IET Energy Systems Integration最新文献

The DC-side stability of the grid-tied converter under different control modes is fully investigated using electrical torque analysis. The small-signal model of a single converter connected to an ideal DC bus under various control modes is formulated. Accordingly, the damping and synchronising coefficient contributed by the DC network and controllers of grid-tied converter are separately accessed using the electrical torque analysis method and the stabilising conditions of the grid-tied converter operating under different control modes are further derived. The system stability mainly corresponds with DC network dynamics under constant active power control mode. On the contrary, the grid-tied converter under constant DC-link voltage control mode has no stability problem. Generally, elevating the DC-link capacitance or decreasing the droop gain can greatly improve the stability margin reserve of the VSC-HVDC links. In addition, the control gains of the classical PQ controller are proven to have limited impacts on DC-side system stability. Finally, the results of numerical simulation prove the validity of the proposed stability analysis method and the stable boundary for the grid-tied converter with different control modes.

The energy storage system (ESS) is a promising technology to address issues caused by the large-scale deployment of renewable energy. Deploying ESS is a business decision that requires potential revenue assessment. Current value assessment methods focus on the energy storage owner or the electricity utility. The system value of the ESS needs to be fully considered to gain a broad understanding of benefits across the whole power system. Thus, this study proposes a system value assessment method of grid-integrated ESS to quantify the total system value-avoided cost based on an improved DC power flow model considering transmission losses. Four typical applications (production cost saving, upgrade deferral, environmental benefit, and transmission loss saving) are chosen to represent the system value of the ESS across the whole power system. In addition, the co-optimisation model considering the “source-grid-storage” coordination operation and battery capacity degradation, is proposed for peak shaving and frequency regulation based on the Chinese power market rule. The proposed method is tested in simulation and experimental studies.

Remote areas in Jordan often rely on expensive and polluting diesel generators to meet their electricity demand. This study investigates 100% renewable solutions to supply the electricity demand of off-grid energy systems through optimal sizing of photovoltaics and energy storage systems. A linear programming approach is proposed to minimise the annualised cost of electricity supply including capital costs of equipment and their operation and maintenance costs. The optimisation determines the size of photovoltaics and energy storage required to satisfy electricity demand at every hour of a selected year. A Jordan campsite was used as a case study to assess and compare the performance of PV-battery storage and PV-hydrogen storage systems from economic and reliability perspectives. The results show that hydrogen storage was more economical for a 100% renewable energy system. However, introducing some diesel generation gave the battery system a significantly lower annualised cost of energy.

In microgrid (MG) systems, traditional centralised energy trading models can lead to issues such as low energy efficiency due to unstable energy supply and lack of flexibility. Peer-to-peer (P2P) trading models have been widely used due to their advantages in promoting the sustainable development of renewable energy and reducing energy trading costs. However, P2P multi-energy trading requires mutual agreements between two microgrids (MGs), and the uncertainties of renewable energy and load affects energy supply security. To address these issues, this article proposed a distributed robust operation strategy based on P2P multi-energy trading for multi-microgrid (MMG) systems. Firstly, a two-stage robust optimisation (TRO) method was adopted to consider the uncertainties of P2P multi-energy trading between MGs, which reduced the conservatism of robust optimisation (RO). Secondly, a TRO model for P2P multi-energy trading among MGs was established based on the Nash bargaining theory, where each MG negotiates with others based on their energy contributions in the cooperation. Additionally, a distributed algorithm was used to protect the privacy of each MG. Finally, the simulation results based on three MGs showed that the proposed approach can achieve a fair distribution of cooperative interests and effectively promote cooperation among MGs.

The application of the security region methodology in a practical distribution system with large scale normally requires large computer memory and high computation time. To overcome this problem, this article proposes a decoupling and dimension reduction method, which can significantly accelerate the calculation of distribution system security region (DSSR) and is important for the application of the DSSR theory in large-scale distribution systems. First, the definition of DSSR dimension reflecting the size of solution space and the time complexity is proposed. And the solution algorithm for DSSR dimension is also given. Second, a decoupling and dimension reduction method suitable for the analysis of DSSR is proposed. Following the method, an incidence matrix can be obtained from the DSSR expressions, which can be further divided into multiple block matrices. According to the feeder combinations of the block matrices, the distribution system can be decoupled into multiple sub-networks for more efficient analysis. Finally, a 10kV distribution network is used in case study to validate the proposed method. The results for a time-consuming calculation, that is, TSC curve calculation, show that the proposed method can reduce the computation time significantly, making the time-consuming calculation suitable for the analysis of large-scale cases.

Islanded microgrid network is sensitive to voltage and frequency fluctuations which becomes more vulnerable in the presence of external disturbance and the intermittent nature of Renewable Energy Sources (RESs). The “Electric Spring” (ES) is one of the most effective and efficient solutions for enhancing operational flexibility and RESs integration. A Self-Excited Induction Generator (SEIG) based Micro hydro system with ES, non-critical and critical loads is considered. Both non-critical and critical loads are connected in 2:1 ratio in parallel with SEIG. The concept of voltage-sensitive and non-sensitive loads and the “power demand following the supply” idea have been incorporated for pointing up the contribution of ES. The non-critical load coupled with a three-phase inverter acts like an ES and can be operated as a Smart Load (SL). SL can compensate the voltage deviation between demand-supply side, therefore mitigating the voltage fluctuations. The effectiveness of ES in terms of voltage regulation at the point of standard coupling has been achieved which improved the overall voltage profile of the hybrid microgrid system which can be observed from various test cases. A hardware in loop microgrid experimental platform is established and its results highlight the excellent performance of the proposed method.

A trilateral control for LCL filter-based system is introduced by the authors with a single grid current sensor in weak grid conditions. The LCL filter increases the complexity when the uncertain nature of the grid comes into the picture. Moreover, the traditional three-loop control technique requires three current sensors on the inverter side, three voltage sensors to sense voltage across the capacitor, and three current sensors on the grid side combined for sensing. A novel trilateral control technique utilising a single sensor is implemented to sense the grid current. This technique has reduced a considerable number of current sensors and voltage sensors. The α axis of grid current is proportional to sensed ‘a’ phase grid current. The β current in the utility grid is acquired by employing the controller reference quantities of the grid current. The computation of another variable, that is, the current in the inverter side inductor and the voltage across the capacitor, is executed by an estimation algorithm. The proposed technique provides the feature of reducing implementation financial value and weight that reduces the complexity and size of hardware. The synchronisation technique is executed by a modified dual second-order generalised integrator digital phase-locked loop for the grid-connected converter. The implemented system offers the advantage of ease of implementation, good performance, and high stability. The validity of the proposed scheme in the implemented system is demonstrated by the simulated waveform obtained on the MATLAB/Simulink platform. Finally, the effectiveness of the proposed system is further justified by the experimental waveform procured from a prototype developed in the laboratory.

Mixed integer linear programming (MILP)–based distributed energy management for networked microgrids embedded modern distribution systems is proposed. Considering the diverse ownership of microgrids, distributed energy resources (DERs) that interface directly with utilities and responsive loads, an alternating direction method of multipliers–based distributed framework was formulated for the scheduling of networked microgrids embedded modern distribution systems by adjusting nodal price signals iteratively. In addition, to make the formulated optimization problems resolvable through more accessible and popular MILP solvers, different linearisation techniques were employed to transform the nonlinear terms into linear or mixed integer linear formats. The proposed MILP-based distributed method preserves all participants' autonomy (e.g., microgrids, DERs that interface directly with utilities and responsive loads), while incentivising them to actively participate in the distribution system operation with price signals. The proposed method is validated with results of numerical simulation using a modern distribution system consisting of multiple networked microgrids, DERs that interface directly with utilities, as well as responsive loads.

The application of Markowitz and tangency portfolio and Black–Litterman models is extended by the authors to energy portfolio selection in transmission-distribution environments with high penetration of renewable energy. As Transmission System Operator (TSO) and Distribution System Operator (DSO) contextually take mutualistic or conflicting positions in their portfolio selection process, their risk-return interactions and behaviours depend on their subjective views on generation and operation. Here, the financial portfolio allocation tool Black–Litterman Model is adapted to incorporate subjective views of the operators to arrive at more intuitive portfolios. The best portfolios are searched within the acceptable risk-return search space of each operator defined by their Markowitz efficient frontiers (EF), for Pareto-optimising their profits. The tangency portfolio approach, which is generally used to determine the portfolio of risky and risk-free assets in finance, is used here to determine the portfolio of renewable (energy-risky) and fuel-based sources (energy-risk-free). The proposed methodology is adopted in an HV–MV interconnected test system operated by one TSO and two DSOs, having wind, solar, coal, gas and nuclear generation technologies. It is observed that completely customisable portfolios can be constructed for TSO and DSO based on their inherent financial and energy risk-return behaviours and posterior views.