It is difficult to achieve accurate distribution of reactive power based on conventional droop control due to the line impedance mismatch in an islanded microgrid. An adaptive virtual impendence method based on consensus control of reactive current is proposed in this paper. A distributed control structure without the central controller has been established. In this structure, each distributed generation unit (DG) is an independent agent, one-way communication is used between the adjacent DGs, and the reactive power sharing is equivalent to a problem of reactive power current consensus. It has been proven that the system is asymptotically stable under the proposed control strategy. When the adjacent DG’s reactive power is not proportionally distributed, the current weight error term will generate a virtual impedance correction term through the proportional-integral controller based on the reactive current consensus control strategy, thus introducing adaptive virtual impedance to eliminate mismatches in output impedance between DGs. Reactive power auto-proportional distribution can be achieved without knowing the line impedance. At the same time, the power control loop is simplified and the virtual impedance compensation angle is employed to compensate the decreased reference voltage magnitude and varied phase angle due to the introduction of the virtual impedance, so the stability of the system can be improved. Finally, the correctness and effectiveness of the proposed strategy are verified by modeling analysis and microgrid simulations.

The multi-microgrid integrated energy system offers multiple effective approaches to promote clean energy utilization as well as carbon emission reduction, etc. Combined with stepped carbon trading mechanism, it proposes a multi-microgrid (MMG) system with CCS-P2G integrated flexible operation method for optimal scheduling. Firstly, based on the microgrids’ “source-load” characteristic, electricity sharing between the source and load type microgrids can be achieved. Secondly, the CCS-P2G integrated flexible operation method is proposed, i.e. introducing HFC (Hydrogen Fuel Cell) and HES (Hydrogen Energy Storage) in P2G can enhance the utilization effect of hydrogen. Moreover, introducing carbon storage equipment in CCS, which can effectively solve the situation of unsynchronized operation times of CCS and P2G. Finally, introducing stepped carbon trading mechanism can be a further way of limiting carbon emission. Based on the above, MMG’s optimal dispatch model has established with objective of minimizing total operation cost by considering economic performance and carbon emission of the MMG system. Above optimal dispatch model is a mixed integer linear problem, which is solved using CPLEX solver. Simulation results show that electric energy interaction between source-type and load-type microgrids enhances renewable energy utilization rate. Compared to CCS-P2G cooperative operation method, the single-day carbon emissions and total operation cost of multi-microgrid system using CCS-P2G integrated flexible operation method are reduced by 37.02% and 6.80%, respectively. Meanwhile, when the stepped carbon trading mechanism was introduced, multi-microgrid system’s single-day carbon emissions is reduced to 5.40% compared to when normal carbon trading was considered, further constraining MMG’s carbon emissions.

Aiming at problems of power allocation and economic scheduling for independent multi-microgrid systems, a bi-level optimization method based on optimal power flow and consensus algorithm is proposed. The novelty of the method is that an independent multi-microgrid system is divided into two layers: in the upper layer, with the predicted output range of the microgrids as the input data, each microgrid is considered as a virtual power supply or virtual load, and taking the minimum network loss as the goal, the energy mutual aid and power allocation among the microgrids are transformed into solving the optimal power flow; in the lower layer, taking the upper layer power distribution scheme as the constraint condition, considering load fluctuation and wind/solar generation uncertainty, the optimal dispatch model of the controllable distributed generator is established based on the distributed theory and the consensus algorithm of equal cost increment, and the "plug and play" of the distributed generator is also realized. An islanded multi-microgrid cluster is taken as an example to verify the economy, security, and reliability of the proposed scheme. The advantages of the scheme have been shown by the simulation example. Simulation results show that the upper-layer method not only realizes the optimal power allocation of microgrids, but also reduces the power loss of the energy mutual aid among the microgrids; through the optimal scheduling of controllable power supply in the microgrid, the lower-level scheme not only improves the economic benefit of the microgrid, but also well suppresses the negative effects of the uncertainties, prediction errors and power fault removal on the multi-microgrid system, which improves the robustness of the system.

In this paper we focus on integration of batteries with ship power systems for three application cases. Presented application cases include two platform supply vessels, one equipped with diesel engines and other with dual fuel engines, and a heavy lift crane vessel. Besides reducing the number of running engines and maintaining original dynamic positioning capabilities, we also demonstrate novel possibilities of battery usage, such as harvesting of waste energy, and implementation of dual fuel engines for dynamic positioning. In all application cases, results indicate significant fuel savings and reduction of running hours due to spinning reserve function of batteries.

The frequency domain spectrum (FDS) method can effectively evaluate the aging state of cross-linked poly-ethylene (XLPE) cable insulation. To more accurately achieve a quantitative analysis of information in the FDS, this paper combines the concepts of fractional element (Cap-Resistor) and fractional calculus, inspired by the Debye model and the multi-branch improvement method of the Cole-Cole (C-C) model, and establishes an improved fractional Zener model based on the existing Cap-Resistor model, and combines the improved fractional Zener model with the Elite Genetic Algo-rithm (EGA) to propose a new method for analyzing the re-laxation polarization information of XLPE dielectric. Six sets of XLPE cable samples with different aging times (including a validation set) are prepared at an aging temperature of 150 °C, and the FDS of the thermal aging samples are meas-ured. Then the FDS are fitted using a modified fractional Ze-ner model: firstly, the least squares method is used to estab-lish the optimized objective function, and the characteristic parameters are extracted and preferentially selected using EGA for analysis, and the fitting equations between aging time and characteristic parameters are established, and the validation results manifest that the error of the characteristic parameters on the aging time characterization of XLPE cable insulation samples is 0.18465 %, which is excellent. The eval-uation method’s accuracy has been validated. This paper in-troduces a feasible approach for analyzing relaxation polari-zation information in XLPE dielectric using an improved frac-tional Zener model and EGA.