Abstract:With the increasing penetration of power electronic devices in the grid, which make the whole system unstable, virtual synchronous generator (VSG), as a new control strategy, can simulate the characteristics of traditional motors and make the system inertial and damped. It get a wide range of concerns. In this paper, virtual synchronous rectifier is analyzed with mathematical model. Under the condition of grid voltage unbalanced, the virtual synchronous generator control strategy is improved in for the purpose of stable DC voltage. The simulation results based on Matlab/Simulink are verified, which simulate the operation of power fluctuation and three-phase unbalance. The simulation results verify the correctness and validity of the proposed method.

Abstract:With the integration of large-scale new energy resources, EVs, microgrids, CCHPs, large electric heating boilers and ground-source heat pump in to power system, it has been converted to be a meshed multi-energy system with the setup for cooling, heating, and electricity. Since power system’s stability can be affected by grid and user sides, a frame work design of coordinated control for multi-energy’s utilization and grid’s stability and security under the scope of energy internet is proposed in this paper. Firstly, this paper introduces mulit-energy utilization in the power system, and investigates its characteristics. Secondly, the control objects for multi-energy’s utilization and grid’s security and reliability were constructed from the aspects of normal and contingency conditions. Lastly, a framework is designed for multi-energy’s utilization and grid’s stability and security, and provides a viable scheme for the utilization of high-penetration new energy.

Abstract:Based on the structural attributes of DC microgrid and diverse micro-sources’ features, the constant DC bus voltage is considered as the control target. For the situation that each unit belongs to different users, the multi-agent system is used to construct the information network, and a DC microgrid regional stability control method based on distributed power self-coordination, self-management and self-organizing network is proposed. The independent sub-region in the DC microgrid system is chosen as the research object, and the system stability control method under different supply and demand is designed to realize the redistribution and optimization of the power supply based on the interactive information. The simulation results demonstrate that the proposed method can be used to maintain the stability of the system, and it can fully reflect the running characteristics of different distributed power supply.

Abstract:Compared with traditional generation technology, photovoltaic generation, which is widely spread and easily connected to the grid, has an excellent ability of self-starting, making it a promising alternative of black-start sources. Given the difference between PV and traditional black-start sources, a two-phase network restoration strategy was presented. In phase 1, PV units are used to restart the first traditional unit within the network, with the objective to maximize the possibility of starting successfully. In phase 2, the one generator started in phase 1 is used as the main power source, while PV units as the auxiliary source, to finish the whole restoration procedure, with the objective to maximize the power generated and minimize the time needed during the restoration. Taking the objectives of the two phases into consideration, an integral optimization method was proposed, which could fix the disadvantages of PV systems such as low inertia and relatively poorer starting ability, while guaranteeing the restoration efficiency. The case study of IEEE 30-bus system has proved the practicability and the effectiveness of the method proposed.

Abstract:In smart grid, residential users who participate in demand side management can schedule household energy consumption appropriately according to the real-time energy price. This paper proposes a kind of energy consumption technology based on cooperative game by considering the participation of household distributed generators. Based on the presented power consumption model, energy cost model, and household load control model, energy consumption among residential users is formulated as a cooperative game; where players are residential users and strategies are their daily consumption schedule. The energy cost of all users is minimized at Nash equilibrium solution. Simulation result shows that users’ cost is decreased and further decreased with distributed generators when users participate in energy consumption scheduling with game approach.

Abstract:With the development of high voltage and large capacity power electronic technology, more and more power electronic devices have been put into operation. Hence, the future power system must be the power system with presence of massive power electronic devices, which is defined as power electronics based power system. However, with the large scale integration of the power electronic devices, the inertia and damping ratio of the power system is decreasing, adversely impact the safe and stable operation of the power system. The virtual generator technology can make the power electronic device emulate the inertia and damping feature of the conventional rotating machine, and help to address the safe and stable issues faced by the power electronics based power system. The basic principles of the virtual synchronous generator and virtual DC generator are described in this paper. Moreover, the application prospective of virtual generator technology in PV generator and wind plant, power electronic transformer, flexible AC and DC transmission, as well as load response and control is introduced. Finally, the development trends of the virtual generator technology are discussed.

Abstract:The peak-valley load difference of urban power grid leads to a large waste of power resources. Urban power network couped to hydrogen energy storage system is proposed here to dissipate surplus power during low load period. Based on the analysis of investment cost and economic benefit in the life cycle of hydrogen storage system, an evaluation model for investment decision making is built which involves three optimization models according to the different investment demands: the minimum hydrogen selling price model, the optimal installed capacity model and minimum selling price model under given payback period. Finally, based on the real data of a certain city grid load, the optimal scheme is analyzed under the different investment demand when the urban power grid coupled to hydrogen energy storage system is implemented in the city.

Abstract:According to the problems about zero-sequence circulating current existed in parallel T-type three-level power converter systems, the equivalent model of zero-sequence circulating current was proposed in this paper. The zero-sequence circulating current was divided into three types according to different exciting sources, namely, conduction zero-sequence circulating current, switching zero-sequence circulating current, hybrid zero-sequence circulating current. Firstly, a scheme sharing neutral buses was proposed to reduce the conduction zero-sequence circulating current. Secondly, a parallel scheme based on improved LCL filter was proposed to reduce high frequency component of switching and hybrid zero-sequence circulating current. And a zero-sequence modulation control method based on proportion resonant controller was used to reduce low frequency component of switching and hybrid zero-sequence circulating current. Finally, parallel T-type three-level power converter systems rated 500 kW were build. Simulation results verify the correctness of reduction methods of zero-sequence circulating current.

Abstract:In order to promote the power generation absorption of new energy like wind/light energy, and realize the maximization of pitch peak benefit, economic benefit and environmental protection benefit of combined optimization dispatching of multi-source hybrid power bases, based on the analysis of time-space characteristics of multi-source hybrid power, we put forward a combined optimization dispatching model of multi-source hybrid power that takes the minimum of operating cost, wind curtailment volume, light curtailment volume and water curtailment volume of thermal power unit as the optimization goal, and provide a reference method for the sending system combined optimization dispatching of multi-source hybrid power bases under the background of ultra-high voltage power transmission. The example takes multi-source hybrid power bases in the Xinjiang region and in the eastern part of a region as study abject, which have significant temporal and spatial differences. Through the calculation and analysis of practical examples, the model is verified theoretically can promote the absorption of new energy and reduce the operation cost of thermal power units.

Abstract:With the rapid development of power grid and power supply, system characteristics are undergoing profound changes, reasonable grid-related generator protection parameters is an important factor to ensure the safe and stable operation of power system. After pointing out the specific content of grid-related generator protection, Combined with the reality of State Grid East China Branch, this paper analyzes the connotation of standards, and puts forward the corresponding standard implementation opinions for the links of frequency abnormal protection and Loss-of-field protection that are easy to emerging questions. This paper introduces the specific specifications and practical working methods of the work for the special check of the grid-related generator protection in State Grid East China Branch, summarizes hazards and solutions of the problem in verification and shares typical cases. Finally, it is suggested that a long-term management mechanism should be established to ensure the continuous development of relevant verification work.

Abstract:Wind speed is an important parameter for the operation of wind energy conversion systems (WECSs), and its obtaining affects the control of WECSs. A wind speed observation based on Newton-Raphson Method is presented, which uses the real-time states collected in the operation of WECS to estimate the tip speed ratio. Then the estimated can be calculated by the relationship of the tip speed ratio and the wind speed. Finally, the wind speed observer is respectively verified by simulation and the wind turbine simulator based experiment. According to the emulational and experimental results, the wind speed observer has a satisfactory performance, meeting the desired goals.

Abstract:In order to research the whole seismic performance of the new indoor substation roof frame-GIS complex building, the finite element models of the conventional frame and roof frame are made. Considering the uniform up and down stiffness of the roof frame-GIS building, the seismic response of the structure system which has an upper and lower structure interaction is made. The vibration characteristics and dynamic characteristics could be concluded by the modal and time-history analysis. By comparing and analyzing these numerical results, it can be seen that the lateral stiffness and the connection node of the new indoor substation roof frame should be strengthened.

Abstract:Taking low-voltage switchgear for research object, based on a large number of domestic mainstream manufacturers, arithmetic mean value of percentages of components of several typical configurations from the total cost was regarded as cost sensitivity of various components of the low-voltage switchgear for analyzing similarities and differences of cost sensitivities of domestic and joint venture manufacturers. Using multiple regression analysis method and on the premise of ensuring voltage level, function and type, the cost of low-voltage switchgear can be obtained by inputting low-voltage switchgear’s capacity, rated current and rated compensation capacity so as to establish a cost estimation model for low-voltage switchgear, which was useful to guide determination and estimation on purchasing target price of power grid materials.

Abstract:The application of large-scale eectric vehicles (EVs) poses a threat to grid stability if charged without control. It needs expansion of the grid capacity and leads to major investment in current grid and capacity-wasting in low-load time. This paper proposes a solution based on two-level electric vehicles charging management system (EVCMS) to optimal demand side management by means of scheduling charging time and setting charging rates. The influence factors for power management include electricity prices, state-of-charge (SOC) of the battery, electricity available, park duration and others. All these can be achieved through charge terminals (CTs)

Abstract:In this paper, the influence of distributed energy on the harmonic of active distribution network is studied. Firstly, the distributed energy in active distribution network is classified according to the type of harmonic source, which includes current type and voltage type harmonic source. Then harmonic current’s generation, propagation and superposition rules are analysed by simulation method, as the harmonic source’s power, the load at connected point and connected point change. The generation and propagation of harmonic voltage in ADN are studied, considering the power and connected point of the harmonic source’ change. As the simulation results, the conclusions are drawn to guide the connected points’ selection of the units in ADN.

Abstract:Gas insulated line (GIL) occupies an increasing proportion in the transmission system. The promotion of DC GIL can improve the existing DC transmission mode, and has a very strong economic benefits. Compared with AC GIL, the major technical difficulties and differences of DC GIL are insulation issues. Studies on DC GIL insulation issues are helpful to its operation, maintenance, and life prediction.Domestic and foreign researches on DC GIL are widely introduced from two aspects: the overall insulation design and internal partial discharge detection. It can provide a better cognition and reference for further study on DC GIL insulation problems.

Abstract:The conception of stress-strength interference model for mechanical reliability analysis is introduced and the reliability model of cylindrical helical spring is given in this paper. Combining the strength degradation model, the phenomenon of spring reliability decreasing with the operation times is investigated, where the reliability of the spring is correlated with the operation times of the high voltage circuit breaker. According to the stress relaxation model and combination of stress relaxation factor which considering the reliability model with strength degradation, the stress-strength interference model considering stress relaxation and strength degradation is built. After that the life of breaker’s energy-storing spring is predicted. Finally, the feasibility of this method is verified by the calculation example of a specific energy-storing spring.

Abstract:In the distribution automation system, the distribution network structure is complex, and devices, graphics and models change frequently. There are some difficulties of graphics and models management in the distribution of automation operation and maintenance. A multi-version hierarchical subscription mechanism method based on graphics and models fine change is presented. Through the unique source distribution network equipment transaction management, data and topology changes are hierarchically subscribed. Multi-version database management mechanism is used to build device data structure. By quickly building the hierarchies and topologies between devices, matching and updating the distribution graphics and models, the correctness of distribution automation system graphics and models can be improved comprehensively, and the maintenance efficiency of the graphics and models can also be improved, which ensures the application requirements of research and analysis based on distribution network models.

Abstract:Due to lack of debugging method of flexible HVDC system, a kind of automatic debugging method used for flexible HVDC sub-module based on modular multilevel converter is put forward in this paper, and a test device including manager unit, MMC control and simulation unit, sampling unit and energy supplying unit is designed. The energy supplying unit can control energy output to provide power supply for sub-module. The MMC control and simulation unit can simulate valve control protocol to control sub-module to realize function test. The sampling unit acquires related voltage state of sub-module. The manager unit combines the sampled voltage with communication state for making test judgment, so as to complete automatic debugging of sub-module. Engineering practice shows that the method is fully applicable to the requirements of site acceptance test and factory acceptance test.

Abstract:In traditional locating fault methods using on high voltage lines, the traveling wave method has drawn attention at home and abroad with better anti-interference and higher ranging accuracy. However, when multiple faults occur on the transmission line, its error will become large because of traveling wave’s overlap. In order to solve this problem, this paper proposes the improved distributed traveling wave fault location method after analyzing the transmission characteristics of traveling wave on transmission line in fluctuation process and conventional method’s limitations. Firstly, this improved method fits the characteristic curve of the traveling wave head using its arriving time which reaches the multiple measurement points. And then, it uses the curve above to solve the specific position of the fault occurs. Finally, the effectiveness of this method is verified by using PSCAD to construct and simulate the 500 kV transmission line model.

Abstract:Based on the smart substation process layer according to the characteristics of the network transmission message, this paper analyzes the requirements of the switch’s transmission bandwidth, storage and forwarding delay, zero loss packet under the strong electromagnetic interference, sampling synchronization, flow control, configuration management and so on. A method is presented for the smart substation process layer network switches the overall development scheme, and the switch test and pilot operation were introduced and analyzed.

Abstract:The DC line fault waveform of a high voltage DC transmission project is analyzed in this paper, and the conclusion that the lightning strike was the action reason of DC line protection is drawn. Based on the retrieval and analysis of lightning data, all the potential causes that can lead the voltage of pole 1 to -535 kV are eliminated one by one. In the meantime, the lightning is also considered to provide the energy which was the reason of voltage variation from +500 kV to -535 kV. At last, optimization strategy of travelling wave protection and voltage derivative protection is proposed based on the characteristics of the lightning back flashover and the lightning shielding failure to prevent the two protection malfunction.

Abstract:The problem of measurement configuration mainly includes the types of measurement, the location of measurement and the quantity of measurement. Based on the selection of measurement types, an algorithm model of distribution network measurement system layout is established to determine the measurement location and measurement quantity for the requirement of integral observability of distribution network, making the measurement to achieve the goal of minimizing costs. On the basis of this measurement system model, combined with the concrete IEEE14 node network, the evaluation index of this measurement system is tested and optimized according to the specific power system state estimation example to verify the effectiveness and correctness of the measurement system.

Abstract:Reliability assessment for selected paths is one of the focuses in path selection of transmission line planning and design process. Considering the disadvantages of conventional methods which adopt average annual failure rate, a transmission line path design method based on reliability analysis is proposed in this paper. Based on statistics for historical failure information of existing lines in the area where selected paths cross, failure rate of each month of selected paths is calculated in monthly scale and its monthly time behavior is fitted. Owing that the power supply output connected to the selected path may be also time-varying, the monthly time behavior of power supply output is then fitted. Finally, according to fitting functions of selected path failure rate and power supply output, the reliability level corresponding to the selected path can be reflected through calculating the expected energy loss of full year, which can provide important reference for comparing several selected paths and choosing the optimal path.

Abstract:In order to maintain the water flux of reverse osmosis membrane treatment at low temperature，now raw water heating device is always set in water treatment system of the power plant. It describes the conventional steam heating scheme and the optimized water-water heating scheme of reverse osmosis influent in a gas turbine power plant, studying the optimization reason，emphatically analyzing the feasibility and advantage of water-water heating scheme, introducing the system design and equipment configuration of optimized scheme. By comparing to the investment costs and benefit of the two schemes, it is concluded that the the optimized heating scheme has more economic benefits and can be popularized within certain limits.

Abstract:Low load peak operation of coal-fired unit the flue gas temperature from the economizer outlet enters the SCR denitrification device is low, deviated from the temperature window of the denitrification catalyst, resulting in low efficiency of denitrification, even the denitrification system is not normal put into operation, resulting in the concentration of nitrogen oxides emission exceeded, has become the main factors restricting the unit’s depth peak capacity. This paper introduces several SCR inlet flue gas temperature upgrading technology for realizing the emission of NO_x of coal-fired unit, and compares the technical characteristics of each other, and provides reference for the power plant to carry out the whole working condition denitrification Reformation.