Embedded grids have been increasingly adopted into applications such as More Electric Aircraft where different power converters are interconnected to each other. Interactions between the grid components poses the risk of instability to the system, more so when in the presence of reduced passive filters. An approach of automated and scalable tuning of such embedded grids with consideration for the dynamics introduced by a PLL is presented in this paper. A structured state feedback optimal control approach is proposed which enables a controller to be synthesised is such a way that maximum performance of the grid can be achieved, whilst guaranteeing power converter synchronisation to the grid, and avoiding instability due to converter interaction, and PLL dynamics.

Abstract-This paper presents an automated and scalable approach for the tuning of power converters control systems in embedded power grids. These are composed by different power converter interconnected to each other and are increasingly adopted in a range of applications among which micro-grids and more electric aircrafts. The interaction between the grid components may lead to instability, especially in presence of small passive filters. A structured state feedback optimal control approach is proposed to jointly design all power converters controllers in a coordinated way to maximize the performance of the grid and avoid instability due to converters interaction.

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Over the last few decades, the consolidated goal of reducing greenhouse gasses has increased the relevance of renewable energy research, electromobility, energy storage, and distributed generation, micro-grids, among others. Micro-grids, systems working in islanding mode, are particular cases where some disadvantages are present due to the wide variations which may appear across their electrical quantities. Variations on the voltage amplitude and the frequency are intrinsic in the operation of weak grids, because they have low inertia and therefore the load must be able to cope with these variations, otherwise loads may trip electrical system protection. Particularly, on power electronic drives, these frequency deviations will lead to increased system nonlinearities, entailing a more critical controller design. To overcome these issues, this paper presents an implementation of a resonant controller with self-tuned gains. The strategy imposes a constant sampling time which allows these controllers to be used in variable frequency environments. In addition, the computational capacity required for the digital board is also considered. The simulated and experimental results provided demonstrate the good performance of this proposal. INDEX TERMS Resonant control, variable frequency environment, micro-grids. I. INTRODUCTION A. Research gap Power Generation has gained popularity in recent years due to the need to generate electric power in alternate directions and from varying kinds of sources. [1], [2]. However, power management for these systems results in a difficult task, as some sources may be working at the maximum power point of injection regardless of the actual power consumption, for example, renewable energies. Therefore, power generation and power consumption may differ, resulting in the global system being out of balance [3]. This problem becomes critical when power systems are small micro-grids, which are usually noted as being low inertia systems. In these cases, ineffective power management leads to variations on the voltage amplitude, mainly associated to the reactive power, and frequency variations, due to active power regulation. In addition, weak grid systems will feature these issues when large loads are either connected or disconnected, making the voltage vary in amplitude and frequency, which are typical occurrences in aircraft and ship power systems [4]-[6]. Electric devices connected to these kinds of sources should be robust under these variations, thus helping to hold the system stability and avoid tripping the inbuilt protections.

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