With the development of the autonomous and supply-production-sale integrated We-Energy (WeE), the Energy Internet performs a fully distributed structure, and the fluctuation of power injections cannot be neglected. This paper investigates an energy management problem with operation security constraints for WeE-based Energy Internet in a distributed way. Firstly, considering the complex power injections caused by the high flexibility and strong robustness of WeE, the steady-state voltage security region (SVSR) for WeE is established. The voltage excursion index for WeE is proposed to quantify the voltage security margin between the operation state and the security boundary. Secondly, the SVSR-based energy management model for WeE with linear coupled equations and box inequalities is constructed to minimize the operation cost. Thirdly, a fully distributed energy management strategy is proposed based on the alternating direction method of multipliers (ADMM). Furthermore, the discrete nonlinear system analysis theory proves the proposed strategy's convergence and optimality. The energy management strategy guarantees operation reliability and eliminates the risks of voltage off-limit. Finally, the effectiveness of the fully distributed energy management method with SVSR for WeE is verified by simulation results.

Due to the influence of meteorological conditions, shipboard photovoltaic (PV) systems have problems such as large fluctuation and inaccurate prediction of the output power. In this paper, a short-term PV power prediction method based on a novel digital twin (DT) model and BiLSTM is proposed. Firstly, a PV mechanism model and a data-driven model were established, in which the data-driven model was updated iteratively in real time using the sliding time window update method; then, these two models were converged to construct a PV DT model according to the DS evidence theory. Secondly, a BiLSTM model was built to make short-term predictions of the PV power using the augmented dataset of the DT model as an input. Finally, the method was tested and verified by experiments and further compared with main PV prediction methods. The research results indicate the following: firstly, the absolute error of the DT model was smaller than that of the mechanism model and the data-driven model, being as low as 5.62 W after the data update of the data-driven model; thus, the DT model realized data augmentation and high fidelity. Secondly, compared to several main PV prediction models, the PV DT model combined with BiLSTM had the lowest RMSE, MAE, and MAPE; the best followability; and the smallest absolute error under different weather conditions, which was especially obvious under cloudy weather conditions. In summary, the method can accurately predict the shipboard PV power, which has great theoretical significance and application value for improving the economy and reliability of solar ship operation.

The distribution grid experiences node voltage fluctuations due to the growing uncertainty of large-scale renewable energy sources A practical solution is establishing a chance-constrained optimal model to deal with the uncertainties. However, using this method needs to know the accurate probability distribution of node power injections, which has limitations in application. Therefore, this paper proposes a distributionally robust chance-constrained optimization method for power grid operation based on the ambiguity set of probability distributions. Firstly, considering voltage security constraints, this paper establishes a chance-constrained model to minimize the cost of active power regulation. Besides, based on the Wasserstein ambiguity set, a linearized method is proposed to convexify the objective function. Moreover, the conditional risk value (CVaR) is applied to convert the uncertain model into a deterministic model. The effectiveness of the proposed method is validated through optimization results obtained for the modified PG&E69-bus distribution grid.

Reactive power sharing in distributed generators (DGs) is one of the key issues in the control technologies of greenship microgrids. Reactive power imbalance in ship microgrids can cause instability and potential equipment damage. In order to improve the poor performance of the traditional adaptive droop control methods used in microgrids under high-load conditions and influenced by virtual impedance parameters, this paper proposes a novel strategy based on the deep reinforcement learning DQN-VI, in which a deep Q network (DQN) is combined with the virtual impedance (VI) method. Unlike traditional methods which may use static or heuristically adjusted VI parameters, the DQN-VI strategy employs deep reinforcement learning to dynamically optimize these parameters, enhancing the microgrid’s performance under varying conditions. The proposed DQN-VI strategy considers the current situation in greenships, wherein microgrids are generally equipped with cables of different lengths and measuring the impedance of each cable is challenging due to the lack of space. By modeling the control process as a Markov decision process, the observation space, action space, and reward function are designed. In addition, a deep neural network is used to estimate the Q function that describes the relationship between the state and the action. During the training of the DQN agent, the process is optimized step-by-step by observing the state and rewards of the system, thereby effectively improving the performance of the microgrids. The comparative simulation experiments verify the effectiveness and superiority of the proposed strategy.

Safely completing voyages is vital for all-electric ships (AESs). However, the existing voyage scheduling methods focus on the generation cost and merely consider the impact of the operation state of the shipboard power system on navigation security. Hence, considering power supply capacity constraints (PSCC), this paper establishes a chance-constrained optimal model for the joint generation and voyage scheduling of AESs. Firstly, considering the N-1 criterion, the linear expressions for PSCC of AESs are expressed based on the interconnection topology of shipboard inverters. Secondly, the explicit chance-constrained expressions for PSCC are established based on the Cornish-Fisher series expansion. Thirdly, a coordinated model is established for joint generation and voyage scheduling and solved by dynamic programming. The actual voyage data are used for simulations, and the results demonstrate the effectiveness of the proposed method.

Due to the high penetration of virtual power plants (VPPs), the bi-directional power flow between VPPs and active distribution grids makes the grid operation complex. Without congestion management, the operation schedule only considers the economic benefits, and power flow constraints might be violated. Hence, it is necessary to conduct power interaction within the operation constraints. This paper proposes a coordinated economic dispatch method under voltage security constraints. The linear expressions were derived by simplifying the AC power flow equations to reduce the computation complicity. Then, optimal economic dispatch models with voltage security constraints were established for the active distribution grid and VPPs, respectively. Meanwhile, the transacted power and clearing price were set as the communication variables, and a coordinated strategy was proposed for the overall optimal goal. The modified IEEE 33-node and PG&E-node distribution grids were utilized for the simulations, and the results affirmed the validity of the proposed method.