A distributed control system is proposed which uses the Conservative Power Theory (CPT) and a consensus algorithm to share imbalance and harmonics between different converters in three-phase four-wire droop-controlled Microgrids (MGs). The CPT is used to identify the balanced, unbalanced and distorted components of the currents and powers in the system. Control loops based on virtual impedance and implemented in the stationary a-b-c frame are then used to distribute these components between the various converters in the MG. The magnitudes of the virtual impedances are adaptively calculated using a novel consensus-based distributed control scheme with the aim of sharing imbalances and harmonics according to the residual VA capacity of each converter whilst regulating the imbalance and distortion at their output to meet the appropriate IEEE power quality standards. Extensive simulations show that the proposed distributed control has excellent performance, and experimental validation is provided using a laboratory-scale 4wire MG.

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. I. INTRODUCTIONHE more-electric aircraft (MEA) concept is one of the major trends in modern aerospace engineering aiming for reduction of the overall aircraft weight, operation cost and environmental impact. Electrical systems are employed to replace existing hydraulic, pneumatic and mechanical actuators. As a consequence, the onboard installed electrical power increases significantly and this results in challenges in the design of the aircraft electrical power systems (EPS). The tendency is to replace traditional AC distribution with highvoltage DC distribution. This can increase efficiency, reduce weight and remove the need for reactive power compensation devices [1], [2].In literature, the primary power distribution in aircrafts has been traditionally based on the single-generator-per-bus paradigm with switched distribution providing the connectivity and system integrity. Instead, the proposed "single-bus" concept uses the micro-grid approach in which all the generators and loads are connected to a single distribution bus. This single bus configuration has been widely used in other applications such as residential microgrids [3]. Such a system has the potential to considerably reduce the EPS weight since bus mass is reduced and load and generator fault isolation function can be integrated in power converters; in addition the controlled power sharing between generators has the potential to reduce generator capacity and operate at maximum efficiency levels.As the parallel operation of multiple generators is a promising solution for the MEA EPS, appropriate power sharing among the different power sources needs to be carefully considered. From the communication point of view, overall control of DC systems can be divided into three categories: distributed control, centralized control and decentralized control [4].

In this paper, an isolated high step-up ratio dc–dc converter aimed to be used in interface systems between low-voltage renewable energy sources, such as photovoltaic panels and fuel cells and the utility grid, is presented. The converter is based on the active clamp flyback topology with a voltage multiplier at the transformer secondary side. Such configuration, while naturally clamping the rectifier diode voltages thus avoiding the use of dissipative snubber circuits, allows the reduction of the circulating current during the active clamp operation due to the resonance involving the transformer leakage inductances and the diode parasitic capacitances. Experimental results taken from a 300-W-rated prototype are reported, showing the absence of parasitic oscillations after diodes and switch transitions and high efficiency, in agreement with the theoretical expectations

Abstract-Stability analysis of power-converter-based AC systems poses serious challenges not only because of the non-linear nature of power converters, but also because linearisation is not generally applied around a steady-state operating point, as in the DC case, but around a time-periodic operating trajectory. Typical examples are single-phase and unbalanced three-phase systems. In this paper, two general methods to assess stability of the aforementioned systems are presented. Both are based on the Linear Time Periodic (LTP) systems theory. The first is model-based and relies on the evaluation of the eigenvalues of the linearised model, assuming a complete knowledge of the parameters. By contrast, the second proposes a set of smallsignal current injections to measure the Harmonic Impedances and applies the LTP Nyquist Criterion, so that stability of the system can be assessed with a black-box approach, without relying on knowledge of the system parameters. The basic LTP systems theory is reviewed in order to provide a mathematical justification for the second method. As case study, a simple network, consisting of a source full-bridge converter in AC voltage-control mode and a load full-bridge converter in AC current-control mode including PLL, is considered. Analytical results based on average modelling and simulations based on both average and switching models are presented, showing good accuracy in the identification of the stability thresholds for both the proposed methods.