High Dynamics Control for MMC Based on Exact Discrete-Time Model with Experimental Validation

Due to the complexity of the system, the control of the Modular Multilevel Converter (MMC) constitutes an intensive research activity. The stored energy inside the MMC presents a new degree of freedom which can be exploited to provide ancillary services (oscillation damping for example). In order to do so, the response time of the energy loop has to be as fast as possible. However, when a cascaded approach is used to control the structure, this purpose cannot be achieved without fast inner loops. This paper presents a novel inner loops controller in order to get a high response dynamic. These controllers have been developed based on exact discrete-time models obtained from an analytic calculation of exponential of matrices. A pole placement method using feedback control has been chosen to derive their control laws. For stability matters, a pole location analysis is used to set appropriately the controller parameters which are the sampling period and the controller gains. After validation with offline simulations and in order to show the advantages of the proposed controllers compared to the existing solutions, experimental tests have been performed using a real small scale MMC.