Design and stability analysis in photovoltaic systems with quasi-Z source inverters and multi-terminal connection to the AC network

Photovoltaic (PV) energy systems are becoming one of the most popular green energy systems. Power converters are used in these systems. Among these, the use of quasi-Z source inverters (qZSI) is growing. However, instabilities can appear in multi-terminal grid-connected AC power electronics, such as PV power systems, due to the interaction between the power electronics controls and the grid. The literature lacks models of qZSI-based PV systems, and the stability assessment of grid-connected qZSI-based PV systems is still not well known. This paper provides a dq-real admittance transfer matrix model in qZSI-based PV system domains derived from the small-signal average state space model. A systematic procedure to study multi-terminal qZSI PV systems connected to the AC grid using the nodal admittance method is also described, in which the proposed qZSI PV system model is incorporated into the nodal admittance matrix to study the stability problems. Thus, the AC network dynamics in the presence of qZSI-based PV systems can be investigated using impedance-based stability criteria. The proposed model and procedure are applied in a stability study of two applications where solutions are presented to improve the stability problems. In these applications, the two main causes of instability in PV-qZ systems connected to the AC grid are analyzed in detail. The study is validated using PSCAD/EMTDC simulation.

Published paper:

Model of quasi-Z-source inverter-based PV power systems for stability studies of multi-terminal AC grid-connected PV power systems
Monjo, L.; Sainz, L.; Pedra, J.
International Journal of Electrical Power & Energy Systems