| In this thesis, a single-phase voltage-source uninterruptible power supply (UPS) for 60Hz and 400 Hz applications is discussed. Two control strategies, namely a two-loop controller and a three-loop controller are developed. The control systems developed in this thesis have the following features: (1) stable operation at 60Hz and 400Hz, (2) no need of an external current signal, (3) high output quality, and (4) fast dynamic response. To meet these specifications, dynamic models which take into consideration the feedback variables and switching function are developed. Two suitable PI controllers for the current and voltage loops are selected according to frequency response analysis. Meanwhile, second-order feedback filters are designed to guarantee a perfect output waveform. As a result, the two-loop controller employs the output filter capacitor current and the load voltage as feedback variables while the three-loop controller uses the inverter output current as the third feedback variables.;SIMULINK models of the proposed controllers are implemented, and the steady-state and dynamic response, THD of the output voltage and voltage utilization are presented at the two standard frequencies of 60Hz and 400Hz. It is shown from the simulation results that the performance of the controllers meets the requirements. Moreover, computer simulation results of the output voltage waveform, the total harmonic distortion, voltage utilization and dynamic response show that the three-loop controller has a better performance. |
