Study On The Simulation Of HVDC Systems With A Real-Time Digital Simulator

In China much attention has been paid to the application of the High Voltage Direct Current (HVDC) transmission. Compared to ac technology, the DC power system offers many advantages and benefits to the overall power system especially in submarine power cable systems. long- distance power transmission and interconnection between different ac power networks. LingBao back-to-back HVDC project is the first one whose DC control and protection equipments are all made by Chinese manufacturer. This system will connect HuaZhong 220kV electric-network to the XiBei 330kV system. To ensure the utilities of the project will work well after they are set in the station, much efforts should be made to extensively test proposed control principles as well as the actual control hardware before installation in the converter terminal stations. This paper presents a study on the simulation of LingBao HVDC system with the real-time digital simulator. Based on this model, physical controls are connected to the simulator and a closed loop operation with external control is taken.Firstly, the paper describes the theory of electromagnetic transient simulation and HVDC transmission. Electromagnetic transient simulation is based on concepts introduced by H.W.DofRrael in his classic paper of 1969. According to the Dommel algorithm, all passive components within the network can be converted to an equivalent resistor in parallel with a current source applying the trapezoidal rule of integration. The equivalent resistance value is time invariant and depends on the component type and its parameters. The current injection on the other hand is time and history dependent and must be updated each time a new system state is produced. Thus, the power system can be turned into a network composed of resistors and current soiaces. It easy to set up the nodal algebraic equation of this network .With solving the equation, we can get every state variable of the power network.Secondly, the thesis expounds the test model setting up at RTDS in detail and some special tteateaent methods to some certain problems. Because of the HVDC system impossible to ran without control system, so in order to make the feasibility of the RTDS model verify before the device inserting the test circuit, a DC control system is put up using typical or generic coflfteols modeled internally. In this way, the test model can break away from the external equipments and run independently.Finally, a function test has been taken on the equipments according to the "testing outMnes" after the RTDS was joined with the control and protection utilities. Many practical studies involving HVDC systems and controls have been carried out using real time simulation. 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 on RTDS is proved to accord with the demands for this experiment which tests the whole function of the system and every individual event performance.