When the high voltage direct current (HVDC) transmission is running under the monopoleground- circuit operation mode, slight direct current (DC) will be coupled into the nearby alternating current (AC) power grids and so has some negative influences, called DC bias phenomenon, on current transformers (CT). In this paper, based on Preisach magnetization theory, a digital simulation method of CT is established and then its correctness has been verified by error calibration experiments. After that, the inherent mechanism of DC bias phenomenon is analyzed and concluded by simulating the coupling relationships among the magnetic flux density of iron core, exciting current and coupling DC. Most importantly, we have built a coupling DC monitoring network for Jingpin to south of Jiangsu (J2SJ) HVDC project in China’s Jiangsu Province, and based on the monitoring data and analysis results of CT’s error varying with coupling DC, the actual influence of J2SJ HVDC on CT measuring accuracy is evaluated quantitatively.

Photovoltaic (PV)-assisted charging station for electric vehicles (EVs) is a typical integration of consuming renewable resources locally. In this paper, PV-assisted charging station's optimal operation model is built by taking charging cost and charge/discharge cycle number of energy storage system as objective function. Particle swarm optimization (PSO) based on penalty function is applied to solve the objective function considering output constraints, SOC constraints, etc. Simulation results show that the charging station optimization scheduling strategy can effectively control the charging cost and reduce the off-peak difference of load, which is of great significance to control economic cost of charging station and maintain the stability of power system. Optimization method for scheduling put forward in this paper provides theoretical for city charging infrastructure demonstration.

Rapid and accurate eddy-current calculation is necessary to analyze eddy-current couplings (ECCs). This paper presents a general 3D analytical method for calculating the magnetic field distributions, eddy currents, and torques of ECCs with different Halbach magnet arrays. By using Fourier decomposition, the magnetization components of Halbach magnet arrays are determined. Then, with a group of H-formulations in the conductor region and Laplacian equations with magnetic scalar potential in the others, analytical magnetic field distributions are predicted and verified by 3D finite element models. Based on Ohm’s law for moving conductors, eddy-current distributions and torques are obtained at different speeds. Finally, the Halbach magnet arrays with different segments are optimized to enhance the fundamental amplitude and reduce the harmonic contents of air-gap flux densities. The proposed method shows its correctness and validation in analyzing and optimizing ECCs with Halbach magnet arrays.

With the large amount of distributed generation in use, the structure of the distribution system is increasingly complex. Therefore, it is necessary to establish a method to improve load reliability. Based on the reliability model of distributed generation, this paper investigates the time sequential simulation of a wind/solar/storage combined power supply system under off-grid operation. After classifying the load by power supply region, the load weight coefficient is established, which modifies the reliability index of the load point and system. The modified expected energy not supplied (EENS) is adopted as the objective function, and the particle swarm optimization algorithm is used to solving the optimal energy scheduling for improving the load reliability. Finally, the load reliability is calculated with a hybrid method. Using the IEEE-RBTS Bus 6 system as an example, the correctness and validity of the proposed method are verified as an effective way to improve load reliability.

How to perform accurate calculation of heat balance and quantitative analysis of energy efficiency for building clusters is an urgent problem to be solved to reduce building energy consumption and improve energy utilization efficiency. This article proposes a method for the heat balance calculation and energy efficiency analysis of building clusters based on enthalpy and humidity diagrams and applies it to the energy management of building clusters containing primary return air systems and heating pipe networks. Firstly, the basic structure and energy management principle of building clusters with a primary return air system and a heating pipe network were given, and the heat balance calculation and energy efficiency analysis method based on i-d diagram was proposed to realize the accurate calculation of heat load and the quantification of energy utilization. Secondly, the energy management model of the building cluster with a primary return air system and a heating pipe network was established to efficiently manage the indoor temperature and the heating schedule of ASHP, HN and HI. Finally, the proposed method was validated by calculation examples, and the results showed that the proposed method is beneficial for improving the energy economy and energy efficiency of building clusters.