Browsing by Keyword "Capacitor voltage ripples"
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Item Closed-loop discontinuous modulation technique for capacitor voltage ripples and switching losses reduction in modular multilevel converters(2015-09-01) Picas, Ricard; Ceballos, Salvador; Pou, Josep; Zaragoza, Jordi; Konstantinou, Georgios; Agelidis, Vassilios G.; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn this paper, a new discontinuous modulation technique is presented for the operation of the modular multilevel converter (MMC). The modulation technique is based on adding a zero sequence to the original modulation signals so that the MMC arms are clamped to the upper or lower terminals of the dc-link bus. The clamping intervals are controlled according to the absolute value of the output current to minimize the switching losses of the MMC. A significant reduction in the capacitor voltage ripples is achieved, especially when operating with low modulation indices. Furthermore, a circulating current control strategy suitable for this modulation technique is also proposed. Simulation and experimental results under various operating points are reported along with evaluation and comparison results against a conventional carrier-based pulse width modulation method.Item Discontinuous modulation of modular multilevel converters without the need for extra submodules(Institute of Electrical and Electronics Engineers Inc., 2015) Picas, R.; Ceballos, S.; Pou, J.; Zaragoza, J.; Konstantinou, G.; Agelidis, V. G.; Balcells, J.; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn this paper, a new approach to the discontinuous modulation technique for the operation of the modular multilevel converter (MMC) is presented. Discontinuous modulation is based on adding a zero-sequence to the original modulation signals so that each MMC arm is clamped to the upper or lower terminals of the dc-link bus during some intervals. In combination with a circulating current control, the original discontinuous modulation can reduce the capacitor voltage ripple amplitudes and the switching power losses. However, additional submodules (SMs) are required to control the circulating current. This new approach presents a clamping algorithm that eliminates the requirement of additional SMs. As a result, the conduction losses are reduced while the capacitor voltage ripples are maintained low. Simulation and experimental results on a silicon-carbide-based MMC are reported and compared against the original discontinuous modulation and a conventional carrier-based pulse-width modulation.Item Submodule power losses balancing algorithms for the modular multilevel converter(IEEE Computer Society, 2016-12-21) Picas, R.; Pou, J.; Zaragoza, J.; Watson, A.; Konstantinou, G.; Ceballos, S.; Clare, J.; POWER ELECTRONICS AND SYSTEM EQUIPMENTTolerance and component aging can cause significant differences in the capacitance values of the submodules (SMs) in a modular multilevel converter (MMC). Depending on the modulation technique, capacitance mismatches may produce uneven switching transitions of the SMs, hence imbalances in the power losses that can lead to reliability problems. In this paper, a new algorithm that helps to achieve evenly distributed switching and conduction losses within the converter SMs is presented. The proposed algorithm is based on a modification of the common voltage balancing algorithms, balancing a weighted function of voltage and losses. Even distribution of power losses is achieved at the cost of slightly increasing the capacitor voltage ripples. The effectiveness of the strategy has been demonstrated by simulation results of a high-power grid-connected MMC.