35kV Large Capacity STATCOM And Its Grid-connected Magnetic Bias Correction

With the further development of China's power network,reactive power is studied more and more deeply in power system.As the advanced reactive power compensation,the Static Synchronous Compensator(Static Synchronous Compensator,STATCOM)is of great significant in ensuring supply reliability and improving power quality.Compared with other instructures,the cascade STATCOM with high efficiency,low cost,a few more output levels,etc.,is more suitable for high-voltage power transmission environment,so cascade STATCOM has broad application prospects.This paper introduces the necessity of reactive power control in power system and development status of STATCOM.We discuss the topology and mathematical models of Cascade STATCOM(Cascade STATCOM).Taking 35 kV Cascade STATCOM into account,we analyses carrier phase shift PWM modulation strategy,as well as the balance control method of the DC side capacitor voltage.With the MATLAB/ Simulink simulation platform,It shows that 35 kV Cascade STATCOM with carrier phase shift PWM modulation can effectively reduce the switching frequency and harmonic content.Furthermore,the results also verify that STATCOM based on cascade structure can effectively regulate the system reactive power,and the system obtains good dynamic and steady state characteristics,so it is Suitable for high-voltage power transmission environment.In addition,the paper makes a detailed description in the biasing magnetic phenomena from upstream transformer of 35 kV Cascade STATCOM hanging on the grid.The causes of the inverter bias magnetic behavior,the inverter bias magnetic detector and magnetic bias correction method is also discussed.For 35 kV Cascade STATCOM connected to the grid,the biasing magnetic is detected by advanced instantaneous feedback control,and the establishment of a closed-loop control system will correct the bias magnet.The simulation models are implemented by MATLAB/Simulink,The results have proven that the correction is able to achieve the bias magnetic suppression of 35 kV Cascade STATCOM.