSI paired with an EMRAX 228 generator. Inverter efficiency data was obtained and analyzed for two types of transistors/drivers and the speed-torque curve applicable for a 3 kW turbine. It is shown that the suggested solution improves the efficiency of SSWTs’ inverters.

Average-Value Modeling of Direct-Driven PMSG-Based Wind Energy Conversion Systems

Control design and stability analysis of direct-driven permanent magnet synchronous generator (PMSG)-based wind energy conversion systems (WECSs) typically involve extensive time-domain simulations and frequency-domain analyses. Those studies rely on accurate and computationally efficient models of WECSs. Detailed switching models can accurately describe the transients of power-electronic converters, but they suffer from low computational efficiency due to the repeated switching events. In this paper, a numerically efficient model is developed for a direct-driven PMSG-based WECS. Analytical and parametric average-value modeling techniques are applied to its switching subsystems, including a 12-pulse diode rectifier, a three-phase-interleaved boost converter, a dual three-phase voltage source inverter (VSI), and a crowbar circuit. The average-value models (AVMs) improve the simulation efficiency by representing the terminal characteristics of switching subsystems with a set of algebraic equations. In addition, numerical linearization techniques can be directly employed for them to obtain frequency-domain characteristics. The proposed model is verified against the detailed switching model and existing AVM in MATLAB/Simulink. It is shown to have excellent accuracy in both time-domain and frequency-domain studies while maintaining high computational efficiency.