UHVDC Transmission System Of Real-time Digital Simulation Research

In China much attention has been paid to the application of the High Voltage DirectCurrent （HVDC） transmission. Compared to ac technology, the DC power system offersmany advantages and benefits to the overall power system especially in submarine powercable systems、long-distance power transmission and interconnection between different acpower networks. Yunnan-Guangdong±800kV and Xiangjiaba-Shanghai±800kV UHVDCprojects, of the highest DC voltage in the world, were announced to be put in operation inJune and July2010respectively, which opens a new page for HVDC development in China.This paper presents a study on the simulation of a UHVDC system with the real-time digitalsimulator. Based on this model, physical controls are connected to the simulator and a closedloop operation with external control is taken.Firstly, the paper describes the theory of electromagnetic transient simulation and HVDCtransmission. Electromagnetic transient simulation is based on concepts introduced byH.W.Dommel in his classic Paper of1969.According to the Dornrnel algorithm,all Passivecomponents within the network can be converted to an equivalent resistor in parallel with acurrent source applying the trapezoidal rule of integration. The equivalent resistance value istime invariant and depends on the component type and its parameters. The current injectionon the other hand is time and history dependent and must be updated each time a new systemstate is produced. Thus, the power system can be turned into a network composed of resistorsand current sources. It is easy to set up the nodal algebraic equation of this network. Withsolving the equation, we can get every state variable of the power network.Secondly, because of the HVDC system impossible to run without control system,so inorder to make the feasibility of the RTDS model verify before the device inserting the testcircuit,a DC control system is put up. In this way, the test model can break away from theexternal equipment and run independently.Finally, a function test has been taken on the equipments according to the “testingoutlines” after the RTDS was joined with the control and protection utilities. Many Practicalstudies involving HVDC systems and controls have been carried out using real timesimulation. Studies have been performed on the experiment results both for developmental purposes and for testing purposes.After summing up to the testing Program and experimental results, the model built onRTDS is proved to accord with the demands for this experiment which tests the wholefunction of the system and every individual event performance.