Impact of Integrated Hybrid PV/Wind Generation on Harmonic Power Flow in Medium-Voltage Grid

Abstract

The renewable energy sources such as wind energy or solar energy play an increasingly significant role as electric supply resources and as an integral part of the electrical grid. The negative influences on the power quality of renewable energies derive mainly from two typical characteristics of renewable sources: their randomly varying availability which can lead to frequency variation, to grid insta-bility, and to a total or partial loss of load power supply and the presence of a static converter as output interface of the generating plants that introduces voltage and current harmonics into the electrical system that negatively affect the system power quality. As the availability of wind varies in a different manner than the sun radia-tion does, the hybrid wind/photovoltaic (PV) generation may increase the resultant availability and consequently reduce the negative impact on power quality of the voltage and current of the host network. One of the many aspects of power qual-ity is the harmonic content of voltages and currents. Harmonics can be analyzed in either the frequency domain or in the time domain with post-processing using Fourier analysis. This chapter uses the Power Factory software to carry out the analysis of harmonics in the integrated power system in the frequency domain. The analysis comprises harmonic power flow including harmonic power flow according to International Electrotechnical Commission (IEC) 61000-3-6 and flicker analysis according to IEC 61400-21. Harmonic load flow calculates actual harmonic indices related to voltage or current distortion and harmonic losses caused by harmonic sources (usually nonlinear loads such as current converters). In the harmonic power flow calculation, the program carries out a steady-state network analysis at each frequency at which harmonic sources are defined. The flicker analysis performs the calculation of long-and short-term flicker disturbance factors introduced by wind turbine generators. The effect of renewable units on the host grid depends, among other things, on the grid topology. Therefore, this impact on the power quality is studied using a typical medium-voltage (20 kV) distribution network. The test grid is a 20-bus distribution 82 A. Hamzeh and A. Sandouk system including 12 transformers, 7 cables, 7 × 20 kV buses, 6 × 0.69 kV buses, 7 × 0.4 kV buses, and 5 general loads. A wide range of simulations have been carried out, and the simulation results have been thoroughly discussed, and very important findings have been concluded. The conclusions would be a useful aid for planning and operation of renewable integration in medium-voltage distribution systems.