A FUZZY LOGIC BASED SWITCHING METHODOLOGY FOR A CASCADED H-BRIDGE MULTILEVEL INVERTER

Abstract

In this project, an unusual switching technique is implemented using a fuzzy logic approach. The proposed technique simplifies the conventional method by eliminating the traditional logic gate design. The fuzzy logic pulse generator acts as a look-up table as well as a pulse generator. Based on the modulation index as input, controlled membership functions (MFs) and rules of the fuzzy logic controller (FLC) opens various possibilities in producing pulses directly. The proposed technique is evaluated on the cascaded multilevel inverter with symmetric and asymmetric operations using selective harmonic elimination pulse width modulation (SHE-PWM). MFs are designed based on the pre-calculated firing conditions for different modulation index values.

Existing System

In the existing system, the firing angles are supplied to the logic gate design block which develops the individual pulse trains for the respective semiconductor switches

Proposed System

The proposed switching scheme is developed based on the fuzzy logic controller. The FLC usually used to control the complex nonlinear systems having an indescribable mathematical model and also used to minimize the error in place of PI controllers. But, in the proposed switching approach, the FLC is used as a direct pulse generator without using any logic gate design. Herein, the proposed technique is evaluated for symmetrical 7-level. Fuzzy logic operates on specific MFs (input MFs and output MFs) with definite rules, making it more reliable and efficient. Mamdanian FLC is intuitive and has widespread acceptance over Takagi-Sugeno FLC. Thereby Mamdanian FLC is considered, and here, the input MFs are constructed with the offline calculated switching instants (by Newton–Raphson method) for different mi values, which acts as a look-up table. Closed input MF with sharp endpoints is the main selection criteria for input MF and singleton output MF to obtain gating pulses. Though triangular and trapezoidal MFs are satisfying the criterion for input MF, pulse pattern cannot be visualized easily.

Architecture

Symmetrical 7-level CHB MLI

FLC pulse generation structure for bridge B1