Relay Protection And High Voltage Ride Through Strategy Based On Substation Area Information

With the continuous development of photovoltaic(PV)power generation technology,the installed capacity of centralized grid-connected PV power stations is increasing.PV power stations still follow the configuration of a conventional distribution network protection,and configure staged current protection on the collector line.However,the fault characteristics of PV are affected by the control strategy,and the staged current protection is no longer applicable.In the recovery phase of the collector line fault,the reactive compensation device is out of adjustment,which will result in transient over-voltage and cause the renewable energy to cascade trip off the grid.How to improve the collector line protection in PV power stations and improve the high voltage ride through(HVRT)capability of PV has important research significance.Based on the control strategy of PV grid-connected inverters,the paper builds a model of PV power station in PSCAD/EMTDC,and analyzes the adaptability of the current protection on the collector line.The LVRT current output by the PV may cause the stage II of current protection on the non-faulty collector line to malfunction.In order to solve this problem,the idea of substation-area-protection(SAP)can be used.However,The conventional SAP principles may not be suitable for PV power stations.Therefore,the adaptability of the SAP principle based on the generalized differential protection,the comparison of current amplitude and the direction comparison is analyzed.For the SAP principle based on the direction comparison,the influence of the fault characteristics of PV on the directional elements based on the positive sequence fault component(PSFC)is analyzed from the perspective of the protection principle.It is pointed out that the directional element based on the PSFC may have the problem of sensitivity reduction or even misjudgment due to the non-constant impedance angle of,the PSFC of the PV.In response to this problem,a directional comparative SAP principle based on improved directional elements is proposed.The improved directional element divides the operation zone into forward/reverse sensitive area and insensitive area,and combined with the auxiliary criterion of current amplitude comparison,it can accurately identify the fault direction.The SAP comprehensively identifies the fault location based on the output result of the improved directional element.The simulation results verify the effectiveness of the proposed SAP scheme.Aiming at the problem of HVRT in the PV power station,it is pointed out that the redundant reactive power output by the reactive compensation device during the voltage recovery phase causes the transient over-voltage.The adaptability of the conventional HVRT strategy of PV grid-connected inverters based on reactive power control under cascading fault scenarios is analyzed,and it is pointed out that the existing HVRT strategy cannot absorb redundant reactive power in time.The shortcoming of the existing SVC cut-off strategy with fixed delay is analyzed,and the problem is pointed out that the SVC cut-off control is difficult to coordinate with the operating time of circuit breakers.To solve this problem,a HVRT strategy based on substation area information is proposed to realize the coordinated control of reactive power and voltage between PV,SVC and protection.The SAP uses the trip signal of a circuit breaker to send a cut-off command to the TSC,and dynamically adjusts the TCR trigger angle according to the voltage increase.On the basis of the conventional HVRT strategy of PV,the reactive current compensation is formed by the differentiation of voltage to time,and the reactive current reference value is compensated.The simulation results verify the effectiveness of the proposed HVRT strategy based on substation area information.