A UPFC for Voltage Regulation in LV Distribution Feeders With a DC-Link Ripple Voltage Suppression Technique

The large-scale integration of distributed photovoltaic generation causes several power quality issues in low voltage (LV) distribution networks. Network voltage profile variations severely affect the LV distribution networks. The four-leg unified power flow controller (4L-UPFC) has series and shunt converters that can address the power quality issues. However, instantaneous power theory shows that second-order harmonic voltage (2ωHV) appears at the dc-link capacitor of the 4L-UPFC during any unbalanced operations. This article proposes control strategies for series and shunt converters that will simultaneously regulate the load voltages of a distribution feeder while suppressing the 2ωHV term on the dc-link of the UPFC. A controlled negative sequence current from the shunt converter is used to suppress the 2ωHV term on the dc-link. The active suppression of the 2ωHV term allows electrolytic capacitors to be replaced with small long life ceramic or film capacitors, and this does not require additional passive compensation. Stability analysis of the control loops demonstrates the overall stability of the converter system. The proposed control methods have been implemented on a Texas DSP (F28377D). An experimental demonstration on a laboratory scale prototype shows that the proposed control methods can effectively regulate the load voltages at LV distribution feeders and suppress the 2ωHV on the dc-link of UPFC during unbalanced loads and supply conditions. © 1972-2012 IEEE

Power quality impacts and mitigation measures for high penetrations of photovoltaics in distribution networks

© Springer International Publishing AG 2017. Island power systems often have high costs of generation in comparison to most large-scale continental power systems due to a high reliance on diesel generation. Many island systems are small with many being sub-megawatt in size. Apart from the issues of the economies of scale, the costs in island systems are increased by the difficulties of remoteness in terms of fuel delivery and access for maintenance. Island systems often have access to good renewable resources such as wind, biomass and solar resources. These have been successfully harnessed in many systems to reduce the reliance on diesel generation. Island power systems often have very high fractions of renewable energy. Many renewable technologies are now mature and reliable and the costs of solar systems have continued to reduce. The economics of the situation drive increasing interest and usage of PV systems. Some technical challenges emerge once a considerable fraction of the consumer energy is to be supplied from renewable sources. These key issues are intermittency and voltage control. Intermittency is reduced with a technology diversified and a spatially diversified portfolio of generation sources. Highly responsive backup generation, load demand control and storage are often used to compensate for the intermittent generation of renewables. Voltage can be easily controlled in new systems that are specifically designed to work with renewables. Older systems may need modifications such as partial reconstruction or the retrofitting of regulation devices