Probing the Impact of Reduced DC Capacitor Size in Variable Speed Drive Loads on Voltage Stability of the Distribution Network at High PV Penetration

Abstract

The Variable Speed Drives (VSD) are anticipated to replace the Induction Motors (IM) by 50%, in 2020, in developed cities of Europe [1]. Therefore, it is essential to incorporate VSD loads while analyzing voltage stability studies in the distribution network with high PV penetration. The collective load response from VSD loads tend to slow the rate of change of node voltages of distribution system, during the PV ramping events. However, this dynamic load characteristic of VSD is dependent on its capacitor size. Meanwhile, there is trend for reducing the capacitor size in VSD load at equipment level. Thus, this paper investigates the impact of reducing DC capacitor size in VSD load, on voltage stability of distribution system during PV ramping events. For the investigation, the paper involves United Kingdom General Distribution System (UKGDS) where load is modeled with combination of static load, IM, and VSD. It is determined that the maximum PV penetration reduces from 80% to 50% when the capacitor size in VSD is lowered from $360\mu F/kW$ to $25\mu F/kW$ respectively. Furthermore, the increased VSD penetration could delay and even avert the voltage collapse from PV ramping events during grid contingency condition. It is revealed that the minimum VSD penetration required to avert instability during such condition, even at 100% PV penetration, increases from 50% to 65% when the capacitor size of VSD is reduced from $360\mu F/kW$ to $25\mu F/kW$ respectively.