Disturbance-State Modeling and Oscillation Analysis of Modular Multilevel Converters under P/Q Control Mode

Abstract

To investigate the oscillation problems in power systems with modular multilevel converters (MMCs), a disturbance-state model of the MMC under P/Q control mode is established based on the harmonic state-space (HSS) method. Firstly, the basic structure of the MMC with P/Q control is presented, including the circuit structure and the controller structure. Next, the dynamic characteristics of each module in the MMC are described with the time-domain state-space model or the s-domain transfer function. The complete controller structure is considered, including the P/Q outer-loop controller, the inner-loop control, the phase-locked loop (PLL), the circulating current suppression control (CCSC) and the control delay. On the basis, the disturbance-state HSS model of the MMC and its corresponding steady-state condition are established by the HSS method. Lastly, the case studies are performed to verify the accuracy of the proposed model, based on an MMC based test system in PSCAD/EMTDC. Moreover, one oscillation phenomenon in test system is illustrated by analyzing the AC-side impedance characteristics based on the proposed model. The results indicate that the MMC system under P/Q control mode has certain oscillation risk due to its negative resistance effect and the proposed model could be applied to its oscillation analysis.

Review of Dynamic and Transient Modeling of Power Electronic Converters for Converter Dominated Power Systems

“…Frequency and harmonic stability analysis has been performed in the literature with small-signal models. The review performed by [77] investigated the concept and history of harmonic stability analysis and the use of linearized models identified in [25], [81]- [84] to capture harmonics. A harmonic state-space small-signal average model was used in [71] to examine the harmonic interaction between inverters and the grid voltage, and it was validated for the time and frequency domain.…”