Probabilistic Small Disturbance Stability Analysis Of Active Distribution Network Considering Distributed PV Randomness

In recent years,with the gradual depletion of fossil energy and the further emphasis on environmental protection,new energy is gradually infiltrating into all aspects of power generation,transmission,distribution,and electricity use.Among them,the new energy is connected to the distribution network in the form of distributed power generation.While alleviating the power supply pressure and improving the utilization rate of new energy,it also brings various challenges to the distribution network.Power sources such as distributed PVs are connected to the distribution network in the form of power electronic interfaces.The control mode has the characteristics of small inertia and fast response,which results in poor anti-disturbance performance and easy to lose stability when disturbed.Further,due to the stochastic nature of distributed PV power generation,active distribution networks often operate at different steady-state operating points,whereas distributed PV controllers are designed only at a specific steady-state operating point.System instability may be induced when the steady-state operating point deviates too much.Therefore,it is of great significance to study the small disturbance stability of active distribution networks with distributed PV access,especially considering the stability of distributed PV randomness.However,the current research mainly focuses on deterministic stability analysis.When considering the stochastic stability problem,only the single-machine infinite system structure is considered.Although the structure is simple and easy to analyze,the power generation correlation and dynamics between multiple distributed power sources are neglected.Interaction.Aiming at this problem,this paper has conducted in-depth research on the random stability of active distribution network with multi-distributed-PV access.The main work is as follows:1.The 33-node active distribution network simulation model including distributed PV power generation system is built,and the nonlinear differential equation model of the system is established based on the simulation model topology.After linearization,the small disturbance state-space model of the system is established.Based on the eigenvalue analysis method,the detailed small disturbance stability analysis is carried out,and the critical eigenvalues and damping ratios that can directly reflect the stability index of the system are found.And through sensitivity analysis,we found the weak parts of the system that are related to the critical eigenvalues.2.The small disturbance model order of the active distribution network is high,and it is feasible to perform deterministic analysis at a specific working point.However,when the uncertainty is considered for the uncertainty analysis,the computational cost is too large,so it is necessary to reduce the order of the small disturbance model so as to simplify the analysis.From the perspective of multi-time-scale characteristics of the system,based on distributed PV control bandwidth analysis and network time constant analysis,the active distribution network is divided into three time scales.Since the critical eigenvalues calculated in 1 mainly depend on the DC voltage control time scale,a simplified model of distributed PV,line and load modules on the time scale is derived,and the combined distribution network DC voltage control time scale is generated.Reduced order model.The comparison between the simulated waveform and the eigenvalue distribution of the reduced-order model and the detailed model verifies the effectiveness of the proposed time-scale reduction model of the DC voltage control of the active distribution network.3.Considering the stochastic characteristics of distributed PVs in the small disturbance reduction model of the active distribution network,it brings a large degree of uncertainty to the steady state operating point of the active distribution network.Stability problems may occur at large steady-state operating points,and deterministic small-interference stability analysis at this time may lead to unreliable analysis results.Aiming at this problem,a small disturbance probability stability analysis method considering distributed PV randomness is proposed to efficiently and accurately analyze the randomness of multiple distributed PVs to the small disturbance stability of active distribution network.Based on the probability distribution method,the key eigenvalue damping ratio of the system is established as the orthogonal polynomial model of each solar solar irradiance.The model is used to estimate the influence of each distributed PV and calculate the probability of system instability.The effectiveness of the proposed method is verified by a 33-node active distribution network simulation.