Abstract:Distributed generation (DG) are critical components for active distribution system (ADS). However, this may be a serious impact on power system due to their volatility. To this problem, interactive load and battery storage may be a best solution. This paper firstly investigates operation characteristics of interactive load and battery storage, including operation flexibility, inter-temporal operation relations and active-reactive power relations. Then, a multi-period coordinated activereactive scheduling model considering interactive load and battery storage is proposed in order to minimize overall operation costs over a specific duration of time. The model takes into accounts operation characteristics of interactive load and battery storage and focuses on coordination between DGs and them. Finally, validity and effectiveness of the proposed model are demonstrated based on case study of a medium-voltage 135-bus distribution system.

Abstract:This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications.

Abstract:This paper deals with two new methods, based on k-NN algorithm, for fault detection and classification in distance protection. In these methods, by finding the distance between each sample and its fifth nearest neighbor in a predefault window, the fault occurrence time and the faulty phases are determined. The maximum value of the distances in case of detection and classification procedures is compared with pre-defined threshold values. The main advantages of these methods are: simplicity, low calculation burden, acceptable accuracy, and speed. The performance of the proposed scheme is tested on a typical system in MATLAB Simulink. Various possible fault types in different fault resistances, fault inception angles, fault locations, short circuit levels, X/R ratios, source load angles are simulated. In addition, the performance of similar six well-known classification techniques is compared with the proposed classification method using plenty of simulation data.

Abstract:The increasing penetration of inverter-based distributed generations (DGs) significantly affects the fault characteristics of distribution networks. Fault analysis is a keystone for suitable protection scheme design. This paper presents the modelling methodology for distribution networks with inverter-based DGs and performs fault simulation based on the model. Firstly, a single inverter-based DG model based on the cascaded control structure is developed. Secondly, a simulation model of distribution network with two inverter-based DGs is established. Then, different fault simulations are performed based on the Real Time Digital Simulator (RTDS). Theoretical analyses are conducted to justify the simulation results, including the equivalent circuit of distribution networks with inverter-based DGs and the solution method for loop currents.

Abstract:Background: The increasing penetration of a massive number of plug-in electric vehicles (PEVs) and distributed generators (DGs) into current power distribution networks imposes obvious challenges on power distribution network operation. Methods: This paper presents an optimal temporal-spatial scheduling strategy of PEV charging demand in the presence of DGs. The solution is designed to ensure the reliable and secure operation of the active power distribution networks, the randomness introduced by PEVs and DGs can be managed through the appropriate scheduling of the PEV charging demand, as the PEVs can be considered as mobile energy storage units. Results: As a result, the charging demands of PEVs are optimally scheduled temporally and spatially, which can improve the DG utilization efficiency as well as reduce the charging cost under real-time pricing (RTP). Conclusions: The proposed scheduling strategy is evaluated through a series of simulations and the numerical results demonstrate the effectiveness and the benefits of the proposed solution.

Abstract:The optimal configuration of battery energy storage system is key to the designing of a microgrid. In this paper, a optimal configuration method of energy storage in grid-connected microgrid is proposed. Firstly, the two-layer decision model to allocate the capacity of storage is established. The decision variables in outer programming model are the capacity and power of the storage system. The objective is the least investment on the battery energy storage system. The decision variable in inner programming model is the charging and discharging power of battery. The objective is the lowest power fluctuation on the connection line. Then a case containing a grid-connected microgrid with wind power, photovoltaic, battery energy storage and load is studied, and the multi-scenario probabilistic method is used. The last result of energy storage configuration is calculated through the probability of each scene.

Abstract:Recent advances in battery energy storage technologies enable increasing number of photovoltaic-battery energy storage systems (PV-BESS) to be deployed and connected with current power grids. The reliable and efficient utilization of BESS imposes an obvious technical challenge which needs to be urgently addressed. In this paper, the optimal operation of PV-BESS based power plant is investigated. The operational scenarios are firstly partitioned using a self-organizing map (SOM) clustering based approach. The revenue optimization model is adopted for the PV-BESS power plants to determine the optimal operational modes under typical conditions for a set of considerations, e.g. power generation revenue, assessing rewards/penalties as well as peak shaving/valley filling revenue. The solution is evaluated through a set of case studies, and the numerical result demonstrates the effectiveness of the suggested solution can optimally operate the BESS with the maximal revenue.

Abstract:Digital substations are mostly important in the future of the electric power industry which makes their testing a critical process to ensure the required reliability and security of the grid. The paper introduces the definition of a digital substation and efficient testing, as well as the requirements for isolation during testing. It later describes testing related features in IEC 61850 Edition 2 and testing methods that can be used in digital substations. Maintenance testing examples and testing tools requirements are also presented. And remote testing principles are described at the end of the paper. The proposed remote testing by controlling the test system in a remote substation from the convenience of the engineering office brings significant benefits by improving efficiency and safety, as well as reducing outage times.

Abstract:Concerning the rapid development and deployment of Renewable Energy Systems (RES) and Energy Storage System (ESS) including Power-to-Gas (PtG) technology can significantly improve the friendliness of the integration of renewable energy. The purpose of this paper is to develop a coordination strategy between a battery energy storage and a PtG system. A simulation case is created with an electrical and a natural gas grid as well as steady-state models of RES and PtG. Charging strategies are developed accordingly for the ESS as well as production strategies for the PtG system. The size of the ESS is then observed with regards to the RES and PtG systems. As a result, it is found that surplus energy from RES can be stored and then used to support the electrical grid and the natural gas grid. It is also concluded that the capacity of the ESS can be affected, given a proper charging and production strategy, which needs to be tailored to each system. As shown in the paper, due to an improper charging strategy in the first quarter of a month, the ESSPC size has increased from its optimal size of 314 MWh to roughly 576 MWh. It can also be seen that given a proper charging strategy, this capacity can be less than 200 MWh.

Abstract:The Photovoltaic (PV) plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics, as it connects to the power grid through the voltage-source converters. High penetration PV in power system will bring several critical challenges to the safe operation of power grid including transient stability. To address this problem, the paper proposes a control strategy to help the PVs work like a synchronous generator with variable inertia by energy storage system (ESS). First, the overall control strategy of the PV-based virtual synchronous generator (PV-VSG) is illustrated. Then the control strategies for the variable inertia of the PV-VSG are designed to attenuate the transient energy of the power system after the fault. Simulation results of a simple power system show that the PV-VSG could utilize the energy preserved in the ESS to balance the transient energy variation of power grid after fault and improve the transient stability of the power system.