Abstract
Over the last decades, plants devoted to the generation of green energy significantly increased their number, together with the demand of same electrical energy, also stored in battery systems. This fact produced the growth of energy conversion systems with advanced performances with respect to the traditional ones. In this circumstance, multilevel converters play a significant role for their great advantages in performances, flexibility, fault-tolerability, employment of renewable energy sources and storage systems and finally yet importantly reduced filter requirements. In this context, this paper faces the performance of a cascaded H-bridge 5 level inverter in terms of harmonic distortion generated and injected into the grid. Through an accurate analysis that takes into account the pulse width modulation (PWM) multicarrier modulation techniques (phase disposition PD, phase opposition disposition POD, alternative phase opposition disposition APOD, phase shifted PS) and related reference signals (sinusoidal reference; third harmonic injection THI reference, switching frequency optimal SFO reference), a framework of distorting harmonics is presented by comparing twelve cases. The results obtained from the simulations are reproduced and validated in a prototype system of five level cascaded H-bridge multilevel inverter. A deep discussion of control and filtering system is provided to justify the choice of the best modulation technique to adopt.
Highlights
The increased demand of green energy has led to the development of even more performing structures allowing the generation and storage of energy in DC form
Aim of this section is to design the LCL filter parameters with the step-by-step method for each modulation techniques taken into account
LCL filter requirements andSwpitachrianmg fereteqursencoyf regulators were deter1m0 kiHnzed in the precedent sub-sections (2.2I.ndLucCtaLncFeialntedrreDsiestsaingcne oaf nthde t2ra.3ns.foCrmoenrt(rloowllesirdeDreepsiogrtned).) In108t.h23eμfHol2l5owmΩare reported the results obtaineLdCLinfilstiemr rueqlautirieomneanntsaalnydsipsafroamr eetaecrshomf roegduulaltaotrisownetreecdhenteirqmuineesdtainkethne ipnretocedaecnctosuunb-t and have been compseacrteiodnsth(2e.2r.eLsCuLltFsilatemr oDnesgigtnheanmd o2.d3.uClaotnitoronllewr iDthestighne).sIanmthee cfaolrlroiwerarseigrnepaolrst.ed the results obtained in simulation analysis for each modulation techniques taken into account and have been
Summary
The increased demand of green energy has led to the development of even more performing structures allowing the generation and storage of energy in DC form. The carrier number nc of the level shifted multicarrier PWM in function of the number of the converter level nL, is equal to: nc = nL − 1 These strategies lead to elimination of all carriers and related sideband harmonics up to the switching frequency. For a five-level inverter two carrier signals with mutual phase shift equal to π/2, Figure 2b, are necessary. This scheme leads to elimination of all carriers and associated sideband harmonics up to the 2nHB times of the switching frequency. The FPGA (field programmable gate array) is another example of digital controller, composed by a matrix of configurable logic blocks (CLBs) with completely reprogrammable connections This fact leads to a higher flexibility with respect to a DSP, allowing the realization of specific hardware structures in dependence of the nature of applications. The FPGA system significantly reduces the execution time of the control algorithm, increasing, the performances of the related system
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