Research On Risk Assessment Method Of Distribution Network With Distributed Generation In Island Status

When the distribution network with distributed generation is disconnected from the main power supply,the distributed generation can also bear part or all of the power supply capacity.However,because the output of distributed generation is greatly affected by environmental and climatic conditions,the risk of safe and stable operation of island distribution network is also great.It is of great significance to evaluate the operation risk of island distribution network with distributed generation and put forward corresponding countermeasures to further improve the planning level of distributed generation and promote the development and utilization of new energy to be more coordinated with the public power grid.Based on the research status at home and abroad,combined with the risk source analysis of distribution network operation,this paper obtains some problems existing in the risk assessment of island distribution network with distributed generation,and puts forward some solutions.By establishing the power model and outage model of each component of the distribution network,the sequential Monte Carlo method is used to simulate the output and operation state of the distributed generation,and the improved push back method is used to calculate the power flow of the island distribution network.Finally,the risk assessment indicators are calculated based on the power flow data,and the corresponding risk response strategies are put forward.Considering that the islanding distribution network loses the balance node and the small frequency deviation changes the output of load and distributed generation,the power flow calculation method based on the assumption of constant frequency can no longer accurately reflect the operation state of islanding distribution network.Therefore,this paper uses the improved forward and backward substitution method to calculate the frequency and node voltage of island distribution network,so as to further evaluate the risk of island distribution network more accurately.Considering that the influence of weather factors on distribution network lines is greater than that of transformers and circuit breakers,a distribution line outage model considering weather factors is established.The distributed generation adopts the structure of multi unit grid connected power generation,and the local fault does not affect the rest of the power output.A partial outage model of distributed generation is proposed.Based on the historical data,the output and load data of distributed generation are simulated by Monte Carlo method to overcome the impact of intermittent output fluctuation and inconsistent load fluctuation on risk assessment.This method also takes into account the risk points of output characteristics of distributed generation.Based on the simulation results of distributed generation output and load data with 15 min period length and 1mth time span,the method of dynamic Island division and the evaluation method of power flow calculation results are adopted to make the risk evaluation results of island distribution network more accurate.Finally,taking an actual distribution network as an example,this paper makes an empirical study on risk assessment,and puts forward the corresponding risk response strategies,so as to provide some guidance for the planning of distributed generation in distribution network.