# The Impact of Distributed Energy Storage on Distribution and Transmission Networks' Power Quality
## 2 Methodology  
Harmonics, system reliability (interruptions due to voltage frequency perturbations arising from insufficient loading or overloading of the network), and voltage characteristics are all factors to consider when evaluating power quality (i.e., voltage swell, short-term voltage sag, or voltage phase angle shift as a result of a load which is usually connected to the network at a particular point). This study examines the impact of ESS on the transmission and distribution system's power quality voltage characteristics, specifically the compensatory effect of BESS on the voltage magnitude and phase angle parameters of power quality. It must be mentioned that the voltage angle is an important factor in the system's power quality since it plays a significant role in the efficiency with which energy flows through the system. The current and voltage waveforms should both be sinusoidal and in-phase (aligned with each other) such that maximum useful power flow is achieved. The power factor describes how much of the voltage and current is producing useful (active) power with respect to the maximum it could be delivering. For linear loads that only have resistance, capacitance, and inductance, the voltage and current waveforms remain sinusoidal, and only the phase/alignment of the waveform changes. When the voltage and current waveforms are not in phase, the power factor drops below 1. A Static Synchronous Compensator (STATCOM) has not been used in the current analysis. Although STATCOM has excellent behaviour in reactive power control and in voltage stability, it cannot respond to power flow control and harmonic reduction [35]. A BESS has multiple applications as a grid supporting unit. Most common applications consider the ability of a BESS to decouple electric power generation and consumption in different contexts. A grid consisting of renewable energy sources connected with power electronic converters can experience difficulties with harmonic voltages and reactive intrush currents. Reactive currents may cause a voltage drop in the line impedances. A BESS can be used to simultaneously exchange active power between the battery and the grid and improve the power quality of a microgrid. With independent cascaded control of currents and active and reactive power, a BESS can control the reactive power balance and therefore ensure voltage stability [36]. The following research questions determine the scope of this project:  
* Determine whether ESS integration within the power system may be used to regulate the defined power quality parameters within the UK Electricity System Grid Code [37] for voltage magnitude and normalize the variation in voltage phase angle within the 5% compliance processes band. * Compare and contrast the impact of centralized versus distributed ESS integration design on power quality compensation. * Determine if distributed integration topology has a greater impact on power quality compensation at the distribution or transmission network level. Voltage rise is the main limiting factor for the integration of photovoltaic (PV) generation in low voltage networks. Inverter voltage control techniques have been developed to provide effective voltage control and support higher penetration of PV generation integration [38]. In most cases, the use of PV-inverter is for overvoltage limitation than to face undervoltage problems. However, PV inverter would be effective in the grid's topology presented in this paper under certain conditions. The case of PV inverters has not been studied because there are some reasons that BESS are more preferable to PV inverters. To be more specific, BESS operate at night, and their role is crucial when it is getting dark, when the electric load usually has its highest peak, helping as well in voltage regulation. BESS also:  
1. Have the ability to act as both load and generator, depending on the real power reference and the state of charge;
2. Can act as a reference bus in islanded operation, setting frequency and bus voltage;
3.