Elisabetta Tedeschi

High-Bandwidth Multisampled Digitally Controlled DC–DC Converters Using Ripple Compensation

This paper investigates multi sampled digitally controlled switched-mode power supplies with switching ripple compensation. In digital controllers for power converters, the main bandwidth limitations come from A/D conversion time, computational delays, and small-signal delay of the digital pulsewidth modulator (DPWM). In hard-wired digital-controller technologies, such as in dedicated digital IC and/or in field-programmable gate arrays (FPGAs), the calculation delays can be made negligible with respect to the switching period; thus, when fast ADCs are used, the overall phase lag is dominated by the DPWM. The multi sampling approach can strongly reduce the DPWM delay, thus breaking the bandwidth limitations of conventional single-sampled solutions. In this paper, the additional aliasing effects, which would require a filtering action, are avoided, exploiting the periodic nature of the switching ripple under steady-state conditions using a repetitive-based filtering action. Simulation and experimental results on a 1.2-V-10-A 500-kHz synchronous buck converter, where the digital control has been implemented in the FPGA, confirm the properties of the proposed solution.

Effect of Control Strategies and Power Take-Off Efficiency on the Power Capture From Sea Waves

The choice of the most suitable control strategy for wave energy converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control, are well known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs implies a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper, the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient tradeoff between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Tunable Control Strategy for Wave Energy Converters With Limited Power Takeoff Rating

In wave energy converters (WECs), the maximum power extraction would be achievable at the expense of a very high rating of the electric and power electronics equipment. The goal of this paper is to show how a convenient tradeoff between high-power extraction and viable electrical device rating can be achieved by a proper choice of the WEC control strategy. Referring to a direct coupled point absorber in heave operating in regular waves, it will be analytically shown how most common control techniques impact on both the power performance and the power takeoff (PTO) rating. Thus, a tool that can assist in the preliminary PTO sizing by taking into account the main constraints imposed by the application is obtained. Following, an adaptive control strategy including a reactive component is proposed, whose goal is to improve the overall system performance when the WEC is already operative in the sea. Its effectiveness in increasing the average power extraction while respecting the PTO peak power constraint is proved by computer simulations in both regular and irregular waves, and specific analyses also including the PTO force/torque limitation are finally developed.

Analysis of power extraction from irregular waves by all-electric power take off

The choice of the most suitable control strategy for Wave Energy Converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control are well-known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs requires a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient trade-off between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Modeling and Control of a Wave Energy Farm Including Energy Storage for Power Quality Enhancement: the Bimep Case Study

This paper presents a complete wave-to-wire approach to the modeling of wave energy farms. It captures all the main peculiarities of such applications, from the variability of sea waves to the issues related to the grid integration of a multi-MW wave farm, including the hydrodynamic modeling of wave energy converters (WECs). The paper specifically discusses the different levels of control of a wave farm and their integration and coordination. These are crucial to meet the power quality requirements at the point of common coupling (PCC) and ensure the efficiency of the power transfer from the waves to the main electric grid. A specific real-time technique for the centralized control of a wave farm is also proposed, which is exemplified with reference to the PCC voltage control in the real test case of bimep. Critical cases of weaker grids are also considered to extend the validity of the analysis.

Effect of energy storage on a combined wind and wave energy farm

The combined installation of wind and wave energy converters is being proposed more and more often as a solution to exploit the potential complementarity between these two natural resources and to share the costs of their offshore infrastructures. This paper uses real meteorological data to evaluate the difference in the power performance of a single wind turbine and a combined wind/wave energy farm. The proposed case study considers a wind turbine coupled to wave arrays including a different number of point absorbers and the importance of an optimized tuning of the Wave Energy Converters to maximize the output power is shown. As a further step it is assumed that the farm is equipped with an energy storage device. The impact of its power and energy rating and of its efficiency on the achievable smoothing of the output power is analyzed.

Effect of the generator sizing on a wave energy converter considering different control strategies

Purpose – The purpose of this paper is to investigate the impact of control strategy selection on the power performance of wave energy converters for different ratings of the Power Take‐Off (PTO) system.Design/methodology/approach – The case of a point absorber equipped with an all‐electric PTO is considered. The effect of control techniques and electrical generator design is analyzed from a theoretical standpoint and then verified through integrated hydrodynamic‐electric simulations.Findings – It has been proved that control parameters that maximize the power extraction from the waves can be derived based on the power and torque constraints imposed by the electrical machine.Originality/value – An optimized and integrated approach to the control strategy selection and generator design for point absorbers has been presented, which maximizes the electric power generation from sea waves under real conditions and represents a good trade‐off for the PTO from both the technical and the economic standpoint.

Reactive and harmonic compensation using the conservative power theory

This paper explores the use of the conservative power theory for active shunt compensation, and provides experimental validation of reactive compensation and harmonic filtering. It is aimed to provide a more in-depth review of how the conservative power theory operates as a control algorithm for a shunt compensator. Also there is discussion on some of the challenges associated to practical implementation of active filters.

Energy storage sizing by stochastic optimization for a combined wind-wave-diesel supplied system

In this paper a stochastic procedure is applied to the problem of sizing storage system for an isolated power system with significant wind and wave energy penetration. The case study has analyzed real data from three Canary Islands (La Gomera, Lanzarote and Fuerteventura) in order to find the optimum energy storage size (ESS) in terms of economic profitability. The results show that the storage deployment is significantly suitable whenever the power penetration of wind-wave resources is at least 50% of the local maximum power demand. The results show that the reduction in the cost of energy is larger when the renewable power penetration is 100% than when it is 50%. At the same time the study shows that an uneven combination of wind and wave resources makes the use of an ESS more profitable compared to equally source share plants.

A study of biomass in a hybrid stand-alone Micro-Grid for the rural village of Wawashang, Nicaragua

Stand-alone MicroGrids based on renewable energy sources have emerged as a suitable way of ensuring reliable energy supply in rural areas without access to electricity grids. Planning of such stand-alone grids should ensure systems that provide electricity with high security, reliability and an acceptable impact on the environment, all at a minimum cost. Transition away from traditional use of biomass for cooking and heating in developing countries, to more efficient, modern uses with less negative impacts on the local environment, is also an important measure on the way towards sustainable use of energy. This paper presents technical and economical investigations of the potential for using biomass for electricity generation in a micro-grid for the village of Wawashang, Nicaragua. The simulation tool HOMER is used to evaluate a reference case based on only photovoltaic (PV) power generation with battery energy storage compared to a case including a biomass steam turbine based on local biomass resources. The results show how the use of biomass in combination with PV reduces the impacts of seasonal variations and results in a more reliable and cost-effective system.