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Voltage source converter‐based DC systems face severe overcurrent problem under DC line faults, which causes significant influence on security, reliability and stability of the power system. As the theoretical basis for relay coordination and protection, the transient fault analysis of voltage source converter‐based DC systems needs an in‐depth study. Based on the conventional fault analysis, an accurate transient fault analysis method for the DC pole‐to‐ground fault and pole‐to‐pole fault through freewheeling diode switch state signals is proposed. In the capacitor discharge stage, fault current calculation error is reduced by taking into consideration the current fed from the grid side. In addition, through detailed analysis of the conduction condition and state of the freewheeling diode, clear calculation equations of transient fault currents are obtained. With the prior knowledge of fault response characteristics, definitions of freewheeling diode switch state signals assist in unifying calculation processes of different fault stages and simplifying transient fault calculation. Finally, a typical simulation model of the voltage source converter‐based DC system was built in PSCAD/EMTDC software. The simulation results verified the conciseness and correctness of the proposed fault analysis method compared with the conventional fault analysis. [ABSTRACT FROM AUTHOR]

Multi-battery energy storage systems (MBESSs) are widely adopted to overcome the uncertainty problem of renewable energy sources. However, state-of-charge (SOC) imbalance issue of MBESSs brings great challenges to the optimal dispatching strategy and the lifetime management strategy for the MBESS. This study proposes a distributed equalisation strategy for the MBESSs to solve the stated problem. An equitable operation optimisation model is proposed in the distributed equalisation strategy. The equitable optimisation model can be simplified as a convex quadratic optimisation problem. An equitable approximation method is utilised to solve the convex quadratic optimisation problem according to the Karush–Kuhn–Tucker optimality conditions. Based on the equitable approximation method, the SOC balance process is distributed into different iteration steps. The iteration of the SOC balance process is implemented by the communication system connecting the distributed management systems (DMSs). The distributed SOC balance step is implemented by the DMSs of the batteries. The proposed strategy is validated by a hardware-in-the-loop simulation system based on the RT-LAB. Test results show that the proposed strategy ensure the SOC balance and improve the robustness of the MBESS. [ABSTRACT FROM AUTHOR]

Direct‐current (DC) line faults are a major issue in ultra‐high‐voltage direct‐current systems due to the complex and wicked environment. Thus, reliably detecting and isolating the DC line faults are not a trivial engineering task. This study proposes a DC line protection scheme based on resonance frequency. The scheme mainly consists of a fault discrimination criterion and a faulty pole selection criterion. The fault discrimination criterion is based on the phase of the resonance frequency impedance, and it is deployed to differentiate the faults on the protected DC line from the external faults. The faulty pole selection criterion is based on the ratio of the resonance frequency currents, and it is employed to select the faulty pole. The sensitivity analysis demonstrates that the performance of the proposed protection is promising. The simulations carried out in PSCAD/EMTDC under various conditions verify the feasibility and validity of the proposed protection scheme. [ABSTRACT FROM AUTHOR]

The six-sequence component method is widely used in short-circuit calculation of double-circuit lines. However, this method can be used to decouple only two parallel transmission lines whose parameters are exactly the same. In this paper, a new sequence component method is introduced to deal with the lines whose parameters are not exactly the same. Mutual impedances between phases of the same line are decoupled first, and then the zero-sequence mutual impedances between different lines are decoupled. Six new independent components are obtained after decoupling. System impedances are modified based on the relationship between voltages and currents of the new sequence components and the traditional sequence components. According to the boundary conditions of the faults, the characteristics of new sequence components are studied, and the corresponding sequence networks are discussed. According to the combined sequence network, new sequence currents can be calculated, and the phase currents can be obtained easily from the new sequence currents by a transformation matrix. PSCAD simulation results demonstrate that the short-circuit calculation method proposed in this paper is appropriate and practical to deal with the two parallel transmission lines with different parameters and partially coupled transmission lines. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The energy consumption statistics of buildings shows that cooling takes up a considerable portion of the energy demand. The peak-valley characteristics of cooling demand coincides with that of the electrical load in the microgrid. Thus the management of the cooling demand side can regulate the peak-valley demand and stabilize power fluctuations. This paper proposes a new energy management strategy that reduces the investment and loss of the battery energy storage system ( BESS) by applying ice storage air-conditioning ( ISAC) to the microgrid. Based on the load characteristics and BESS investment, the capacities of the chillers and the ice tank are analyzed. Penalty functions of ISAC and BESS are designed, according to which the stabilization command is dispatched. Finally, an actual case is analyzed by the proposed strategy, and the results verify the feasibility and effectiveness of the energy management strategy. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Quadruple-circuit lines with asymmetric parameters have been widely built to increase power transmission capacity. The asymmetric parameters of the lines lead to different current characteristics compared with traditional lines. A cross-differential protection scheme based on negative sequence fault current is proposed to overcome the deficiency of traditional protection scheme. The fault superimposed networks of quadruple-circuit lines are discussed to analyze the fault sequence currents of each line. Differential currents are deduced to form the relay criterion. The threshold values of protection are calculated according to characteristics of superimposed fault sequence currents. Corresponding operational logic is also introduced to ensure the stability and reliability of protection. Finally, the reliability of the proposed protection scheme is verified. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Quadruple-circuit lines with different self-impedances have been applied in power system with the development of power industry. However, the different self-impedances in quadruple-circuit lines will cause problems in fault analysis and related relay protection in the lines. The impedance matrix of these lines is different from that of symmetrical lines, and existing methods cannot completely eliminate all mutual impedance. A new method is proposed to decouple these asymmetrical quadruple-circuits lines in this paper. The phase-to-phase mutual impedance is eliminated first, and then the line-to-line mutual impedance is eliminated according to the circulating current method. The mathematical deduction is formulated to ensure the complete decoupling of the impedance matrix. The fault conditions can be used to obtain the relationship between the independent sequence networks, which can be used to calculate the fault current. Power Systems Computer Aided Design (PSCAD) simulations indicate that the decoupling method is suitable for fault analysis of the quadruple-circuit lines with different self-impedances. The related fault analysis method is quite accurate and easy to be applied. The fault analysis accuracy is not affected by the fault resistance, fault type, fault location, or length of lines. [ABSTRACT FROM AUTHOR]