| Enhancing the proactive coping capacity of power grid after occurrence of high-impact low-frequency events is a vital requirement and challenge for electric industry's development,driven by the factors including the increasing frequency and intensity of extreme weather events,the growing reliance of society to electricity,the mounting interruption cost,etc.This enables the power grid to get through the whole process influenced by such an event as smoothly as possible and at the lowest cost and further to restore from it as quickly as possible,and this has great significance for guaranteeing the normal functioning of society and safeguarding the security of peoples' lives and properties.The aim of enhancing the proactive coping capacity of power grid after occurrence of disturbance is to make the grid respond to the impact and consequent influence of the disturbance in a far more resilient way.In terms of the main influencing process of a disturbance,after occurrence of the disturbance,the power grid may confront a degradation of functioning.Once the damage situation is known,the grid enters a process of gradually restoring the lost loads and infrastructures and then keeps operating until returning to the pre-disturbance level.Accordingly,the key to enhance the proactive coping capacity of power grid after occurrence of disturbance lies in the actions of resourcefully controlling the influencing process of disturbance,quickly restoring the lost loads and infrastructures,and,in addition to them,sustaining the continuous operation of the grid under the extreme circumstances in which some vital infrastructures cannot be restored in a short time.Due to the merits including bi-directional and flexible controllability of power and rapid response,electrical energy storage has great potential in boosting the power grid resilience,especially the newly-emerged mobile energy storage technology that further improves the flexibility of energy storage utilization and its performance in enhancing power grid resilience.Therefore,to address the urgent demand for enhancing power grid resilience,this dissertation does in-depth research on how the energy storage resources can be scheduled accurately and efficiently to boost the power grid resilience to a higher level after disturbances,and develops the relevant models and strategies for controlling influence of disturbances,improving the grid restoration,and sustaining grid's life.The main contents of research are summarized as follows:(1)Research is carried out on the ability of energy storage resources to control and interrupt the deteriorating process of power grid operating states under the impact of disturbances.Aiming at one typical and long-lasting disturbance in the current AC/DC hybrid grids,namely,repetitive commutation failures of high-voltage DC transmission lines,and the resulted deteriorating process of the sending-end power system transient stability,this dissertation proposes an emergency control strategy with the flexible power support of energy storage resources.This strategy adopts a framework based on model predictive control and uses the extended equal area criterion as the tool for analysis.The rolling optimization problem is solved approximately in an analytical way.Specifically,at the theoretical level,the model to recursively forecast rotor angle and speed of the equivalent one-machine infinite-bus system of sending-end system is constructed based on reasonable approximation of the dynamic and nonlinear changing process of the system states.Then,with the purpose of compensating the transient stability margin necessarily for the sending-end system,the analytical solution of the optimal control input that should be provided by energy storage is further derived.At the practical level,with the proposed strategy and the current measures for disturbance detection,and through the rolling performance of such a process of “disturbance detection? state forecast ? control calculation and implementation”,the energy storage resources can stimulate the sending-end power system continuously and precisely based on their capability of rapid and flexible power support to realize the objective of controlling and interrupting the deteriorating process of the system transient stability under the case of repetitive commutation failures,and that allows the sending-end system to safely get through the disturbing process resulting from repetitive commutation failures of high-voltage DC transmission lines.In addition,aiming at the possible problems of insufficient available capacity for control and over-limit system states,the remedial control method involving blocking of high-voltage DC transmission lines and traditional measures for emergency control is proposed.(2)Research is carried out on the ability of energy storage resources to improve the post-disturbance restoration process of power grid loads.The model with enhanced computational efficiency for space-time scheduling of mobile resources is developed.The concept,model and strategy for scheduling of separable mobile energy storage resources are further developed based on the idea of decoupling the energy storage modules and the carriers,which are adopted to improve the restoration process of power grid loads with other mobile energy resources.Specifically,the research includes the following contents:1)The major space-time models adopted in existing studies about scheduling of mobile energy resources in power grid have the common deficiency,namely that the model size increases dramatically with the scheduling scope,and that forces the existing models to experience a degraded computational efficiency.Especially,a high delay to the actual execution of scheduling can be resulted when many nodes are involved in and a small time step are required for the scheduling.To address this issue,this dissertation develops a novel and more compact space-time model,which characterizes the behaviors of mobile resources during the scheduling by constructing linear constraints from the two aspects,namely the transition between parking and traveling states and the required travel time.The comparison results in case studies show the advantage in computational efficiency of the proposed model over the existing two models.2)In the current scheduling methods of mobile energy storage resources,the energy storage modules and the carriers are scheduled as one whole.To further extend the flexibility and feasibility of such a scheduling and thus to explore a more optimal result or performance,in this dissertation,the energy storage modules and the carriers are innovatively decoupled,i.e.,they are treated as independent components in the scheduling.A novel concept,referred to as the scheduling of separable mobile energy storage resources,are then proposed,and the programming model for the scheduling is derived based upon the interactive behavior among modules,carriers,and nodes of the power grid.In addition,to bridge the gap that lies in the fuel delivery issue which is usually neglected by the current studies about the scheduling of mobile generators,this dissertation develops the model for scheduling of fuel tankers coordinated with the operation of mobile generators.Based on the above,a strategy for power grid loads restoration,involving the joint scheduling of separable mobile energy storage resources,mobile generators,fuel tankers,and topology reconfiguration,is proposed,and the restoration performance is improved through the coordination between these measures.(3)Research is carried out on the ability of separable mobile energy storage resources to strengthen the post-disturbance survivability of isolated power grid.A strategy based on the internal and external coordination is proposed for strengthening the survivability of isolated power grid.Specifically,from the grid's external point of view,the separable mobile energy storage resources are scheduled to rebuild the links for energy transmission from the outside “stranded” sources to the isolated grid.The energy and power supplies are successively sustained by separable mobile energy storage resources through round trips between the two locations and alternate behaviors between charging and discharging.On the other hand,from the grid's internal point of view,demand response is scheduled with the energy payback effect considered to timely relieve the operating stress of the power grid by reducing demand of some nodes within the allowable range and to maintain the grid operation.Accordingly,to realize this strategy and considering the uncertainty of power output of renewable energy generation and loads of the grid,a two-stage robust optimization model is constructed and further solved by the column-and-constraint generation method.In this dissertation,in-depth research is done on the utilization of energy storage resources for enhancing the proactive coping capacity and resilience of power grid after occurrence of disturbance.The models and strategies for flexible control and space-time scheduling of energy storage resources are developed with the purposes of controlling,restoring,and surviving.These results of the research can make a good expansion of the value and utilization of energy storage resources in power grid,help to improve the ability of power grid to control,interrupt,and well respond to disturbances and their impact in an active way,and have good theoretical and practical values. |
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