Energy storage is seen as one of a number of crucial technologies if the integration of renewables in distribution networks increases. The work in this thesis considers how to operate energy storage to overcome issues presented by solar photovoltaic (PV) in low voltage (LV) distribution networks. Two control strategies have been developed and applied in a smart grid laboratory to mitigate voltage rise and reverse power flows caused by PV. The first strategy examines the performance of non-coordinated control of energy storage for voltage support. The second strategy involves coordinating the on-load tap changer (OLTC) and energy storage for voltage support and reducing reverse power flows, and it illustrates that coordinated storage unit is a more effective and viable alternative to upgrading network infrastructure. After considering a single storage unit in the network, strategies for controlling multiple storage units are investigated. The main objective of this method is to solve overvoltage with multiple energy storage in LV networks with a proliferation of PV systems. The scheme is based on voltage sensitivity analysis and a battery aging model which influences which storage units are operated to maintain the network voltage within limits. The battery aging model is included to improve to reduce degradation when operated to resolve voltage excursions thus reducing the maintenance and battery replacement costs. To get a better performance of the storage unit for voltage support, a systematic model that includes the PV generator and the energy storage based on linearized differential equations is constructed. The model was used to examine: the dynamic performance of battery storage systems and their active and reactive power voltage regulation feedback controller; small disturbance of active and reactive power exchange with the power system; a methodology to utilise active and reactive power of the energy storage for voltage support. In summary, the study presented by this thesis shows energy storage can be operated in the LV distribution network where significant amounts of PV generators are installed. It allows distribution network operators to have a deeper understanding of how to operate single and multiple energy storage units in future LV distribution networks.

An electrical grounding system is an important element to ascertain a safe environment for both humans and equipment during fault or transient conditions. The performance of grounding systems under lightning current is quite different from the conventional frequency based power. In order to understand the grounding grid behaviour under lightning current, researchers typically carry out experiments on actual grounding systems or on laboratory scaled models. Although experiments can provide insights of the actual grounding operation, the shortcoming is that a large area of lab space is required which reflects into high costs. As an alternative, computer simulation has been introduced, and can be categorised into three different approaches, namely circuit approach, transmission line approach or electromagnetic approach. In this work, the simulations are performed based on the electromagnetic approach under three dimensions (3D) mode due to its accurate results. For further understanding, a comparison between circuit and electromagnetic approaches is also carried out, where the resulting outcome shows that the circuit approach underestimates the impulse impedance at injection point compared with simulations by the electromagnetic approach. When the electromagnetic approach is applied, a finite element method is used to solve the partial differential electromagnetic equations in the time domain. Thereafter, the simulations results are validated with the existing published results covering the electromagnetic simulations by using the method of moment (MOM), and as well as actual field experiments. In addition, simulations are performed to understand the effect of different parameters, including lightning current, soil parameters, grounding design, and location of injection point of lightning current. Moreover, a comparison study is carried out for potential rise between power frequency and impulse current at different grid sizes. The study shows the potential generated at injection point for both current and saturation point when the grid size reaches a certain point. It’s important to consider both types of current to get better grounding grid design. Besides that, empirical equations are used out to calculate the effective area under lightning conditions, where the effect of the down-conductor is taken into consideration as part of the grounding model. The effective area is an important parameter for the optimization of the grounding grid design when increasing grounding size does not improve the impulse impedance. Transient ground potential rise (TGPR) above the ground is another interesting parameter to analyse. In this work, a good correlation is shown between the effective area and the impulse impedance at the injection point with rising transient ground potential. It is found that the TGPR is larger when it is closer to the injection point, but only lasts for a few microseconds. Step voltage evaluations are performed for different standing positions of the human above the grid, including the distance of the step voltage location from the injection point, and the effect of grid size to step voltage value.

Voltage fluctuation and power losses in the distribution line are problems in distribution networks. One method to mitigate these problems is by injecting reactive power into the network using a Static Synchronous Compensator (STATCOM). This can be used both for regulating the voltage and reducing the losses. A STATCOM is critically dependent on a grid synchronisation scheme that can accurately track the changes occurring in the grid phase and frequency. The Modular Multilevel Converter (MMC) is a promising topology for STATCOM applications because of its simple modular circuit structure that allows for higher voltage ratings, and conventionally uses a stack of sub-modules which are either two-level half or H-bridge converters. As a novel alternative, the thesis investigates the practicality of a STATCOM based on a three-level flying capacitor (FC) converter. Two variants of this topology are presented; the FC Half-bridge and FC H-bridge. A comprehensive study is undertaken to compare these with the Half and H-bridge sub-module under STATCOM operation. Most importantly, an FC H-bridge-based STATCOM is investigated for reactive power compensation. The challenges of multilevel, multi-module PWM control schemes achieving good waveforms at low switching frequency, whilst maintaining module capacitor voltage balance, are thoroughly addressed. Simulation results validate the operation for both line voltage regulation and power factor correction. An experimental power system with an FC-based STATCOM rig is designed and built, and validates the simulation results for power factor correction. It demonstrates correct operation of a control scheme that includes a system for maintaining capacitor voltage balance. Another new contribution is the investigation of a phase locking technique based on the Energy Operator (EO). The method, combining two different EO computations, is shown to achieve fast and accurate detection of frequency and phase angle when combined with an appropriate filter, and crucially operates well under unbalanced voltage conditions. The technique is compared with two other well-known phase locked loop (PLL) schemes, showing that it outperforms the others in terms of speed and accuracy. A hardware implementation of the EO-PLL validates the principle, showing the simplicity of the method.

The transmission and distribution networks are facing changes in the way they will be planned, operated and maintained as a result of the rise in the deployment of Low Carbon Technologies (LCTs) on the power grid. These LCTs provide the benefits of a decarbonised grid and reduce reliance on fossil fuels and large centralised generation. As LCTs are close to the demand centres, a significant amount will be deployed in distribution networks. The distribution networks face challenges in enabling a wide deployment of LCTs because they were traditionally built for centralised generation and most are operated passively as demand patterns are well understood and power flows are unidirectional to load centres. The opposite will be the case for distribution networks with LCTs. Utilities that own and operate distribution networks such as the DNOs in the UK will face a host of problems, such as voltage and thermal excursions and power quality issues on their networks. Traditional reinforcement methods will be expensive for DNOs, so they are considering innovative solutions that provide multiple benefits; this is where Energy Storage Systems (ESS) could play a role to provide multiple technical and economic benefits across the grid from voltage and power flow management to upgrade deferral of network assets. This is due to the multifunctional nature of ESS allowing it to act as generation, transmission, demand or demand response based on requirements at any specific time based on the requirements of the stakeholder involved with the asset. ESS is technically capable of providing benefits to DNOs and other stakeholders on the electricity grid but the business case is not proven. Unless multiple benefits are aggregated, investment in ESS is challenging as they have a substantial capital cost and some components will require more frequent replacement than traditional network assets which typically last between 20 – 40+ years. As a result there is a reluctance to include them in future distribution network planning arrangements. IV Furthermore, the electricity regulatory and market design, which was set up in the time of traditional centralised generation and networks, limits investment in ESS by regulated bodies such as DNOs. The regulations and market structures also affects revenue streams and the resulting business case for ESS. This thesis investigates the feasibility of ESS in distribution networks by first studying the effect of current electricity regulatory and market practices on ESS deployment, investigating how ESS can be used under the present rules, and establishing whether there are limitations that can be reduced or removed. Secondly, short and medium term planning is carried out on model Medium Voltage distribution networks (6.6 kV) provided by the IEEE and Electricity North West Limited to establish the technical and financial viability of investing in ESS over conventional reinforcement methods by:  Assessing the impact of the proliferation of LCTs in distribution networks using both deterministic and stochastic methods under different scenarios based on current developments and government policies in the UK. This stochastic evaluation considers both spatial and temporal aspects of LCTs in distribution networks with datasets obtained from real distribution network customers;  Developing and applying ESS voltage and power flow management, and market control algorithms to resolve distribution network issues resulting from growing LCTs and allowing ESS to participate in the electricity spot market over a planning period up to the year 2030;  Providing a framework for assessing the business case of ESS under a DNO or third-party ownership structure where technical and commercial benefits from network asset upgrade deferral, energy arbitrage, balancing market and ancillary services (frequency response and short term operating reserves), distribution and transmission system use of system benefits are evaluated; V  Optimising the operation of ESS considering multiple technical and commercial objectives to establish the technical benefits and revenues that can be obtained from an ESS deployment and the trade-off of benefits that applies for differing ownership types. The simulation results show that, under the scenarios investigated, ESS can be used as a technical solution for DNOs. They show that the ESS capital costs can be offset by aggregating benefits from both technical and commercial applications in distribution networks if regulatory and market changes are made. The conclusions offer a perspective to DNOs and third parties’ considering investing in ESS on the electricity grid as it evolves towards a more active, decarbonised system.

This thesis presents and validates a model for designing multimode SOA-like waveguide devices. This model was used to design an active vertical coupler wavelength converter device making use of both crossgain and cross-phase modulation. The simulated output extinction ratio was over 30dB for a maximum input pump level of under 6 dBm. A multi-quantum well wafer structure was designed and ordered. Two rounds of devices were designed and multiple fabrication processes developed. These included three levels of etch depth, for which one depth was required to be correct within a small tolerance. Also, the dry plasma etch was required to create totally internally reflecting mirrors in a two step etch so much development was required for this step to keep the surface optically smooth. After the fabrication process development devices were successfully fabricated with good quality waveguides and totally internally reflecting mirrors. Characterisation of completed devices exhibit couphng and gain variation due to carrier modulation. The extinction ratio of the devices has been measured as over 30dB with varying current injection. The transmission extinction ratio has been measured as over 20dB with varying injection current. It was discovered that the fabricated devices have a low quantum efficiency (?e). This prevented high carrier concentration which made optical saturation too small to observe. Although all-optical wavelength conversion was not demonstrated, the successful modulation of the coupling due to carrier population changes by injection current has dnonstrated the operation principles. Optical saturation of the carrier density and modulation of the coupling should be achievable with a wafer design that has improved carrier confinement in the active layer. Probable solutions to all these problems have been described which should result in high quality devices.

Automatic and Co-ordinated Voltage Regulation (CVR) contributes significantly to economy and security of transmission grids. The role of CVR will become more critical as systems are operated closer to their capacity limits due to technical, economic and environmental reasons. CVR has 1 min resolution and owing to the inherent complexity of the task, CVR is enabled through zoning-based Reduced Control Models (RCM) i.e. simplified models of the network suitable for Voltage Control. RCM not only enables CVR bus also affects its performance and robustness. This thesis contributes towards improved CVR through thorough investigation of the RCM. As a starting point, with current power systems structure in mind, this work investigates static RCM schemes (i.e. fixed Reduced Control Model for all network configurations). To that end this thesis develops: (1) a novel generic framework for CVR modelling and evaluation and (2) new zoning-based RCM approaches using Complex Network Analysis. The evaluation of CVR in conjunction with both static and adaptive RCM schemes are based on a novel framework for CVR modelling and evaluation. This framework is generic and can be used to facilitate the selection and design of any of the CVR components. As a next step, due to the fact that a single RCM cannot be optimal for all network configurations, adaptive RCM (i.e. RCM determined in an online event driven fashion) is investigated using the proposed framework. This concerns future transmission grids where RCM is driven by the need for reliability rather than economy of measurement points at a planning phase. Lastly, this thesis examines zone division in an interconnected system ranging from EHV down to MV, and assesses the required degree of co-ordination for the voltage control of these zones. Essentially, this last item extends the scope of this work’s contributions beyond a single transmission-level Independent System Operator (ISO).