Voltage Quality Probabilistic Evaluation On Distribution System Containing Distributed Generators

In recent years,energy crisis and environmental pollution problem is increasingly outstanding,it makes use of renewable energy distributed generation technology developed energetically.But most distributed generation output are volatile,it exits a series of power quality problems in the current distribution network of the power system,especially in the voltage quality.The evaluation of voltage quality become more complicated.How to evaluate the voltage quality of distribution system containing distributed generation reasonably has become an important problem to study.The access of distributed generation that makes the operation of the power distribution system and control face more uncertainty.It makes the deterministic flow calculation method no longer apply.The concept of probabilistic load flow(PLF) need to be introduced in considering many kinds of random factors. The thesis proposes the probabilistic load flow calculation method based on the 2n+1 point estimate method,and this method was used in the probabilistic load flow calculation of system integrated with distributed generation.It builds the probabilistic model of load and distributed generation, and through the probabilistic load flow calculation,the related characteristic value of node voltages are obtained.Combing with theory of semi-invariant and Gram-Charlier series expansion, the probability distribution function curves is obtained.And the influence of distributed generation was analyzed by comparing the power system unconnecting distributed generation.Taking the IEEE 30-bus system containing distributed generation as the case,the proposed method has more accurate testing result and reduces the computational burden when compared with the Monte Carlo method,it verifies the validity of the proposed method.On this basis,the thesis also proposes the continuous power flow method based on the 2n+1 point estimate method,and combined with Cornish-Fisher series.It builds the probabilistic model of load and distributed generation to obtain the statistic feature of critical point of voltage stability and the probability distribution function of load margin.Simulation results of IEEE 34-bus system show that using the proposed method can evaluate the static voltage stability of distribution network effectively,and the proposed method has the advantages of high speed and precision comparing with the results by Monte Carlo simulation.