DQ-Transformation Approach for Modelling and Stability Analysis of AC-DC Power System with Controlled PWM Rectifier and Constant Power Loads

In this paper a technique for analysing aircraft frequency wild power systems with constant power loads is developed and demonstrated. Power electronic based loads often behave as constant power loads, especially when feeding machine or actuator drives under current and speed control. The constant power (CP) loads can affect the stability of the power system. The problem is a particular issue in aircraft power systems as the proportion of CP loads increases with the advent of the more-electric aircraft. This paper deals with stability analysis of a three-phase frequency-wild AC power system with a CP load fed through a vector-controlled front-end PWM converter. The mathematical model suitable for stability analysis is derived using the DQ-transformation method. It is shown how the proposed approach can be applied to study the power system behaviour under different loads and parameters variations, as well as to assess the power system stability margins. The study is supported by intensive simulations that verify the reported theoretical results.