Requirements for inertial response (IR) from wind turbines (WTs) have been implemented or drafted by power systems (PSs) operators worldwide. This is a response to the replacement of conventional power plants using synchronous generators by non-synchronous, power electronics-based generation and the resulting effect on frequency dynamics in the case of contingency events. The additional active power provided during operation in IR mode must be drawn from the rotating masses. A re-acceleration accompanied by reduced active power output follows the activation phase. The allowed depth and duration of the post-inertial recovery will be regulated in future versions of grid codes, e.g. in Québec and Ireland. This study describes an improved version of an IR control system that enables a more PSs-friendly provision of such short-term frequency support. The new controls allow adjusting the duration of the recovery period. Potential negative effects of IR from WTs on the PS in the form of a second frequency nadir during the recovery phase can be minimised. The outcome of simulations and of field testing will be presented. All results shown in this study include the initial and the future inertia emulation performance which allows easy comparison of the two controls.

This study presents the Hydro-Québec TransÉnergie experience regarding the grid code compliance tests that have been performed for the integration of wind power plants using type-III and type-IV technologies. Tests discussed in this study were conducted in two phases: validation of the performance requirements for each project and type tests on a single wind turbine generator for each technology involved. The study presents examples of results for each test module and measurements from online monitoring. Technical challenges are discussed and performance issues that were raised through the process are explained.

Modern wind power plants (WPPs) are equipped with sophisticated controllers that allow various schemes to be used by manufacturers to meet grid code requirements. This includes active and reactive power controls as well as voltage control. Voltage control can be achieved in a number of different ways to satisfy the different grid codes, but also the project specific needs. Hydro-Québec TransÉnergie (HQT) has performed numerous dynamic studies related to the integration of WPPs and optimisation of their control schemes including voltage control. This study presents the HQT experience with various voltage control issues including tuning of the WPP controller and study cases of angle and voltage stability issues.

This study addresses a detailed design and tuning of a wind power plant voltage control with reactive power contribution of wind turbines and static synchronous compensators (STATCOMs). First, small-signal models of a single wind turbine and STATCOM are derived by using the state-space approach. A complete phasor model of the entire wind power plant is constructed, being appropriate for voltage control assessment. An exemplary wind power plant located in the United Kingdom and the corresponding grid code requirements are used as a base case. The final design and tuning process of the voltage controller results in a guidance, proposed for this particular control architecture. It provides qualitative outcomes regarding the parametrisation of each individual control loop and how to adjust the voltage controller depending on different grid stiffnesses of the wind power plant connection. The performance of the voltage controller is analysed by means of a real-time digital simulation system. The impact of discretising the controller being initially developed in continuous-time domain is shown by various study cases.

In this study, a technical and economic comparative analysis for evaluating the performance of various electrical photovoltaic (PV) plant configurations is presented. This methodology assessment is based on a holistic approach that calculates the levelised cost of energy (LCOE) considering the capital and installation cost of the PV components, as well as, the operation and maintenance costs over the lifetime of the project. Also, the potential economic impact of the installation of batteries for providing flat-output response is investigated. Moreover, a sensitivity analysis is included for considering both economic and technical uncertainty on the LCOE. The presented methodology compares the performance of six different configurations in three hypothetical PV power plants (1, 50 and 200 MW) located in Golden, Colorado, USA. The results obtained demonstrate that although some PV power plant configurations present better efficiency (higher performance ratio), they are not the most cost-effective solutions because of the requirement of extra equipment or the inclusion of expensive technologies. Finally, the benefit of including batteries into the system is shown for flat output operation. The results show that in spite of their inclusion increases the LCOE, extra revenues can be obtained when providing such services.

This study discusses the impact of market rules on the generation (and curtailment) from intermittent energy sources (IES), such as the design of support schemes, the priority dispatch rule for IES, negative prices and economic compensation for IES curtailment. It also describes the approaches applied in some European countries and alternative designs. An evaluation of these different market rules is assessed for the Spanish 2020 scenario by using a system operation model. The results show that with a feed-in-tariff and the priority dispatch rule, more generation from IES is fed-in into the system, and lower emissions are obtained. With negative prices and demand response, the feed-in-tariff scheme provides lower demand costs. With market remuneration and ex-post remuneration (as implemented in Spain in 2015), IES generation fed-in in the system is reduced and demand costs are increased. Furthermore, the curtailment of IES increases with higher penetration levels of IES. The increase in the curtailment is significantly higher for wind power as generation and demand are less correlated than solar generation and demand. The design of curtailment compensation and support schemes together become crucial to incentivise IES investments with higher value for the system.

Reliable condition monitoring (CM) highly relies on the correct extraction of fault-related features from CM signals. This equally applies to the CM of wind turbines (WTs). Although influenced by slowly rotating speeds and constantly varying loading, extracting fault characteristics from lengthy, nonlinear, non-stationary WT CM signals is extremely difficult, which makes WT CM one of the most challenge tasks in wind power asset management despites that lots of efforts have been spent. Attributed to the superiorities to empirical mode decomposition and its extension form Hilbert–Huang transform in dealing with nonlinear, non-stationary CM signals, the recently developed variational mode decomposition (VMD) casts a glimmer of light for the solution for this issue. However, the original proposed VMD adopts default values for both number of modes and filter frequency bandwidth. It is not adaptive to the signal being inspected. As a consequence, it would lead to inaccurate feature extraction thus unreliable WT CM result sometimes. For this reason, a precise feature extraction method based on optimised VMD is investigated. The experiments have shown that thanks to the use of the proposed optimisation strategies, the fault-related features buried in WT CM signals have been extracted out successfully.

Reliability analyses are essential for the design of hybrid photovoltaic/wind/battery systems. The selection of design criteria is an important task and has to ensure proper reliability and optimal configuration. In the literature, loss of power supply probability (LPSP) and loss of load hours (LOLH) are the most common reliability criteria used for this matter. This study presents a comparative analysis on LPSP and LOLH design criteria based on a Monte Carlo simulation, taking into consideration uncertainties in the variables involved in the design process. Moreover, two new statistical design criteria are proposed, aiming to avoid over-sizing of the optimal configuration. According to the obtained results, LOLH is a stricter design criterion compared with LPSP, leading to a more reliable energy system. In addition, the optimal configuration selected by using the proposed statistical design criteria showed better performance when compared with the solution based on LPSP or LOLH.

This study presents an efficient optimisation strategy for solving coordinated economic dispatch problem with wind–hydro–thermal complex power source structure. The wind–hydro–thermal coordinated dispatch aims to minimise the total fuel costs of coal-fired thermal power units while satisfying all kinds of operating constraints. To better handle the random variables in the constraints introduced by wind power and load demand during analysis, a probabilistic analytical model is employed to describe the uncertainty of wind farm power output first; moreover, then an improved convolution method is applied to calculate the total stochastic power consisting of load demand and power output of wind farm. The two-stage stochastic linear programming method and stochastic chance constraints are employed to further form a new deterministic objective function with penalty items taken into account. An enhanced particle swarm optimisation method is applied in the solution of the proposed model. Finally, the simulations are performed on a 6-bus test system and a real-sized China power grid test system to investigate the effectiveness and validity of the proposed optimisation strategy.

This study considers maximising conversion between the mechanical and electrical powers for heaving point absorbers (HPAs). The objective is implemented by generating the buoy's velocity reference by designing the intrinsic resistance. The authors designed the intrinsic resistance using a rapid procedure involving the mechanical and electrical models of HPAs. The electrical power conversion can be improved by tuning a weighting constant with the constraints on the maximum value of the control force and the power take-off utilisation index. The value of the intrinsic resistance is varied based on irregular sea states, which are characterised by their significant heights and peak angular frequencies. A simple robust proportional-integral-derivative (PID) controller is utilised in the servo feedback control system to follow the velocity reference. The PID controller is designed using the complex polynomial stabilisation to convert the robust performance into a set of linear programming problems. A set of admissible PID controller is obtained to satisfy the robust performance specifications. The authors tested the proposed method in various nominal and perturbation scenarios, and its performance was compared with existing reference and non-reference based HPA control strategies.

The impact of distributed generation (DG) units on the voltage stability has become a challenging issue especially when squirrel cage induction generator (SCIG)-based wind DGs are utilised. Optimisation methods are tools which can be used to place and size the DG units in the distribution system, so as to utilise these units optimally within certain constraints. This study aims to optimally size and allocate advanced wind energy based DG technology with innovative reactive power capability, reduced capital cost, and improved energy capture capability to improve voltage stability. Therefore, a new combination of SCIG and doubly-fed induction generator (DFIG) based DG configuration is proposed. In this configuration, the reactive power absorbed by SCIG is supplied by DFIG, and therefore, the combined system operates at unity power factor, which makes it feasible to comply with the IEEE 1547 standard. A methodology is proposed to optimally size and allocate the DG system with an objective function to improve the voltage profile considering numerous technical and economic constraints. The performance of the proposed DG configuration is compared with DGs that utilise SCIG with a parallel reactive power compensation. IEEE 30-bus test system is used to demonstrate the effectiveness of the proposed methodology.

Flywheel systems are quick acting energy storage that enable smoothing of a wind turbine output to ensure a controllable power dispatch. The effectiveness of a flywheel depends on how well it can be controlled to respond to fluctuating power output from intermittent sources. A quadratic Lyapunov function based non-linear controller is proposed which is designed based on an implicit understanding of the system including its inherent nonlinearities. Two different configurations of flywheel designs have been studied. The controller ensures asymptotic stability of the system as well as obtaining a better and more reliable performance than linear proportional–integral controllers in tracking rapid changes in power references. A further benefit is that the tuning of the proposed controller remains unaffected by changes in the system parameter and operating conditions. The efficacy of the algorithm is verified using non-linear time-domain simulation in MATLAB.

In recent years, the strategic goals of many countries have included the achievement of high photovoltaic (PV) integration in electrical grids. Therefore, many governments have introduced incentive-based policies in an effort to encourage the private sector to invest in PV-related projects. However, these kinds of projects require a positive net present value (NPV) in order to be sponsored by non-governmental organisations. In this study, the authors investigate the impact of haze on PV systems in Malaysia due to open burning in Sumatra. As a developing country, Malaysia is aiming to increase the installation of renewable-energy (RE) sources, and thus it has implemented a feed-in tariff (FiT) mechanism. As the efficiency of PV cells increases and the cost/Wp decreases with time, the expected NPV, return-on-investment and payback period for PV systems installed in 2015 is expected to be significantly reduced. The FiT rate in Malaysia is significantly higher and the purchase agreement is longer compared with many similar countries; these make Malaysia a preferred choice for PV system investments. However, environmental disturbances such as haze have a negative impact on the yield of PV systems. During the months of September to October 2015, the transboundary haze episode in Kuala Lumpur reduced the power produced from PV systems by 17.8%. This study shows the impact of haze on PV systems, and analyses the effect of haze on the Malaysian RE action plan. This study proposes a method to estimate the reduction in power yield during the haze.

This study aims to conduct the sub-synchronous (SS) resonance analysis of a multi-machine power system incorporating doubly fed induction generator (DFIG)- or permanent magnetic synchronous generator (PMSG)-based wind farm. The linearised equations involving the dynamics of steam turbine generator, wind farm, shunt capacitor, transmission line, and load are derived, and the detailed state matrix formation process pertinent to each component is presented. Taking the IEEE 16-machine-68-bus test system as example, the eigenvalue analysis along with participation factor is applied to investigate the impacts of the series compensation level of transmission line on the modal frequencies and damping ratios of two groups of oscillatory modes of interest: namely, the SS mode of the series-compensated transmission line and the shaft modes of the studied steam turbine generator before and after one of the un-studied steam turbine generators is replaced by the DFIG- or PMSG-based wind farm. Some useful conclusions and comments are drawn.

Hydrogen for supplying fuel cells is oftentimes produced by reforming hydrocarbon fuels like natural gas. As a by-product of this process, carbon monoxide (CO) is produced, whose concentration can be as high as 500 ppm during start-up. The presence of such a contaminant in the fuel flow of the fuel cell has serious side effects derived from the reduction of its active area due to poisoning; which translates in reduced output voltage and power. To cope with this problem, the development of a power converter and current modulation technique is presented in this study. It is shown that the use of the proposed converter allows increasing CO tolerance of the stack, thus allowing the system to continue operation while showing minimal degradation in output voltage and power.

In this study, a ‘two-stage’ deterministic algorithm an for efficient transmission expansion planning with renewable energy (RE) resources under the assumption that existing conventional generators provide the reserve to mitigate RE generation forecast error has been proposed. Zero-RE penetration has been considered as a ‘reference scenario’, as well as cost-minimisation objective has been considered as a planning criterion in Stage 1. In the proposed algorithm, Stage 2 is required to be solved only if the network performance degrades in relation to the reference scenario. In Stage 2, congestion cost is also incorporated as a sub-objective. Here, the locational marginal prices of the unit scheduling problem obtained from the solution of Stage 1 have been used to calculate the congestion cost. In addition to being computationally tractable, the proposed algorithm guarantees performance improvement in the network. The planning horizon is divided into smaller blocks to facilitate delayed investment. When implemented on an IEEE 24-bus reliability test system, the proposed algorithm generated minimum cost plan with better performance.

The signal processing-based bearing fault diagnosis in wind turbine gearbox is considered challenging as the vibration signals collected from acceleration transducers are, in general, a mixture of signals originating from an unknown number of sources. Even worse, the source number is often larger than the number of installed sensors, and hence the fault characterisation is effectively an under-determined blind source separation problem. In this study, a novel sparse component analysis-based algorithmic solution is proposed to address this technical challenge from two aspects: source number estimation and source signal recovery, to enable accurate and efficient bearing fault diagnosis. The source number estimation is implemented based on the empirical mode decomposition and singular value decomposition joint approach. The observed signals are transformed to the time–frequency domain using short-time Fourier transform to obtain the sparse representation of the signals. The fuzzy C-means clustering and l ₁ norm decomposition methods are used to estimate the mixing matrix and recover the source signals, respectively. The proposed solution is assessed through simulation experiments for scenarios of linearly and non-linearly mixed bearing vibration signals, and the numerical result confirms the effectiveness of the proposed algorithmic solution

Much attention has been continuously paid on the model development and stability analysis of the doubly fed induction generator (DFIG) widely applied in wind power generation. Similarly, this study develops the form-standardised state-space model in the dq reference frame of the DFIG with stator winding inter-turn fault (SWITF). Compared with those previously developed, it is definitely preferable for the simulation and stability analysis of the DFIG with SWITF due to its standard form. Moreover, for the DFIG with SWITF working in stator-voltage-oriented control frame, the small-signal stability analysis is conducted using MATLAB simulation, yielding the conclusion that SWITF will never eradicate the DFIG's small-signal stability but deteriorate it to some extent. This conclusion is further validated by means of the Lyapunov stability theory. As a kind of contribution of this study, the analytical expressions of the eigenvalues of the DFIG with SWITF are derived. Case study based on an MATLAB/Simulink demo routine is completed to demonstrate the validity of the model development and small-signal stability analysis of the DFIG with SWITF.

In the marine industry, it is important to improve the performance of tida turbines to reduce power generation costs. Modification of existing tidal turbine models is necessary to boost performance. The main objective of the present study is to investigate the hydrodynamic performance of a model variable length blade tidal turbine by modifying the baseline rotor to improve the performance using blade element momentum theory (BEMT). The QBlade BEMT simulation results were validated with the available published data and are in good agreement. Furthermore, the key performance parameters (i.e. thrust, moment, and power coefficient) and power output were predicted using the BEMT code for different blade configurations of the model rotor. The simulation results were compared with a standard conventional fixed blade turbine model. Based on the results from the simulations, with the increase in the rotor blade lengths, the performance parameters, particularly peak power coefficients, were observed to be improved up to 10%. The power extraction was also enhanced up to 79% below-rated tidal velocities without any loss in performance at the rated condition. Hence, the model is more efficient compared to the conventional models.

Research on direct-drive wave energy converter linear generators has mostly focused on synchronous inner permanent magnet (PM) linear generators. In this study, an outer-PM tubular linear generator is designed to increase the power density and distance of relative movement. The motion equations of heaving buoys are derived on the basis of hydrodynamic theory. Two buoys are designed in accordance with the real wave condition in the Yellow Sea in China. The design process of the proposed generator is elucidated. Considering cogging force and voltage, the authors optimise the linear generator and determine the final parameters. The generator performance is evaluated using the finite element method. The integrated wave energy converter system consists of a linear generator, inner buoys, outer buoys, an electricity post-processor, and a communication component. The system is manufactured and placed in the Yellow Sea based on the design results. The measured voltage is highly consistent with the simulation data. All results show that the system is well suited for wave energy conversion.

This research presents a model of a utility-scale photovoltaic unit (USPVU) enhanced with an embedded hybrid energy storage system (HESS), suitable for stability studies in transmission systems. The main goal of this model is the simultaneous provision of primary frequency control and dynamic grid support. The primary frequency control includes both droop response (achieved by the frequency sensitive mode [FSM] operation) and inertial response (IR). To obtain these grid support functions, the research designed a suitable voltage and frequency (V–f) control, which coordinates the photovoltaic (PV) maximum power point tracking control, HESS converter control, and PV inverter control. Firstly, a midterm assessment of energy requirements in the sized HESS, based on frequency data, validated the energy availability of the enhanced USPVU for primary frequency control, according to new prequalification rules for energy-constrained units. Then, transient stability assessments were performed on a representative transmission system to check the performance of the added FSM and IR in USPVUs with dynamic grid support. The results of the frequency phenomena in the IEEE 39-bus system showed that the enhanced USPVU shared primary frequency control responsibilities with the conventional generation. This was achieved with two criteria to dispatch and commit conventional units by USPVUs.