Hybrid DCAC converter Control for Inrush Current Protection

S. Mastelone, S. Almer, D. Martini, P. Raboni

filed 2016 // 29 June 2017

DC/AC converter comprising a new control device and method for managing inrush current transients during operation without requiring additional external devices or emergency operating modes forcing the DC/AC converter to shut down. The present invention is particularly, but not exclusively, aimed at grid connected DC/AC, converters, often subject to inrush current phenomena due to perturbations in the grid.

Photovotaic Inverter control method for operating an hybrid PV and genset microgrid without interphering with genset controller

P. Raboni, D. Martini

filed 2015 // 1 July 2017

A hybrid power system (1 ) is disclosed. The system comprises a plurality of dispatchable power resources (7.i; 7.j) and a first controller (12) for controlling the dispatchable power resources. The system further comprises a power resource section (5) responsive to environment conditions and a second controller (17) for controlling the power resource* section (5) responsive to environment conditions. The second controller (17) is configured and arranged for measuring a total power (∑Pgenset) generated by the plurality of dispatchable power resources (7.i; 7,j) and a total power (∑PPV) generated by the power resource section (5) responsive to environment conditions; and for generating a power curtailment signal (PVcurtailment), when required, for reducing the total power (ΣΡPV) generated by the power resource section (5) responsive to environment conditions.

Identification of the best power plant layout for large offshore wind farms connected via VSC-HVDC links

F. Careri, C. Genesi, P. Marannino, M. Montagna, P. Raboni, S. Rossi, et al.

Energy Market (EEM), 2011 8th International Conference on the European, 2011, pp. 281-287. // 27 May 2011

The overall purpose of this paper is to find out the best choice in terms of generator technology for large offshore wind farms connected to the EHV network by means of VSC-HVDC transmission: besides the traditional benefits compared with HVAC and line commutated HVDC, this technology allows variable frequency operation, in order to increase the overall production of the wind farm. Two different types of generators - Squirrel Cage Induction Generator (SCIG) and Doubly-Fed Induction Generator (DFIG) - are compared in variable frequency operation: the related power plant layouts are analyzed, for different wind speed conditions, by means of a slightly modified version of an online optimization algorithm. The resulting programs are coded in MATLAB® environment and some tests are carried out.

Intelligent control for a DC micro-grid system

M. Martino, Y. F. Quinones, P. Raboni, and Z. Chen

Universities Power Engineering Conference (UPEC), 2012 47th International, 2012, pp. 1-5 // 7 September 2012

This paper presents the dynamic response of a DC - micro-grid (DC-MG) controlled in master-slave mode. The benefits of the micro-grids (MGs) are the low cost in terms of power electronics converters and the high reliability and quality, even in case of loss connection to the transmission system. A DC-MG in fact can survive in standalone mode if properly managed. The considered system is made by a photovoltaic array (PV), a wind turbine (WT), a gas engine (GE) and an energy storage system (ESS). The DC-MG behavior is analyzed in different scenarios to demonstrate the efficacy of the control for all the units, especially in case of variable weather conditions with different DC loads. Thus the voltage level of the system and the power flow are shown, out of a detailed description of the power electronic interfaces featuring the distributed generators (DGs).

Reduction method for active distribution networks

P. Raboni and Z. Chen

2013 IEEE Grenoble, 2013, pp. 1-6 // 20 June 2013

On-line security assessment is traditionally performed by Transmission System Operators at the transmission level, ignoring the effective response of distributed generators and small loads. On the other hand the required computation time and amount of real time data for including Distribution Networks also would be too large. In this paper an adaptive aggregation method for subsystems with power electronic interfaced generators and voltage dependant loads is proposed. With this tool may be relatively easier including distribution networks into security assessment. The method is validated by comparing the results obtained in PSCAD® with the detailed network model and with the reduced one. Moreover the control schemes of a wind turbine and a photovoltaic plant included in the detailed network model are described.

Modeling and control of low voltage flexible units for enhanced operation of distribution feeders

P. Raboni, H. Weihao, S. K. Chaudhary, and Z. Chen

IECON 2013 - 39th Annual Conference of the IEEE, 2013, pp. 7469-7474 // 13 November 2013

In some networks Distributed Generators (DGs) are phasing out conventional power plants in terms of power production but still large efforts are required for providing ancillary services. In this paper the usage of fast response units like a Micro Turbines (MT) and a stationary Electric Vehicle Battery (EVB) is proposed for providing primary regulation in grid connected mode and for hierarchically manage an islanded LV distribution feeder. The unit models are described and a novel EVB model directly based on manufacturer's data is proposed and evaluated comparing its performances with SimPowerSystems library block. Moreover a voltage dependant power term is applied to the Voltage-Source Converter (VSC) control scheme of the EVB for improving the performances of the islanded feeder. The control is tested in case of under frequency and consequent load shedding occurring at the residential feeder of CIGRE C6.04.02 benchmark network.

Modelling, Control and Integration of Distributed Generators for Enhanced Ancillary Services

P. Raboni

PhD Thesis, Department of Energy Technology, Aalborg University, Aalborg Universitetsforlag, 2016 // 31 January 2016

The increasing share of Distributed Generators (DGs) poses concerns about network stability and their fair participation to the electricity market. Their aggregation in Virtual Power Plants, sometimes in combination with load prosumers, could represent an answer to these issues. Nevertheless Technical Virtual Power Plant still offer limited ancillary services, as reactive power management and spinning reserve. Focus of this thesis is on the control of DGs for providing further and higher quality ancillary services. In particular LV dispatchable DGs, hereinafter called flexible DGs, as stationary battery units (SBUs), microturbines (MTs) and Diesel Engines (DEs) appear promising solutions. The models of a SBU derived from a commercial Electric Vehicle battery and a MT are proposed. Both units are Voltage Source Converter (VSC) interfaced and, following recent Power Electronics state of the art, they are equipped with an LCL output filter. The thesis starts deepening the design of current control scheme for a stable operation in grid connected mode. Such flexible units offer on the other hand the possibility to survive a LV feeder in the future case of intentional islanding or for black start service. Therefore the design of the voltage regulator is developed proposing the compensation of the voltage drop on to grid side inductance. Moreover considering the hierarchical control a comparison between direct and reverse droop configurations is proposed. The participation to local reactive power market implies the precise control of reactive power through DGs. While reactive power regulator tuning is straightforward in case of current controlled VSCs, it is more challenging in case of synchronous generator interfaced DGs, as DEs and small CHP units, due to the high system order introduced considering the electrical machines, real exciter and network equations. The analytical tuning of the same regulator is here developed starting from small signal analyses of the plant, with an approach fitting to any reactance to resistance ratio of the equivalent Thevenin model regarded for representing the network. Such time consuming tuning procedure is then compared with an automated regulator design based on multiple time domain runs driven by a Simplex Optimisation. In particular some novel objective functions relying on typical step response indexes are proposed and assessed.

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Design of reactive power regulator of synchronous generators by considering grid impedance angle for characteristic index objectives

P. Raboni, S. Chaudhary, and Z. Chen

Design of reactive power regulator of synchronous generators by considering grid impedance angle for characteristic index objectives // 27 October 2016

Effects of low reactance to resistance ratio in distribution networks are widely studied but little work dealing with the tuning of voltage and reactive power regulators of small synchronous generators has been reported. This study endeavours the design of a proportional integral controller for the reactive power regulator to fulfil the characteristic index (CI) objectives, which are based on the step-response characteristics. Two small-signal models of the reactive power regulator have been developed from the well-known k-parameter model and they are validated. Apart from offline tuning of the regulator, these models can be used to assess system robustness and stability. In addition to the analytical approach, the same regulator is tuned optimally by means of multiple simulations. Proposed objective functions rely on the CIs tracked during the sequence of runs, whereas the traditional cost functions are formulated on the basis of the integral of an error. This difference makes them suitable for the cases where the entire step-response data series are unavailable. The performances of differently tuned regulators are compared considering a test system including a 100 kW Diesel Generator Set equipped with a brushless exciter.

Energy transition technology roadmap. Distinguishing hype from reality – 2020 strategic technological plan and business targets

Daniele Rosati, Pietro Raboni, Carlalberto Guglielminotti

White paper // 23 may 2017

Climate change and global warming in particular may be a controversial scientific theory, particularly in the US, but its growing impact on business is undeniable. The energy generation landscape, to begin with, is being disrupted by the growth of renewables; transport is witnessing the affirmation of the electric car, in its pure form or as a hybrid, and, most pervasive of all, the search for energy efficiency is creating new businesses – think for example smart metering or behind-the-meter distributed generation – and is modifying existing ones in a variety of ways. Our vision of the macrotrends shaping the energy transition is consistent with the narrative of Bloomberg New Energy Finance's New Energy Outlook, to which we make extensive reference in this overview.

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