Abstract:The unified power flow controller (UPFC) can improve the power flow distribution in power grid by regulating the line power flow quickly and flexibly. For the maturely developed region grid with stable grid structure, the UPFC device is a suitable solution for the unbalanced power flow problem. Taking the Nanjing west grid UPFC project as an example and considering the primary system structural characteristics of this double-circuit line UPFC project, the architecture and configuration of the control and protection system is studied in detail. The final scheme of this project is proposed, and the proposed scheme can meet the requirements of the double-circuit line UPFC project in terms of economy, flexibility and reliability.

Abstract:The UPFC is capable to control the power flows over transmission lines and to improve the distribution level of power flows in power grid. Based on the Nanjing UPFC project, the protection function deployment for the UPFC device with double circuit line connection mode is proposed. A complete partition protection strategy consists of grid-side AC protection zoon, valve-side AC protection zoon and converter protection zoon and a multi-level protection strategy composed of module protection, valve-controller protection and system protection are provided. The proposed protection system and strategy have been tested in RTDS, and the testing results are presented.

Abstract:In this paper, a new method of UPFC auxiliary damping controller parameters tuning based on test signal method is proposed. First, the small signal stability of power system is analyzed using the test signal method. Then the testing signal is scanned at the line active power setting point of UPFC while the active power flow in the parallel AC tie line is oscillated. The open-loop transfer function between the line active power setting point of UPFC and the active power flow in the parallel AC tie line is identified by Fourier resolution and curve fitting. Finally, the parameters of UPFC auxiliary damping controller are tuned based on the root locus rules of the classical control theory. The proposed parameter tuning method is validated by the simulation results of a simple case and a real power grid.

Abstract:The series converter is the key equipment of the unified power flow controller (UPFC). The performance of its control system is directly related to the regulating ability of UPFC. This paper presents a crossing-coupled method and a system to control the series converter of UPFC. The Bode diagram of the control system is drawn to determine the PI controller parameters. A 380 V UPFC system simulation model is established in MATLAB to calculate the power injected to the line by the series part, the voltage of the DC bus and the changes of the voltage phase angle of the sending terminal. The results showed that the cross-coupling control system has a small interaction when the power flow is changed by UPFC, which verifies the effectiveness of this control system. This paper provides a reference for the future designs and applications of UPFC.

Abstract:In order to solve the transmission channel bottleneck problem will occur in Nanjing 220 kV western grid, a series unified power flow controller (UPFC) is planned to install into the grid. Considering the actual situation of the power grid, a method for selecting the UPFC capacity is proposed. In this method, sensitivity analysis of UPFC capacity to promote Nanjing western network supply ability is given through power flow calculation in PSASP. Finally, the suitable UPFC capacity for Nanjing 220 kV western power grid is presented.

Abstract:As one of the most powerful flexible AC transmission system (FACTS) devices, the unified power flow controller (UPFC) can control the active and reactive power on the transmission line independently, optimize the system power flow distribution as well as improve the system stability. In this paper, the control strategy of the existing MMC-UPFC is analyzed. Based on the analysis, a particle swarm optimization based approach to optimize the control parameters is presented. The proposed approach takes the tracking ability to the reference value as the optimization objective. The MMC-UPFC model of a real system and the optimization algorithm are realized in Matlab and PSCAD/EMTDC. Simulation results show that the proposed approach is effective.

Abstract:The UPFC is capable to control bus voltage and line power at the same time, which can improve power system stability greatly. The power-flow and electro-mechanic transient simulation model of UPFC is the basis for power system simulation. Based on the basic theory and control characteristic of UPFC, this paper proposes a method to duel with UPFC in power flow program and a simplified model for UPFC in electro-mechanic transient simulation program. In the power flow simulation, UPFC is equivalent to power injection of both ends and PV bus type. In the electro-mechanic transient simulation, some inner control sections and fast control sections are ignored which are fast and have smaller influence on the whole characteristic, so that the simplified simulation model is proposed for series power control and shunt voltage control. The simulation model is developed in PSD-BPA software and is contrast with the detailed model in MATLAB. The results show that the simplified model has good accuracy.

Abstract:This paper proposes a stochastic load flow algorithm considering unified power flow controller (UPFC), which is based on the equivalent power injection model. The steady state power flow considering is obtained by the Newton-Raphson method. The Jacobian matrix is acquired by linearizing the formulas of power grid. After calculating the semi-invariant of each random variable, probability density of bus voltage and line power is computed comfortably. In the end, the simulation results on the IEEE-14 test system validate the proposed method.

Abstract:In order to solve the problems existing in Nanjing west power grid, the first unified power flow controller (UPFC) in china is built, which is also the first UPFC project using MMC topology in the world. With multiple converters Nanjing UPFC has many operating modes. Considering the high flexibility, reliability and complexity of the UPFC project, it is necessary to research its operating modes. The five operating modes are introduced, and the settling method for main device failures is discussed. The research can be taken as a reference for the future UPFC projects.

Abstract:Modular multilevel converter is seen as the future development of AC-DC conversion in power system and attracts more and more attention for its superiority such as modular, low losses, low harmonic and so on. Based on the features of MMC, this paper compares related existing MMC circuit topologies, analyzes its critical technology, and summarizes its extensive application research on power system, so as to have an outlook for its broad prospects.

Abstract:Some operating constraints, such as unbalanced power flow distributions and limited transfer capacities of the power imported channels, exists in the current and developing Nanjing western grids. Therefore, the power supply to the grid cannot meet load increase. However, the Nanjing western grid is located in the center of Nanjing, which makes it huge-invested and hard-implemented to build a new transmission channel or to expand the transmission capacities of the current channels. To solve this problem, UPFC (unified power flow controller) is applied to balance the power flows among the current transmission channels and to increase the power-imported capacities. Meanwhile UPFC induces large impacts to the system reliability. In order to improve operating reliability, the dynamic electromechanical dynamic characteristics and control strategies for the grid have been investigated. In the end, the UPFC electromechanical dynamic model and system control strategy are proposed, which are the theoretical basis for guaranteeing system operating reliability.

Abstract:Combining the line commutated converter (LCC) and the full bridge modular multilevel converter (FMMC), the LCC-FMMC hybrid HVDC system which is more flexible and excellent is proposed. The control sequence of hybrid DC power flow is presented, and the relationship of the interaction between the AC and DC systems during power flow reversal is analyzed. The AC voltage control strategy and the capacitor voltage balancing control strategy are proposed for the problems of the AC voltage fluctuation on the LCC side and the sub-module capacitor voltage balancing. The simulation results show that the proposed control strategy can effectively realize power flow smooth reversal while guaranteeing the AC voltage on the LCC side stable and the sub-module capacitor voltage balanced.

Abstract:Firstly, the protection configuration and operation strategies for the unified power flow controller (UPFC) in the Nanjing western power gird are introduced. After analyzing the effect of the UPFC on AC protection, the protection configuration for the lines with UPFC is optimized. Then, the cooperation strategy for the UPFC protection and AC protection is analyzed, and the coordination principle for the Nanjing western power gird UPFC protection and various kinds of AC protections are introduced. As the first UPFC engineering in China, the Nanjing Western Power Gird UPFC protection system configuration and action strategy provides a reference for the future study and application of Flexible HVDC transmission system protection.

Abstract:The Nanjing western power grid unified power flow controller (UPFC) project is the first UPFC project based on the modular multilevel converter (MMC) technology. This project is an important achievement of flexible alternating current transmission system of China. The valve hall which contains the converters has a high level requirement of temperature, humidity and cleanliness. So the construction and management of the valve hall room becomes the most significant step of the whole project. With the analysis of the circumstances of the valve hall, this paper builds the mathematic models of the temperature and humidity. According to the analysis, a series of control method is applied to the hall, such as the staged control method, the heating and ventilating system, the fresh air system and the monitor systems. All the control methods form a strict control system to maintain the micro positive pressure in the valve hall.

Abstract:This paper introduces the working structure of the series transformer in detail, analyses the importance of the partial discharge test of transformer, proposes a partial discharge test method for the series transformer, and finally the article gives an outlook for future development trend of partial discharge test.

Abstract:The local oscillation occurs occasionally in the electric network of large-sized mine. This paper focuses on the oscillation problem in a steel enterprise with a mass of special loads. The possible reasons of the local oscillation is analyzed firstly, and then the simulation considering the mentioned reasons including the impact characters of special load, the excitation mode of local generators, etc. are implemented. It is manifested that the changes of impact load, the location of impact load and the excitation mode of a local generator may significantly affect the oscillation in the small grid. Moreover, the larger the change of impact load is, the larger possibility of the oscillation will be, and the closer the distance between the impact load and generators is, the more significant the oscillation will be. If the exciter of local generator is operated in the constant power factor mode, the generator tends to oscillate more easily than in other modes. The simulation results suggest that the constant voltage mode is a good choice for the exciting regulator, connecting the local grid to the outer power grid improves its reliability, and the impact loads should be reasonably distributed.

Abstract:Due to the application of many new technologies, complicated system structures and virtual electrical secondary circuits, the commission of intelligent substation becomes a long period, much manpower, complicated commissioning process and quality hard to control project. In this paper, the method of project management is used to improve the management of intelligent substation. By analyzing the statistical data between before and after using the method, it is found that the improved management can shorten the period, promote the quality and control the costs effectively.

Abstract:Solar energy is regarded as the most powerful weapon to resist haze, while photovoltaic (PV) generations are facing severe challenge due to frequently-occurring haze. In this paper, the basic principle of PV cells is introduced and the mechanism of haze's affection to PV output power is analyzed. A group of so called similar days are chosen, and then the standalone affection of haze to PV output is analyzed while other factors are guaranteed to be nearly the same. The actual output power of a certain PV plant in Jiaxing validates the reliability of the proposed method.

Abstract:The current multiple indicator evaluation methods for the current situation of power grid are mostly based on the accumulated experience of staff or by defining indicators to measure the impacts on power grid, and there isn't a quick way to judge the influence levels of indicators of the current situation of power grid, so this paper proposes a method called correlation analysis to research the multidimensional evaluation of the current situation. The correlation analysis is to determine the correlative degree size of each index, and longitudinal comparison is to analyze the current influence level of each indicator for revealing the weakness of power grid. Finally, the simulation results verify the proposed method, and it provides the theoretical basis of system reliability for power grid construction.