Research On Dynamic Reactive Power Demand Characteristics And Counter-measures Of Received Power Grid In AC/DC Hybrid Power Systems

With the power transmission from west to east and nation wide interconnection of powergrids, DC Transmission System has become the main form of large regional interconnectionand long-distance transmission. The China Southern Power Grid equipped with the structureof eight-AC-main lines and five-DC-main lines up to2010. Because the normal operation ofthe DC transmission system is highly dependent on the converter station AC bus voltagelevel，dynamic reactive power demand levels and the support of reactive power at thereceiving power network have gained wide attention in theory circle and engineeringboundary.HVDC is very sensitive to the fault of the inverter-side AC system.The voltagedisturbance of the inverter station may cause commutation failure in HVDC and lead todynamic changes of reactive power and active power. The HVDC system in normal operationneeds to consume reactive power which is about40%-60%of the active power oftransmission. This demand may be a substantial increase in short-term transient process, so ithas a effect on the recovery of the grid voltage and load. When AC system is weak, the mutualinfluence between HVDC and induction-motor load is more outstanding. The operation of thesystem shows that the received AC stength and the characteristics of dynamic reactive powerduring fault and its recovery process have a significant effect on the recovery characteristicsof HVDC. The previous studies about commutation failure have been focused on the recoverycharacteristics of active power, but the research of the dynamic reactive power characteristicsduring fault and its recovery process is lack. In addition, the configuration of dynamicreactive power compensation device such as SVC and capacity selection is lack of theoreticalbasis.In response to these issues, the paper recommends the electromagnetic transientsimulation software package PSCAD/EMTDC, by taking CIGRE HVDC as the researchobject. A detailed study is conducted of dynamic reactive power demand in different voltagelevels. Q-V external characteristics model of HVDC inverter station in commutation failureand its recovery process was established initially. Then for different load models especiallyinduction-motor load model, Simulation research and mathematic modeling for therelationship between the reactive power and voltage is established. Finally, the paper analyzesthe mutual influence of dynamic reactive power between HVDC and induction-motor load.The calculation method of dynamic reactive power requirements is propoaed. The paper madeprimary study on the location and capacity of dynamic reactive power compensation device SVC.The research result of the project can be used for quantitative analysis of dynamicreactive power demand in AC and DC grid and guidance configuration of dynamic reactivepower compensation device...