Abstract
Distributed Generators (DGs) connected to the network integrally affects the feeder voltage profiles in distribution systems. In recent years, a growing number of DGs to the distribution networks demand appropriate attention for smart voltage control techniques. Electric utilities conventionally maintain distribution voltage within an acceptable limit using transformer tap changer located at Medium Voltage (MV) side. Traditionally, tap changers receive control signals from single bus and change the tap positions to maintain voltages accordingly. Penetration level, location and intermittent behaviour of the DGs integrated with the distribution system will change this trend. In this research, UK Low Voltage (LV) network with renewable inverter based DGs is modelled on Matlab/Simulink and On-Load Tap Changers (OLTC) are installed at both MV and LV transformers. Conditional controller is designed to pick up the most appropriate signals from different buses to change the tap position of transformer. Energy storage batteries, acting as active load, are analysed along with OLTC to maintain voltages within statutory limits. Recommendation of integrating Energy Storage Systems (ESS) at distribution network is discussed in this research to level up the load profile and stabilize the system voltages.Penetration level of renewable energy such as solar and wind power into the grid is sharply increasing worldwide. Renewable roof top DGs power production more than consumption would allow the power to flow in reverse direction. The flow of active power on LV network in reverse direction would affect the radial feeder overcurrent protection along with voltage level. Impact of increasing level of renewable roof top inverter based DGs on the UK distribution network protection is investigated. Studies were commenced to mitigate the effect of small scale embedded generation (SSEG) on the system fault levels. Residential inverter based DGs penetration level is modelled on the UK typical low voltage network considering the fault level stability limits. Based on the penetration level of DGs, energy storage in the form of battery bank is determined to charge and discharge according to daily load cycle. Short circuit analysis results are compared with the UK passive network to investigate the impact of the DGs on the short circuit currents at the distribution transformer. In this study, power flow from the transformer secondary is kept within limits to avoid malfunctioning of relays. The flow of reverse power in the presence of inverter based DGs is confined by energy storage elements. EVs batteries are represented as active power load to manage the flow of short circuit current.
The inherent intermittency of the solar and wind power generation poses one of the great challenges to next generation smart grid. Battery Energy Storage Systems (BESS) are used to curtail the power during time when the system has low demand. These systems are capable of absorbing and delivering real power to grid. High penetration level of inverter based renewable DGs would lead to reduce the inertia of grid by desynchronizing the conventional expensive synchronous generators. Inertia less inverter based DGs would reduce the transient stability of existing distribution network. In this research, the impact of battery storage systems on the transient stability of low inertia distribution network with high penetration level of inverter based DGs is investigated. Energy storage batteries are found to have a positive impact on the transient stability.
Electrical Vehicles (EVs) are widely promoted in many countries nowadays as a tool to offset the C02 emission from transportation. Therefore, battery storage and Battery Electric Vehicles (BEV) are anticipated to play a vital role in the Distribution Network (DN). The power flow and quality will be affected by the penetration level of the BEV. Voltage variation, losses, harmonics and charging efficiency are the indicating factors to be observed in the DN, particularly the residential sector. It is expected that these factors are affected by the EV owner behaviour, the local load status and greatly by the environment. In this research, lead acid battery is charged inside environmental chamber at different temperatures. Power quality parameters like Total harmonic Distortion of Current (THDi), efficiency of charger and Power Factor (PF) etc. are investigated during charging cycle of the battery. The environmental impacts and load status on the battery behaviour have been studied. Computer simulation using Matlab/Simulink and experiment tests are conducted to identify the controlled variable(s) that could be used by the smart meter to regulate the DN operation under different operating conditions.
| Date of Award | 2016 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Mohamed Emad Farrag (Supervisor) |