Study Of The Synchronization And Stability Of Power Grids Based On The Theory Of Complex Networks

After years of research, It has made great progress about complex networks both in theory and in application. Applying the complex network theory to research networked problems for revealing the nature law hidden behind them can help us have a better understanding about the characteristics of actual networks, so as to take advantage of their benefits and avoid the harm.A power grid is a typical complex network, its safe and stable operation is related to national economy and people’s livehood. The sharp increase of electric power demand not only placed great pressures on the energy conservation and environmental protection, but also brings an extraordinary challenge for the operation of future power grids. How to solve the issues of energy, environment and power grid security are great challenge that power researchers have to face. Using complex network theory to analyze the security of power system can reveal its inherent characteristics and evolution law to prevent the chain collapse in power network and to provide some references for the power grid transformation and construction in the future.In this paper, we have considered the current research status of complex network theory and dynamic characteristics in power grids to study synchronization and stability issue of power grids, including the following aspects:1. Study the relationship between the dynamic behavior and coupling strength in power grids. Taken the second-order Kuramoto phase oscillators as IEEE14bus system nodes, made the system power keep balance, the system operation states under different coupling strengths K have been observed, then the minimal coupling strength Kc is obtained for the network synchronization. Study shows that if the coupling strength exceeds a critial value K≥Kc, all the nodes in the system run at the same frequency Ω, the power grid is in synchronization, the larger the coupling strength, the better synchronzability.2. Study the effect of the disturbance on the power grid stability and desynchronization wave propagation. Capability of a power system to regain a steady state after disturbances and a relationship among the minimum value of perturbation△pmin and duration of disturbance At and coupling strength K are studied in IEEE14bus system. Study shows that when the coupling strength K and duration of disturbance At are constant, the system relaxes back to a synchronization state or not is depending on the strength of perturbation. If a perturbation exceeds the minimum perturbation△p>△pmin, the system loss of synchronization. When the duration of disturbance△t within a certain range, the shorter the At, the larger the△pmin. The results also presented that the minimum perturbation Apmin has a linear relation with coupling strength K, the larger the coupling strength K, the greater of△pmin. In order to study the minimum value of node perturbation (△pi)min that causes loss of synchronization in the network, perturbations are applied to each node in IEEE14bus and IEEE118bus systems. The study found that the minimum value of node perturbation (Api)min is related to its degree, the higher the degree of a node, the larger the minimum perturbation is needed, it means that a node with a higher degree can resist a stronger disturbance. The cascade instability process after disturbance has been observed by applying perturbation to a single node in IEEE118bus system. Simulation results show that the perturbed node deviate from its steady state, then "drag" its neighbors away from their original states, eventually spread to the whole system.3. Study the effect of appending a new generator node on the power grid synchronization performance. A new generator node has been connected to a generator node or a load node in the IEEE14bus, IEEE57bus and IEEE118bus systems respectively. Then the correlation coefficient of the original system and two different access mode of the new systems is calculated, and all of these systems synchronization performances are compared by the average order parameter r∞. The results indicate that a network which the new generator node directly connected to a load node has a better synchronous ability than the network which the new generator node is directly connected to a generator node.4. Study the effect of distributed generation on power grid synchronous ability and anti-disturbance. Different amount of distributed generations are respectively added to IEEE57bus and IEEE162bus systems to investigate the systems synchronization performance and ability to resist disturbance. Large amounts of simulations show that not only the critical coupling strength Kc decreases and the self-organized synchronization is promoted, but also the system anti-disturbance ability is enhanced when more distributed generations are presented in power system.