Research On Emergency DC Power Support Control And Damping Of Low Frequency Oscillation For Hybrid Multi?infeed HVDC System

The line commutated converter based high voltage direct current?LCC-HVDC?,especially in Ultra-HVDC systems?UHVDC?,is in an influential position in the electric energy transmission field due to its advantages of trans-regional,long-distance and bulk power.As the latest generation of transmission technology,the voltage source converter based high voltage direct current?VSC-HVDC?has gradually penetrated into the field of transmission,and has great application potential in clean energy accommodation.Therefore,the future power grid will inevitably have multiple LCC-HVDC and VSC-HVDC feeds into the same or close electrical distance system,which ultimately form a hybrid multi-infeed HVDC?HMIDC?.The HMIDC system has the advantages of both LCC-HVDC and VSC-HVDC,it is a new type of HVDC topology.This paper focuses on HMIDC research:1)Considering reactive power coordinated control of HMIDC system research into emergency DC power supportAccording to the characteristics of LCC-HVDC and VSC-HVDC,respective additional emergency DC power support?EDCPS?controllers are designed,and a coordinated control strategy based on a HMIDC system for EDCPS is proposed.Considering the differences in system recovery performance between LCC-HVDC and VSC-HVDC in providing emergency DC power support,the emergency power support priority issues and power allocation schemes for LCC-HVDC and VSC-HVDC are discussed in detail.To maintain the stability of the receiving-end AC system during boosting power process and to ensure the active power is raised to the specified value,this paper also designs an additional reactive power controller that can make full use of the ability of VSC-HVDC to support the reactive power of the AC system.Finally,a hybrid three-infeed HVDC system consists of two parallel LCC-HVDC and one VSC-HVDC is built on PSCAD/EMTDC and simulated.The effectiveness of the proposed approach is verified based on this hybrid three-infeed HVDC system.2)Research on damping control to suppress low frequency oscillation for HMIDC multi-point of fall systemTo solve the problem of low-frequency oscillation?LFO?caused by insufficient damping in the HMIDC system,the first step is to obtain the related oscillation modes and transfer function of the controlled plant,which are identified by the total least squares estimation of signal parameters via rotary invariance technology?TLS-ESPRIT?.Second,according to the multiobjective mixedH₂/H_?output feedback control theory with regional pole assignment,an additional robust damping controller is designed in this paper.Then,the control-sensitive point for suppressing LFO based on the small disturbance test method is determined,which is suitable for determining the installation position of the controller.Furthermore,the balanced truncation method is adopted to reduce the order of the controller to avoid problems that are not easily applied in practical engineering due to the high order of the controller.Finally,the time-domain simulations are performed to verify the correctness of the control-sensitive point selection and the effectiveness of the controller in a hybrid dual-infeed HVDC system on PSCAD/EMTDC.