Gareth A. Taylor

Flow Batteries for Enhancing Wind Power Integration

Providing frequency response capability from wind farms is technically feasible, but relies on spilling the wind. Wind intermittency and the planned expansion in offshore wind power in the U.K. are expected to lead to increased requirements for frequency response capability. This may necessitate times where wind farms operate in a frequency sensitive manner and output only a proportion of the available power. Compensating for spilt wind energy would likely lead to increased costs of balancing the power system. This paper highlights the alternative to spilling wind to provide frequency response capability: using wind farm level energy storage. The Vanadium Redox Flow Battery is shown to be capable of providing this and other benefits to the wind farm. The work further demonstrates that ίow batteries could often be incorporated with reactive power compensation equipment such as a wind farm level IGBT SVC. The control of the power electronic interface of the battery is introduced and a control method for supporting the dc link under grid faults is developed and simulated. This control is shown to give the added benefit of supporting the fault current contribution through an extended and severe fault. The capability of the Vanadium Redox Flow Battery to enhance power and energy applications is then explored by considering integrated control with a wind farm to energy time shift and provide frequency response. A novel controller is introduced, which manages the state of charge of the ίow battery while providing some output smoothing to the wind farm and a variable level of reserve for the power system. The simulations of this controller also demonstrate that the energy store can be used to time-shift some of the wind farms energy to times of higher prices.

Novel application of detrended fluctuation analysis for state estimation using synchrophasor measurements

The phasor measurement unit (PMU), with its ability to directly calculate synchronized positive sequence voltages and currents (magnitude and phase), offers a more current and accurate view of the power system compared to that provided by traditional measurements and state estimation (SE). However, the high-resolution data, provided at rates of 50 Hz and 60 Hz (dependant on nominal frequency), capture any transient or dynamic events occurring on the network, potentially distorting the intended steady-state view at various points of the power system. In this paper we propose the use of detrended fluctuation analysis (DFA) to detect and isolate such events for alternative investigation. Comparisons are made between the state estimator and installed PMUs on the high-voltage transmission system of Great Britain.

Proposed Shunt Rounding Technique for Large-Scale Security Constrained Loss Minimization

Optimal reactive power flow applications often model large numbers of discrete shunt devices as continuous variables, which are rounded to their nearest discrete value at the final iteration. This can degrade optimality. This paper presents novel methods based on probabilistic and adaptive threshold approaches that can extend existing security constrained optimal reactive power flow methods to effectively solve large-scale network problems involving discrete shunt devices. Loss reduction solutions from the proposed techniques were compared to solutions from the mixed integer nonlinear mathematical programming algorithm (MINLP) using modified IEEE standard networks up to 118 buses. The proposed techniques were also applied to practical large-scale network models of Great Britain. The results show that the proposed techniques can achieve improved loss minimization solutions when compared to the standard rounding method.

Frequency control using Vanadium redox flow batteries on wind farms

Vanadium redox flow batteries offer many advantages over other energy storage technologies. In the context of wind farm operation, these batteries could greatly enhance the interaction of intermittent renewables with the power system and can provide ancillary services such as frequency control. This allows renewable sources to behave more like conventional plant. In this paper a novel power system model of a Vanadium redox flow battery is introduced and validated, demonstrating the importance of round trip efficiency modelling. It is then proposed to use such batteries as energy storage on a large wind farm, connecting through an IGBT SVC. It has been clearly demonstrated that such an implementation enables fast active power regulation that permits both the wind farm and storage to provide frequency regulation services. Several methods of controlling the energy storage to provide a power reserve response to large frequency deviations are also analysed, including a critical evaluation and analysis of the associated losses from such schemes.

myTrustedCloud: trusted cloud infrastructure for security-critical computation and data management

Cloud Computing provides an optimal infrastructure to utilise and share both computational and data resources whilst allowing a pay-per-use model, useful to cost-effectively manage hardware investment or to maximise its utilisation. Cloud Computing also offers transitory access to scalable amounts of computational resources, something that is particularly important due to the time and financial constraints of many user communities. The growing number of communities that are adopting large public cloud resources such as Amazon Web Services [1] or Microsoft Azure [2] proves the success and hence usefulness of the Cloud Computing paradigm. Nonetheless, the typical use cases for public clouds involve non-business critical applications, particularly where issues around security of utilization of applications or deposited data within shared public services are binding requisites. In this paper, a use case is presented illustrating how the integration of Trusted Computing technologies into an available cloud infrastructure -- Eucalyptus -- allows the security-critical energy industry to exploit the flexibility and potential economical benefits of the Cloud Computing paradigm for their business-critical applications.

Inertia Estimation of the GB Power System Using Synchrophasor Measurements

A novel procedure for estimating the total inertia of the Great Britain (GB) power system is presented. Following an instantaneous in-feed loss, regional variations in the estimate of inertia are obtained from measured frequency transients using installed synchronised phasor measurement units (PMUs). A method is proposed to first detect a suitable event for analysis, and then filter the measured transients in order to obtain a reliable estimate of inertia for a given region of the GB network. The total inertia for the whole system is then calculated as a summation, with an estimate also provided as to the contribution to inertia from residual sources, namely synchronously connected demand and embedded generation. The approach is first demonstrated on the full dynamic model of the GB transmission system, before results are presented from analyzing the impact of a number of instantaneous transmission in-feed loss events using phase-angle data provided by PMUs from the GB transmission network and also devices installed at the domestic supply at 4 GB universities.

Parallel detrended fluctuation analysis for fast event detection on massive PMU data

Phasor measurement units (PMUs) are being rapidly deployed in power grids due to their high sampling rates and synchronized measurements. The devices high data reporting rates present major computational challenges in the requirement to process potentially massive volumes of data, in addition to new issues surrounding data storage. Fast algorithms capable of processing massive volumes of data are now required in the field of power systems. This paper presents a novel parallel detrended fluctuation analysis (PDFA) approach for fast event detection on massive volumes of PMU data, taking advantage of a cluster computing platform. The PDFA algorithm is evaluated using data from installed PMUs on the transmission system of Great Britain from the aspects of speedup, scalability, and accuracy. The speedup of the PDFA in computation is initially analyzed through Amdahls Law. A revision to the law is then proposed, suggesting enhancements to its capability to analyze the performance gain in computation when parallelizing data intensive applications in a cluster computing environment.

Application of phasor measurement units to estimate power system inertial frequency response

The inherent reduction in inertial frequency response resulting from a shift in generation mix towards renewables, is presenting a range of operational planning challenges for transmission system operators (TSOs) globally. Dictating the ability to maintain frequency following significant mismatches in supply and demand, it is of great consequence to the real-time operation of the power system. In this paper we discuss the estimation of system inertia constant using synchronised data, provided by installed phasor measurement units (PMUs). Results are presented from analysing the impact of over 50 transmission system events that were observed on the electricity transmission network of Great Britain.

Prospective Wide Area Monitoring of the Great Britain Transmission System using Phasor Measurement Units

National Grid, the Transmission System Operator for Great Britain, has recently installed a Wide Area Monitoring System (WAMS), to improve the real-time view of the power system. Phasor Measurement Units (PMUs) have been installed, primarily through upgrades to digital fault recorders, as an extension to dynamic system monitoring. This paper reviews the development of WAMS on the GB System and presents the experiences so far, detailing both existing and future applications of synchrophasor technology, such as oscillation analysis, model validation and improved situational awareness.

Big data analytics on PMU measurements

Phasor Measurement Units (PMUs) are being rapidly deployed in power grids due to their high sampling rates. PMUs offer a more current and accurate visibility of the power grids than traditional SCADA systems. However, the high sampling rates of PMUs bring in two major challenges that need to be addressed to fully benefit from these PMU measurements. On one hand, any transient events captured in the PMU measurements can negatively impact the performance of steady state analysis. On the other hand, processing the high volumes of PMU data in a timely manner poses another challenge in computation. This paper presents PDFA, a parallel detrended fluctuation analysis approach for fast detection of transient events on massive PMU measurements utilizing a computer cluster. The performance of PDFA is evaluated from the aspects of speedup, scalability and accuracy in comparison with the standalone DFA approach.