Research On An Online UPS System Based On Isolated Bidirectional DC/DC Converter

Uninterruptible power supply(UPS)is a kind of uninterruptible power supply system with rectifier and inverter as its main components,because it can improve the power quality and provide reliable power for the load,is widely used in recent years.For ships,because of the complex navigation environment,the stability and reliability of the power supply system is very important to the navigation safety of ships,so the emergence of marine UPS to provide guarantee for ship power supply,to meet the power supply needs of important equipment in emergency situations,such as ship navigation,communication,lighting,emergency equipment,etc.At present,UPS usually has a special charging circuit for battery,which makes the system volume and cost increase.For this special object of ship,this paper proposes an on-line UPS based on isolated bidirectional DC/DC,and the traditional charging structure is replaced by bidirectional power transmission of DC/DC,and the main components of the system are studied on the basis of this structure.Now,UPS usually has special battery charging circuit,makes system volume,the cost increase,therefore for this particular of ship in this paper,based on an isolated bidirectional DC/DC on-line UPS,through bi-directional DC/DC power bidirectional transmission to realize the replacement of traditional charging structure,and based on the structure of system main components were studied.This paper first introduces the development and classification of UPS,describes the structure and working principle of different types of UPS,introduces an on-line UPS structure based on isolated bidirectional DC/DC for ship object,and then studies the structure and control of three main links of rectifier,DC/DC and inverter.In the rectifier,firstly,the mathematical model of the rectifier in three coordinate systems is derived,and then the double closed-loop structure of the voltage oriented control method is designed.Because the double closed-loop control has many parameters and the setting is complex,this paper proposes a control scheme which uses the predictive power control to replace the current inner loop.The design of the predictive power control system is completed by the derivation of the discrete-time model of the rectifier and the selection of the cost function;In the DC/DC link,this paper selects a bidirectional full bridge DC/DC converter with isolation function,and briefly describes the structure of the converter,and then introduces the single-phase-shift control and dual-phase-shift control methods of the converter in detail,aiming at the power return problem of phase-shifting control,the dual-phase-shift control can effectively reduce the power return and improve the efficiency of the converter;In the last part of the inverter,a three-level T-type inverter with small conduction loss,high efficiency and small total harmonic distortion of the output voltage is selected.Then,the working mode and converter process of the inverter are analyzed.Then the discrete-time model of the predictive control is obtained by deriving the vector representation of the inverter output voltage.In the cost function,the balance of neutral point potential and the realization of control objectives are achieved.Because there are 27 kinds of switch state combinations in three level t-inverter,there are a lot of on-line calculations in the model predictive control.Therefore,this paper sums up the inverter control as a pattern recognition problem,introduces the neural network control method,and introduces the neural network training principle and the controller realization in detail.Through the design and simulation of the above three links control system,in the rectifier part,not only the output DC voltage can follow the given value,but also guarantees the unit power factor operation of the system,and the total harmonic distortion of the AC side current is less than 3%;In the DC/DC part not only realizes bidirectional power transmission,but also greatly reduces the return power of the converter,which improves the working efficiency;In the inverter part,the dynamic and steady-state performance is improved obviously by adding neural network,and the output voltage quality can be guaranteed for different types of load,and the total harmonic distortion is far less than 3%.