Hybrid HVDC System Control Method Based On The RTDS Simulation Research

Hybrid HVDC is a new high-voltage direct current transmission technology,developed on the basis of the traditional HVDC and HVDC Light technology,based on the Current Source Converter(CSC)and the Voltage Sourced Converter(VSC).It combines the advantage of the traditional HVDC(large capacity,high reliability,mature technology and low-cost)and HVDC Light(capability of working in the state of passive inverter and controlling active power and reactive power of the system independently,high stability of transmission,high quality of output voltage waveform).Hybrid HVDC is only in the theoretical stage,but due to the feature of learning from each other,it will get more and more attention.Firstly,a list of the existing topology of Hybrid HVDC model is presented,then the most representative topolopy,precisely,the double-ended Hybrid HVDC model was selected as the simulation object.Then two completely different working principles and mathematical models of converter stations is analyzed,laid a theoretical foundation for the establishment of the simulation model.Secondly,the control method of Hybrid HVDC was analyses in different level,that is system level,converter station level and valve level.The system-level control play a global role of the system control;the valve level control vary depending on the characteristics of the semi-controlled device or a full-controlled device;the most important control level is the converter station control,it is the level to control a commutation unit of the HVDC,and to control the phase of inverter’s trigger.This paper discusses different control strategies due to different system requirement.Most importantly,the simulation model used in this paper were designed based on the Real Time Digital Simulator(RTDS).It contains controller of CSC station using strategy of fixed DC current and minimum limit of firing angle and controller of VSC station using strategy of fixed DC voltage(or active power)and fixed reactive power(or AC voltage).The Hybrid HVDC simulation model is established and studied with both ends connecting active network.RTDS(Real Time Digital Simulator)is based on electromagnetic transient calculation theory through the multiprocessor parallel computing to achieve real-time power system simulator.It can meet high simulation precision of HVDC simulation requirements and has good human-computer interaction interface.Its biggest advantage is able to reflect the real time of the power system operation condition.In this paper,the Hybrid HVDC simulation model with RTDS is established.The steady-state characteristics of the system under different control modes was analyzed,so as the step change response of DC current,DC voltage and reactive power.The corresponding dynamic time,the rectifier firing angle,the DC current,the DC voltage of both side,the AC voltage and current of the inverter side,the active power and reactive power of both sides was observed and recorded.Through the experimental phenomena and results summary,conclusions can be drawn: the Hybrid HVDC model based on the RTDS,can meet the control requirement basically,and have good operating results.It is feasible.