Effect of load models on AC/DC system stability and modulation control design

An investigation is conducted of the effect of load models on the modulated AC/DC system. Static load is modeled as a nonlinear function of load bus voltage, and dynamic load is modeled by an equivalent induction motor. DC power and relative power modulations are considered for the modulation controllers. A method for eigenvalue sensitivity calculation is developed to predict the effect of load characteristics on the system stability. Eigenvalue sensitivity and simulation results show that static and dynamic load characteristics can have a considerable effect on the system stability. The impact of static and dynamic load modules on the modulation controller gains obtained via optimal control theory is examined and it is shown that load models can have a marked influence on the controller gains. It is also shown that there are specific situations where the choice of load model can make a difference in system stability prediction