Research On Dedicated Uninterruptible Power Supply Based On Digital Control Technology

As the rapid development of power electronics and the advancement of switching devices, uninterruptible power supply have been widely used in the fields of industry,energy, transportation, shipping, etc. This uninterruptible power supply studied by my topic is applied to power supply system of a ship. when the utility power is lost and oil pump system is fault, it is used to offer lubricating oil for the unit of rotated bearing to avoid overheating and damage of the rotor turbine, thus the uninterruptible power supply is very important for maintaining the normal operation of the ship electric power.In this paper, the inverter is mainly composed of two parts: BOOST converter and three phase inverter. The input of BOOST converter is comprised of mains supply and battery power supply, besides they have different voltage ranges. Therefore BOOST converters require to maintain a stable output voltage over a wide input range, which is very vital to provide a stable DC bus voltage level for three-phase inverter. The latter stage converts the stable DC bus voltage to 380V/50 Hz sinusoidal voltage. The main work of this thesis focuses on the design of digital control systems of BOOST converter and three-phase inverter and stable operation of two-stage cascade converter.First of all, according to the work condition of the uninterruptible power supply, the paper set up small signal model of the BOOST converter in CCM. When it is in the CCM mode, its transfer function has a RHP zero, which causes the instability problems of system.Moreover, taking the switch of input voltage that leading to the stability problem of the latter stage converters into consideration, This article adopts the method of feedforward control in order to improve system dynamic performance when the input voltage switches.Secondly, the mathematical model of three-phase inverter based on the d-q coordinate system is deduced and the outer voltage loop and inner current loop PI controller is designed; Similarly, quasi-PR controller is designed in ?-? coordinate system. Through simulations and experiments prove that these two methods can achieve good steady-state performance and the ability to inhibit the load disturbance for three-phase inverter.Finally, cascade stability of BOOST converter and three-phase inverter is analyzed,then the paper expounds the cascade system stability analysis of the impedance of the specification and analyzes cascade system stability in the open-loop and closed-loop control,using multiple ways to improve the stability of the cascade system from the aspects of software and hardware. At last, simulations and experiments were used to verifyclosed-loop control system designed in second and third chapters of the text which could enable stable operation of the cascade system. The inverter starter can output a stable AC voltage whether the switch of input voltage or a sudden increase and sharp reduction of impedance load.