This paper proposes a novel modulation technique to be applied to multilevel voltage-source converters suitable for high-voltage power supplies and flexible ac transmission system devices. The proposed technique can generate output stepped waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. The main power devices switch only once per cycle, as is suitable for high-power applications. In addition to meeting the minimum turn-on and turn-off time requirements for high-power semiconductor switches, the proposed technique excludes from the synthesized waveform any pulses that are either too narrow or too wide. By using a systematic method, only the polarities and the number of levels need to be determined for different modulation levels. To verify the theory and the simulation results, a cascaded converter-based hardware prototype, including an 8-b microcontroller as well as modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for the reduction of harmonics in multilevel converters, and both the theoretical and simulation results are well validated. Index Terms-High-voltage power supplies, multilevel converters, pulsewidth modulation. I. NOMENCLATURE Number of switching angles. th level dc voltage. Odd harmonic order. th switching angle. Minimum turn-on time of the semiconductor device. Minimum turn-off time of the semiconductor device. Maximum function. Line frequency. Amplitude of the fundamental component. Amplitude of the th harmonic voltage. Voltage of dc sources. Multilevel modulation index. II. INTRODUCTION R ECENTLY, multilevel voltage-source converters have become an important technology in high-power applications. Several multilevel converter topologies [1]-[4] and modulation Manuscript
This paper proposes a novel modulation technique applying in multilevel voltage source converters suitable for high voltage power supplies and flexible ac transmission system (FACTS) devices. The proposed technique can generate output stepped-waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. 'The main power devices switch only one time per cycle, suitable for high power applications. For the proposed harmonic reduction technique, the theoretical analysis is presented. By using a systematic method, only the polarities and the number of levels are required to be determined for different modulation levels. Computer simulation results are then provided. To verify the theory and the simulation results, a cascade inverter based hardware prototype including a low cost 8-bit microcontroller and modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for harmonic reduction in multilevel converters, and that both theoretical and simulation results are well validated.
With the rapid increase in photovoltaic (PV) power generation in microgrids, PV power fluctuations can initiate negative impacts on microgrid operations. This study presents a simulation analysis of PV power smoothing method based on hull enhanced linear exponential smoothing (HELES) technique using an energy storage system (ESS). The proposed method is employed to mitigate PV power fluctuations in microgrid systems. The ESS is allowed to charge and discharge for smoothing the PV output power based on a smoothing power reference provided by the HELES technique. The proposed method is investigated to acquire the smoothing performance considering smoothness and smoothing accuracy. In simulation analysis, the proposed method is analysed on the microgrid under both grid-connected and islanding modes to obtain its dynamic performance. The simulation results demonstrate that the proposed method evidently offers superior smoothing performance compared with the existing methods. Accordingly, the smoothing accuracy is successfully improved, and the ESS capacity is significantly reduced by improving smoothing accuracy. Moreover, the smoothness is effective to mitigate PV power fluctuations by using the proposed method. Eventually, the dynamic performance can be satisfactorily improved, and state of charge variation is reduced and also conserved to be available for unexpected PV power fluctuations.
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