Analysed small signal state-space model of an active rectifier

This paper presents a small signal state-space model of an active rectifier. The model considers the reference frame, the variation of frequency and control dynamics. It is suitable for analysing small signal stability of active rectifier loads in networks where a small load perturbation may cause a frequency disturbance. The model is formed by separating the active rectifier into sub sections. Each subsection is modelled independently before being consolidated into a single small signal state-space equation. A sensitivity analysis of the active rectifier is also presented which identifies the states most associated with each mode. This indicates possible feedback signals for the design of controllers to improve the system stability. The model is tested using rapid prototyping power converters configured as the active rectifier itself and the system load. The laboratory arrangement allows the active rectifier to be connected to either the public network via isolation transformers or a private network where the voltage and frequency are fully controllable. During the experimentation the active rectifier is shown to have negative impedance characteristics which are known to cause destabilising effects in networks.