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The dynamics of current controller is usually neglected for simplification when assessing microgrid transient stability. Utilizing the Takagi–Sugeno method, this letter thoroughly examines the effects of current controller on transient stability estimations and reveals that completely ignoring the dynamics of current controller can cause overestimation on transient stability. The findings highlight a significant overestimation on lower boundary of angle about 29.2% even if current controller performs fast dynamics with bandwidth more than 28 times the fundamental frequency. Recognizing the impracticality of including current controller dynamics in microgrids with multiple converters, this letter proposes a stability-enhanced method through phase compensation in the current controller, which can improve the accuracy of transient stability assessments while still omitting current controller dynamics. In addition, a guideline for parameter design of phase compensation is provided. Theoretical findings are verified by hardware-in-loop experimental results based on OPAL-RT platform.

Electric vehicles with different output power levels can use wireless power transfer (WPT) systems. Different vehicle assemblies (VAs) may be charged by different ground assemblies (GAs) in charging stations. However, the overall efficiency of the WPT system may drop significantly when the power class difference between GA and VA is large. To address this issue this article proposes a dc-link parallel ac-link series multi-inverter multirectifier architecture for high-power WPT systems. Modulation, power transfer capability, and power sharing from the design aspects are investigated. A detailed power loss analysis and an easy-to-implemented power loss optimized control method based on mutual inductance identification are presented in this article. Finally, experimental results are obtained from a 20-kW LCC-LCC WPT system to validate the analysis and proposed system operation.

The requirement of high power rated, efficient and high power density grid connected converters has increased due to their extended use in multiple applications such as battery chargers. The proliferation of electric vehicles (EVs) in the transportation market is essentially associated with the performance and reliability of battery chargers. An efficient, compact and fast battery charger is indispensable in order to provide a way to charge an EV in a short time. In view of this fact, this article proposes a soft-switching three-level T-type vienna rectifier, which can be used as a front-end power stage converter in an on-board EV battery charger. The proposed topology achieves high efficiency and high power density by employing soft-switching strategy, which is achieved by incorporating a simple auxiliary network in the proposed circuit. The reduced component stresses and simple control strategy make it an appealing candidate for EV industries to develop this front-end PFC rectifier as a fast battery charger. The high switching operation with reduced power losses, regulated DC at the output, low-harmonic grid current and power factor correction operation are achieved with the proposed topology. The construction, operating principle and simulation analysis of the proposed converter are discussed in detail. In order to show the stand-point of the proposed scheme, a fair comparison of the proposed soft-switched converter with an existing soft-switched 3-level neutral-point diode-clamped converter is carried out in terms of the number of components and complexity in the PWM signals generation. Additionally, an efficiency comparison of the suggested converter is carried out with some existing well-known rectifier topologies at different power loads. The practical implementation of the proposed power converter scheme is checked by building a laboratory-prototype to perform an experimental analysis.

Multimodule isolated converters incorporating excellent features of galvanic isolation, bidirectional power flow, and simple control are widely adopted in medium-voltage (MV) high-power dc–dc applications. However, the converter size and dc-link capacitor voltage balancing are significant concerns in galvanically isolated cascaded dc–dc converters. This article proposes a new design of an integrated transformer implementing toroidal cores named toroidal core multilimb transformer (TCMLT), employed in a dc–dc modular isolated bidirectional dual-active-bridge (IB-DAB) resonant converter topology. The modular design structure of the proposed transformer can be conveniently constructed and implemented for more number of participating modules conforming the compactness constraint. Moreover, an external coupling winding is implemented in the TCMLT structure to resolve the dc-link voltage balancing issue. This coupling winding method substitutes the expensive complex control circuits, which consequently results in cost reduction and reliability enhancement. Besides, the reluctance model of the proposed structure is analyzed. Based on the reluctance model, a common mode–difference mode (CM-DM) electrical circuit is realized for the proposed scheme. Furthermore, unlike the conventional approach of implementing U, UI, and EI cores for multilimb transformer (MLT) structure with separate limbs, a synthesis method of TCMLT in toroidal form is proposed. The comparative study of the proposed design with the conventional U-core MLT confirms that the proposed TCMLT offers less leakage inductance with significant size reduction. Finally, to validate the efficacy of TCMLT, a three-limb laboratory-scale prototype is employed in a 6-kW cascaded IB-DAB resonant converter topology.

ABSTRACTThe control of DC microgrids is a growing area of research. DC distribution networks present an effective solution to the integration of stochastic energy sources as renewable energy and renewable storages. A communication layer is required to exchange measured and estimated values for the secondary control loop. Faults and failures within the communication layer lead to malfunctions and divergence in system values. The control structure is presented using adaptive droop based secondary control for detection of communication islanding and stabilize the operation of the system. Recent years, more robust techniques and methodologies have been suggested to increase system resilience, but the communication islanding detection has not been addressed in DC microgrid at the multi-level control. This work, therefore, modifies the secondary level control to include a communication failure detection scheme that identifies communication islands within this network. Adaptive droop is employed to mitigate the effect of communication islands and regulate current sharing. The proposed scheme is verified using system-level simulations and analytical studies.

Large‐scale integration of electric vehicles (EVs) into residential distribution networks (RDNs) is an evolving issue of paramount significance for utility operators. Similarly, electric load forecasting is an operational process permitting the utilities to manage demand issues for optimal energy utilization. Unbalanced voltages prevent the effective and reliable operation of RDNs. This study implements a novel framework to examine risks associated with RDNs by applying a residential forecasting model with a stochastic model of EVs charging pattern. Diversified EV loads require a stochastic approach to predict EVs charging demand; consequently, a probabilistic model is developed to account for several realistic aspects comprising charging time, battery capacity, driving mileage, state‐of‐charge, travelling frequency, charging power, and time‐of‐use mechanism under peak and off‐peak charging strategies. Peak‐day forecast of various households is obtained in summer and winter by implementing an optimum nonlinear auto‐regressive neural‐network (NN) with time‐varying external input vectors (NARX). Outputs of the EV stochastic model and residential forecasting model obtained from Monte‐Carlo simulations and the NARX‐NN model, respectively, are utilized to evaluate power quality parameters of RDNs. Performance specifications of RDNs including voltage unbalance factor (VUF) and voltage behavior are assessed in context to EV charging scenarios with various charging power levels under different penetration levels. This research work contributes to the knowledge regarding the operational process of future power networks to examine risks associated with distribution networks by applying a forecasting‐based residential model with a stochastic model of electric vehicles (EVs) charging pattern including various uncertainties to account for realistic scenarios.