Research On Dual-loop Control And Current Limiting Technique For 400Hz Inverters

It's universally acknowledged that the medium frequency inverter is widely used in the field of aviation, marine areas and locomotives. It is one of the most important part of the AC power. The double-loop control strategy and current-limiting protection technology are investigated in this thesis based on a 10 kVA middle frequency 400Hz/115 V inverter.Firstly, the mathematical model of control targets with isolation transformer in the output terminal is introduced. Then several kinds of double-loop control strategy were compared and the double-loop with current feedback of filter inductance as inner loop and output voltage as outer loop which include feed-forward of load current. Although the controller was designed in the continuous domain, the influence of digital control delay was taken into account. The inter loop used PR(Proportional Resonant) controller for more convenient threshold set of current-limiting and low-order resonant controllers were designed in the outer loop to improve the quality of output voltage except fundamental frequency proportional resonant controller. The simulation and experimental results show that the output characteristic of inverter is good.Secondly, variable parameter PR control strategy was designed to improve the reliability of the inverter. This control strategy decreases the PR parameter to reduce the harmonic content of inductance current order. The THD of output current is small when short circuit fault occurred and this also suppressed the noise of isolation transformer. The simulation and experimental results show that the current-limiting strategy is good.Finally, the strengths and weaknesses of the double-loop control strategy designed in this thesis are summaried and the next step of the work is presented.