Consensus algorithm-based secondary control, such as virtual impedance, is typically used to achieve power-sharing and ensure stable operation in microgrids. The introduction of communication, however, increases the system's vulnerability. Communication failure, e.g., under cyber attack or disruption, can lead to a huge loss. To solve this, this article proposes a signal reconstruction approach for the miscommunicated signals. The power-sharing convergence, both in normal conditions and under communication failure, is analyzed via the Lyapunov method. The feasibility and effectiveness of the proposed approach are validated on a lab-scale microgrid.

Distributed secondary control achieves voltage restoration and power sharing through communication among adjacent units but exposes the microgrid to potential cyber-attacks. Traditional mitigation strategies modify the secondary controller after the attack, addressing the issue only postoccurrence. Furthermore, in microgrid planning, the structure of the communication network significantly influences the resilience to attacks, but it remains to be explored. This article presents a proactive defense mechanism by designing a resilient communication network. The proposed method quantifies the impact of attacks and develops a multiobjective optimization algorithm to design the network, considering quantified attacks, convergence, time-delay robustness, and communication costs. The method is validated through OPAL-RT simulations of an islanded microgrid with ten converters.

For electrolyzer applications, traditional solutions using line frequency transformers plus rectifiers are bulky, heavy and have low controllability. The Solid State Transformer (SST) could be a promising solution to solve the mentioned issues. This paper compares the semiconductor ratings and capacitance of five different Modular Multilevel Converter (MMC) based Solid State Transformer (SST) topologies. The results show that the DRU (Diode Rectifier Unit)-MMC based topologies have the lowest semiconductor ratings and capacitance. Because of the unidirectional power flow requirement, the source side MMC of Back-to-Back (BtB) MMC based SST could be replaced by DRU, thus the cost is drastically saved. Another interesting finding is that the DRU-MMC energy ripple is much lower than half of the energy ripple in BtB MMC, which is different from HVDC MMC.

Green hydrogen production uses renewable energies to energise the electrolysers for hydrogen production. The present paper compares possible solutions and configurations of a medium-frequency transformer (MFT) as part of a solid-state transformer (SST) in green hydrogen production applications. The single-phase and three-phase MFTs are compared and it is shown that a Yd three-phase MFT is the optimum choice for applications that require high power delivery and step-down of the voltage. A summary of previous works about MFT is also provided. Three-phase SST based on modular multilevel converters (MMC) is then described and various cases are investigated to obtain the optimum operational frequency. A 25 MVA, 400 Hz, 25.4 kV / 560V oil-immersed MFT design is presented and is shown that the proposed 400 Hz transformer saves 69% of the active parts' weight compared to a conventional line-frequency transformer (LFT).

This paper presents the study of a 100kW electric vehicle (EV) fast charger based on a 12-pulse rectifier cascaded with two buck-type DC-DC converters. The proposed circuit operates with a triangular current shaping method which considerably improves the current harmonics performance of the system. The studied circuit is particularly suited for high power battery charging, being relatively simple to operate, requiring a low active semiconductor count (only two active switches), and because it employs circuit technologies well-established in the high power market. Above all, this EV fast charger meets the requirements of isolation, high efficiency, high output voltage and good power quality (low THD and unity power factor). This paper describes in detail the analytical modeling of the studied circuit, including the current harmonic input filter design which meets the grid standard requirement, and the loss modeling of the semiconductors and passive elements. The modeling and simulation results of the proposed 100 kW system are presented and analyzed.

In emerging fast-charging stations, DC fast chargers (DCFCs) are employed which rely on power electronics and control to achieve the required performance. Harmonic emission induced by the complex system behavior is of great concern in the DCFC system. This paper proposes a harmonic emission model for the typical electric vehicle charger design, i.e., two-level active front end. The technique is based on the Fourier series method and the impedance model which is able to reveal the harmonic current emission of DCFCs under different grid conditions. Time-domain simulations are presented subsequently to validate the proposed model.

The range anxiety and relatively long charging time issues of electric vehicles (EVs) have boosted the development of fast charging technology. With charging light EVs being the main focus in the past decade, a trend of promoting the charging infrastructures dedicated to heavy-duty EVs (HDEVs) such as E-trucks, and Ebuses has emerged to further the electrification of global transportation. Accordingly, the market is calling for advantageous standards, architectures, and power electronic circuits specialized in the fast charging of HDEVs. For the charging of HDEVs, the power rating of chargers can reach an ultra-high-power level (>1 MW) to ensure a charging time comparable to the refueling time of internal combustion engine (ICE) vehicles. At this power rating, the classic full power processing (FPP) two-stage AC-DC plus DC-DC architecture has limited space for improvement in terms of the efficiency and effective cost of the charger circuits. This thesis proposes a solution to the HDEV fast charger topologies. Firstly, the state-of-the-art EV fast charging technology, concepts of the hybrid rectifier, and partial power processing (PPP), which could be beneficial in advancing the charging architecture are reviewed. Based on the results of the literature review, a new unidirectional Input-Parallel-Output-Series (IPOS) three-phase hybrid rectifer topology is proposed and analyzed. This topology is derived from the Input-Parallel-Output-Parallel (IPOP) hybrid rectifier in [1] by connecting the DC-links in series instead of in parallel. The IPOS topology is beneficial at ultrahigh power rating to interface heavy-duty EV batteries which require a high and wide output voltage range, enabling the system to deliver an output voltage range of 800∼1500 V to interface the next-generation of EV batteries with available 600/1200V commercial semiconductors. Besides, the proposed topology is efficient, cost-effective, and scalable with the grid input current harmonic components in compliance with the IEEE-519 standard. The benefits of the IPOS topology are supported by circuit derivation, control strategy, analytical modelling, simulation, and experimental verification of the current modulation technique. Index terms— fast charging, hybrid rectifier, partial power processing, power factor correction, AC–DC converter

Balancing converters are an integral part of a bipolar dc grid. Resonant converter topologies are interesting for power electronics engineers due to their soft switching capabilities. A series resonant converter topology is promising as a balancing converter in a bipolar dc grid. The series resonant converter is usually a non-inverting topology. However, in the balancing converter application, the converter is used as an inverting type, like a buck-boost converter topology. In this paper, the soft switching capabilities of this converter are shown and analyzed for four distinct converter modulation schemes.

In this paper, the output impedance of a three-phase inverter based on a dual current control (also called double synchronous reference frame current control) is modelled, which includes: the current loop gain, the control delay, and the Phase-Locked Loop (PLL). The impact of these parameters on the impedance is then analysed by a sensitivity study. The model is derived using transfer matrices and complex transfer functions, and it results in a compact impedance formulation that can be used in harmonic small-signal stability studies and system-wide steady-state harmonic calculations.

In recent years, electrical vehicle (EV) starts showing its unique advantages that the conventional combustion vehicles do not have. Together with the increasing interests on EV, the motor drive with higher efficiency and lighter weight also becomes more attractive. A promising solution is to apply the wide band gap (WBG) components including gallium nitride (GaN) and silicon carbide (SiC) in the motor drive. Thus, the performance of the GaN, SiC and Si based motor drive in this application are compared. Besides, as the current maximum current rating of the GaN and SiC MOSFET is limited and insufficient to satisfy the large phase current in the acceleration and braking process, the inverter topology that adds the parallel MOSFETs in one position is considered. To reduce the time and cost for the development, this paper proposes the modelling of the motor drive, with which the voltage and current stress, power loss, thermal and electromagnetic performance can all be evaluated. The modelling to be introduced consists of the 1-D power loss, simplified thermal modelling of the motor drive and the 3-D modelling of the electromagnetic performance, detailed thermal performance of the motor drive. In the 3-D modelling, to make the heat transfer simulation closer to the realistic, computational fluid dynamic (CFD) is used to evaluated the heat transfer coefficient on the surface with forced air-cooling.

In this paper, magnetically-coupled impedance source (MCIS) three-phase four-switch inverters are introduced for renewable energy applications. This inverter utilizes two single-phase MCIS inverters to obtain a three-phase output, where less component-count is achieved in order to reduce the inverter volume. On the other hand, as a result of the reduced number of switches, the proposed inverter suffers from higher voltage stresses. The MCIS inverters are first reviewed. Then, the modulation and operation principle of the MCIS three-phase inverter topology are introduced before sizing the passive components. A comparison among the similar candidates is done. Finally, the analysis is verified by simulations.

This paper presents a family of cost-effective magnetically-coupled impedance source inverters for renewable energy systems. The inverters are derived from magnetically-coupled impedance source networks, featuring low cost and no ground leakage current when used in PV system. The numbers of required semi-conductor switches is reduced. More important, the elimination of leakage currents makes it particularly suitable for high-efficiency photovoltaic (PV) applications. A comparison among prior-art PV inverters is then performed. The Performances of the inverters are evaluated analytically as well as by simulations. The analysis and simulation show the superiority of the proposed inverter in terms of leakage current suppression and low cost.

The basic Zero-Voltage Switching (ZVS) three-level DC-DC converter has one clamping capacitor to realize the ZVS of the switches, and two clamping diodes to clamp the voltage of the clamping capacitor. In order to reduce the reverse recovery loss of the diode as well as its cost, this paper proposes to remove one of the clamping diodes in basic ZVS three-level DC-DC converter. With less components, the proposed converter can still have a stable clamping capacitor voltage, which is clamped at half of the dc link voltage. Moreover, the ZVS performance will be influenced by removing the clamping diode. But as long as the clamping capacitor is properly selected, the degradation of the ZVS performance can be neglected. The impact of the clamping capacitor on the ZVS performance is mathematically analyzed as well.

Converters with reduced switch counts usually face some performance tradeoffs, which make them suitable for some applications but not others. The same applies to the nine-switch converter, which is a reduced-switch version of the back-to-back twelve-switch converter. The nine-switch converter has since been shown to experience a higher voltage stress, which can be lowered in some cases. A corresponding evaluation of its current stress is however lacking, and is hence addressed now by computing its switch currents when used for ac-ac, ac-dc, dc-ac and dc-dc energy conversions. Relevant expressions, application requirements and simulation results are presented for identifying cases, where the nine-switch converter can have an improvement in performance despite its reduced switch count.

Wind speed variations make the power of wind turbine system to fluctuate, which could increase the thermal stress of the power converter and reduce its lifetime. In order to relieve this problem, short-term energy storage technologies are applied to improve the thermal performance of a 3 MW grid side wind power converter. The cost, weight and cycle life of the energy storage technologies are evaluated based on a typical low speed high turbulence wind profile. In detail, a wind turbine system model is established and its control strategy is illustrated, which is followed by the power control method of the energy storage system. Then the conventional thermal evaluation approach is simplified for evaluation with long term wind profile. The case studies are done to address the optimal power size and capacity of the energy storage system by comparing the improvement of the thermal performance. Also, the two promising candidates, ultracapacitors and batteries, are compared.