Research On Protection Scheme Of AC Distribution Network Considering Distributed Generation

The combination of distributed generation technology and large power grid can effectively improve the reliability of power supply.However,the access of distributed generation has changed the topology of the single-side power supply of the traditional distribution network,which may lead to bidirectional power flow and over-voltage in distribution lines.Therefore,in view of the problems caused by the distributed generation connecting to the AC distribution network,this thesis studies the relay protection scheme of the distribution network with the access of distributed generation.The main research contents are as follows:The control system of Inverter Interfaced Distributed Generation is modeled,the fault characteristic of Inverter Interfaced Distributed Generation is analyzed,and the corresponding fault current calculation model is determined.At the same time,the adaptability of traditional fault analysis method of distribution network under the condition of distributed generation access is analyzed,and the fault characteristic analysis method suitable for active distribution network is proposed.A protection scheme based on the direction of current fault component is proposed for active distribution network with the ability of measuring voltage and current.The structure of distribution network protection system is established.The fault component of current is selected as the fault feature.According to the proposed criterion,the direction of fault component of current at circuit breakers at both ends of each section is determined,and the fault section is determined and removed.A protection scheme based on current amplitude and phase condition is proposed for active distribution network which only has the ability of current measurement.The fault characteristics of the line are analyzed on the amplitude-phase plane,and the fault location is determined by the different amplitude and phase conditions of the current at both ends of the fault line and the non-fault line.On this basis,an improved criterion is proposed,which can realize the flexible adjustment of the braking performance of the protection criterion.A relay protection scheme for active distribution networks with uneven measurement capability is proposed.Aiming at the area with good measurement capability,a protection scheme based on regional current direction is proposed,which realizes regional protection of distribution network by controlling circuit breakers around small area.For the area with poor measurement capability,a reclosure scheme matching with DG re-grid timing is proposed,which can effectively utilize the existing protection configuration resources of the distribution network with the advantage of economy and engineering practicality.Finally,the simulation of the proposed protection scheme is carried out in PSCAD/EMTDC.The simulation results verify the effectiveness of the schemes.