Sizing Local Storage based Li-ion Ultra-capacitors Preventing Sags and Swells of a Voltage in Distribution Networks with PV Plants

Local and distributed PV solar plants become more and more widespread power generating facilities providing significant percentage of electricity supply. Together with numerous advantages massive rooftop PV installations (up to 5-10 kW) and utility-scale local plants of 5-20 MW in the low (LV) and middle (MV) voltage distribution networks produce a problem for voltage regulation. Rapid deviations in PV power inherent in this type of energy generate uncertainty in voltage control. Tap changers which are applicable to this purpose have sluggish reaction and occasionally couldn't be able to compensate fast changings of solar electricity. Together with the fluctuations of the consumer's power demands such disturbances can cause dangerous voltage instabilities. As a result, the protection system should disconnect PV stations from electricity supply what negatively affects electricity costs and reliability of the network. One of the possible solutions for mitigation voltage deviations is intermittent energy storage based on ultracapacitors (UC) usage. UC application can improve the voltage stability hence increasing complexity of energy equipment and energy costs. Therefore, the selection of UC bank should be done suitably considering technical and economic aspects of the problem. Current work represents a solution for improving the situation with local voltage regulation based on the appropriate selection of UC bank.