Research On Control Strategy Of VSC-HVDC And Implementation Of Its Experiment System

VSC-HVDC greatly extends the range of application of HVDC. It has been a highlight of transmission and distribution field for the excellent characteristics of control flexibility, environmental protection, power exchange, green energy supply and improving power quality. There are still many application questions needing to be further studied, especially for no practical VSC-HVDC project operating in our country.This dissertation focuses on the attention to mathematical model, control strategy and experiment system of VSC-HVDC and deeply studies the founding of mathematical model and control system framework, the design of controller and the development of experiment system. It includes the following contents.1. The mathematical models in abc and dq0 coordinate are derived. Based on omitting high-frequency component of switching function, a dynamic equivalent circuit of VSC-HVDC is founded. By use of the dynamic equivalent circuit, the dynamic performances of VSC-HVDC system are easily gained. The analysises to the VSC-HVDC system static performances further reveal the operation mechanism of VSC-HVDC.2. The control system framework of VSC-HVDC is founded. A four-layer structure of the control system framework of VSC-HVDC is proposed concretely, which is made up with the DC system control layer, converters control layer, separate control layer and valves control layer. The paper clarifies the basic control functions of the control system of VSC-HVDC and points out that the redundancy configuration and the multi-layer structural design are necessary. Based on the principles of configuration of each layer, the paper describes the control functions and scope of each control layer at details. In view of the close correlation between the control system and the protection of VSC-HVDC system, the paper further discusses the coordination issues between them.3. VSC-HVDC H_∞controllers are designed. Focus on the shortcoming of PI controllers design and from point of view of improving the control system robustness, the H_∞controllers of supplying to passive network and active network are design according to H_∞theory. For the sake of restraining the influence from disturbances of AC system voltage, the H_∞controller considering disturbances of AC voltage is designed. 4. VSC-HVDC experiment system is designed and implemented. It includes main circuit, control subsystem and monitor subsystem. By use of the experiment system, the tests of supplying to passive network and active network are gone on. A fuzzy adaptive PI controller that can automatic regulate PI parameters is implemented. The experimental results show that the fuzzy adaptive PI controller is effective.5. Three basic connection types of multi-terminal VSC-HVDC system, including Parallel, Series and Hybrid connection, are proposed. Hybrid connection can be divide two kinds of connection types again. One is series-parallel type and the other is parallel-series type. The structure diagrams and characteristics of the three types are analyzed. Simulation results show that the proposed connection types are feasible.