Static Synchronous Compensator Based On Cascaded H Bridge Converter And Its Control

With the development of The Times,the depletion of fossil energy and environmental pollution are becoming more serious.The utilization of renewable energy is the fundamental way to solve the energy and environmental problems.Under the general trend of energy structure transformation,the scale of new energy power generation develops in a "distributed and large-scale" way.The integration of new energy power generation systems with increasing installed capacity into the power grid has a certain impact on the power quality of the power grid,which is mainly reflected in the two aspects of reactive power imbalance and harmonics.With the improvement of the performance of high-power power electronic devices and the development of power electronic control technology and FACTS technology,Static Synchronous Compensator(STATCOM),as a large-capacity,efficient and stable reactive power compensation and harmonic control device,is the most effective tool to improve power quality,and it has been widely used in medium voltage distribution network system.The cascade H-bridge topology has the characteristics of high reliability,flexible design,low current harmonics,large capacity and so on.This topology is the mainstream trend applied to STATCOM devices.Therefore,static synchronous compensator based on CHB converter(CHB-STATCOM)is taken as the main research object,and some key problems in its control method and parallel operation technology are studied in this paper.This paper first analyzes the current new energy power generation grid on the power quality,discusses the necessity of reactive power compensation and harmonic control devices,and summary the development status of STATCOM equipment at home and abroad.At the same time,the purpose and key problems of parallel operation of STATCOM system are analyzed,and the development history of parallel operation technology is expounded.The main circuit of the MW CHB-STATCOM system and its parallel system is analyzed,and the mathematical model of the system is established.In this paper,a traditional cascade PI-PWM technology applied to STATCOM is designed.The voltage control outer loop and current control inner loop are designed by PI controller to realize multi-objective control,and the carrier phase-shifted PWM scheme which is more suitable for multi-level converter is adopted.The advantages and disadvantages of the scheme are analyzed by PLECS simulation.Based on the basic control,in order to further optimize the control performance,the model predictive control(MPC),as a research hotspot in the field of power electronic control,is studied,and its advantages in CHB-STATCOM system are analyzed.An efficient MPC based on cascade structure is designed to effectively solve the problems of complex weight coefficient modulation and large amount of calculation.The advantages and reliability of the proposed control scheme are proved by the relevant simulation experiments.Based on the actual demand of large reactive load field,this paper further studies the flexible configuration of multiple STATCOM parallel systems according to the market requirements.The stability of CHB-STATCOM parallel system is greatly reduced due to the problem of zero sequence circulation.Therefore,this paper first analyzes the mechanism of zero-sequence circulation in CHB-STATCOM parallel system,and then designs a practical circulation suppression scheme based on it.The practicability of the circulation suppression scheme in 10MVar parallel STATCOM system is verified by simulation.