IET Energy Systems Integration最新文献

This study focuses on stability of weak grid connected voltage source converter (WG-VSC) in Low-frequency mode (LFM) (around 1–10 Hz), which is dominated by interactions among phase-locked loop (PLL), outer loop control and weak grid condition. In order to clearly reveal LFM mechanism of WG-VSC, a simple but effective PLL-equivalent model has been proposed. First, a generic small signal model consisted of PLL and ‘outer loop & WG’ two parts is derived. Then, the transfer function of complicated ‘outer loop & WG’ part is divided into two parallel channels, representing the impact of active side control and reactive side control on LFM of WG-VSC respectively. Finally, based on the multi-mode decomposition theory, a simple but effective second order PLL-equivalent (E-PLL) model is obtained for LFM stability analysis of WG-VSC. The effectiveness of E-PLL model has been verified by simulation results in PSCAD/EMTDC and experimental results based on a hardware platform.

This study presents a grid interactive solar photovoltaic (PV) system proficient with low voltage ride through capability. When the supply voltage drops more than 10%, the solar PV system remains connected and continues to supply the active power to the loads as well as to the grid. Along with the active power supply, the solar PV array system supplies the reactive power for stabilising the system. Due to the supply of both the active and reactive powers, there is a chance for a grid fed inverter (GFI) current to exceed the maximum current limit. It may result in the tripping of inverter protection. Therefore, a current limiting logic is incorporated to keep the inverter current within the safe limit. The unbalanced voltages are responsible for circulation of negative sequence currents in the system. As the prime aim of the present work deals with the supply of positive sequence currents to the grid, it is required to estimate the positive and negative sequence voltages separately. Intending the estimation of sequence voltages from unbalanced supply voltages, a frequency adaptive higher order complex filter (FAHOCF) is used. A MATLAB model of grid interactive solar PV array is developed and simulated results are verified with test results.

The interactive demand of electrical power between integrated energy microgrid (IEMG) and smart distribution network (SDN) is growing rapidly with the increase of distributed generation (DG) installed capacity. When SDN and IEMG are connected through a single gird-connected point, the renewable power consumption may be limited by tie-line capacity. A distributed optimal dispatching method of the SDN considering the IEMG with multiple gird-connected points is proposed. The impact of various flexible resources is also considered. Firstly, a IEMG connection mode, in which each IEMG can be connected to multiple nodes of the SDN, is designed. A distributed optimal dispatching method is proposed, by which the IEMG operation privacy and the SDN responsibility to consume renewable power can be considered. Then, the electric power on tie-lines is taken as the coupling variable to establish the IEMG and SDN coordinated dispatching model. The model can be solved by adjusting the power upper limits of tie-lines circularly. Finally, the improved IEEE 33-bus system is analysed based on the proposed method. It is found that when the IEMG is with large DG installed capacity, multiple gird-connected points can improve the SDN operation flexibility and increase the operation benefits of all entities.

A distribution system is connected with many non-linear loads, and generated harmonies are mitigated by using distribution static compensator (DSTATCOM) which is coupled at the point of common coupling through a voltage source inverter (VSI) and filter circuit. High-frequency switching ripples are generated along with the output of the VSI during pulse width modulation switching. Inductor-capacitor-inductor (LCL) filter is used to suppress the high frequency switching noises. Still, the primary concern about the LCL filter is generation of resonance peak at the resonance frequency. The conventional synchronous reference frame $��d�q�$ current controller with LCL filter has a complex coupling between $��d�$ and $��q�$ axis; hence decoupling is very difficult. This research article presents a new technique based on active damped dual loop $��\alpha �\beta �$-frame current controllers to control the DSTATCOM with LCL filter for achieving improved load compensation. The dual loop controller is enhanced by using capacitor current in the inside loop and grid current at the outside loop with proportional resonant (PR) regulator parallel with harmonic compensator (HC). The proposed method effectively dampens the resonance peak under stationary reference frame $���\left(�\alpha �\beta �\right)��.�$ The PR controller offers unlimited gain at the fundamental frequency and HC can offer more gain at the specific harmonic frequencies. Hence, characteristics of the PR and HC controllers used together to achieve minimum steady-state error and the problematic decoupling are ignored. The complete DSTATCOM model with proposed control scheme is discussed with PR and (PR + HC) controllers separately under balanced, unbalanced source voltage. Stability analysis is carried out through B

The high emission intensity of coal-fired power plants (CFPP) leads to the inevitable next step towards energy transition, the coal phase-out. One challenge is the subsequent use of still-functioning assets. Re-purposing these assets avoids value loss and creates new opportunities for coal regions. Therefore, this study considers the sector coupling technologies Power-to-Gas (PtG) and Gas-to-Power (GtP) as re-purposing options. First, a multi-variable Mixed-Integer Linear Programming optimisation model is established. This model includes the participation of the plant in the current (2020) and future (2030, 2040) electricity and natural gas spot-markets and the balancing power market while fulfilling existing contracts, and allows for determining the re-purposing technologies' operating profiles. By applying a techno-economic analysis, investment recovery periods of the considered re-purposing technologies are assessed, which range between two (GtP) and over ten (PtG) years. A sensitivity analysis accounting for current energy prices and technological advancements reveals capital expenditure has the highest impact on this Return-On-Investment period. Additionally, a case study considering the Austrian energy grids is performed to account for the grid impact of integrating these technologies at former CFPP sites. Thus, it is found that the investigated sector coupling technologies have the potential to compensate for grid congestions even in profit-optimised operation.

With the high-proportion integration of renewable energy and power electronic equipment, the inertia supporting ability of new power system continues to decline, which seriously threatens the frequency stability of power grids. In order to clarify the operation boundary, and realise the rapid analysis and prediction of the minimum inertia demand of new power systems, this study proposes a minimum inertia demand estimation method based on deep neural network (DNN). Firstly, this study establishes the system frequency response model of new power systems containing diverse inertia resources including renewable energy, induction machine and so on. Considering the constraints of rate of change of frequency and maximum frequency deviation, the minimum inertia demand estimation model is established to ensure the system frequency stability. DNN is introduced to effectively map non-linear relations in complex situations, which can quickly estimate and predict the minimum inertia of new power systems. Adam algorithm is utilised to optimise the input weight matrix and hidden layer feature vector of the network to improve accuracy. Finally, the simulations and analysis are conducted in IEEE-39 system to verify the accuracy and generalisation ability of the proposed method in this paper.

This article introduces and describes the integrated energy system of the Low Emission Oil and Gas Open reference platform. It is a hypothetical case meant to represent a typical oil and gas installation in the North Sea. The aim of this detailed specification is to serve as an open reference case where all the information about it can be publicly shared, facilitating benchmarking and collaboration. The relevance of this reference case of an off-grid energy system is not limited to the oil and gas industry, since it can also be seen as a special kind of electrical micro grid. The remote offshore location makes it especially relevant for studying offshore wind power and ocean energy sources like wave power. The specification has an emphasis on the energy system and electrical configuration, but also includes a basic description of the oil field and processing system. The intention is that it will serve as a basis for energy system studies and relating power system stability analyses regarding the integration of renewable energy sources. This allows for comparisons of a base case with different design modifications, new operational planning methods, power management strategies and control concepts. Examples of possible modifications are the replacement of gas turbines by wind turbines, addition of energy storage systems, a more variable operation of loads etc. The last part of the article demonstrates the behaviour of the reference platform implemented in two software tools: one for operational planning and one for dynamic power system analyses.

The rapid development of photovoltaics (PVs) and load caused a significant increase in peak loads and peak-valley differences in rural distribution networks, which require load peak shifting and line upgrading. Large peak-valley differences also bring challenges on the safe operation of the utility power grid. Considering the integration of a high proportion of PVs, this study establishes a bilevel comprehensive configuration model for energy storage allocation and line upgrading in distribution networks, which can reduce peak loads and peak-valley differences. In the upper level, a minimum annual planning cost is obtained by developing the installation capacity of centralised energy storage in transformer stations, the installation location and capacity of decentralised energy storage on lines and a scheme of line upgrading. In the lower level, the minimum total annual operation cost of the distribution network is obtained by developing an optimal scheduling for the centralised energy storage in transformer stations and decentralised energy storage on lines. Simulation results show that compared with the conventional energy storage planning strategy, the configuration investment can be reduced by 467.66 million yuan at least with the proposed strategy.

In the transition to carbon neutrality, conventional energy systems are experiencing a radical change with the proliferation of distributed energy resources (DERs), including distributed generation (especially renewable power generation), energy storage, flexible demand and electric vehicles. With the support of advanced control, information and communication technologies, DERs in nearby geographical areas form local energy systems (LESs) for facilitating local power and energy balance and supporting the operation of bulk energy systems. Local energy markets (LEMs) are potential arrangements for achieving effective and efficient management of LESs and further paving the path towards fully transactive energy systems.

This Special Issue focuses on LEMs for LES integration, including four papers covering different key aspects. The brief description for the papers is presented as given below, and we encourage the readers to refer to the papers for more details.

Virtual power plants (VPPs) are an important framework where DERs can be grouped to participate in both local and bulk energy markets. There are two papers on VPPs in this Special Issue. In the paper ‘Aggregating buildings as a VPP: Architectural design, supporting technologies, and case studies’, Luo et al. focussed on industrial/commercial/residential buildings and designed a comprehensive architecture of building VPPs with the relevant key supporting technologies identified. One prominent contribution of the proposed architecture is identifying the need for interaction between VPP management systems and existing building energy systems and the associated Internet of Things (IoT) devices, with good sense of practical application. Besides the well-known technical VPPs and commercial VPPs, Luo et al. also proposed ‘occupant-centric VPPs’ (O-VPPs), which is able to facilitate local energy sharing, resilience enhancement and energy usage knowledge sharing among buildings.

The other paper on VPPs is ‘Virtual Power Plant (VPP) scheduling with uncertain multiple locational marginal prices (LMPs)’. This paper focussed on another important practical issue when applying VPPs in practice—the DERs managed by a VPP may be located in different parts of an electricity transmission network, thus faced with different levels of LMPs. Khandelwal et al. proposed a scheduling framework that tackles this issue, and at the same time considering the correlated price uncertainties and addressing them using the Markowitz's mean-variance criterion.

Local electricity markets are the most heavily researched LEMs. The paper ‘Hosting a community-based local electricity market in a residential network’ established a simplified modelling approach where the market and network model simulations are performed in a cascaded and decoupled fashion. Saif et al. evaluated the network impact of the local electricity market and the implications of different types of DERs (mainly photovoltaics and energy sto

Residential heating faces the challenge of heating interruption when an electric power outage occurs. As a promising heating electrification form, regenerative electric heating (REH) equipped with thermal energy storage (TES) has the flexibility of maintaining the building indoor temperature within the desired range during power outages and reducing the operation cost during normal operation states. However, the allocation and scheduling of the limited thermal energy in TES for the above two purposes is impacted by many uncertainties, for example, outdoor temperature, irradiation, and duration of power outages. Overestimation of the thermal energy required for power outages in the TES can improve the heating supply reliability, but it will also increase the REH operation cost to some extent, and vice versa. To address this problem, an affine arithmetic-based model predictive control approach (AA-MPC) for an optimal REH scheduling method is proposed to balance the heating supply reliability during power outages and operation economy of REH at the same time. An REH-based residential building energy system model is developed to describe the building thermal load associated with the outdoor temperature and irradiation. Then, the required thermal energy for emergency building heating provided by the hot water tank (HWT) is determined using the minimum thermal demand of residents during a power outage, which is constrained by the minimum comfort temperature threshold. Based on this, an AA-MPC approach that takes the thermal energy for emergency building heating as a time-varying constraint of the HWT is developed to determine the optimal REH scheduling that considers emergency residential building heating under the above uncertainties. Numerical studies show that the proposed method can maintain minimum thermal demand for at least 2 h when a power outage occurs under uncertainties. At the same time, it can reduce the impact of uncertainties on the operation cost and reduce economic problems caused by emergency heating to a certain extent. Compared to the interval arithmetic-based model predictive control approach, the operation cost intervals of the proposed method are reduced by 57.3%, 0.3%, and 32.5% under low, middle, and high prediction error levels respectively.