This study addresses the mitigation of wind turbine loads and fatigue such as blade bending moments, tilt and yaw moments etc. Currently, the wind turbine blades are normally controlled to turn collectively to limit the excess of wind power above rated wind speed conditions without any load attenuation. The individual pitch control (IPC) is a promising way to reduce the wind turbine loads. This study presents a proportional resonant (PR) IPC, which does not need the measurement of blade azimuth angle and multiple complex Coleman transformations between rotational coordinate frame and stationary coordinate frame. The new strategy can attenuate the 1p and higher harmonics on the wind turbine blades as well as 3p on the hub without any filters. The wind turbine code fatigue, aerodynamics, structures and turbulence is applied to a doubly fed induction generator-based wind power generation system. The simulations are performed on the National Renewable Energy Laboratory 1.5 MW upwind reference wind turbine model. The simulation results are presented and discussed to demonstrate the capability and effectiveness of the proposed PR IPC method.

The vanadium redox flow battery (VRB) is a large stationary energy storage system; which presents high-speed response and overload capacity characteristics. The VRB produces a dc voltage between two terminals; so a power conditioning system composed principally by a dc/ac flexible ac transmission system (FACTS), is required in order to connect the battery to the power system. In this regard, this study proposes a new FACTS compensator for controlling the VRB based on a 12-pulse thyristor converter with commutated capacitors on the ac side. This type of compensator offers a good transient response with low-power converter losses. Simulations of the FACTS compensator employing Matlab/Simulink software validate the proposal and show the good performance of the proposed device.

High wind energy penetration levels in modern power systems draw attention towards wind farms expected role during frequency drops. Wind farms positive contribution required by system operators basically depends on the amount of kinetic energy stored in wind turbines rotating parts and how to manage it during frequency deviations elimination. This study presents an algorithm to estimate and control the quantity of extractable kinetic energy stored in a wind farm during frequency drops. Moreover, it manages stored kinetic energy release within a given time span to achieve positive participation in frequency drops clearance. The proposed method is based on tuning the tip speed ratio before and during the frequency drop according to several factors. The recovery time required by the wind turbine to retain its normal speed is also a function of several parameters including turbine inertia and the incoming wind speed. The proposed algorithm's impact on power system frequency is analysed by assessing the expected enhancement in frequency deviation. A hypothetical grid is considered as the benchmark including detailed modelling for wind speeds, wind turbine and wind farm to improve the creditability of the obtained results. Presented research work outcomes highlight the impact of wind farms replacement for conventional generators. Executed simulations proved that applying the proposed algorithm neutralises wind energy penetration influence on system frequency response, even more, it causes solid improvements unless the incident wind speed is too slow or the frequency drop is too high. Simulation environments are MATLAB and Simulink.

Wind generators provide efficient harvesting of wind energy at the cost of worsening the inertial response during load-frequency events. The inertial response may be improved, however, by emulating the response of synchronous generators by means of additional control loops that sense frequency deviations. Energy reserve is needed in such a case if overloading, stalling or power request for speed recovery are to be avoided. In this study, the authors formulate an optimal problem to achieve the aim of conciliating the opposite objectives of minimum loss of power production and required minimum inertial reserve. The solution to the problem gives the pitch angles and the associated, modified speed against power tracking characteristics needed to support high kinetic energy storage with minimum loss of power production. The analyses confirm that a proper reserve can be maintained, mainly at low wind speeds, with a reduced amount of de-loading.

Occupants of dwellings with photovoltaic (PV) systems can often benefit financially by time-shifting their use of electricity in relation to the times when the PV is generating. This financial benefit is owing to differences between the import and export prices, which in some cases can be a factor of four or more. Quantifying the exact financial benefit in terms of the dwelling's effective electricity prices is, however, not trivial; it depends on the physical meter arrangement, the dwelling's electricity tariffs (including any feed-in-tariff), the instantaneous levels of PV generation and household demand. This study reviews typical metering and tariff configurations for the UK, and Germany, and systematically considers how the effective price may be calculated. This study reviews and expands upon general advice for occupants aiming to reduce electricity bills: demand should be kept below generation; external irradiance is a useful proxy for determining effective electricity prices. Furthermore, designers of feed-in tariffs should consider that focusing on generation payments encourages consumption typically around mid-day, which may be counterproductive from a grid-balancing and environmental perspective. Conversely, a focus on export payments discourages mid-day consumption but may increase the risk of over-voltages in local networks.

Owing to the natural variability of tidal flow, the curve of available power against time at the site of a tidal stream plant is typically spiky. This means that, for the power peaks to be fully exploited, the installed capacity of the plant would have to be large relative to its mean power output. In practice, a balance should be struck between the percentage of the total resource that is exploited and the installed power (and installation cost) of the plant. The purpose of this study is to examine this problematic through a case study: a tidal stream plant proposed for Ria de Ortigueira, a large estuary in north-west Spain with a tidal range of 4.5 m. A numerical model of the estuary hydrodynamics is implemented, calibrated and successfully validated using field data. The model is used to determine the tidal flow patterns. The question of the installed capacity is examined for the two areas with the greatest potential as tidal stream sites. It is shown that the nominal power that is required can be greatly reduced by relinquishing the peaks of the power curve, with only a slight reduction in the energy output.

This study shows a methodology for state-space representation of large wind power plants, through models that include the dynamics of the internal grid. The methodology presented fundamentally separates plant and controls at the stage of formation of the model. It is shown then that most of the plant can be built up from elementary RL branches – with special clarification about the reduction of the induction machine to an RL network – that are put together by means of a incidence matrix. The problems and solutions of reference frame dynamics – complex because of the existence of two control frames for the doubly-fed induction generator and different frames in the grid, one for each generator – are also discussed. The control is separately formulated into a gain matrix, and control and plant are put together by simple matrix algebra. As a result, detailed, large systems can be easily formed. The study shows an example in which ten generators are considered and shows that there may appear particular dynamic features when multi-machine systems (rather than single, aggregated machine systems) are represented.

Recent wind energy harvesting technology development has focused on using dc collection and a possible smaller passive grid because of high energy efficient components in the converter system. This study evaluates and compares the hard-switched full bridge converter and the series–parallel LCC resonant converter, both with transformer coupling, and suitable for wind energy conversion system (WECS). Experimental results substantiate their merits and drawbacks in variable wind speed conditions. The unique, previously unexploited feature of the LCC resonant converter is increased gain at low output power, low speed and low input voltage. A hardware wind turbine simulator emulating an actual wind turbine is used, with its design and control briefly highlighted. This study demonstrates the feasibility of utilising an LCC resonant converter for WECS through simulation and experimental results, both at the same power level.

This study presents a grid-tied photovoltaic (PV) system based on the series Z-source inverter. The grid-tied current control strategy, the dc-link voltage control, as well as the maximum power point tracking scheme is realised in the single-stage system. The current control strategy is performed based on dq rotating frame. Indirect dc-link control is adopted to achieve constant peak dc-link voltage and thus can simplify the controller design in inversion stage. The overall control strategy is given and analysed in detail. Simulation and experimental results demonstrate that the proposed system can be applied in PV system with a wide input voltage range, which verify the correctness and validity of the analysis.

With the ever increasing concern on environmental pollution and energy crisis, generation of power from wind is developing very fast. In the proposed wind energy conversion system (WECS), a variable-speed wind turbine, axial-type permanent magnet generator (PMG), Z-source inverter (ZSI) and sensorless maximum power point tracking (MPPT) controller are included. Although the conventional-type induction generator has the advantage of robust construction and maintenance-free operation, it has drawbacks like low-power factor and need for an ac excitation source which is overcome by the PMG. To obtain fixed voltage and frequency, PMG-generated voltage is fed to power converters. Conventionally the three stages of power conversion consist of rectifier, boost chopper and pulse-width-modulated inverter which reduce the efficiency, power quality and reliability of the overall WECS. To overcome these barriers of conventional system a two-stage-based direct-drive WECS is proposed. The maximum power point for each speed is traced using sensorless MPPT controller, which estimates the rotor speed, by using a simple sensorless speed estimator which is given as the input to the MPPT controller. The proposed sensorless MPPT controller for direct-drive WECS along with the ZSI is simulated in MATLAB/SIMULINK and the results are compared with experimental setup.

In this study, a new non-linear dynamic controller is proposed for regulating the output voltage of a DC/DC boost power converter in a stand-alone photovoltaic (PV) system. The controller provides directly the duty-ratio input of the converter, bounded in the permitted range, and as it is proven it achieves the desired voltage regulation independently from the PV source voltage, the converter parameters and the kind of the load. An appropriate mathematical analysis is used to indicate that the proposed control scheme guarantees closed-loop system stability with the state trajectories converging to the desired equilibrium. Particularly, using as generic concept the fundamental property of passivity of the original system, the proposed controller scheme results in a closed-loop system wherein (i) the passivity and damping properties are maintained and (ii) the conditions which exploit these properties in a manner that guarantees stability are met. Extended simulation and experimental results verify effectiveness of the controller for the case of a DC/DC boost converter with resistance-inductance load. The system performance, operating with the proposed non-linear (voltage) controller is compared with that obtained by implementing conventional cascaded (voltage–current) controllers under input voltage step disturbances or load variations. Finally, some experimental resuts for the case of a non-linear load consisted of a three-phase voltage source inverter and a three-phase resistance–inductance load are illustrated.