This paper presents a generalized multilevel direct power control (ML-DPC) scheme for grid-connected multilevel power converters. The proposed method extends the original DPC operating principle by considering only the closest subset of two-level voltage vectors to the present switching state. The implementation of this principle requires the power derivatives for feedback, which can present numerical problems when applied experimentally, mainly due to high measurement noise sensitivity. Therefore, a derivative estimator is proposed based on the converter-grid model in the synchronous reference frame. In addition, a virtual flux observer is developed to achieve synchronization and improve robustness in the presence of grid voltage harmonics. The proposed method is applicable to any multilevel converter topology of any number of levels. In this paper, simulations and experimental results are presented for a seven-level cascaded H-bridge converter.

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This paper proposes a new power converter topology for the Wave Dragon multi-megawatt wave energy conversion platform. The current wave dragon power converter system is composed of several low-voltage two-level voltage source converters in back-to-back configuration; one per turbine-generator. Although this is a well known and proven technology, the use of distributed power electronic converters among all turbines does not bring any additional benefit in terms of efficiency and power quality. The proposed topology remains operating at low voltage and distributed at the generator side, but is combined at the grid side into a three-phase cascaded H-bridge (CHB) multilevel converter operating at medium voltage. This is achieved interfacing each PMSG through a low-voltage full bridge diode rectifier, followed by a boost dc-dc converter connected to the dc-link of the power cells of a 7-level CHB. The proposed configuration allows to concentrate the whole Wave Dragon platform into a single grid-tied converter with higher power quality and efficiency. Control schemes for both grid- and generator-side converters, and simulation results are presented in this paper.@en

This paper presents a generalized direct power control (DPC) scheme for grid connected multilevel converters. The proposed method extends the original DPC operating principle by considering only for selection the closest vectors to the present switching state. This approach requires the power derivatives for feedback, which can present numerical implementation problems in real time. Therefore a grid virtual flux based observer is proposed to overcome this issue. The proposed method is applicable to any multilevel converter topology of any number of levels. In this paper simulations results are presented for a 9 level cascaded H-bridge converter. The proposed solution enables DPC for multilevel converters used in medium voltage applications while improving overall power quality and efficiency of the system.@en