Harmonic Impact Of Inverter Based Distributed Generation And Optimal Harmonic Control Using Improved Gravitational Search Algorithm

Presence of distributed generation (DG) in the distribution system may lead to several advantages such as voltage support, loss reduction, deferment of new transmission and distribution infrastructure and improved system reliability. However, when inverter based DG is connected to a distribution system, it may contribute to power quality problem such as harmonic distortion and resonance. The effect of harmonic not only presents a severe power quality problem but it can also trip protection devices and cause damage to sensitive equipment. In this research, the first objective is to investigate the harmonic impact of different types of DG. For this purpose, a comprehensive study is made to compare the harmonic distortion produced by the different types and number of DG units in a low voltage distribution system. Here, three types of DG units are considered, namely, a mini hydro power, wind turbine doubly fed induction generator and photovoltaic system. The second objective is to determine the maximum allowable penetration level of inverter based DG by considering the harmonic resonance phenomena and harmonic distortion limits. Simulations were carried using the MATLAB/SimPowerSystems software to investigate the impact of DG at different penetration depths. To control harmonic propagation in a distribution system with DG units, an appropriate planning of DG units is considered by determining optimal placement, sizing and voltage control of DG units. Thus, the third objective of this research is to develop an effective heuristic optimisation technique such as improved gravitational search algorithm (IGSA) technique for determining the optimal placement, sizing and voltage control of DG units in a radial distribution system. A multi-objective function is formulated to minimise total power losses, voltage total harmonic distortion (THDv) and voltage deviation in a distribution system. The loadflow algorithm from MATPOWER and harmonic loadflow are integrated in the MATLAB environment to solve the multi-objective optimisation problem. The proposed IGSA technique is compared with other optimisation techniques, namely, particle swarm optimisation (PSO) and gravitational search algorithm (GSA). Test results on the harmonic impact of inverter based DG show the presence of resonance phenomena and harmonic distortion due to the interaction of the inverter based DG and grid impedance. Moreover, the results also indicate that the maximum permissible penetration level of inverter based DG in the test distribution system is found as 50% of total connected load. Four case studies on an IEEE 13 bus and 69 bus distribution system have been conducted to validate the effectiveness of IGSA. The optimisation results shown that IGSA gives the best fitness value and the fastest average elapsed time compared to PSO and GSA