Integrating energy storage systems (ESSs) into the railway power flow controller (RPFC) offers a promising path to enhance the interaction capability and connection compatibility between the railway power systems (RPSs) and the utility. Despite its technical advantages, full consideration must be given to the media-type & configuration of ESS, the rating of RPFC, and the control framework that can compatibly integrate the control & planning for cost-efficiency improvement. For this problem, a novel concept that takes the real-time control and off-line configuration approach in a unified framework is proposed for hybrid ESS-integrated RPFC (HESS-RPFC) in this paper, in which the comprehensive techno-economic performances of the whole system are taken into account. First, a unified analytical power regulation framework is established for HESS-RPFC, in which the functions of energy management (EM) and power quality control are seamlessly integrated. To realize EM, improve RPS’s grid-connection compatibility, and reduce the rating of RPFC, a double-layer power regulation strategy of HESS-RPFC is developed on the proposed framework. Subsequently, a lifetime net benefit-oriented optimization model is formulated and solved, through which, the optimal rating configuration of the whole system and HESS’s mode-triggering thresholds can be obtained. Finally, a comprehensive performance evaluation based on real-measured data is conducted, revealing that HESS-RPFC with the proposed method provides superior economic benefits over single-media ESS schemes, ensures satisfactory grid-connection compatibility for the RPS, and reduces the RPFC’s rating by nearly 46%. Additionally, the real-time execution feasibility of the proposal is demonstrated by hardware-in-the-loop tests.

The frequency and voltage stability of grid-forming virtual synchronous generator (GFM-VSG) grid-tied system becomes significant in inertia and damping support when GFM-VSG is attached to the power network. In this article, we propose a generic open-loop system model for the frequency–voltage induced-stability analysis, where the dynamics of rate of change of frequency (RoCoF) is a dynamic process that acts on the rate of change of voltage and then, in turn, reacts on RoCoF. In addition, frequency self-stability is evaluated by magnitude–phase feedback analytical model, where the frequency dynamics are identified by the interaction between RoCoF and frequency bias (FB). Also, it is found that inertia is the origin of occurrence of low-frequency oscillation, which induces a natural phase bias between RoCoF and FB. It is found that GFM-VSG can operate stably in weak grid but cannot operate well in ultrastrong grid condition. Finally, theoretical analysis is validated by simulations and experiments.

RPFC, as a promising technical route for railway power regulation, its rating determinization, and the related flexible power regulation perplex designers and hinder large-scale applications, especially when the RBE is nonnegligible. In this article, a general power factors full-dimensionally hunted power distribution strategy (PFFDH-PDS), applicable for both offline design and real-time control, is proposed. Two key methods are developed: full-dimensionally hunting the power factors (PFs) under the developed mathematic framework, from which the global optimal compensating power and RPFC's rating can be worked out; and precisely partitioning two-phase loads on their PF-P and PF-PF distributing panels; in both methods, RBE is considered. By adopting PFFDH-PDS, RPFC's rating can be reduced by almost 60% compared to the conventional method, while the system has satisfactory grid-connection compatibility. Finally, the effectiveness and performance of the proposal are verified and conducted by real-measured data.

Developing efficient defensive strategies against cyber-attacks is a major concern of modern power system research. With the goal of minimizing the expected load loss, this article proposes a robust probabilistic substation-based defender-attacker-defender (DAD) model to allocate the substation's defensive resources. The proposed model aims to minimize the risk of cyber-attacks on intelligent electronic devices (IEDs). The game between the defender and the attacker concerning multiple substations, IEDs, and their connected lines is particularly modeled. In addition, we extend the proposed probabilistic DAD model to an observability-ensured DAD model where the existing phasor measurement units in the power grids are considered in the defensive resource allocation. Integrated with the logarithmic transformation and piecewise linearization techniques, a customized column-and-constraint generation algorithm is developed to solve the proposed model. Finally, the numerical results on IEEE RTS 24-bus and 118-bus systems validate the proposed model.

In-depth understanding of the multi-energy consumption behavior pattern is the essential to improve the management of multi-energy system (MES). This paper proposes a data-driven three-stage adaptive pattern mining approach for multi-energy loads, which addresses the issues of complex multi-dimensional time-series mining, uncommon daily loads discovery, typical load classification and parameter setting requiring user intervention. In the first stage, the relative state changes over time between different energy loads are excavated based on Autoplait, which realizes time pattern discovery, segmentation and match for multi-dimensional loads. In the second stage, adaptive affinity propagation (AAP) considering trend similarity distance (TSD) is proposed to classify loads into common and uncommon clusters, where uncommon loads are eliminated and daily pattern is obtained by taking average of common loads. In the third stage, AAP with windows dynamic time warping (WDTW) identifies various profiles to obtain typical pattern of daily loads. Specifically, pattern mining provides the key information of multi-energy loads, which is significant to the applications for the demand side, such as load scene compression, load forecasting and demand response analysis. A case study uses MES data from Arizona State University to verify the effectiveness and practicality of the proposed approach.

In the student-centered cultivation model, innovation ability and engineering skills of solving complex engineering problems is generally considered to be the key goal, which is usually broken down into small independent tasks arranged in different courses to support it from varying ways. However, at the implementation level, the actual training effect is not quite satisfactory due to the weak relationship between different courses and the lack of motivation for teachers to communicate with each other. In this paper, we propose a set of blended learning courses focusing on cultivating innovation ability throughout the undergraduate study period. Based on our design, the blended learning courses integrate MOOC, private course, comprehensive curriculum project, discipline competition and other types of courses, aiming to comprehensively improve undergraduates' innovation ability and engineering skills. These courses are arranged in different semesters and majors according to their general knowledge and specialization. After six years of practice for at least 3 generations of undergraduate students who have completed a whole training plan, we have collected a large number of data and made detailed analysis. It shows that undergraduates who participate in the complete learning process of the blended courses have obvious advantages in professional course scores, scholarship and award proportion.

This paper presents a variable-current charging strategy of Li-ion batteries. Since the battery characteristics vary with state of charge (SOC), it is more reasonable to divide the charging process based on SOC than on cut off voltage. We find an optimal charging pattern of the proposed strategy by Non-dominated Sorting Genetic Algorithm-III (NSGA-III). The Second-order Thevenin model of battery is established to simulate the charging process. Verification experiments are performed and results show that the obtained charging pattern has a temperature and loss reduction of 2.9 °C and 0.5% compared with constant current-constant voltage (CC-CV) strategy under the same charging time and capacity.

In the above article[1], the first-page affiliation information should appear as follows: Li Jiang, Yuduo Huang, Yong Li, Xuebo Qiao, Chun Huang, and Yijia Cao are with the College of Electrical and Information Engineering, Hunan University, Changsha 410082, China, and also with the State Key Laboratory of Advance Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China.

This paper presents an optimal collaborative scheduling method to relieve line overloads during the process of emergency faults. First, the theoretical analysis of power flow control via the voltage source converter based high voltage direct current (VSC-HVDC) system, generator output or load curtailment is investigated. Then, a collaborative scheduling framework is designed based on these two measures, with the comprehensive considerations of total emergency control cost for different steps. Finally, the proposed framework is assessed from the perspectives of performance and economy using a modified New England power system, and the results are compared with two methods. Numerical test results show that the proposed method is capable of eliminating line overloads in an economic way.

In this paper, a power quality (PQ) survey of the large-power electrolytic manganese factory is presented to provide the background introduction of PQ issues. The electrolytic manganese factory consists of 10 rectifier units, which has the electric environment of large current/low voltage. The monitoring object is a 15 MVA rectifier unit. The power quality monitoring lasted 16.5 hours. First, the topology of the large-power supply system is introduced. Then, the measuring results are analyzed in detail, which include the power factor and harmonic. At last, a case study of power quality issue is illustrated, and the recommended solution is given out. The test results indicate that the power quality can meet the relevant requirements with the help of harmonic filter.

The photovoltaic (PV) energy, as clean and renewable energy, has become increasingly important. With energy storage system, the PV power can become schedulable and the use efficiency of PV power can be greatly improved. The tracking output is one of the running modes for energy storage to adjust the PV power generation. However, the research on the tracking output do not consider the fluctuation of PV power generation, the upper and lower limits of prediction errors, or only consider tracking the power curve. In this paper, a novel control method is proposed based on the super short-term prediction PV power and the prediction errors distribution law to obtain the charge and discharge strategy for energy storage ahead. In this control method, the objective function includes three parts, respectively the D-value between the planned output and actual output of PV power and energy storage system, the change of the state of charge (SOC) with different weight, The constraint condition considers the power demand, flexibility requirement and storage costs comprehensive. Then the prediction errors distribution law can be obtained by analyzing prediction errors of the PV power, the proper errors correction parameters can be selected according to the law to get a more accurate predication range and make the energy storage scheduling strategy more flexible. The particle swarm optimization (PSO) algorithm is used to get the optimal charge and discharge power strategy in advance. With the data collected from typical PV power station as an example, the simulation results verify the feasibility and flexibility of the proposed strategy, it also provides effective reference scheme for day-ahead control of battery energy storage systems

The use of integrated shipboard power system (SPS) has greatly contributed to the next-generation vessels development. In this sense, how to realize the reasonable power distribution between hybrid zones in SPS is becoming one of the key problems to ensure system robustness and reliability. In this paper, a flexible power control strategy is proposed for the coordinated operation of the hybrid ac/dc zones in SPS. First, the interactive relationship of the ac/dc interface is analyzed, and the virtual inertia and capacitance are defined to reveal the interactive influence of the ac and the dc subgrids, which leads to a new V-f droop principle. Then, the flexible control strategy is designed based on the droop principle as well as the characteristics of the analogous virtual synchronous generator, and the key parameters' determination are discussed in detail, which can realize a proper assignment of cross-zone supportive power and improve the system dynamic response. In addition, the coordinated control loops are designed with the distributed energy storages and interlinking converters for the implementation of the strategy. Finally, the proposed strategy is validated by the simulation, which shows that the strategy can enhance the power quality and dynamics of the hybrid zones and contribute to the robustness of the whole SPS.

This paper proposes an optimal locating and sizing method of distributed generations (DGs) considering local consumption and power export potential. Based on the analysis of seasonal and temporal characteristics of different types of DGs and load, the proposed DGs locating and sizing model, is to minimize the total costs of DGs depreciation, network power losses, and redundant power. Under the premise of load demand locally satisfied, the optimal location and size of DGs is obtained by reducing the redundant power of DGs. Finally, the IEEE 33-bus test system is applied to validate the effectiveness and practicability of the proposed method.

In DC microgrid, it is common that constant power loads (CPLs) exhibit negative impedance characteristics, which degrades the stability margin of the whole system. This paper focuses on the stability problem of isolated DC microgrid with multiple DC voltage control units and constant power loads. Taking controllers into account, the detailed impedance model of DC microgrid is established, and it shows the interaction between converters through analyzing the minor loop gain by using Nyquist criterion. Meanwhile, resonance is examined using impedance model. Impedances-based stability analysis reveals the influence of different factors on the stability, such as the size of the CPLs and the droop coefficient. To verify the analysis results, the simulation model is built based on PSCAD/EMTDC. The simulation results confirm the validity of the method. With the developed dc impedance and stability analysis method, the DC microgrid system stability characteristics can be evaluated, which can be used for system design to maintain stability.

This paper proposes a mixed-integer quadratic programming (MIQP) model for optimal day-ahead distribution networks dispatch considering Wind Generators (WGs) and topology reconfiguration. Firstly, linearized current injection model is introduced for generators by a series of approximations. Then the day-ahead Switching Operations (SOs) of reconfiguration could be calculated in a linear form based on the fixed characteristic of network topology. Finally, the costs of power loss and SOs are minimized by our model while the linear constraints, e.g. nodal voltage (NV) constraints and branch current constraints, are considered. The simulation results on IEEE-33 system demonstrate that the proposed model is feasible and effective.

Due to the inverter used, DG can not only integrate the active power into power grid but also support the grid with reactive power. This paper proposes an optimal configuration methodology of renewable DG so as to maximize the penetration level of DG considering the temporal characteristics of active-reactive power (P-Q). Further, the uncertainty output of the wind generator, photovoltaic and small hydropower is taken into account by forming typical scenarios based on the cluster analysis of historical data. Simulation on a modified IEEE33-bus distribution system show that a significant increase in maximum penetration can obtain by considering the reactive power of DGs.

This paper proposes a multiperiod optimal dispatch model for hybrid voltage source converter based multi-terminal DC (VSC-MTDC) system and AC grids with consideration of optimal coordination of offshore wind farm (OWF) and battery energy storage (BES). The OWF is connected to onshore AC grid by VSC-MTDC. The VSC capacity limits and Grid Code for OWF connection to AC grid are taken into consideration. Scenario method is employed to model the wind energy output uncertainty. Simulation on the modified IEEE 118-bus system with three OWFs integration via seven terminal VSC-MTDC network is used to validate the availability and effectiveness of the proposed method.

Battery energy storage (BES) and distributed generation (DG) play an important role in active distribution networks. However, harmonic problems could be caused by the inverters in BES and DG, resulting in a poor power quality (PQ). In addition, ensuring acceptable voltage unbalance level is also another crucial PQ issue in distribution networks. Therefore, in this paper, an optimal distribution network operational model (ODNOM) is proposed to consider PQ problems caused by BES and DG. In this model, additional network power losses due to harmonics are considered into the objective function, and the harmonic constraints and voltage unbalance constraints are also taken into account. The particle swarm optimization is used to solve the proposed ODNOM. The simulations on the IEEE 13-bus, IEEE 37-bus, and IEEE 123-bus systems show that a satisfactory PQ can be achieved by the proposed approach while optimizing the total branch active power losses. This paper aims to obtain a satisfactory PQ level while minimizing the total branch active power losses in the day-ahead dispatch of active distribution networks, since inverters-based BES and DG can inject harmonic pollution into distribution networks and voltage unbalance level is also an important issue for supplying good quality electricity to end users. To achieve such an objective, PQ constraints such as the total voltage harmonic distortion (THD) constraints, the individual voltage distortion constraints, and the voltage unbalance factor constraints are considered into the day-ahead scheduling. In addition, the network active power losses of the concerned harmonic frequencies are also considered into the objective function. The simulation results of the unbalanced IEEE 13-bus, IEEE 37-bus, and IEEE 123-bus systems show that the proposed approach can give a satisfactory day-ahead schedule of good quality power for active distribution networks. Also, the case studies indicate that total network power losses and the satisfactory PQ are the two contradictory objectives. The proposed approach can be applied to ensure a satisfactory PQ when making a dispatch plan in distribution networks with inverter-based BES and DG.