The operation of modern distribution networks (DNs) tackles serious challenges due to the integration of distributed generations (DGs). The protection scheme is one of these challenges. Particularly, the occurrence of bi-directional short-circuit current flow that affects the reliability, sensitivity and selectivity of traditional overcurrent relays (OCRs). In addition, the future distribution system with DGs is expected that will be occupied by the meshed networks alongside the classical radial design and alternating between the grid-connected and islanded mode, for enhancing their reliability. The purpose of the present thesis is to introduce practicable protection proposals for such implementations and address pertinent protection issues. In this context, a comprehensive literature review has been introduced in the present thesis critically. The main contribution of this thesis is the introduction of advanced non-standard methods for addressing the coordination problem of OCRs in DNs with a growing integration of DGs in the power system. Firstly, this thesis presents a novel optimal OCR coordination scheme developed using the non-standard current characteristics (NSTCCs) approach. This approach is specifically designed to adjust OCRs. The proposed equation is contingent on a variable dynamic coefficient based on a logarithmic function curve for improving the flexibility of the curve, thus the optimal coordination between OCRs has been obtained throughout different fault modes. For enhancing the performance of the proposed approach on the OCRs coordination in the DNs, two optimization techniques, namely, the genetic algorithm (GA) and hybrid gravitational search algorithm–sequential quadratic programming (GSA-SQP) have been employed. Moreover, Due to the proposed equation including only one variable coefficient, the NSTCCs has efficaciously contributed to reducing the number of constraints to eliminate significant constraints numbers in the coordination between the overcurrent protective relays. Radial networks, including IEEE 9-bus and IEC MG systems as benchmark as well as meshed networks, namely, IEEE 9 and 30-bus systems have been used to test the proposed protection scheme. The results of the proposed optimal OCRs coordination scheme have been compared to standard and nonstandard characteristics reported in the literature. The results showed a significant improvement in terms of the protection system selectivity and reliability by minimizing the operating time (OT) of OCRs, ensuring the coordination between primary and backup relays and demonstrating the effectiveness of the proposed method throughout minimum and maximum fault modes. For radial networks based on GA, the reduction percentages of tripping time by using NSTCCs for IEC MG benchmark without DGs (mode 1), DN with DGs (mode 2) and islanded mode (mode 3) compared to the lowest OT value obtained from literature are 42.24%, 60% and 54.74%, respectively. In addition, for the IEEE9-bus radial network, the comparison is between the proposed NSTCCs, standard current characteristics (STCCs) and nonstandard scheme (NSS) recorded in the literature. The overall OT of proposed NSTCCs on mod 1, mode 2 and mode 3 is reduced by 12.06%, 17.33% and 13.55%, respectively compared to STCCs, while it is reduced by 7.05%, 9.91% and 11.42%, respectively compared to NSS. For meshed networks based on the hybrid GSA–SQP algorithm, the NSTCC approach improves the coordination interval time (CTI) between the primary and backup relays. For IEEE 9-bus system meshed network, the sum of CTI values is reduced compared to the sum of CTI values in ref from literature by 16.87%. The OT of proposed NSTCCs is reduced by 78.97% compared to STCC and 21.33% compared to NSS. Furthermore, the NSTCC decreased the total OT in the meshed 30-bus test system by 54.4% and 37.9% compared to the literature methods STCC and NSS, respectively. The suggested NSTCC technique is an important development that could greatly enhance the reliability and selectivity of power systems. Secondly, this thesis investigates the impact of immoderate fault current owing to the presence of DGs on traditional IEC characteristics. The shape of these characteristics has been adjusted to obtain such characteristics. The non-standard characteristics approach (N-SCA) has been proposed for optimal coordination of OCRs installed in DNs by extending the IEC normal inverse characteristics to fifty plug setting multiplier (PSM). Furthermore, an artificial intelligence hybrid algorithm based on water cycle moth flame optimization (HWCMFO) has been proposed as a new optimization technique in OCRs coordination protection to optimize the maximum PSM limits. Several modes have been implemented and tested with an IEC MG benchmark and carried out in MATLAB and NEPLAN software, the obtained results have illustrated the effectiveness and applicability of N-SCA based on the HWCMFO technique considering the limitation of IEC characteristics. The N-SCA outperforms the conventional approach for various fault locations in the several operational modes. For mode 1, mode 2 and mode 3, the total OT is reduced by 6.32%, 5.61% and only 0.35%, respectively. Particle swarm optimization (PSO) technique is used for comparative purposes. Using the HWCMFO technique reduced the computing speed compared to PSO by 86.59% for mode 1, 29.69% for mode 2 and 89.18% for islanded mode. Moreover, the best cost function values of the proposed HWCMFO technique is reached at less than the PSO technique for all operational modes. For mode1, mode 2 and mode 3, it is reduced by 74.26%, 63.39% and 65%, respectively. Therefore, it is demonstrated that the presented HWCMFO algorithm is suitable for identifying the global minimum objective function value in the OCR coordination.

Commercial Buildings and complexes are no longer just national heat and power network energy loads, but they are becoming part of a smarter grid by including their own dedicated local heat and power generation. They do this by utilising both heat and power networks/micro-grids. A building integrated approach of Combined Heat and Power (CHP) generation with photovoltaic power generation (PV) abbreviated as CHPV is emerging as a complementary energy supply solution to conventional (i.e. national grid based) gas and electricity grid supplies in the design of sustainable commercial buildings and communities. The merits for the building user/owner of this approach are: to reduce life time energy running costs; reduce carbon emissions to contribute to UK’s 2020/2030 climate change targets; and provide a more flexible and controllable local energy system to act as a dynamic supply and/or load to the central grid infrastructure. The energy efficiency and carbon dioxide (CO2) reductions achievable by CHP systems are well documented. The merits claimed by these solutions are predicated on the ability of these systems being able to satisfy: perfect matching of heat and power supply and demand; ability at all times to maintain high quality power supply; and to be able to operate with these constraints in a highly dynamic and unpredictable heat and power demand situation. Any circumstance resulting in failure to guarantee power quality or matching of supply and demand will result in a degradation of the achievable energy efficiency and CO2 reduction. CHP based local energy systems cannot rely on large scale diversity of demand to create a relatively easy approach to supply and demand matching (i.e. as in the case of large centralised power grid infrastructures). The diversity of demand in a local energy system is both much greater than the centralised system and is also specific to the local system. It is therefore essential that these systems have robust and high performance control systems to ensure supply and demand matching and high power quality can be achieved at all times. Ideally this same control system should be able to make best use of local energy system energy storage to enable it to be used as a flexible, highly responsive energy supply and/or demand for the centralised infrastructure. In this thesis, a comprehensive literature survey has identified that there is no scientific and rigorous method to assess the controllability or the design of control systems for these local energy systems. Thus, the main challenge of the work described in this thesis is that of a controller design method and modelling approach for CHP based local energy systems. Specifically, the main research challenge for the controller design and modelling methodology was to provide an accurate and stable system performance to deliver a reliable tracking of power drawn/supplied to the centralised infrastructure whilst tracking the require thermal comfort in the local energy systems buildings. In the thesis, the CHPV system has been used as a case study. A CHPV based solution provides all the benefits of CHP combined with the near zero carbon building/local network integrated PV power generation. CHPV needs to be designed to provide energy for the local buildings’ heating, dynamic ventilating system and air-conditioning (HVAC) facilities as well as all electrical power demands. The thesis also presents in addition to the controller design and modelling methodology a novel CHPV system design topology for robust, reliable and high-performance control of building temperatures and energy supply from the local energy system. The advanced control system solution aims to achieve desired building temperatures using thermostatic control whilst simultaneously tracking a specified national grid power demand profile. The theory is innovative as it provides a stability criterion as well as guarantees to track a specified dynamic grid connection demand profile. This research also presents: design a dynamic MATLAB simulation model for a 5-building zone commercial building to show the efficacy of the novel control strategy in terms of: delivering accurate thermal comfort and power supply; reducing the amount of CO2 emissions by the entire energy system; reducing running costs verses national rid/conventional approaches. The model was developed by inspecting the functional needs of 3 local energy system case studies which are also described in the thesis. The CHPV system is combined with supplementary gas boiler for additional heating to guarantee simultaneous tracking of all the zones thermal comfort requirements whilst simultaneously tracking a specified national grid power demand using a Photovoltaics array to supply the system with renewable energy to reduce amount of CO2 emission. The local energy system in this research can operate in any of three modes (Exporting, Importing, Island). The emphasise of the thesis modelling method has been verified to be applicable to a wide range of case studies described in the thesis chapter 3. This modelling framework is the platform for creating a generic controlled design methodology that can be applied to all these case studies and beyond, including Local Energy System (LES) in hotter climates that require a cooling network using absorption chillers. In the thesis in chapter 4 this controller design methodology using the modelling framework is applied to just one case study of Copperas Hill. Local energy systems face two types of challenges: technical and nontechnical (such as energy economics and legislation). This thesis concentrates solely on the main technical challenges of a local energy system that has been identified as a gap in knowledge in the literature survey. The gap identified is the need for a controller design methodology to allow high performance and safe integration of the local energy system with the national grid infrastructure and locally installed renewables. This integration requires the system to be able to operate at high performance and safely in all different modes of operation and manage effectively the multi-vector energy supply system (e.g. simultaneous supply of heat and power from a single system).