Aiming at complex VSC-HVDC power grid with bipolar structure which contains renewable energy island power sent and isolated power supply, a coordinated control strategy is proposed. The coordinated control system includes wide-area coordinated control system(WCCS) and VSC coordinated control system(VCCS). After VSC fault or DC line fault, WCCS adjusts power of each converter station and other subsystems according to the operation conditions, and each converter station also changes its own control mode or power according to operation conditions and instructions by VCCS. Based on the typical VSC-HVDC power grid, simulation under typical conditions verifies that the proposed strategy can obviously improve the response characteristics of VSC-HVDC power grid under the fault conditions and improve the security and stability of VSC-HVDC power grid.

With the rapid growth of energy demand in China, more and more DC transmission projects are adjacent to buried oil-gas pipeline, which leads to serious electromagnetic effects on buried metal pipeline. Focusing on the protection measures of pipeline, this paper establishes a circuit model based on the study of concentrated grounding device, sacrificial anode, forced cathode drainage measures. Protective effect and regularities of these measures have been studied by simulation. Results show that concentrated grounding device of pipeline can reduce pipe-ground voltage of partial pipeline significantly, but its range of action is too small. Sacrificial anode has a palpable effect of reducing pipe-ground voltage as long distance buried pipeline. What’s more, multipoint connection between sacrificial anode and pipe can obtain a better protection effect. The forced current cathodic drainage protection can also reduce the pipe-ground voltage.

Based on the topology structure of modular multilevel converter (MMC), the internal bridge arm current and the sub-module capacitor voltage are taken as the object of study, by introducing the average switching function, the time domain model under nearest level approximation modulation of MMC is deduced, and then the model is expanded to a dynamic phasor harmonic analysis model so as to obtain the steady-state harmonic components of MMC at AC and DC side. Then, the simulation model of MMC is built in Matlab/Simulink, and the harmonic analysis is carried out by FFT to verify the correctness of the established harmonic analysis model. Finally, the interaction between AC and DC harmonics is analyzed according to the model. The model can provide a theoretical reference for designing MMC filters or studying their harmonic suppression techniques.

When constant direct current(DC) is impressed on DC deep well grounding electrode, electrochemical, corrosion reaction occurs between the well cementing concrete and the steel tube, and the well cementing concrete acts as electrolyte. The reaction leads to the electrical resistivity variation of the well cementing concrete. In order to study the electrical resistivity variation law of well cementing concrete in different conditions with the DC duration, experiments are carried out in this paper. According to the water cement ratio of the practical deep well grounding electrode engineering, the concrete samples are prepared. The DC experiments for concrete samples which are cured for 3~7 days and entirely cured are conducted. The results show that the concrete electrical resistivity conforms to Archie formula at the beginning of curing period, the concrete electrical resistivity during curing period increases with the DC duration and so does the entirely cured and impregnated concrete, while the electrical resistivity of entirely cured and dried concrete decreases with the DC duration. The analysis shows that DC polarization is the main reason leading to the difference of the two trends.

Distributed renewable energy, energy storage and DC load need to be connected to traditional AC distribution network through multistage converter sections, which leads to low energy-efficiency of power system. The AC & DC power distribution technology could reduce the intermediate links during AC & DC power transformation to improve the economy, reliability and operation flexibility of power distribution. This paper summarizes the present research situation and development trend of domestic and foreign AC & DC hybrid distributed renewable energy technologies from the aspects of system structure design, key equipment development and optimization control system development, in order to provide ideas and reference for further research and application of AC & DC hybrid system in the future.

With the expansion of power grid scale, transimission corridor resources become more and more scarce, the possibility of fault occurrence for two crossing transmission lines is intensively increasing. This paper presents a new electromechanical transient simulation method for this kind of fault. Firstly, elimination processing are carried out for both the faulty order network voltage equation and the boundary condition equation in order to obtain additional positive sequence impedance matrix of fault node, and the matrix is processed symmetrically. Then the additional positive sequence impedance matrix of fault node is extended to faulty line nodes. According to the additional positive sequence impedance matrix of faulty line nodes, corresponding transient data card is generated and electromechanical transient simulation method for two crossing transmission lines is proposed. Finally, by using the data of an actual power grid, electromechanical transient simulation is carried out for the fault of two crossing transmission line and ground fault of two crossing transmission line. The simulation results verify the correctness of the proposed method.

Considering the mutual inductance between lines, most of the fault analysis methods construct different compound sequential networks for different fault types, which causes large workload and makes it difficult to debug. Therefore, this paper proposes a short circuit current calculation method for two transmission lines considering mutual inductance between lines. In this paper, the node impedance matrix of the both fault lines’ ends and the impedance of fault lines are used as inputs. The parameters of the original node impedance matrix are modified or expanded by adding tree branches or link branches to deal with mutual inductance between lines or adding fault points. Then, the sequence network equations at the fault point of the two transmission lines can be constructed. This paper presents a universal method for constructing the fault boundary condition matrix for two transmission lines. The phase-sequence transformation is used to construct the fault boundary condition equations for each sequence network. The voltage and the current at each fault point can be solved in conjunction with the sequence network equations. Finally, a fault simulation model of power network is built by PSCAD/EMTDC, and the results verify the correctness of the method.

The existing security and stability control strategy is based on off-line calculated expected modes and failure set, and is difficult to comprehensively cover all special operation modes of the power grid. The existing transient instability criterions based on wide area response are analyzed and compared. By utilizing the coherent variation of power-angle of generator and voltage in oscillation center during the serious fault of the power system, a transient stability discriminant technology is presented considering the time integration of the oscillation center voltage trajectory. A transient stability online pre-detection control system based on wide area response is developed by adopting the centralized control structure scheme, and it can achieve fast and practical discrimination of the power system transient stability status without relying on model. The control system is successfully applied to the northern power grid of Liupanshui in Guizhou, and is operating normally so far to support emergency control during serious fault in power grid.

In this paper, a location and capacity method based on information entropy is proposed. The method uses information entropy to measure the importance of location factors, the fluctuation similarity of maximum consuming photovoltaic power and photovoltaic output. The location target is maximum decision quantization of candidate node, and the capacity target is largest consumptive power. This method may improve the consumptive ability of photovoltaic and reduce discard rate. Finally, an actual power grid in east China is taken as an example to evaluate the rationality of the proposed method, and its validity is proved.

Traditional communication technology between substations of security and stability control (SSC) system has some inherent shortcomings, it does not conform to the trend of current technological development and restricts the expansion and application of SSC. Using intelligent substation process layer GOOSE communication technology, a new communication technology between substations based on IEC 61850 in SSC is proposed in this paper. The key technology of communication network architecture, communication capacity control, data flow control and visualization of decoupling configuration are deeply researched, and the typical project of Brazil Belo Monte SSC application is introduced. This technology has several advantages, such as stable and reliable communication, data transmission capacity, reusability and interoperability. It can meet the demand of information exchange between substations, and it represents the development direction of the communication technology of SSC.

The topology of power grid will change when a failure occurs, which may cause the power system to lose its observability. Existing identification method ignores the influence of this special condition on accuracy of fault location. If the fault can be located accurately, the protection strategy will be taken after failure to prevent the expansion of the fault. In this paper, calculation method of unbalanced current in conventional power grid structure is analyzed, and the relationship between unbalanced current and fault line after fault is studied. Further, several possible phasor measurement unit (PMU) configurations are analyzed, the relationship between PMU configuration position and power system being not observable after fault is discussed, and the variation rule of the unbalanced current value under the condition of losing observability is revealed. By using the unbalanced current calculated value to derive the fault location, a fault location method is proposed, and a fault location process is developed. A 35-node power system is built with BPA simulation software to compare the location effect under different PMU configuration positions. Results show that the proposed method can accurately locate the fault. The proposed method is applicable to the wide-area backup protection with action information from protection devices, and extends the application of short-circuit fault location.

With the openness of the retail side, the distributed generation and the energy storage unit in distribution network can be managed and funded by new energy investment enterprises and energy saving service institutions. Differing from the tradition, these owners which called the independent benefit identity take the benefit maximization as their objectives. This paper proposed the concept of virtual micro-grid agent and established the two-stage game model including the active distribution management system (ADMS), virtual micro-grid agents and power users. Based on the operating mechanism of the active distribution network (ADN) with different stakeholders, the multi-type virtual micro-grid agents are motivated to allocate generation outputs actively through competitive price bidding and users in demand-side can obtain various options of electricity price and time so as to improve the electricity efficiency of terminal users and reduce electricity costs. Finally, the effectiveness of the game model in ADN market operation is varified by simulation.