Analysis of DR’s AC/DC-Side Impedance Modeling Based on Harmonic Linearization

The diode rectifier (DR), characterized by its small size, light weight, and low cost, has significant development prospects in lightweight offshore converters. However, the AC/DC-side interaction between the DR and its cascaded system can easily cause oscillation. Impedance analysis is fundamental for studying the stability of cascaded systems. Based on harmonic linearization, this paper derives a frequency-domain small signal model that includes the DR’s improved switching function and commutation process. Considering the cascaded system impedances and commutation disturbance, the frequency coupling mechanism in the DR’s AC sequence impedance is analyzed. Subsequently, a detailed AC/DC-side impedance model of the DR is established, using an impedance matrix form to uniformly model both AC and DC sides, which can connect with the impedance matrix of multi-harmonic response systems. The results indicate that commutation disturbance and frequency coupling significantly affect the DR’s impedance characteristics in the mid and low frequency bands. Finally, the correctness of the DR’s AC/DC-side impedance model is verified through Matlab/Simulink simulation.