Research On Multi-module ISOP Combined Converter And Its Control Strategy

With the rapid development of science and technology in China,power electronics technology is now widely used in all walks of life,and penetrate into the frontier of science and technology,such as the electric power industry,industrial production industry,etc.At present,China’s power system is gradually transforming into a new energy power system,with the rising electricity consumption in China,some developed areas have a significant gap in electricity consumption,in order to make up for the electricity gap,often need to transfer electricity from other less developed areas,at present,China’s power transmission method is mainly ultra-high voltage AC transmission,AC transmission has a large power limit.Due to the limitation of AC grid transmission capacity,the problem of different frequency of AC grid interconnection in different regions,and improving the grid connection rate of distributed power sources,DC transmission came into being.At this stage,the number of DC transmission lines is increasing,and the high-voltage power electronics equipment,which is the main component of DC transmission,has made a huge breakthrough in recent years.DC transmission voltage is increasing,in order to meet the power system for voltage stability,voltage stress,power limitations and other requirements,multi-module converter input series output parallel(ISOP)in recent years has become a hot issue in the current power professional research.This paper will focus on the problem of equalizing pressure and flow in ISOP systems under modern control techniques and further optimize the control for multi-module ISOP systems based on modern control algorithms.First,the operating characteristics of the single module converter are studied in depth,and there are various connection methods for multi-module converters.In this paper,Dual active bridge DC-DC converter is used as the basic component unit.The implementation method of soft-switching technology is studied for the bidirectional active full-bridge converter(hereinafter referred to as DAB),and the relevant technical parameters are given,and the small-signal model of DAB converter is established by using the state-space averaging method.And the transfer function of DAB with output voltage and input voltage is derived by mathematical derivation.Second,after establishing the small-signal model,extended phase-shift control is used for the single-module DAB converter,and a three-loop control strategy is used for the multimodule ISOP combination converter.The power equalization is achieved through series input-side voltage equalization and parallel output-side current equalization,and the input voltage loop and output voltage loop of the three-loop control strategy are decoupled to reduce the computational effort in the design process of the closed-loop parameters.Finally,for the traditional three-loop control strategy there are problems of large data computation and slow convergence.Optimization of PI parameters using gradient descent algorithm to speed up the rectification of PI parameters.The optimized PI parameters were brought into the simulation model and numerical simulation experiments were conducted and compared with the unoptimized PI parameters to prove the effectiveness of PI parameter optimization.Based on the above work,a model prototype of a 24 W dual-module DAB combination converter is built.A large amount of implementation data was obtained,and the experimental data showed the effectiveness of the control algorithm established in the paper and the rationality of the software and hardware design scheme.