Influence of load characteristics on system dynamics and load-shedding control effects in power grid

Diversified load characteristics may cause utterly different system dynamics such as the frequency dynamic and voltage dynamic, thus having different influence on under-voltage and under-frequency load-shedding control effects. This paper analyzes the four load characteristics such as the constant impedance load, the constant current load, the constant power load and the induction motor. These four loads responses differently and have different active/reactive power dynamics during separations in the power grid. Simulations illustrate that the induction motor may lead to severe oscillations and voltage collapses due to the lack of reactive power supply, thus triggering under-voltage load-shedding control. However, the ZIP loads tend to cause frequency drop because of insufficient active power supply, thus triggering under-frequency load-shedding control. In addition, unlike the ZIP loads, the induction motor is more likely to result in system instabilities after executing the same magnitude of load curtailments. Therefore, it is imperative to execute load shedding at the induction motor first in order to guarantee both the frequency stability and voltage stability.