Emerging Technologies in Power Systems

1. Introduction

Recently, renewable energy resources have been connected to the power system to reduce carbon emissions worldwide. Renewable energy resources, such as wind power generation, photovoltaics, energy storage system, electric vehicles, and fuel cell, are intermittent due to the fluctuation of resources. When the large penetration of renewable energy resource into power systems, operational constraints and technical problems occur. Obviously, it is necessary to introduce a new technology to solve these technical issues.

Moreover, advanced technologies, including digitalization, decentralization, and electrification, are new issues. Then, new technologies are presented, including the active distribution and transmission networks, digital grids, smart grids, micro grids, and multi-energy hubs. This requires the application of various technologies and changes to new operation systems and control systems.

2. The Current Research of This Special Issue

The 13 articles collected in this Special Issue discuss a solution to exploring the state of the art in research and development of emerging technologies in power systems. In the paper [1] entitled “Transformerless High Step-Up DC-DC Converters with Switched-Capacitor Network”, the non-isolated topologies with high boost capability are introduced to use in the renewable source, such as photovoltaic and fuel-cell applications. In this proposed system, the switched capacitor is used to provide high voltage gain and decrease the voltage stress across the devices. Moreover, this converter can operate at high efficiency conversion with low conduction of the main power switches. The next paper [2], entitled “CRM PFC Converter with New Valley Detection Method for Improving Power System Quality”, presents the new valley detection method for power factor correction (PFC) converter. The proposed method can provide an extension of fixed on-time to solve the low efficiency with high switching frequency in light load operating and low power factor. Then, that converter can improve 2.1% of system efficiency and 34.9% of power factor when compared with the existing valley detection methods. This proposed method can be applied for the power converters in home appliances. The paper in [3], entitled “A Study on Input Power Factor Compensation Capability of Matrix Converters”, also introduced the input power factor compensation capacity of the matrix converters with an inductor and capacitor filter in the input side. This paper has been demonstrated with the combination of space-vector control method and conservation energy law. It can be observed that the voltage transfer ratio range is verified by the converter parameters and that unity input power factor achievement is dependent on the quality factor of the converter.

The synchronization and control algorithm for the grid-connected renewable energy systems (RESs) represent additional focal points of this Special Issue. The paper in [4], with the title of “Study on the Capacity of an Active Phase Controller for Autonomous Grid Connection”, presents an active phase controller with the capacity calculation method to connect the distribution network. The proposed control method can eliminate the circulating current of the distributed system when the inverter is connected to the grid. The proposed active phase controller is only used the phase angle of lower than 10° in each connection point and required a small power capacity. In addition, the paper in [5] also introduces the control method grid-connected for single-phase inverter system, entitled “A Stationary Reference Frame Current Control Algorithm for Improvement of Transient Dynamics of a Single Phase Grid Connected Inverter”. The current control method is proposed to enhance the transient dynamic performance of the inverter system. In this method, the disturbance rejection control algorithm and commend feedforward control are implemented to suppress the overcurrent when faults occur in the grid-connected inverter. For the two-stage three-phase grid-connected PV inverter, the paper in [6] with title “Enhanced Control Scheme for a Three-Phase Grid-Connected PV Inverter under Unbalanced Fault Conditions”. This paper introduced the control method for the double grid frequency mitigation and improving the power quality when the power injection and DC-bus voltage operate under unbalance condition. In the DC-DC converter stage, the duty cycle signal is controlled by the maximum power point tracking (MPPT) algorithm. In the three-phase inverter, the frequency-locked loop controls the signal from the PV inverter and the power injection of the grid, and also analyses the phase angle. In addition, the proportional resonant controller with harmonic compensators is used to create the control signals.

The operation and planning problems considering RESs systems are another focus of this Special Issue [7,8,9]. The paper in [7], entitled “Generation expansion planning in the presence of wind power plants using a genetic algorithm model”, is introduced to improve the construction planning of power plants and save the cost of building various types of power plants. This paper discusses a genetic algorithm (GA)-based method for generation expansion planning (GEP) in power systems with wind farms. In addition, the paper considers the constraints of integrating various levels of wind energy into generation. Moreover, it considers cost fluctuations due to the development of the wind farm application and saving these plant construction costs. In terms of power system planning, GEP is essential, and it is expected to improve the economic feasibility of the power system through the proposed model. The next paper [8], entitled “Energy management of a power system for economic load dispatch using the artificial intelligent algorithm”, presents an improved bird swarm algorithm to determine the economic load dispatch problem of power system. This paper considers social coefficients and nonlinear cognitive, which can dynamically change the ratio of individual and social learning of birds. Economic load dispatch (ELD) problems in power systems are very complex due to specifications of nonlinearity and multi-constraints. The proposed method can be considered as a better solution. Operational and planning issues in the power system are also important issues in micro grids. A micro grid is a power system combined with RESs and an energy storage system (ESS) in a small area. The paper in [9], entitled “Real time-based under frequency control and energy management of microgrids”, presents an efficient frequency control and energy management of micro grid. It provides a control method of power, voltage, and frequency in both the connected mode and the island mode. The proposed control approach is developed in a real-time digital simulator (RTDS). This control method improves the stability and reliability of the system in the micro grids.

RES in the power system causes uncertainty problems due to their intermittent characteristic [10,11,12]. The paper in [10], with the title of “Transmission grid expansion planning of a high proportion renewable energy power system based on flexibility and economy”, presents a multi-objective transmission system planning model considering economy and flexibility. The proposed model satisfies several constraints and improves the flexibility, economy, and reliability of the power system. The paper in [11], with the title “Optimal power flow incorporating FACTS devices and stochastic wind power generation using krill herd algorithm”, presents an optimal power flow (OPF) calculation method with the krill herd algorithm (KHA), based on a meta heuristic approach in the power system considering flexibility AC transmission systems (FACTS) facilities and wind power generation. In addition, the uncertainty of wind power generation was taken into account by applying the Weibull probability density function. The proposed approach derives a solution by formulating separate objective functions for fuel cost, power losses, as well as combined economic and environmental costs (CEEC) of power system. The paper in [12], entitled “Flexibility Evaluation Method of Power Systems with High Proportion Renewable Energy Based on Typical Operation Scenarios”, presents a power system flexibility evaluation method based on several general scenarios by clustering the operation scenarios of renewable energy and loads using the modified k-means algorithm. The flexibility evaluation method is expressed as an index by considering the demand balance, power flow, and transmission capacity. It can be considered to solve the problem of the planning and configuration of power systems.

In addition, due to the access to large-capacity RESs, interest in DC distribution system in power systems is increasing. In general, the DC power distribution system has a simple control method, a larger supply capacity, and lower line losses, as compared to the AC power distribution system [13]. However, as the application of LVDC systems with different characteristics of AC systems increases, fault analysis of LVDC systems is essential. The paper in [14], with the title of “Study on Operational Characteristics of Protection Relay with Fault Current Limiters in an LVDC System”, presents the application of the superconducting fault current limiter (SFCL) for limiting the fault current in the LVDC system. The proposed method prevents the malfunction of overcurrent relay and selective protection relay caused by fault current limitation. It can improve economic efficiency as the fault current in LVDC system is limited and there is no need to upgrade the breaker.

3. Future Trends of Emerging Technologies in Power Systems

Over the past few years, power systems have been working to integrate RESs by introducing new technologies, such as power system designs, smart grids, and micro grids. In order to introduce the new technology into the power systems, a lot of verification is required, and efforts are needed to provide stable and reliable energy to customers. Future research related to the operation, planning, and control in power systems with RESs will also require more attention. Furthermore, future research in power electronic applications for RESs related to the DC–DC converter and DC–AC inverter will receive more attention. Both the power converter structures and control methods will be proposed and investigated to improve the presented system.