Development of a new branch of power systems metrology, to support the quantification of ancillary service provision such as power quality improvement and provision of inertia

This PhD position is part of the partnership between the University of Strathclyde and NPL (The National Physical Laboratory, Teddington, London). The position will be primarily based at the Technology and Innovation Centre, George Street, Glasgow, but the successful candidate will also become part of the new “Postgraduate Institute” at NPL, be co-supervised by NPL, and engage with our “Power Networks Demonstration Centre” (http://pndc.co.uk/).

The control loops of typical converters used in renewables mean that they essentially behave as controlled current sources – they aim to produce sinusoidal balanced currents that feed into the national electricity grid. However, loads (and some of the renewable devices) which are connected to the grid often demand unbalanced currents, and currents which contain high levels of harmonics because they are non-linear, and contain power electronic circuits. This creates a mismatch. At present, the remaining synchronous generators and linear loads are the dominant devices which are maintaining the power quality of the electrical network. Every year, more synchronous generators are retired as coal power stations are taken off-line, and replaced with renewable sources like wind and solar. Likewise linear loads like heaters and incandescent bulbs are being replaced by non-linear devices like induction cookers and non-linear fluorescent and LED lighting. Not only is power quality therefore under threat, but also the system inertia is reducing as the rotating generators are retired.

It is possible to reprogram converters to provide power-quality mitigation services, and also to provide inertial support. However, for a manufacturer or operator to be persuaded to do this, would probably require a visible and tangible benefit to be realised, in the form of a realisable financial revenue. Likewise, any synchronous generator connected to the grid, really ought to receive a quantifiable financial revenue for the power quality and inertial services provided. The whole problem area actually goes beyond the concepts of power quality and inertia, and encompasses a fundamental stability issue, whereby if not enough of the installed capacity of generators are behaving in a “grid forming” manner, the entire network can very quickly become completely unstable.

To enable financial payments to be made to “grid forming” devices, the “grid forming” operation has to be quantified in some way, and metered over finite time intervals. This goes way beyond a simple metering of kWh and kVAR. There is an initial challenge to even define new measurands and units, which could be used to quantify “grid friendliness”. For example, would be the measurands, and what would their units be, to quantify the “mopping up” of voltage harmonics on the grid? The same question can be asked for unbalance, and for the determination of real-time provision of inertia and voltage stability. Once the measurands and units have been proposed, the next challenge is to determine practical and realisable methods to carry out the measurements in real-time. What algorithms, filters, and processing is required? What special transducer requirements are there? What accuracy can be achieved? How would a metering device be calibrated and tested for conformity? Most of the above questions are entirely technical, but the project will also include a financial and market aspect. How would a value be placed on these measurands and the service they represent, in the context of modern privatised electricity markets, for example?

The prospective student should have an interest in learning and applying skills related to power networks, power quality, power system measurements, digital signal processing, power-converter control strategies, and power system markets for ancillary services.