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Abstract:As the most comprehensive and complicated FACTS technology, unified power flow controller's technical principle and operation mode are introduced in this paper. Also the converter technology is detailed analyzed as well as the application and background overboard. This paper also discusses the necessity, system scheme, typical topology, converter access technology and DC field scheme of the UPFC project in Nanjing western power grid. At last, the comprehensive benefits of UPFC are demonstrated. Analysis results show that UPFC plays an important role in solving the power flow control problems facing Nanjing western power grid.

Abstract:Flashover voltage is the most important indicator to assess the performance of electrical insulators. This paper proposes a flashover voltage model based on relevance vector machine. In this model, the combination kernel function is selected as the final kernel function; the kernel width and combination function weight of RVM are optimized using differential evolution algorithm; and the salt and non-soluble deposit density on insulator surface and the pollution flashover voltage are selected as the input and output. Simulation results show that the improved RVM model has higher accuracy and generalization ability than BP neural network, SVM model and non-improved RVM model. It overcomes the shortcomings of traditional methods and is suitable for real-time prediction of pollution flashover voltage. The proposed model has certain application value.

Abstract:Considering the influence of wind farm forecast errors on real-time dispatch, this paper studies corresponding dispatch strategy. A real-time dispatch model to optimize the output of generators for wind power integrated system is proposed. In this model, forecast error is considered and Laplace distribution is used to describe the density function of wind power forecast errors. A chance constrained program based on probabilistic load flow is built using Latin sampling methods. An improved genetic algorithm is adopted to solve the chance constrained program model. Lastly, the simulation on IEEE24 system proves the viability of the model. It demonstrates that taking forecast errors into accounts can guarantee the power balance and load flow safety of system. Also, it is able to enhance the ability of accepting wind power for wind integrated system.

Abstract:Considering the principle of fair, efficiency and sustainable, this paper proposes the emission right allocation index system of carbon emission right for the east China. The index system includes 3 aspects and 14 indexes. The initial allocation model of carbon emission right is established using CRITIC and fuzzy optimization method. Compared with other proposals, the proposed allocation is more suitable for the east China. Also, the model provides a reference for other regions.

Abstract:The paper has a detailed analysis on the inter-area low frequency oscillation in aspects of negative-damping effect. Then it proposes the approach of utilizing UPFC to restrain low frequency oscillation after analyzing the disadvantage of PSS in the condition of inter-area oscillation. The paper studies how UPFC contributes to the damping of lines without an additional damping controller, and then proposes a PI control model based on power injection method. A small signal analysis of transient stability with UPFC is proposed. Simulations results show that UPFC is effective to improve transient stability.

Abstract:In this paper, the conventional method for calculating load flow of power systems containing unified power flow controllers (UPFCs) is analyzed. The drawbacks of this approach during performing load flow calculation and dynamic simulation of power systems containing UPFC in PSS/E (Power System Simulator for Engineering) are discussed. A novel two-stage method for calculating load flow of power systems containing UPFCs is proposed. Case studies validate the the proposed method.

Abstract:After reviewing the existing current control methods for inverters,an improved Kalman Filter based current control method is proposed in this paper. In this method, the Kalman Filter kernel is applied to the PI controller in the orthogonal reference frame, which results in a sine current controller without steady error. To improve the dynamic of the proposed current controller, the inverter current tracking error is feedforwarded to the forecast error variance matrix. The simulation results show that the proposed current control method has a good response speed and tracking accuracy.

Abstract:UPFC (Unified Power Flow Controller) has strong capability in power flow control; but the location of UPFC affects the power flow control a lot. This paper selects UPFC location using sensitivity analysis. Firstly, establishing UPFC power injection model under DC power flow reduce the number of control variables. Secondly, defining the active power flow variance function reflect how the grid be affected by UPFC. Thirdly, using the method of sensitivity analyze each candidate line, and then obtain the sensitivity of control variables and determine the location of UPFC. At last, by calculating in the IEEE14 network, the accuracy of this method can be verified. This method is convenient and improves the computational efficiency, especially in the large-scale power system.

Abstract:The unified power flow controller (UPFC) is a FACTS device which has a strong control capability. Its influence on the power flow of real grids should be further studied. This paper establishes the power injected method based mathematical model for the UPFC according to its controlling principle. The power flow model incorporating UPFC is solved by the Newton method. Numerical results of the Jiangsu power grid are presented. The proposed model is practical and effective.

Abstract:As the key equipment in the UPFC, the series transformer plays an important role in the power transmission between the convertor and the AC system. The voltage of the transformer should match the AC system voltage with the DC voltage of the convertor on one hand; on the other hand the transformer can provide the electrical insolation between AC and convertor. The electrical structure of the series transformer is different with the normal one. The primary wings of the series transformer are connected in the lines in split-phase with 6 terminals and the secondary ones are connected to the convertor with the connection of star or delta. The wings of the series transformer should be capable to withstand the short-circuit current of the power system; and the equipment should also be able to withstand four times of over-excitation capacity within certain time, which require a lot to the electric and structure of the transformer. The operation conditions of the series transformer of Nanjing UPFC project have been analyzed. Based on the analysis the key parameters for the series transformer are recommended, and the tolerance conditions of the series transformer have been simulated in the end.

Abstract:Firstly, this paper introduces the basic structure of MMC-UPFC, and then summarizes the research progress of cross decoupling control strategy of MMC-UPFC from three aspects: the traditional MMC-UPFC cross decoupling control strategy, control strategy combined with intelligent algorithm and control strategy based on state feedback. At last, this paper compares the characteristics of the three kinds of control strategies and summarizes the problems should be solved during cross decoupling.

Abstract:Converter valve is the core of Unified Power Flow Controller (UPFC). Water cooling system, as the "guardian" of converter valve, is very important for its safety and reliability. In this paper, the structure of water cooling system is studied. First, a detailed analysis of the structure is carried out from two aspects: the internal cooling system and the outside cooling system. Then, the circuit of UPFC water cooling system is built by analogy method, which makes the structure and each module clear. In the end, the comparison between series water load and parallel water load is presented, and the problem of uneven distribution of parallel channels is discussed.

Abstract:With the load increases, the problems, such as limited transfer capacities of power imported channels, unbalanced power flow distributions and so on, facing Nanjing Western grid increase. This paper studies these problems and analyzes countermeasures. Through the analysis it is found that it is necessary to install UPFC in Nanjing Western grid. The effect of UPFC on the power grid is investigated by calculation. Results show that UPFC can effectively solve these problems.

Abstract:The traditional three-phase four-wire three-phase half-bridge PWM voltage rectifier is widely used in compensating reactive power, harmonic, fundamental negative and zero sequence current. However, it has many problems: the number of its output power level is limited, which may affect the eventual effect of compensation; cascaded H-bridge with star structure can increase the number of its output voltage level, but its ability to compensate the fundamental negative sequence current is limited; Cascade H with triangle structure can increase the ability to compensate fundamental negative sequence current, but it cannot be applied in the three-phase four-wire system. This paper develops a compensation device of power quality in the three-phase four-wire system based on modular multi-level inverter. In theory, the number of output voltage level of modular multi-level inverter can be extended to any value due to the modular nature. This character can optimize the compensation effect and let the modular multi-level inverter suitable for the three-phase four-wire system. The simulation models of modular multi-level inverter are built in PSCAD / EMTDC platform. The simulation results show that modular multi-level inverter can compensate reactive power, harmonic, fundamental negative and zero sequence current for the three-phase four-wire system.

Abstract:The voltage level of power system is an important index to assess the quality of power supply, and is greatly influenced by the distribution of reactive power flow. Firstly, the influence of generator voltage, transformer supply voltage ratio, bus load and reactive power compensation on system voltage was analyzed through formula deduction. Secondly, the mathematical model of voltage/reactive power control of power system was constructed with the objective function of minimum power loss and voltage level constraint, and gravitational search algorithm was introduced to solve the model. Finally, taking IEEE-14 bus system as an example, the normal operation mode, heavy load mode and generator failure mode were analyzed, and test results showed that GSA was effective. The research achievements can provide supports for the optimization of power flow distribution and improve the quality of power supply.