Large-scale integration of renewable energy sources in power system leads to the replacement of conventional power plants (CPPs) and consequently challenges in power system reliability and security are introduced. This study is focused on improving the grid frequency response after a contingency event in the power system with a high penetration of wind power. An energy storage system (ESS) might be a viable solution for providing inertial response and primary frequency regulation. A methodology has been presented here for the sizing of the ESS in terms of required power and energy. It describes the contribution of the ESS to the grid, in terms of inertial constant and droop. The methodology is applied to a 12-bus grid model with high wind power penetration. The estimated ESS size for inertial response and primary frequency regulation services are validated through real-time simulations. Moreover, it is demonstrated that the ESS can provide the response similar to that provided by the CPPs.

In the low-voltage (LV) ac microgrids (MGs), with a relatively high R/X ratio, virtual impedance is usually adopted to improve the performance of droop control applied to distributed generators (DGs). At the same time, LV dc MG using virtual impedance as droop control is emerging without adequate power flow studies. In this paper, power flow analyses for both ac and dc MGs are formulated and implemented. The mathematical models for both types of MGs considering the concept of virtual impedance are used to be in conformity with the practical control of the DGs. As a result, calculation accuracy is improved for both ac and dc MG power flow analyses, comparing with previous methods without considering virtual impedance. Case studies are conducted to verify the proposed power flow analyses in terms of convergence and accuracy. Investigation of the impact to the system of internal control parameters adopted by DGs is also conducted by using proposed method.

Capacitive power transfer (CPT) technology is becoming increasingly popular in various application areas. Due to its limitations, such as low frequency, low coupling capacitance, and the high voltage stress on metal plates, the studies on high power CPT applications fell behind previously. Therefore, the wideband gap (WBG) semiconductor devices and the compensation topologies are further adopted to tackle these limitations. The main purpose of the paper is to review CPT applications in terms of performance parameters, advantages, disadvantages, and also challenges. Initially, the basic principles of CPT technology are examined, which cover compensation topologies, coupler structures, transfer distance, power electronic components, and system control methods. Then, CPT applications are evaluated for performance parameters (i.e., power level, operation frequency, system efficiency, transfer distance) along with compensation types, inverter types, and coupler types. The applications are categorized into six main groups according to industrial topics as safety, consumer electronics, transport, electric machines, biomedical, and miscellaneous. Herein, power level changes from $\mu \text{W}$ to kW ranges, the operation frequency varies from 100s of kHz to 10s of MHz ranges as well. The maximum system efficiency is recorded as 97.1 %. The transfer distance varies from $\mu \text{m}$ range to 100s of mm ranges. The full-bridge inverter topology and four-plate coupler structure are noticeable in CPT applications. Finally, advantages, disadvantages, and challenges of CPT applications are evaluated in detail. This review is expected to serve as a reference for researchers who study on CPT systems and their applications.

In this paper, an economic dispatch problem for total operation cost minimization in dc microgrids is formulated. An operating cost is associated with each generator in the microgrid, including the utility grid, combining the cost-efficiency of the system with demand response requirements of the utility. The power flow model is included in the optimization problem, thus the transmission losses can be considered for generation dispatch. By considering the primary (local) control of the grid-forming converters of a microgrid, optimal parameters can be directly applied to this control level, thus achieving higher control accuracy and faster response. The optimization problem is solved in a heuristic method. In order to test the proposed algorithm, a six-bus droop-controlled dc microgrid is used in the case studies. Simulation results show that under variable renewable energy generation, load consumption, and electricity prices, the proposed method can successfully reduce the operating cost by dispatching economically the resources in the microgrid.

The development of distributed generation system and electric vehicles is bound to strain the distribution network. A typical radial distribution feeder suffers from voltage fluctuation and feeder overload in the presence of a large amount of variable renewable generation. This paper presents a concept of enhancing the power handling capacity of distribution networks using dc grid interconnections. Control of both the active and reactive power exchange between the ac feeder and the interconnecting power converter has been proposed for the voltage regulation at the ac feeder terminal. Besides, the dc grid interconnection also allows the introduction of a common storage system that can be shared by the connected ac feeders and the dc grid connection to other renewable energy resources. The increased power handling capacity and improved voltage profile of the ac distribution feeder using the proposed system is shown through time domain simulations on a test system.

The virtual synchronous generator (VSG) control has been extensively applied for realizing grid-friendly interconnections of power converters. Nevertheless, due to the direct shaft dynamics emulation, low-frequency power oscillations may be introduced in the case of limited damping effects. To solve this issue, power control law modifications have been proposed based on the feedback control theory. Although power oscillations can be suppressed to an acceptable level, the original inertial response of the VSG will be significantly degraded. This letter proposes a new damping method based on the reference feedforward control. The proposed method is able to effectively attenuate poorly damped power oscillations in VSG-controlled converters without affecting the original inertial response. Theoretical analysis and effectiveness of the proposed damping method have been validated by both electromagnetic transient simulations and experiments.