Abstract:The coordinated control of multiple-sources including wind, photovoltaic (PV) and storage brings new challenges to traditional dispatch and control technologies.This paper firstly introduces a framework of wind, PV and storage co-generation monitoring system. Then, key tech-nologies of co-generation monitoring system including day-ahead optimal dispatching, active power coordinated control and reactive power and voltage control are proposed. The framework and the techniques described in this paper have been applied in the National Wind, Photovol-taic, Storage and Transmission Demonstration Project of China, and their validity have been tested and verified.

Abstract:Network frequency control function is incorporated into a grid-connected wind farm-dual battery energy storage system (BESS) scheme. The design of the scheme takes advantage of the rapid response characteristics of the BESS and the in-built short-term over loading capability of the associated power conversion devices. Acontrol strategy to regulate the BESS output power is then proposed. It is shown that the frequency control actionoffered by the BESS complements amicably with that of conventional generators in enhancing the frequency regu-lation attribute of the grid system.

Abstract:This paper presents a nonlinear control approach to variable speed wind turbine (VSWT) with a wind speed estimator. The dynamics of the wind turbine(WT) is derived from single mass model. In this work, amodified Newton Raphson estimator has been considered for exact estimation of effective wind speed. The main objective of this work is to extract maximum energy from the wind at below rated wind speed while reducing drivetrain oscillation. In order to achieve the above objectives,VSWT should operate close to the optimal power coeffi-cient. The generator torque is considered as the control input to achieve maximum energy capture. From the lit-erature, it is clear that existing linear and nonlinear control techniques suffer from poor tracking of WT dynamics,increased power loss and complex control law. In addition,they are not robust with respect to input disturbances. In order to overcome the above draw backs, adaptive fuzzy integral sliding mode control (AFISMC) is proposed for VSWT control. The proposed controller is tested with different types of disturbances and compared with other nonlinear controllers such as sliding mode control and integral sliding mode control. The result shows the better performance of AFISMC and its robustness to input disturbances. In this paper, the discontinuity in integral slidingmode controller is smoothed by using hyperbolic tangent function, and the sliding gain is adapted using a fuzzy technique which makes the controller more robust.

Abstract:Future electric power systems will face new operational challenges due to the high penetration of distributed energy resources (DERs). In Denmark, distribution system operator (DSO) expects a significant congestion increased in distribution grids. In order to manage these congestions and mobilize the DERs as economically efficient as possible in the future distribution grid, the brand newnotion of flexibility clearing house (FLECH) is proposed inthis paper. With the aggregator-based offers, the proposed FLECH market has the ability to promote small scale DERs(upto 5 MW) for actively participating in trading flexibilityservices, which are stipulated accommodating the various requirements of DSO. Accordingly, the trading setups and processes of the FLECH market are also illustrated in detail.A quantitative example is utilized to illustrate the formulation and classification of flexibility services provided by the DERs in the proposed FLECH market.

Abstract:Aging network assets, forced and unforcedoutages, and the way the networks are operated in aderegulated market are of significant concerns to integrate large wind farms in a distribution network. In many cases,the constrained network capacity is a potential barrier tothe large-scale integration of wind power. This paper probabilistically assesses the steady-state security in adistribution network in the presence of large wind farms.The approach incorporates active distribution network operating conditions, including intermittent power outputs,random outages, demand fluctuations, and dynamic interactions and exchanges, and then assesses the steady state security using Monte Carlo simulation. A case study is performed by integrating large wind farms into a distribution network. The results suggest that intermittent outputs of large wind farms in a distribution network can impact the steady state security considerably. However, the level of impact of wind farms does not necessarily correlate with the installed capacity of them.

Abstract:Network reconfiguration is of the oretical and practical significance to guarantee safe and economical operation of distribution system. In this paper, based on all spanning trees of undirected graph, a novel genetic algo-rithm for electric distribution network reconfiguration is proposed. Above all, all spanning trees of simplified graph of distribution network are found. Tie branches are obtained with spanning tree subtracted from simplified graph. There is one and only one switch open on each tie branch. Decimal identity number of open switch on eachtie branch is taken as the optimization variable. Therefore,the length of chromosome is very short. Each spanning tree corresponds to one subpopulation. Gene operations of each subpopulation are implemented with parallel computing method. Individuals of off spring after gene operation automatically meet with radial and connected constraints for distribution network operation. Disadvantages of con-ventional genetic algorithm for network reconfiguration that a large amount of unfeasible solutions are created after crossover and mutation, which result in very low searching efficiency, are completely overcome. High calculationspeed and superior capability of the proposed method are validated by two test cases.

Abstract:In restructured power systems, the traditional approaches of unit maintenance scheduling (UMS) need toundergo major changes in order to be compatible with new competitive structures. Performing the maintenance on generating units may decrease the security level of transmission network and result in electricity shortage in power system; as a result, it can impose a kind of cost on transmission network as called security cost. Moreover, taking off line a generating unit for performing maintenance can change power flow in some transmission lines, and may lead to network congestion. In this study, generating unit maintenance is scheduled considering security and con-gestion cost with N-1 examination for transmission lines random failures. The proposed UMS approach would lead to optimum operation of power system in terms of economyand security. To achieve this goal, the optimal power flow(OPF) compatible with market mechanism is implemented.Moreover, the electricity price discovery mechanism aslocational marginal pricing (LMP) is restated to analyze the impacts of UMS on nodal electricity price. Considering security and congestion cost simultaneously, this novel approach can reveal some new costs which are imposed to transmission network on behalf of generation units; as aresult, it provides a great opportunity to perform maintenance in a fair environment for both generating companies(GenCo) and transmission companies (TransCo). At the end, simulation results on nine-bus test power system demonstrate that by using this method, the proposed UMS can guarantee fairness among market participants including GenCos and TransCo and ensure power system security.

Abstract:The continuum model is a key paradigm describing the behavior of electromechanical transients inpower systems. In the past two decades, much research work has been done on applying the continuum model toanalyze the electromechanical wave in power systems. In this work, the uniform and non-uniform continuum modelsare first briefly described, and some explanations borrowing concepts and tools from other fields are given. Then,the existing approaches of investigating the resulting wave equations are summarized. An application named the zero reflection controller based on the idea of the wave equations is next presented.

Abstract:Flexible AC transmission systems (FACTS)devices can effectively optimize the distribution of power flow. Power flow entropy can be applied as a measure of load distribution. In this paper, a method is proposed to optimize the distribution of power flow with the coordination of multi-type FACTS devices and establishes the corresponding mathematical models. The modified group searcher optimization (GSO) algorithm is proposed, in which the angle search is combined with chaotic search model to avoid jumping into local optimization. Compared with the different optimal allocation of multi-FACTS devices, the optimal allocation of multi-FACTS devices isachieved under the economic constraints. The locations obtained by this method can achieve the purpose of bal-ancing power flow and enhancing the system perfor-mances. The simulations are demonstrated in an IEEE 118-bus power system with two classical types of FACTS,namely static var compensator (SVC) and thyristor con-trolled series Compensator (TCSC). The simulation results show that the proposed method is feasible and effective.

Abstract:This paper discusses the control strategy for energy management in railway transit network with way-side (substation) super capacitor (SC) energy storage system (ESS). Firstly, the structure of the wayside energy storage system is introduced. Secondly, the model ofenergy storage system is built and the control strategy is described. Thirdly, in order to estimate the required energy storage system, a useful method is proposed to predict the instantaneous regenerative energy magnitude which isdelivered to each substation. Finally, the ESS configurationfor each substation is determined. A simplified mathematical model of the whole metro network is established and the main features of the control strategy are developed.Numerical simulations show the efficacy of suggested control strategy and the energy saving obtained for railwaytransit network.

Abstract:An interesting inverter topology is proposed in this paper. It is similar to the typical three-phase full bridge inverter from the topology point of view, but smartly designed for the ground current reduction in single-phase photovoltaic (PV) inverter applications. The oretical analysis is conducted to clarify the operation mechanism of the proposed topology. Performance evaluation is carried outo verify the effectiveness of the proposed topology for the ground current suppression.