A SELF-BALANCING FIVE-LEVEL BOOSTING INVERTER WITH REDUCED COMPONENTS

Abstract

Two-stage boosting multilevel inverters (MLIs) which are highly suitable for photovoltaic power plants are known to suffer because of the high voltage stress on the switches of second stage. One of the ways to confront this issue is through eliminating of the front-end booster. However, this leads to increased structural and control complexity of the resulting integrated boosting MLI. This letter presents a single stage boosting MLI requiring lesser number of switches, diodes and capacitors for renewable power generation applications. It requires nine switches and only one capacitor for five-level voltage generation. The topology has inherent self-balancing capability, thereby does not need additional balancing circuitry. The proposed topology has a uniform peak inverse voltage stress on the switches of value equal to the input DC voltage. A less complicated logic-form-equations based gating pulse generation scheme is designed for enabling the proposed MLI to maintain its capacitor voltage. Further, a comparative study with state of- the-art topologies is carried out to demonstrate the superior performance of the proposed topology. Finally, the feasibility of the proposed topology is validated through experimental tests and the corresponding results are elucidated.

Existing System

In the existing system, cascaded H-bridge (CHB), neutral point clamped (NPC) and flying capacitor (FC) converters are used.

Proposed System

The proposed single-phase five-level (5L) boosting inverter consists of nine power switches, one SC and a single DC source of magnitude Vdc. The arrangement of switches S2, S3, S4, S5, and S6 interconnecting the DC source and SC is referred to as an intermediate switching cell (ISC). The remaining four switches operate only once in every half cycle of the fundamental voltage and thus, are termed as line frequency switches (LFSs). It is evident that only one DC supply is employed for the 5L voltage generation. A photovoltaic cell/array, electric vehicle battery or fuel cell can act as such DC supply. Besides, the proposed circuit arrangement exhibits a uniform blocking voltage across all the switches and has a voltage boosting factor (VBF) of two. Unlike many other structures wherein, an H-bridge is used for the polarity generation, the proposed architecture has an inherent voltage reversal capability. The voltage across the SC is balanced around a voltage of magnitude Vdc without any need for sensors, thus, makes the proposed topology cost effective. Further, with the proposed 5L basic unit, the number of voltage levels (NL) can be increased in two ways. Firstly, by appending additional ISCs and SCs referred to as Method-1 (M1). Secondly, by cascading a number of 5L units referred to as Method-2 (M2) the resulting configuration has a higher NL and VBF. Such an arrangement is highly suitable for the interconnection of multiple DC supplies (renewable sources).

Architecture

Proposed 5L boosting MLI.