Power conditioning system applied to a variable frequency aircraft AC mains

The increasing use of electricity in aircraft, mainly in large airplanes, has been boosted by the trend of replacing pneumatic and mechanical systems by electromechanics (which is coined as More Electric Aircraft - MEA). In this trend, the generator gearbox, which previously kept its rotation constant, therefore it output frequency fixed at 400Hz, is removed, resulting in a variable-frequency operation of the power grid between 360 and 800Hz with an slew rate up to 500Hz/s. The previous changes make researchers and component suppliers focus on power quality. Thus, electric energy conditioners, already deployed in industrial and residential grids, may be adapted for mitigate the unwanted effects in this new aircraft environment. This thesis proposes the deployment of Cascaded H-Bridge Inverters (CHBs) for mitigation of unbalances, reactive and harmonic current components in an aircraft AC grid, in order to comply with MIL-STD-704F, BS-ISO-1540 and ATCC-DO106F standards. The CHB inverter presents advantages, such as interoperability, %voltage and switching frequency distribution through the modules. higher voltage operation and an overall higher switching frequency due the multiple series connection of H-Bridge modules. However, it consists of separated DC links, being necessary to regulate their voltages and keep them following their references. Thereby, this thesis presents a review of the main strategies of DC voltage regulation and develops a linear model for the control and balancing of DC link voltages using the Multiple-Inputs Multiple-Output Control System (MIMO) theory to obtain a Proportional-Integrative (PI) controller. The proposed model is validated by simulations and experimental results for a two-module single-phase CHB prototype with 100kHz switching frequency in a 230V grid at different frequencies. Simulation results show the feasibility of control topology for symmetrical and asymmetric DC links, as well a possible expansion for a three-phase system and n modules per phase. Experimental results show the CHB operating as an Active Power Filter compensating reactive and non-active currents. The appendice provides the Xilinx FPGA control software written in LabVIEW and the conditioning signal hardware proposed for the application. The CHB inverter uses a 100kHz switching frequency, and it may achieve a 2*n*100 kHz current ripple frequency due to the Phase Shift Pulse-Width Modulation (PSPWM) strategy used. Different methods are developed to evaluate the gain matrices of the PI controller, showing that calculation of the integrative part from the proportional one presents the best performance (AU)