Power Quality Performance Evaluation of Multilevel Inverter With Reduced Switching Devices and Minimum Standing Voltage

摘要

Multilevel inverters (MLIs) have been extensively employed to improve the power quality of the photovoltaic (PV) systems. However, the need for large number of components, higher standing voltage, and high harmonic content in the output of a conventional MLI greatly affects the system efficiency. Asymmetrical MLIs have been therefore developed as a suitable alternative to address these issues. This article aims at developing such a hybrid asymmetrical structure suitable for PV application that has a high level per component ratio and minimum standing voltage. The proposed MLI is assembled using a reduced switch H-bridge-based (RSHB) MLI structure with n asymmetrical repeating units and different level doubling circuit (LDC) combinations. The two dc sources used in the repeating units are in the ratio of 1:n voltage ratio, and using n such units, the proposed MLI structures, i.e., PS1 and PS2 can synthesize 4n + 5 and 4n + 7 levels, respectively, at the output instead of 2n + 3 levels with only RSHB MLI. Comparative analysis reveals that both PS1 and PS2 have fewer switches, low standing voltage, less power loss, and lower cost. A 3.9-kW standalone solar PV system is considered for performance evaluation of the PS1 structure applying both the selective harmonic elimination and carrier-based pulsewidth modulation control schemes. In light of this, dc-link voltage balancing and self-voltage balancing mechanism of the LDC are warranted. Extensive simulation of the proposed MLI is performed in MATLAB/Simulink platform under a change in modulation index, sudden load change, frequency change, and step change in solar insolation. Furthermore, theoretical and simulation findings are validated experimentally by performing similar tests on a prototype of the proposed 17-level MLI.