This study proposes the control schemes for the cluster of houses for power management in islanded mode. A centralised control scheme has been used in the cluster of the photovoltaic (PV)-integrated houses. Each PV-integrated house consists a battery energy storage system (BESS) connected through a bidirectional three-phase voltage-source converter (VSC). Control strategy for bidirectional three-phase VSC to integrate the BESS to the AC network has also been proposed for controlling the charging/discharging of the BESS. The references used by the controller are detected by the charging or discharging of the battery. The algorithm has been developed to allow flow of power from one house to other house in islanded mode. Simulations are carried out to verify the robustness of the proposed control schemes under different operating conditions.

Partial shading of a photovoltaic (PV) installation has an inconsistent impact on power production. This study investigates the effect of partial shading on PV performance. The experiments were carried out with a 90-W PV module under both variable and constant irradiations with shaded area increased from 0 to 80% to observe the effect of variable solar radiation at certain shading points. The effect of shading under irradiation levels from 300 to 800 W/m² was investigated. At a 600 W/m² irradiation level, the shading impact factor was 1.25 with a 25% shading, while at 75% shading the impact factor decreased to 0.86. Results also show that for every 100 W/m² increase in irradiation level, the electrical power output was enhanced by 3.89, 3.37, 2.27, and 2.02 W at 0, 25, 50, and 75% shading, respectively. The efficiency level was increased by 0.29, 0.27, 0.25, and 0.22% at 0, 25, 50, and 75% shading, respectively. Increasing the shaded area by 10% causes a 12.41 W drop in power output and a 2.3% drop in electrical efficiency. Partial shading not only deteriorates the PV performance, but also causes long-term degradation of the module.

This study considers the design and testing of a laboratory scale test rig for wave energy converters (WECs). The main element of the test rig is a double-sided permanent magnet linear generator (PMLG). In this study, the authors describe the detailed design of the PMLG. The objective of the design is to find the detailed parameters of the PMLG to meet the targeted electromotive force (EMF) voltage with respect to the designed physical constraints. The design procedure is easy to follow and emphasises the practical aspects to construct the PMLG. A spreadsheet table was generated using the procedure to find the design parameters. Therefore, a designer can easily modify the parameters based on the physical constraints and the targeted EMF voltage. In addition to that, the authors explain the procedure to find the rating temperature for the generator. Finally, this PMLG is integrated with other components to form the test rig. The experiment is conducted to show how close the performance of the constructed PMLG is, in term of its EMF voltage and rated thermal, to the designed values. Additional tests were also conducted to test the performance of the test rig using various scenarios similar to ocean wave profiles.

As the load demand in a microgrid increases, more distributed generators (DGs) should be installed to meet the demand, which makes the microgrid expansion planning very important. To obtain the optimal expansion strategy, a tri-level expansion planning framework is presented for an isolated microgrid in this study, which is composed of demand expansion, capacity optimisation and operation optimisation. The uncertainties of load forecasting are considered. Latin hypercube sampling method is utilised to generate the load demand scenarios. Controllable load is also considered in the expansion, which can be switched off and on as required. Considering the complexity of the operation optimisation problem, particle swarm optimisation is used to obtain the planning results. Finally, numerical simulations for an isolated microgrid in Weizhou Island, Guangxi, China are utilised to validate the effectiveness of the proposed model as well as its solving algorithm.

The doubly-fed induction generator (DFIG) system currently occupies close to 50% of the wind energy market. The vector control is the proven and state-of-the-art solution for its back-to-back power converters by using the dual-loop controller design: the inner current and the outer voltage/power. This paper focuses on the modelling of power converters and the parameters design of proportional-integral controller. According to the Bode plots, the relationship among the switching frequency, inner loop bandwidth, and outer loop bandwidth can be found. At least one-tenth difference between them is necessary for the sake of either the switching harmonic mitigation or the fully decouple of the dual loops. The procedure to design bandwidth for the grid-side converter and the rotor-side converter is thoroughly addressed and explained on a real-scale 2 MW and a down-scaled 7.5 kW DFIG systems. On the basis of the relationship between the controller bandwidth and the rise time, the theoretically designed bandwidth is able to be verified in both the simulation and the experiment.

A modular resonant DC/DC converter for DC microgrid system applications is provided in this study. Half-bridge circuit cells are connected in series to reduce the voltage stress on each half-bridge circuit, so that power metal–oxide–semiconductor field-effect transistors with high-frequency operation can be used at high-voltage DC/DC converters and the converter size can be reduced. To balance input split voltages, flying capacitors are used and connected between each half-bridge circuit. Therefore, input split voltages can be balanced automatically in each switching cycle without using the complexity control scheme. Resonant circuit is used in each half-bridge cell to realise the zero-voltage turn-on for power switches and zero current turn-off for rectifier diodes over the wide load range. Therefore, the proposed modular resonant DC/DC converter with high-circuit efficiency can be achieved. The output sides of half-bridge circuit cells are connected in parallel to reduce the current stress of all passive components. Finally, the circuit performance of the proposed converter is evaluated by experiments.

The electric power industry landscape is continually evolving. As emerging technologies such as wind and solar generating systems become more cost effective, traditional power system operating strategies will need to be re-evaluated. The presence of wind and solar generation (commonly referred to as variable generation or VG) can increase variability and uncertainty in the net-load profile. One mechanism to mitigate this issue is to schedule and dispatch additional operating reserves. These operating reserves aim to ensure that there is enough capacity online in the system to account for the increased variability and uncertainty occurring at finer temporal resolutions. A new operating reserve strategy, referred to as flexibility reserve, has been introduced in some regions. A similar implementation is explored in this study, and its implications on power system operations are analysed. Results show that flexibility reserve products can improve economic metrics, particularly in significantly reducing the number of scarcity pricing events, with minimal impacts on reliability metrics and production costs. The production costs increased due to increased VG curtailment – i.e. including the flexible ramping product in the commitment of excess thermal capacity that needed to remain online at the expense of VG output.

Multiple sub-/super-synchronous frequency components were detected when sub-synchronous oscillation (SSO) occured in permanent magent synchronous generator (PMSG)-based wind farm in Northwest China. This caused three 600 MW turbine generators to trip because of torsional oscillation of the shaft. Then for one year, for eliminating the multiple frequency components, the relevant wind farms have been tripped for 111 times. The tripped wind power sometimes could even be up to 300 MW. However, the multiple frequency components' producing mechanism is still not clear. This study explains the mechanism by analysing the response characteristics of grid-side converter (GSC) controller to the sub-synchronous frequency component. When a sub-synchronous frequency component is fed into GSC controller as an input signal, the expression for the output signal is derived. Furthermore, the frequency transformation relationship between input and output signals, the amplitudes of multiple frequency components in output signals are all discussed in detail. The theoretical analysis is then validated by the simulation results and the on-site data measured by the phasor measurement unit (PMU). With the theoretical analysis, the main frequency components which should be suppressed are determined. The multiple frequency components can be mitigated not by tripping wind farms any more. This is conducive to the accommodation of renewable energy.

Power generation from decentralised renewable energy (RE) sources has been increasingly used worldwide. The authors apply portfolio theory (PT) to solar and wind resource forecast, combining those two intermittent RE sources in different percentages to investigate the resultant effects on the prediction error with the use of a proposed impact factor. They use solar and wind data from a weather station in Brazil's Northeast region. The use of PT to improve resource forecast of the specific solar and wind conditions found in that Brazilian region is a pioneer project and an original contribution of their research. Traditionally, PT has been used in the finance sector to reduce investment risks by diversifying applications. Considering predictability, the efficient frontier indicates an optimum portfolio for the period under investigation composed by 30% solar and 70% wind resource, obtained by the smallest calculated standard deviation. The obtained average forecast error for wind speed was −1.54% and for solar irradiance was 3.16%; the average forecast error resulting from the integration of 30% solar and 70% wind was −0.13%. This study innovates by using PT to solar and wind forecast in the planning phase, before the installation of wind and solar plants.

Integration of large-scale utility-owned distributed generation (DG) units can be a vital technique in relieving transmission line congestion and improving the reliability of the power grid. However, the impact of DG installation on line congestion management is significant at locations where transmission lines are most heavily loaded. This study presents a novel probabilistic method to forecast the most heavily loaded lines in the transmission network that might be at a higher risk of congestion. The proposed method can be utilised for determining candidate lines to install DG with the objective of relieving line congestion. The proposed method adopts the cumulative probability distribution function that accounts for the uncertainty of line loading. Furthermore, a congestion improvement ratio is developed to investigate the DG location impact on line congestion. The forecasting method is tested on a small modified IEEE 5-Bus system. In order to demonstrate the proposed forecasting method on a larger and more complex system with several generators, the method is also tested on IEEE 30-Bus test system. The simulation results have confirmed the effectiveness of the proposed method.

Wind generation (WG) is the most widespread renewable energy resource in the world. However, this implementation inevitably leads to an increase in the problems caused by WG, e.g. frequency oscillations, power fluctuations or voltage variations. To overcome these problems, the use of a power conditioning system (PCS) coupled with a vanadium redox flow battery (VRFB) is proposed in this study. The PCS is composed of a distribution static synchronous compensator connected to a dc/dc chopper. The PCS/VRFB detailed model is presented and a three-level control system is developed. This control system allows the PCS/VRFB to perform a decoupled reactive and active power flow control. The dynamic response of the PCS/VRFB is evaluated through simulation tests, and performance characteristics of the device are obtained by means of the variation of the power references. The results obtained demonstrate that the PCS/VRFB offers a good transient response and the control system proposed allows mitigating the problems caused by wind power generation.

Energy yields of photovoltaic power plants are directly related to the availability of the global solar radiation (GHI). An accurate performance analysis of these power plants depends strongly on the quality and the reliability of the solar resource assessment. This study proposed to improve the accuracy of the GHI database provided by satellites. Two quality improvement methods have been proposed and evaluated in this study. The first developed method consists in combining a GHI satellite-derived database with the best ground station models, while the second one consists in performing a linear correction of a satellite database. The purpose of this study is to investigate the quality improvement method that gives more accurate GHI prediction. The comparison between the two developed methods shows that the resulting combination method database achieves higher GHI prediction accuracy than the linearly corrected satellite database. This combination reduces the uncertainty of the original satellite database by 1.95%, with a resulting relative root-mean-square error (rmse%) reaching 4.74%.

A new topology and effective power transfer scheme with minimum number of converters is proposed for a grid connected wind/photovoltaic (PV) system. Distributed generation sources considered are permanent magnet synchronous generator (PMSG)-based wind energy conversion system and PV array system. Two voltage source converters with a common DC-link serve as wind side converter (WSC) and grid side converter (GSC), respectively. The PV array is directly tied to the DC link without any power converter providing variable DC-link voltage. The Perturb and Observe technique extracts the maximum power from PV and the DC-link voltage is set to the maximum power point (MPP) voltage of the PV array. The output DC voltage of WSC is regulated to an MPP PV voltage using an outer proportional–integral voltage control loop. The maximum power from the PMSG and stator voltages is utilised to generate the reference currents for WSC to make stator currents to follow stator voltages. With unity power factor control, the overall VA of the WSC would contribute to the active power transfer and thereby reduce the kVA rating of the WSC in the proposed configuration. GSC tracks the maximum power from wind and PV array, and serves as a shunt active power filter to compensate for the current unbalance due to the connection of non-linear loads at the grid. All these functions are accomplished simultaneously. Various power transfer modes of operation are simulated through MATLAB/Simulink software and its results are validated through dSPACE Digital Signal Processor.

Wind energy systems with permanent magnet generators, especially axial flux permanent magnet generators (AFPMG), have been quite popularly studied and employed recently. However, a known shortcoming of such systems is that they can operate efficiently only in a very limited range of wind speeds, which corresponds to about 70 to 110% of the rated speed of the generator employed and the energy available outside of this wind speed bracket is not accessed at all, and in fact, wasted. Moreover, the absence of any means of excitation control to maintain a regulated output voltage under varying speed conditions calls for expensive power converters. This study presents a novel methodology to obtain a constant output voltage from an AFPMG under varying wind conditions, through the integration of field poles and their control, along with modifications in stator winding. This significantly enhances the power extraction capability of the system over a much wider operational range (corresponding to 25–125% of the rated speed) while eliminating the requirement of a DC–DC converter to maintain constant output voltage. The details of the design of the constant voltage AFPMG and the results establishing the effectiveness of the methodology have also been presented.

The development and reasonable utilisation of wave energy have great realistic significance for solving environment pollution and energy crisis. A direct-drive system with no middle conversion devices such as gear and turbine, which has a simple structure and good stability, is widely applied to wave power systems. First, the study analysed the structure of a tubular permanent magnet linear generator. The structure of short primary and long secondary is chosen for wave power systems because of the convenience of installation and higher power density. Then, based on finite-element analysis, the structure of the generator is optimised by parametric analysis and genetic algorithm. A prototype is manufactured according to the optimised size, and the electromagnetic parameters are measured to verify the accuracy of simulation. Finally, a double floating direct-drive wave power system is installed in the port of Lian Yungang, China, and the system is tested by still and dynamic water; the results show that the system can effectively convert wave energy into electricity.

Grid voltage disturbances result in high magnitudes of rotor currents and DC-link voltage of the doubly-fed induction generator based wind turbines (DFIG-WTs), which may lead under severe fault conditions into deactivation of the machine side converter (MSC) and violation of the fault ride through (FRT) requirements of the grid codes. In this essence, several solutions were proposed, which vary between installing extra hardware components and control modification. However, the extra costs as well as the control limitations degrade the feasibility of the proposed solutions. In this study, new techniques are proposed to enhance the FRT through peak short-circuit current reduction of the DFIG-WT. The new techniques are developed based on the open-loop and close-loop dynamic response of the DFIG. The new techniques utilise the available MSC voltage, in order not to violate the voltage limits, to increase the rate of change of the DFIG internal transient voltage and to increase the magnitude of the transient impedance. Additionally, the mean variance mapping optimisation is used to optimally tune the gains in the second two techniques. The new techniques were implemented in a manufacturer-based simulation model, and the simulation results show their effectiveness, where the maximum peak current reduction achieved was 23.6%.

The micro-grid is a key interface between renewable energy sources and the utility. A micro-grid can work under islanded mode or grid-connected mode. To confirm the seamless transform of a micro-grid from islanded mode to grid-connected mode, synchronisation of the islanded micro-grid to the utility is an essential challenge. In this study, replacing first-order low-pass filter by sliding Goertzel transform based filter, a control strategy with an extended phase-locked loop is presented for the inverter applications in islanded micro-grids. It can ensure the synchronisation between the micro-grid voltage and the utility voltage, and guarantee the seamless reconnection of the micro-grid from islanded mode to grid-connected mode. Considering the influence of the voltage deviation between the micro-grid and the utility voltages in the synchronisation process, detailed analyses are proposed. Analytical non-linear model and small-signal model are presented to prove the fast and effective reconnect performance. Simulated and experimental results are provided to verify the validity and effectiveness of the proposed control strategy. This study is of interest for the seamless transform control of islanded micro-grids.

This study investigates the dynamic participation of wind power plants (WPPs) in the automatic generation control (AGC) task. The pre-specified model of wind farm in the AGC studies has been used. It is shown that operating of WPPs at the command mode results in a significant improvement in the frequency behaviour of power system due to their faster response. However, the WPPs may change their operation mode from the command mode to the maximum power point mode according to the wind speed conditions and load variations. This reduces the improvement in the frequency response. In this condition, the shortage in the wind power should be compensated by the conventional units. Thus, the share of different units becomes uncertain (but bounded) when the WPPs participate in the AGC task. To address this challenge, this study provides the robust stable frequency operation of power system under uncertain shares of different units in the AGC task using the Edge theorem. Simulations are performed on an IEEE 39-bus test system connected to some wind farms in different buses. Results confirm the robust stability of the underlying power system, and hence, the effective capability of the wind farms to participate in the AGC task.

Multiple microgrid (MMG) operation concept of community microgrid (MG) provides enhanced resiliency and reliability through self-healing, enabling a high penetration of distributed generations (DGs), power interchange between MGs and real-time communication. In this study, the methodology of optimal design of low-voltage greenfield distribution grids based on multiple MGs in the presence of uncertainties is presented. The electrical and geographical borders of MGs community are determined using some important criteria such as power balance and spatial distribution of load. Within MGs, both of dispatchable and non-dispatchable DGs are considered. The external grid is assumed as a backup for each MG in abnormal conditions. The proposed method determines the optimal borders of MGs, optimal size and site of DGs for each autonomous MG simultaneously. The imperialist competitive algorithm is used to optimise the total cost of optimal MG clustering problem. The method is implemented to a vacant area with residential and commercial customers. The MGs optimal service area, DGs location, size and type within each MG and LV feeder's route are indicated and compared both for deterministic and probabilistic planning cases.

The application of active filtering in large offshore wind power plants (WPPs) is presented in this study. The harmonic challenges such as sources of harmonic emission and resonances are identified and briefly explained. Also modern remedial harmonic mitigation methods as of active filtering are described and their application in real-life WPP systems demonstrated. It is underlined that WPP components such as widespread medium-voltage cable system and offshore grid transformers can introduce significant low-frequency parallel resonances which can cause a significant harmonic voltage distortion at the point of common coupling. Active filtering in modern grid-side converters used in wind turbines is applied simultaneously keeping sufficient harmonic/noise rejection. Extensive harmonic stability studies are also shown to prove the overall system robustness.