Equivalence analysis of different sequence impedance modeling methods

The sequence impedance has a clear physical meaning and can be directly measured by commercial equipment, so it is widely used for stability analysis in the field of electrical engineering. It can be transformed from dq impedance indirectly or calculated based on Harmonic State Space (HSS) theory directly. This paper analyzes the equivalence of the above two methods. Firstly, the dq impedance model of grid-connected converter is established, and the equivalence of impedance in dq domain and sequence domain is proved by mathematical transformation. Then, modified sequence impedance model of grid-connected converter is established considering the frequency coupling phenomenon. On the other hand, the impedance model can also be obtained from HSS modeling with h order harmonics. Subsequently, the relationship between the modified sequence impedance and HSS impedance can be found. The former is a special case when the latter takes h=2. When considering the coupling effect of higher harmonics, HSS impedance model has higher accuracy. Finally, the accuracy and the equivalence of the above-mentioned two methods are verified by frequency sweep.