Analysis of motor starting in a weak microgrid

Induction motor loads form an integral part of any electrical load network and possess a unique characteristic. The high reactive power drawn from the system by motor during start up causes voltage drop which may affect other loads in the network. This drop is more pronounced in a weak microgrid, which do not have the capability to quickly compensate the drop. The only way to determine voltage drop due to starting current or vice-versa is simulation studies. The initial work is aimed at filling this gap by providing a methodology to determine a relationship between the starting current and the voltage drop as a function of short circuit current values at that point. The impact of motor starting on the voltage profile is studied for a standard network. Subsequently, a control methodology is proposed for an inverter based source to improve the power quality during motor starting. The methodology makes use of the existing infrastructure with limited additional investments, if any to cater to reactive power requirements during motor starting. For study, a network energized by inverter interfaced photovoltaic array and a generator is considered. The studies have been performed based on computer simulation carried out using PSCAD™/EMTDC™ software package.