| With interconnection of the large area power grid, a large number construction of HVDC power transmission project and constant expanding of new energy power generation using in power grid, power grid operation is more and more complex and its mode has changed greatly. The off-line analysis and control strategy usually have been difficult to meet the need, the online analysis and control system of security and stability become necessary tools of power grid dispatching center.Auxiliary decision-making of prevention control of potential faults is very important function in online security and stability analysis and control system, but given the complex large power grid of high dimension, strong time-varying and strong nonlinear essence, the robustness and the calculation speed of the decision algorithm is still difficult to meet the requirements of on-line calculation. It is not suitable to obtain the global optimal solution as the evaluation criterion of the effectiveness of the calculation method. Based on the physical phenomena and control mechanism, the quantitative information can be extracted from the simulation trajectory or modal analysis in the process of search every time, then the control performance index can be calculated to guide the next step search direction in the process of optimization calculation and the distribution of a variety of computing tasks in the parallel computing platforms, so as to obtain the feasible and optimization adjustment scheme as far as possible and meet the requirements of online calculation of prevention control of the actual large power grid.After the state of emergency appearing, based on the power grid dynamic real-time information of wide area measurement system (WAMS), the characteristic value reflecting power grid emergency state can be extracted, then control recommendations are given qualitatively, but the emergency control measures cannot be quantitatively determined. To put aside a lot of unrealistic assumptions to obtain the quantitative decision of artificial emergency control, the simulation calculation based on system model must be used. Using the method with measured trajectory data and on-line pre decision calculation combined, decision support for emergency control of artificial can be provided.According to the transient stability preventive control, dynamic stability preventive control and comprehensive auxiliary decision making control of a variety of security and stability issues, the calculation methods based on the analysis of the current method of all kinds of prevention control are put forward to satisfy the online control adaptability requirements of the complex large power grid. Based on the power grid dynamic real-time information of wide area measurement system (WAMS) combined with digital simulation method, a method of artificial emergency control decision support technology is proposed to aim at the online emergency control problem of low frequency oscillation and voltage instability.(1) Based on the stability modes and generators participation factor provided by the extended equal area criterion (EEAC), calculation method is put forward for online transient stability preventive control. According to the control performance index which control cost divided by the sum of the participation factor which weighed by margin of fault, the head and tail pairing are involved in the control based on sorted index of generators, adjust gradually until all fault transient angle stability margin shall meet the requirements. In the cluster computing system adopting distributed parallel computing, heuristic algorithm based on extended equal area criterion was improved by enumeration parallel manner, adjustment schemes which come from the result of head and tail pair are sent to the compute nodes and computed in parallel, and ultimately the scheme can meet the requirements is choiced as a aid decision measures in the computational results. Using this method can improve the calculation speed greatly.(2) The method of small disturbance and large disturbance dynamic stability auxiliary decision-making is presented that calculates online the power generation adjusting actions according to the result of state estimation and the parameters of element model in order to improve the damping of weekly damped mode to assigned security value. The power output of the key generators is reduced and the generation adjusting actions for controlling multi-weekly damped modes coordinately can be obtained. Parallel computing method is used and can meet the accuracy and real-time requirements of control measures at the same time.(3) Most voltage instability predictor(VIP) based on PMU data use local node or branch measurements to calculate the voltage stability index through the Thevenin equivalent on the system, which did not make full use of a large number of PMU information under the system, whether can accurate early warning of actual power system voltage instability is worth discussing. According to the real-time operation state of power network collected by SCADA system, PV curve and QV modal analysis can be calculated, then static voltage stability margin and voltage stability auxiliary decision can be obtained. In order to improve the real-time warning, the PMU measureing voltage of key node weighted by participation factor and critical voltage distance is obtained, based on the critical voltage and participation factor of key nodes calculated by PV curve and QV modal analysis, then the real-time voltage stability margin is got from the distance. When the voltage stability margin does not meet the requirements, the control measures to improve the voltage stability margin is obtained by matching between the current value and the target value difference and the gear division margin value of pre decision calculation, according to the pre decision calculated control measures which increase voltage stability margin to different gear position value.(4) At present, the actual PSS generally only use the signal of the machine side, the inhibition of the regional oscillation mode is limited. According to the information of generator power angle, generator active power, bus voltage phase angle, line active power and transformer active power measured by the PMU real time, power system low frequency oscillation events is monitored on-line and the oscillation mode and strongly correlative units are identified. Combined on-line analysis of low frequency oscillation and the small-signal stability auxiliary decision-making, the method of real-time control of low frequency oscillation is proposed. As the high voltage direct current (HVDC) system can be quickly controlled and have high overload capacity, DC power support can be used to damp low frequency oscillation by changing the powerflow of the AC tie-line. The selection of DC line, the time of power support and the support amount have been studied. According to the mechanism for the effect of generator voltage control on oscillation damping in power system, the method of generator voltage control based on wide-area information is proposed for on-line damping low frequency oscillations.(5) A variety of safety and stability problems in large interconnected power grid are intertwined, and various safety and stability problems may occur at the same time nowadays. Therefore, it is necessary to consider the coordination between the various security and stability problems in the calculation of auxiliary decision. In this paper, the calculation method of online security and stability comprehensive assistant decision-making of power system is proposed. To ensure assistant decision-making of the security and stability problem that has greater influence on the power system is given in priority, the calculation sequence of various security and stability problems is obtained based on sorting results according to the importance and complexity. To avoid conflicting control measures of all kinds of assistant decision-making functions are given, the sensitivity or participation factor of the candidate control measures for security and stability index is taken as the security and stability constraints in the coordination and optimization process. To avoid the same class control measures are adjusted at the same time in the assistant decision-making searching, the previous assistant decision-making results in the queue are taken into account. For multiple types of safety and stability problems which the coupled relationship is not strong, the decomposition coordination method is used to improve the computational speed. recursive iteration is used to solve the problem of control measures for possible conflict.Numerical simulations based on the actual grid have proved that algorithms showed above are effective and practical. The results of this research not only contain theoretic meaning, but also provide practical on-line security practical preventive control and emergency control decision support tool by integrating with the engineenng. |
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