Advanced Optimisation and Forecasting Methods in Power Engineering—Introduction to the Special Issue

A Solid-State Transformer as Enabling Technology for Microgrids for Integration into the Power Distribution System: An Overview

Guest Editorial: Situational awareness of integrated energy systems

In this communication, expressions for the group velocity and the direction of power flow along an idealized tensor impedance boundary condition (TIBC) and a printed-circuit tensor impedance surface (PCTIS), are found. A PCTIS consists of a patterned metallic cladding over a grounded dielectric substrate. The patterned metallic cladding is modeled by a tensor impedance sheet. Expressions for the surface impedance of a TIBC and a PCTIS are reviewed. From these expressions, the group velocity and direction of power flow are derived as a function of transverse wave vector. A PCTIS exhibits spatial dispersion due to the electrical thickness of its substrate while a TIBC does not. As a result of this spatial dispersion, a PCTIS can have the same surface impedance as a TIBC for a given transverse wave vector, but a different direction of power flow. The expressions for direction of power flow along a TIBC and a PCTIS are verified with a full-wave electromagnetic solver.

Energy Storage Systems (ESS) are an attractive solution in environments with a high amount of renewable energy sources, as they can improve the power quality in such places and if required, can extend the integration of more renewable sources of energy. If a large amount of power is needed, then supercapacitors are viable energy storage devices due to their specific power, allowing response times that are in the range of milliseconds to seconds. This paper details the design of an ESS that is based on a modular multilevel converter (MMC) with bidirectional power flow, which reduces the number of cascaded stages and allows the supercapacitors SCs to be connected to the grid to perform high-power transfers. A traditional ESS has four main stages or subsystems: the energy storage device, the balancing system, and the DC/DC and DC/AC converters. The proposed ESS can perform all of those functions in a single circuit by adopting an MMC topology, as each submodule (SM) can self-balance during energy injection or grid absorption. This article analyses the structure in both power flow directions and in the control loops and presents a prototype that is used to validate the design.

Implementation of distributed energy resources based on renewable energy sources in existing electrical systems leads to a change in the direction and magnitude of power flows and, as a result, to a change inthe parameters of the network operation mode. The aim of the work is to study power flows in power supply systems with distributed generation facilities. To achieve this goal, power flows in the electrical system with thepower supply system, solar power plant, battery and load are analyzed. The results of the experiments showed that at the power supply point of the load of the electrical system, a low value of the power factor and the occurrence of a reactive power flow into the power system are observed. The results obtained on the value of the power factor in the electrical system with a solar power plant, can be used for further research and in practice.

Stochastic flexible transmission operation for coordinated integration of plug-in electric vehicles and renewable energy sources

A new type of multi-port isolated bidirectional DC-DC converter is proposed in this study. In the proposed converter, transfer of power takes place through addition of magnetomotive forces generated by multiple windings on a common transformer core. This eliminates the need for a centralised storage capacitor to interface all the ports. Hence, the requirement of an additional power transfer stage from the centralised capacitor can also be eliminated. The converter can be used for a multi-input, multi-output (MIMO) system. A pulse width modulation (PWM) strategy for controlling simultaneous power flow in the MIMO converter is also proposed. The proposed PWM scheme works in the discontinuous conduction mode. The leakage inductance can be chosen to aid power transfer. By using the proposed converter topology and PWM scheme, the need to compute power flow equations to determine the magnitude and direction of power flow between ports is alleviated. Instead, a simple controller structure based on average current control can be used to control the power flow. This study discusses the operating phases of the proposed multi-port converter along with its PWM scheme, the design process for each of the ports and finally experimental waveforms that validate the multi-port scheme.

This paper proposes a new control method to apply soft switching DC-DC converter to the control system of power flow between traction and regenerating loaded on Electric Vehicle (EV). According to the level of current setting, DC-DC converter changes operation mode between soft switching and hard switching in order to use complementary control without detecting polarity or direction of power flow. EV power flow control system becomes simple by means of soft switching method via complementary control with hard switching on boundary region between traction mode and regenerating mode. So the dynamic performance was improved by eliminating the complexity of boundary line control. The operating principle of the proposed practical control method was verified by experiment of practical EV.

A new model of power system to identify critical elements for smart and bulk power transmission grid environment is presented in this paper. Proposed bidirectional power flow model under complex network framework can quantify the criticality of nodes whose removal would trigger cascading failure. The proposed model based centrality, which is an extension of nominal power flow based model, is able to find nodes whose removal exerts more stress on the system. Several measures of impact like path length increase, boosted connectivity loss, raised load loss and increase in number of overloaded lines justify the use of bidirectional power flow based model to evaluate the criticality in smart grid environment. Change in direction of power flow in various random lines of the test system has a very little effect on the rank of nodes in the critical list.

In this paper a bidirectional switched boost converter is proposed. Conventional Z-source converter (ZSC) requires two inductors and two capacitors of equal inductance and capacitance which is difficult to realize in practice. Switched boost converter (SBC) is an improved derivative of ZSC comprising of one inductor and one capacitor which overcomes the stability issues associated with it. But power flow is limited to one direction in case of SBC. In AC-DC hybrid micro grid and in some energy storage applications bidirectional power flow is the most essential requirement. Proposed bidirectional switched boost converter (BSBC) retains the advantage of SBC and provides additional advantage of bidirectional power flow which makes it more suitable for AC-DC hybrid micro grid. Unaltered voltage gain is achieved at the AC bus and DC bus in both the directions of power flow. The Matlab simulation results are shown to verify the operation and theoretical analysis of proposed BSBC converter.

A description is given of an artificial power-transmission line which duplicates, in considerable detail, an actual transmission system. Each unit of the artificial line represents about ten miles of the actual line. Methods are given of calculating the correct distribution of inductance between self and mutual, and of calculating the correct distributtion of capacity between wire and wire, and wire and ground. It is shown that this artificial system will duplicate very closely, even under extreme conditions of short circuits and grounds, many of the phenomena occurring on the actual system. A description is given of some oscillographic tests, made on this line, of the magnitudes and phase relations of current and voltage at different points, when the line was subjected to various types of short circuits and grounds. The data are presented in the form of vector diagrams; one for each point of the line where readings were taken. In addition to the diagrams, arrow-headed lines are shown at each station. These indicate the magnitudes and directions of power flow for each phase (as shown by star-connected wattmeters) and the total power flow. It is shown that the total power flow is not always toward the short circuit (or ground). Hence, two-wattmeter principle relays will not always indicate toward the short circuit (or ground) and may sometimes operate the wrong switch. With a three-phase short circuit the direction of power flow for each phase, and consequently the direction of total power flow, is always toward the short circuit.

The development of the Blue-Angel light HEV started already in its 1st generation in 1992. In 2006, the 3rd generation redesign, first as a HEV and later on as a full EV with range extender, was started. The current design-concept is presented in this paper. Emphasis is put on the energy storage integration with a so called SAM2 storage 3rd generation which stands in communication with the energy management of the appropriate building. This paper presents the integration of Blue-Angel in the strategic field of research "living and mobility" of CC IIEE1 of the Lucerne University of Applied Sciences and Arts as well as the V2G concept. In this concept, PHEVs and EVs can be utilized for harnessing renewable energy and for providing power for both residential and commercial customers. The amount and the direction of power flow amongst the sub-systems, which include the grid, renewable energy sources, household load and Blue- Angel is part of a new management system. The proposed system is an open and universal platform and is expected to gain popularity amongst both commercial and residential users interested in resolving the global energy crisis. The system components will be demonstrated in a show-area platform of the Lucerne University of Applied Sciences and Arts in Horw-Lucerne as well as in a local utility.

Centralized Generation operates to receive power from the substations and distributed to consumers. Thus, the power flow goes from the highest voltage level to the lowest voltage level in the unidirectional direction without interacting the distribution with the generation. With the presence of Distributed Generation (DG), such as the photovoltaic (PV) system in the distribution system, depending on the insertion level of this generation, a change in the direction of the power flow may occur and bi-directional flows may occur. Therefore, some technical issues due to fluctuations, increased harmonic distortion and unavailability of the system affecting power quality must be addressed. The main object of this paper is to analyze the impact of harmonics with the insertion of photovoltaic generation in a Brazilian real distribution system with the use of OpenDSS software for simulation.

Network Interconnection Studies of Distributed Generation

Accurate line parameters are an important foundation for refined regulation and protection setting of distribution networks. In recent years, the topology of the circular distribution network, which has gained practical promotion, is complex and the direction of power flow is variable, making it difficult to apply the traditional radial network method for identifying line parameters. In this paper, a "time plane" based algorithm for identifying distribution network line parameters is proposed. In response to the situation where some distribution networks cannot collect voltage phase angle information from all nodes, it is proposed to analyze the power and voltage data that can be obtained by existing measurement equipment in the distribution network, and use a digital way to reflect the physical system to achieve visualization of the distribution network topology structure and line parameters. To achieve this goal, firstly, based on multiple sets of measurement data under time cross-sections, a linear regression topology and line parameter identification model is established according to the power flow equation, and preliminary calculations are made; Secondly, based on the concept of "electricity consumption", the line loss is used to infer the line parameters for each segment; Finally, the Adaboost algorithm was used to fuse the parameter identification results of the "time plane" and obtain the final distribution network parameter identification results. The feasibility of this method was verified using an IEEE 33 node example.