Abstract: A power flow calculation and AC/DC hybrid power flow calculation method for a flexible DC transmission system, the method including: according to the flexible DC transmission system under different control strategies, constructing a unified power flow model with a unified structure; determining a current main converter station, a current control strategy and an initial value and a limit value thereof, and forming the power balance equations under the current control strategy according to the unified power flow model; updating the current DC node voltage according to the voltage variation obtained by solving the power balance equations, and, if the updated DC node voltage exceeds the limit value, switching the control strategy; and if the updated DC node voltage does not exceed the limit value and the iteration constraints are not satisfied, alternating the main converter station according to the priority until iteration is completed.

Abstract: A method and system for optimizing power grid emergency load-shedding based on proliferation and reduction evolution. The method includes the steps of obtaining upper and lower limits data of allowed load-shedding amount of each load and boundary threshold data of transient security and stability constraint indexes of a power grid; and obtaining an optimal power grid emergency load-shedding scheme based on these data and an evolutionary optimization method, wherein the key of the evolutionary optimization method to work is proliferation and reduction evolution strategies. The proliferation strategy with multiple evolution search operators is proposed to generate many temporary candidate schemes. The reduction strategy of temporary candidate schemes includes two key steps, that is, pre-screening of based on a surrogate model and validation based on time-domain simulation.

Abstract: A fast search method and system for cascading failures in hybrid AC/DC power systems. The fast search method for cascading failures in hybrid AC/DC power systems includes: Determining the initial failures and forming a failure set of the first-stage failure, setting the DC blocking or the failure level reaching the threshold as the search stop condition; Judge the cascading failures in the failure set of the current stage can trigger DC blocking, if a cascading failure can trigger DC blocking, store the DC blocking failure as the next-stage failure. Otherwise, cascading failures are searched on the AC side and the failure set of the next stage is determined based on the pruning search method and the outage risk value; If the search stop condition is satisfied, stop the search, otherwise, the number of failure stages is increased by one and return to judge the cascading failures to continue the search.

Abstract: A rolling early warning method and system of dynamic security risk situation for large scale hybrid alternating current/direct current grids, which includes: constructing the original feature set of the fast total transfer capability (TTC) estimation model; generating the training sample set of the fast TTC estimation model based on the network topology and the forecast information of a period of time in the future; constructing the fast TTC estimation model based on stacking denoising autoencoders and extreme learning machine; generating the future operating conditions (OCs), and determine the type of preventive control actions needed to ensure the system security based on the fast TTC estimation model and the heuristic search algorithm; and conducting the layered and hierarchical early warning for OCs according to the type of operating state and the type of preventive control actions that is needed.

Abstract: A method and system for online decision making of generator start-up, determining the lines to be restored step by step based on the real-time power system data to guide the initial stage. The black-start unit is determined, and the units waiting to be restored are selected from all units. The training set including labeled samples to establish a value network. During generator start-up, the blackout area is judged, the state of power system is identified, the availability of equipment is judged, and the characteristics of generators are collected. The total generation capability is used as search objective for Monte Carlo tree search. Based on the value network, Monte Carlo is applied to search the next line to be restored during generator start-up. Parallel computation adopted to check the constraints for the restoration of alternative lines. The results of Monte Carlo are summarized to determine the line to be restored next.

Abstract: A fast search method and system for cascading failures in hybrid AC/DC power systems. The fast search method for cascading failures in hybrid AC/DC power systems includes: Determining the initial failures and forming a failure set of the first-stage failure, setting the DC blocking or the failure level reaching the threshold as the search stop condition; Judge the cascading failures in the failure set of the current stage can trigger DC blocking, if a cascading failure can trigger DC blocking, store the DC blocking failure as the next-stage failure. Otherwise, cascading failures are searched on the AC side and the failure set of the next stage is determined based on the pruning search method and the outage risk value; If the search stop condition is satisfied, stop the search, otherwise, the number of failure stages is increased by one and return to judge the cascading failures to continue the search.

Abstract: A method and system for online decision making of generator start-up, determining the lines to be restored step by step based on the real-time power system data to guide the initial stage. The black-start unit is determined, and the units waiting to be restored are selected from all units. The training set including labeled samples to establish a value network. During generator start-up, the blackout area is judged, the state of power system is identified, the availability of equipment is judged, and the characteristics of generators are collected. The total generation capability is used as search objective for Monte Carlo tree search. Based on the value network, Monte Carlo is applied to search the next line to be restored during generator start-up. Parallel computation adopted to check the constraints for the restoration of alternative lines. The results of Monte Carlo are summarized to determine the line to be restored next.