Research On Optical Fiber Signal Multiplexing Technology Of MMC Sub Module

Because modular multilevel has many advantages,such as high expansibility,high output voltage level and small output current ripple,In these applications,the modular multilevel converter needs to transmit multiple signals.If all signals are transmitted with independent optical fibers,this will cause a significant increase in system complexity and cost.In this regard,this paper takes the sub-module of the modular multilevel converter as the research object,and proposes a structure based on optical fiber time-division multiplexing technology to improve the utilization rate of the sub-module optical fiber,greatly reduce the number of optical fibers in the system,and then simplify The structure of the system and reduce the cost of the system,the main contents of the article are as follows:Firstly,combined with the typical topology of the modular multilevel converter,the system analyzes the working principle of the modular multilevel converter submodule,which mainly introduces the working principle of the half-bridge submodule,based on the working principle of the submodule The mathematical model and basic working principle of the modular multilevel converter are also analyzed.Secondly,the detailed analysis of the control principles of the sub-modules in each state and the signals that need to be sent and received.The analysis shows that the modular multilevel converter sub-module can only exist in one working state at a time.In each state,the signal transmission between the sub-module and the controller needs to be performed through the optical fiber,and the optical fiber utilization rate and the number of optical fibers can be optimized by planning the signal transmitted by the optical fiber.The driving signal is divided into three frequency bands,and only two optical fibers can be used to realize all signal transmission.Among them,the upstream optical fiber transfers the capacitor voltage signal and the fault signal converted into frequency signals.The downstream optical fiber transmits the switch tube drive signal,the thyristor drive signal and the pre-equal voltage drive signal.The single-chip computer determines the frequency of the signal to determine the switch tube drive signal is used to drive the switch tube on the main circuit of the modular multi-level converter sub-module.Either it is sent to the thyristor for bypassing the faulty sub-module,or it is presupplied as a voltage-equalized drive signal to the switch tube connected in parallel on the output side of the energy source for regulating the capacitor voltage balance of the modular multi-level converter sub-module.Finally,this paper builds an experimental platform of modular multilevel converter submodules to verify the hardware and software design of the submodules.The experimental results show that the sub-module control scheme based on optical fiber time-division multiplexing proposed in this paper can achieve all signal transmission with two optical fibers.This control scheme effectively improves the modular multi-level converter sub-module fiber Utilization rate,which simplifies the structure of the system and reduces the cost of the system.