• Energy Research

With the implementation of the concept of "Energy Internet", the integrated energy system as the physical carrier of the Energy Internet has been further developed. A regional integrated energy system optimal operation model considering flexible heating load is proposed. Firstly, combined with the basic principles and operation characteristics of typical equipment in the integrated energy system, the main equipment model of the integrated energy system is formed. Based on the user's work and rest rules, a flexible heating load model considering the user's flexible comfort constraints is constructed to increase the system's operation flexibility. Then, a mathematical model for the optimal operation of the regional integrated energy system based on the bus-based structure is constructed. Finally, three different heat and power dispatch methods are defined to analyze the benefits of the combined heat and power dispatch in an integrated energy system. The simulation results show that the optimal operation model of regional integrated energy system considering flexible heating load can improve energy efficiency and reduce the system operation cost.

The coupled single-port circuit has been proposed for online voltage stability assessment based on wide-area measurements and grid equations. This circuit can explicitly reflect the influence of grid and load on voltage stability. However, it does not consider the impact of power generation. A novel Thevenin equivalent (TE) circuit considering the influence of source-grid-load on voltage stability is proposed in this paper. First, the impact of source-grid-load on the voltage of an individual load bus is divided into three parts according to the node-voltage equation. They are then decomposed into two components, respectively associated with the TE voltage and the TE impedance according to the TE circuit’s characteristics. Finally, an online identification method for the parameters of the proposed TE circuit based on wide-area measurements is developed. Compared with the coupled single-port circuit, the proposed method has the advantage of being able to consider the influence of power generation on voltage stability and being consistent in form with traditional TE circuit without requiring approximation. Case studies on the IEEE 118-bus system illustrate the accuracy and effectiveness of the proposed method.

This paper proposes a new distributed dispatch scheme to realize efficient coordinated real-time dispatch of the coupled transmission grid and active distribution grids (ADGs). In the proposed scheme, on the one hand, the concept of optimal power exchange interval is introduced to coordinate the transmission grid and ADGs so that the reserve capacity support from ADGs can be incorporated in the dispatch optimization of the transmission grid. On the other hand, uncertainties of renewable distributions are considered to ensure the robustness of dispatch decisions. With the analytical target cascading (ATC) method, the centralized distributionally robust dispatch model for the integrated transmission-distribution system is decoupled, leading to a number of independent small local optimization problems for the transmission grid and ADGs. Meanwhile, the diagonal quadratic approximation is adopted to develop an iterative coordination strategy where all local optimization problems are solved in a parallel manner, increasing the computational efficiency. By using the constrained cost variable technique (CCV) and a new affine policy, the original non-convex dispatch model is reformulated as a linear optimization problem, which ensures the convergence of the iterative process and further reduces the computational burden. Case studies on three test systems verify the effectiveness and efficiency of the proposed scheme.

With the energy storage cooperatively participating in AGC of the interconnected power grid, this paper proposed energy storage acti power control performance evaluation standard. called ES (energy storage) standard, for multi-area power grid. The index was a combination of the basic ideas of both NERC's control performance standard (CPS)and unit control performance standard (UCPS). The ES standard used the energy output factor of energy storage to reflect the energy storage participation in the active control and constrained the power grids AGC behaviors with the energy storage cooperatively participating by generalized area control error. The standard evaluated two kinds of different AGC control objectives. It can be used to guide the energy storage active power control method. Finally, the comparative analysis was run for the active control guidance of the ES standard and CPS through simulation. The simulation results show that compared with the CPS, the ES standard promotes the energy storage balance the frequency fluctuations coordinately with AGC units in power grid. It is more adapt to evaluate the energy storage active power control performance.

Abstract In deregulated environment, the wind power producers (WPPs) will face the challenge of how to increase their revenues under uncertainties of wind generation and electricity price. This paper proposes a method based on deep reinforcement learning (DRL) to address this issue. A data-driven controller that directly maps the input observations, i.e., the forecasted wind generation and electricity price, to the control actions of the wind farm, i.e., the charge/discharge schedule of the relevant energy storage system (ESS) and the reserve purchase schedule, is trained according to the method. By the well-trained controller, the influence of the uncertainties of wind power and electricity price on the revenue can be automatically involved and an expected optimal decision can be obtained. Furthermore, a targeted DRL algorithm, i.e., the Rainbow algorithm, is implemented to improve the effectiveness of the controller. Especially, the algorithm can overcome the limitation of the conventional reinforcement learning algorithms that the input states must be discrete, and thus the validity of the control strategy can be significantly improved. Simulation results illustrate that the proposed method can effectively cope with the uncertainties and bring high revenues to the WPPs.

Abstract Direct current (DC) microgrids are gaining popularity due to their simpler structure and high energy efficiency. This paper investigates the design of an integral backstepping controllers for the DC microgrid involving renewable distributed generators and hybrid energy storage system (HESS). At first, the generic DC microgrid mathematical model is derived. Then, the controllers are designed for PV unit, wind unit, and HESS with the main control objective to regulate the common DC bus voltage. After that, the asymptotic stability of the DC microgrid is ensured through the control Lyapunov function. Finally, the energy management system is adopted to ensure the power balance under variable power generation. The performance of the proposed framework is verified by simulating it on MATLAB/Simulink and comparing the results with adaptive Lyapunov redesign and sliding mode control. Also, the effectiveness of the developed control approach is further validated through real-time controller hardware in the loop experiments.