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This study presents a three-phase tri-state buck-boost integrated inverter suitable for stand-alone and/or grid-connected photovoltaic (PV) energy applications. The usage of the special features of the tri-state operation coupled with a modified space vector modulation allows the inverter to present a remarkable degree of freedom for the controllers' design, that is, input and output can be independently controlled. As the input can be autonomously controlled, this converter is very attractive for interfacing renewable energy sources as PV panels, once the main duty cycle D 1 controls the maximum power point tracking and the second duty cycle D 2 is responsible to feed the output. It should be pointed out that there are no power electrolytic capacitors in this integrated inverter, which results in a major advantage for the structure working life and it is the first time in the literature that this inverter is used to feed power into the grid. Throughout this study the system is described, the modulation and control schemes are presented and interesting experimental results are available in order to confirm the outstanding features of this proposal.

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a b s t r a c tThis paper proposes a methodology for the active and reactive power flow control, applied to a grid-tie three-phase power inverter, considering local and/or regionalized power flow control necessity in the forthcoming distributed generation scenario. The controllers are designed by means of robust pole placement technique, which is determined using the Linear Matrix Inequalities with D-stability criteria. The linearized models used in the control design are obtained by means of feedback linearization, aiming to reduce system nonlinearities, improve the controller's performance and mitigate potential disturbances. Through multi-loop control, the power loop uses active and reactive power transfer adapted expressions to obtain the magnitude of the voltage and power transfer angle to control the power flow between the distributed generation and the utility grid. The methodology main idea is to obtain the best controllers with the lowest gains as possible placing the poles in the left-half s-plane region, resulting in fast responses with reduced oscillations. In order to demonstrate the feasibility of the proposal a 3 kVA three-phase prototype was implemented and a comparison with conventional controller is performed to demonstrate the proposed methodology performance. In addition, anti-islanding detection and protection against over/under voltage and frequency deviations are demonstrated through experimental results.

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