Novel Level Shifted PWM Technique for Unequal and Equal Power Sharing in Quasi Z Source Cascaded Multilevel Inverter for PV Systems

 ABSTRACT:

 Conventional Phase Shifted Pulse Width Modulation (PS-PWM) is a usual switching technique for Z source/Quasi Z Source (qZS) based Cascaded Multilevel Inverters (CMI) (qZS-CMI). PS-PWM scheme causes higher switching losses and creates electromagnetic interference (EMI) problem for higher number of cascaded modules. To address these issues, novel modified Level Shifted PWM (LS-PWM) technique is proposed with the aim of obtaining equal power from cascaded modules under abnormal condition. The direct use of the Alternate Phase Opposed Disposed PWM (APOD-PWM) results in an unequal power sharing between the qZSI modules, under all operating conditions. An effective carrier rotation is incorporated in the conventional APOD-PWM to make the equal power sharing between the qZSI modules. The proposed scheme is an excellent solution for the Photovoltaic (PV) systems to address the problem of partial or complete shading, temperature variation, PV module failure, and dust accumulation on the PV panels. Furthermore, the relation between the PSPWM and APOD-PWM is geometrically obtained, which indicates that the proposed modulation scheme gives higher voltage gain over LS-PWM and PS-PWM techniques. Additionally, detailed switching loss analysis for the proposed PWM methods are added to validate low switching losses and thus high efficiency. The MATLAB Simulink simulations are presented to verify the proposed modulation. Experimental prototype is developed, and the experimental outcomes validate the improved performance of the multilevel qZSI with proposed modulation.

 

KEYWORDS:

 

1.      Cascaded Multilevel Converter

2.      Impedance Source inverter (Z/qZSI)

3.      Phase Shifted Pulse Width Modulation

4.      Level Shifted Pulse Width Modulation

5.      Equal power distribution

6.       Photovoltaic (PV)

 

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:  

A novel APOD-PWM technique (equal and unequal power sharing) for the qZS-CMI has been reported in this article. This paper presents the relation between shoot through duty and modulation indices of PS-PWM and APOD-PWM. The proposed modulation technique (for qZS-CMI) combines the advantages of APOD-PWM (subsidiary of LS-PWM) and PS-PWM, resulting in high quality output voltages and harmonic free input currents drawn from the PV panels. The equal and unequal power sharing together, overcomes the drawbacks of conventional techniques. These APOD-PWM for qZS-CMI can be applied to the PV systems to address the real time problems of partial shading, dust accumulation, temperature variation and power distribution among the operating modules. To verify the advantages with proposed PWM techniques, detailed switching loss analysis, simulation and experimental results are presented. With carrier rotation in proposed PWM, equal utilization is observed whereas without carrier rotation, highest efficiency is observed. The proposed APOD-PWM techniques have nearly same THD as conventional schemes and higher voltage gain and power yielding capability with higher efficiency than PS-PWM thereby validating its feasibility for qZSI related applications.

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