Small-disturbance Linearization Method for Converter Interfaced AC Power Systems Based on Operating Points of Internal-voltage Amplitude/frequency and Networks’ Active/reactive Current

Increasingly frequent occurrences of oscillations with unknown mechanisms in today’s power system ask for returning to the energy exchange essence of oscillation to understand and analyze system dynamics. Units have to regulate their internal-voltage amplitude/frequency(A/F) once the imbalance between input and output active/reactive(A/R) power or current arises after disturbances, and then in networks A/R current and power of output port in each unit are further adjusted. In this closed-loop dynamic process, energy stored by units corresponding to internal-voltage A/F and that stored by networks corresponding to A/R current exchange with each other on a certain energy storage level. Thus, operating points and relevant small disturbance relationships for system dynamic analysis have to be defined and built both from internal-voltage A/F and A/R current representing system energy. However, due to lacks of understandings on above energy connotation contained in dynamics, existing studies rarely understand and analyze AC system dynamics from the perspective of energy exchange. This paper therefore aims to propose a small disturbance linearization method of AC power systems based on internal-voltage A/F and A/R current operating points. Taking a converter interfaced AC power system as an example, by elaborating energy exchange mechanism on a certain energy storage level between converter and networks in dynamics of internal-voltage A/F and A/R current being updated iteratively under constraints of original system structure and its closed-loop operation principle transferring A/R power, this paper clarifies steady internal-voltage A/F and A/R current as operating points of AC systems’ dynamic analysis and their physical connotations representing energy storage level. Based on above operating points, small disturbance nonlinear relationships of converter and networks among internal-voltage A/F and A/R current as well as physical cognition and corresponding mathematical method of their linearization are presented. The applicability of relevant linearized relationships is then shown by simulation, and dynamic behaviors of AC and DC electrical variables are explained at last. © 2024 Chin.Soc.for Elec.Eng. 1081.