A Decoupled Control Strategy For HVDC Light

HVDC Light is a new type HVDC based on Voltage Sourced Converters (VSC) Technology, which was recently developed. As it is built up with VSC which consist of IGBT (insulated gate turn-off bipolar transistors), instead of Current Sourced Converters (CSC) used in traditional HVDC, the current will be cut off easily, and with the pulse-width-modulation (PWM) technology it can be used for passive inversion. As a result, supplying to passive load with HVDC Light has being come true. The VSC technology has many more superiorities, such as small cubage, strong function, decreasing filter device and simplying conversation structure. For these reasons, this technology is named HVDC Light. Besides the superiorities of traditional HVDC, HVDC Light is also possible to feed AC systems with low short circuit power or even passive networks, to control the active and reactive power exchange flexibly,rapidly and independently, not to supply short current, and to change power flow direction easily without changing the polarity of DC link and so on. Used in the field of supplying power to the isolated and distance load or multi-terminal HVDC Light networks and so on, HVDC Light performs better economically and good control characteristics. Additionally, the voltage drop in the transmission line will be decreased and the voltage quality will be increased by using HVDC Light technology.In this paper, the control method of HVDC Light is mostly studied. Firstly,the mathematical models of both the steady state and the dynamic state are set up. And using the Parker matrix, an equivalent continuous-time state-space model of VSC in the synchronous dq reference frame is presented. Then the structure of control system and the basic control method are introduced for designing VSC controllers. The VSC controller designed in this paper is based on the strategies of deviation decoupled control,and the characteristics are analyzed from the mathematical calculations process , then the second-order filter and LC filter are designed. For validating the VSC controller and the filters, the Matlab/Simulink simulation models are established .The simulation results verify the validity of the mathematical models, and demonstrated that the controller is convenient and efficient; moreover, the power flow and the stability of HVDC Light system can be controlled rapidly,and all the basic control method can be achieved by this controller,even also verify the characteristics of it . At last, by the analysis of FFT the results show that the filters are efficient and meet the demand greatly.