Analysis for low frequency oscillation on the DC side of AC/DC distribution network based on PET control characteristics

Abstract

With the development of new energy, energy storage, and flexible DC technology, AC/DC hybrid distribution networks have gradually become an important development direction for future distribution networks. The access of a large number of power electronic devices has brought dynamic problems such as low frequency oscillations to the distribution network. In order to deeply study the low frequency oscillation problem on the DC side of AC/DC distribution networks, detailed modeling of key links is conducted such as H-bridge series and isolated bidirectional active bridge structures, three-phase inverters, and three-phase Buck converters in the main valve tower of power electronic transformer. Through time domain simulation, the 4 Hz low frequency oscillation phenomenon on the DC side of the AC/DC distribution network in the actual project is reproduced, and the correctness of the established mathematical model is verified. Based on the established mathematical model, qualitative analysis is conducted on key influencing factors such as power and controller parameters, and the final conclusions are as follows: power level and Buck link voltage loop control parameters affect system stability, the integral coefficient of the current loop in the Buck link affects the oscillation frequency.

Keywords

• ac/dc distribution network
• power electronic transformer
• low frequency oscillation
• three-phase buck converters
• time domain simulation
• causes of oscillation