Research On The Power Control Of Flexible HVDC System

With the fast development of new power energy transmission mode like new energy power transmission,transactions in different power grid market, Traditional transmission methods can not meet these new requirements. Based on the Voltage source converter (VSC) technology, the flexible HVDC technology is a highly developing mode of power transmission. It can have huge advantage like the independent control of active, reactive power; do not increase the short-circuit system capacity; asynchronous link between power grids. The main role of flexible HVDC system is to control the direction and size of tide between different power grids, so it is of great significance to research the instantaneous power calculation methods and control strategies in flexible HVDC system.As the establishment of flexible HVDC converter mathematical models start with, we establish the converter 's steady-state model based on the rate and phrase of output voltage and the mathematical model based on the three-phase power static,two-phase rotating static. So it provides a theoretical basis to power control strategy analysis, control system design and analysis.With the mathematical model of flexible HVDC system, and combine with all kinds of the control strategy of PWM converter, respectively, introduce the methods of instantaneous power calculation based on the analysis of orientation voltage and based on virtual flux of analysis and have analysis of the power control methods based on the hysteretic comparator.In the basis of the analysis, three flexible HVDC system control modes have been given: the control model based on the directional voltage power, the control model based on the power hysteretic comparator, the power-control model based on virtual flux, and discuss them with the advantages and disadvantages in detail. Than have the conclusion that the power-control model of virtual flux is the most suitable for flexible HVDC system, the MATLAB / Simulink simulation results verify the validity of all the analysis results.A 15 KVA of flexible HVDC experimental system is established. The steady state and dynamic system characteristics is good, the results verify the effectiveness of the selected control strategy.