Research On Power Flow Control Technology Of Static Synchronous Series Compensator

Nowadays,the scale of power system increases gradually and the structure is becoming more and more complex.As a result,such problems as the asymmetric flow distribution,voltage asymmetry,voltage drop and harmonics are seriously degrading the power quality.In order to improve the line transport capacity and guarantee the system stability,Dr.Narain.G.hingorani coming from USA proved concept of Flexible AC Transmission System(FACTS)for the AC transmission network.Static Synchronous Series Compensator(SSSC)is to provide fast,continuous and precise control and enhance transmission line power flow and voltage controllability.In order to ensure the application of SSSC for the multi-scale model,main parameters,start-up strategy,the steady control method and the auxiliary control development need to be studied.This paper has done a more in-depth study on the above aspects.1)This paper analyzes the basic operation principle of SSSC,the comparison of the main topology and the mathematical models.Based on the full bridge of H-SSSC,this paper proposes a design principle for main circuit parameters,including filter,DC voltage,capacitance and inverter.Firstly,this paper considers the series features of SSSC to design the output voltage and the number of sub-modules;Secondly,this paper combine with power fluctuations and harmonic component of voltage to determine the capacitor voltage value;Finally,according to the harmonic principle and filtering purpose this paper designs the suitable filter circuit for SSSC.2)This paper analyzes the SSSC series compensation function,and builds the SSSC multi-scale analysis and calculation model in the current mainstream software.Analyse the operation constraints of SSSC in the system,and propose the self-starting control method for H-SSSC.Analyze the cascade H bridge multilevel structure in SSSC and get the mathematical models.Give the single phase locked loop and a novel two DC voltage strategy.The first level controls angle is obtained by the DC side capacitor,then get the voltage regulator by controlling the magnitude of the deviation for each sub-module capacitor voltage."Three-step" strategy combines the single-phase locking strategies and the DC voltage equalization.After blocking independent empowerment,zero-voltage state and real empowerment loss in full control,and ultimately reach the reference value into operation.Build the equivalent model of Tianjin with H-SSSC starting model in PSCAD/EMTDC,which verifies the correctness of the self-starting strategy.3)This paper proposes a damping controller based on improved model.It analyzes the mathematical mechanism of the SSR of the power grid with SSSC.Based on the single machine infinite bus system this paper proposes an improved model considering the transient characteristics of SSSC.By using the dispatch signal and measurement signal as the input signals of SSSC,the system of SSR can effectively be suppressed.Reasonable design parameters can effectively inhibit the SSR.Get the optimal damping control parameters of SSR directly from the algorithm level.PSCAD/EMTDC simulation results show that the damping value of the optimal damping control parameter is positive.And the experimental results show that this method is effective for the suppression of the SSR.