Abstract-Three-phase multilevel inverters are used in many medium-and high-power applications such as motor drives and grid-connected systems. Despite numerous PWM techniques for multilevel inverters have been developed, the impact of these modulation schemes on the peak-to-peak output current ripple amplitude has not been addressed yet. In this paper the analysis and the comparison of current ripple for two-and three-level voltage source inverters are given. Reference is made to optimal and popular modulation, so-called centered PWM, easily obtained by both carrier-based modulation (phase disposition, with proper common-mode voltage injection) and space vector modulation (nearest three vectors). It is shown that the peak-to-peak current ripple amplitude in three-level inverters can be determined on the basis of the ripple in two-level inverters, obtaining the same results as by directly analyzing the output voltage waveforms of the three-level inverters. This procedure can be readily extended to higher level numbers. The proposed analytical developments are verified by both numerical simulations and experimental tests.Index Terms-Multilevel inverters; three-level inverter; output current ripple; carrier-based PWM; space vector PWM.

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Determination of current ripple in three-phase PWM voltage source inverters (VSI) is important for both design and control purposes, since this is the most popular conversion topology for energy conversion systems. In this paper the complete analysis of the peak-to-peak current ripple distribution over a fundamental period is given for three-phase VSIs. In particular, peak-to-peak current ripple amplitude is analytically determined as a function of the modulation index. Minimum, maximum, and average values are also emphasized. Although the reference is made to continuous symmetric PWM, being the most simple and effective solution to minimize the current ripple, the analysis could be easily extended to either discontinuous or unsymmetrical modulation, both carrier-based and space vector PWM. The analytical developments for all the different subcases are verified by numerical simulations.I.

This paper presents the novel topology of Photo Voltaic (PV) power generation system with simple Maximum Power Point Tracking (MPPT) algorithm in voltage operating mode. Power circuit consists of high output voltage DC-DC boost converter which maximizes the output of PV panel. Usually traditional DC-DC boost converters are used for such application, but they are not the most suitable solution due to output limitation, lower efficiency and require more sensors with complex control algorithm. Further on, the effects of parasitic elements are suppressed, as well as the power transfer efficiency of DC-DC converters for PV integration. Hence, to overcome these difficulties this paper investigates a DC-DC boost converter together with the additional parasitic component within the circuit to provide high output voltages for maximizing the PV power generation. The proposed power system circuit substantially improves the high output-voltage by a simple MPPT closed loop proportional-integral (P-I) controller, and requires only two sensor for feedback needs. The complete numerical model of the converter circuit along with PV MPPT algorithm is developed in numerical simulation (Matlab/Simulink) software. A detailed performance analysis is carried out under both PV panel irradiation (high/low) and load regulation conditions. Numerical results obtained in this paper are in the agreement with the theoretical developments, proving the effectiveness of the proposed topology. Index Terms-DC-DC boost converter, Pulse width modulation (PWM), Power transfer efficiency, Photo voltaic power generation, PI controller, Maximum power point tracking (MPPT), High voltage application.

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