Research On Decoupling Control Technology Of Ring Network Based On Back-to-back Converter

The current world,the energy crisis continues to increase,environmental pollution is deteriorating,which makes solar energy,wind energy and other green renewable energy is being more widely developed and used.In view of the increasing use of power electronics in the application of new energy sources,this paper analyzes and studies the control strategies of the back-to-back converter in the three-phase grid balance and failure based on the two-level back-to-back converter,And in the preliminary test platform for a simple verification.Firstly,the application of back-to-back converter in wind power generation,flexible DC transmission,microgrid and energy storage system is introduced.The research status of back-to-back converter at home and abroad and the current application of VSC converter are introduced.Topology;in the text,the author also lists the current application of a wide range of several back-to-back converter system wiring.Secondly,the transient mathematical model of the back-to-back converter in the three-phase grid voltage balance is established.Based on this,the transient mathematical model of the three-phase grid unbalanced under the double synchronous rotating coordinate system is established.The analysis shows that the negative sequence component caused by the voltage imbalance of the three-phase grid causes the AC side active power and reactive power of the back-to-back converter to contain the second harmonic component.Again,phase-locked loop technology is an important part of the back-to-back converter system control strategy,especially when the phase-locked loop control technology is particularly important when the three-phase grid voltage is unbalanced.Based on the single phase synchronization system,the software phase-locked loop based on the bi-second-order generalized integrator and the decoupling software phase-locked loop based on the double synchronous coordinate system are designed.The analysis shows that the two phase-Can eliminate the power grid imbalance caused by the negative sequence components on the PLL performance to achieve the purpose of phase lock,and can quickly detect positive and negative sequence components in real time.Finally,based on the back-to-back converter mathematical model,the direct current control strategy of the back-to-back converter under ideal conditions and the negative sequence voltage feedforward compensation control strategy are studied by using the three-phase phase-locked loop technology.In the design of a simple experimental platform for a preliminary verification.