A New Switched-Capacitor Five-Level Inverter Suitable for Transformerless Grid-Connected Applications

Abstract

Transformerless grid-connected inverters have been extensively popular in renewable energy-based applications owing to some interesting features like higher efficiency, reasonable cost and acceptable power density. The major concern of such converters is the leakage current problem and also the step-down feature of the output voltage which causes a costly operation for a single stage energy conversion system. A new five-level transformerless inverter topology is presented in this study, which is able to boost the value of the input voltage and can remove the leakage current problem through a common-grounded architecture. Here, providing the fivelevel of the output voltage with only six power switches is facilitated through the series-parallel switching of a switched-capacitor module. Regarding this switching conversion, the self-voltage balancing of the integrated capacitors over a full cycle of the grid's frequency can be acquired. Additionally, to inject a tightly controlled current to the local grid, a peak current controller-based technique is employed, which can regulate both the active and reactive power support modes. Theoretical analyses besides some experimental results are also given to corroborate the correct performance of the proposed topology.

A novel common‐ground switched‐capacitor five‐level inverter with adaptive hysteresis current control for grid‐connected applications

“…Even though it offers an inherent FC voltage balancing, its minimum required value of the input voltage is still 320 V. Here also, although the D2T5L inverter presented in [22] has a two‐time voltage boosting capability like the proposed one, it lacks in having CG feature and needs more number of active power switches. By contrast, the converter presented in [34] is SC‐based like the proposed topology; so, it offers a CG feature with a two‐time voltage boosting ability. However, although its number of power switches is less than the proposed one (it requires seven switches but the proposed topology needs eight switches), its per unit value of the overall TSV and number of power switches that are involved into the capacitors charging loop is higher than the proposed one.…”

“…Such feature makes an appropriate condition from the overall conduction loss viewpoint. • The charging inrush current of the involved capacitors is another important point that is common among all the SC-based structures and it is worth addressing [32][33][34].…”

“…However, although its number of power switches is less than the proposed one (it requires seven switches but the proposed topology needs eight switches), its per unit value of the overall TSV and number of power switches that are involved into the capacitors charging loop is higher than the proposed one. In additional, the maximum PIV across the switches in [34] is , while this value for the proposed structure is . The higher value of PIV per switch causes higher maximum Volt–Ampere rating of the semiconductors for the structure presented in [34].…”

“…In both these cases, an additional inductor has been involved in the CPC cell; hence, it might bring additional losses. To further improve the quality of the injected current to the grid through such CGTLIs, some advanced versions of the 3L-and 5L-based structures have been presented recently, where the flying-capacitor (FC) and switched-capacitor (SC) concepts have been put forward [30][31][32][33][34].…”

“…Here, the 5L FC-based topologies presented in [30,31] need the additional charge balancing control procedures to maintain the balanced voltage for the FC cell, while it possesses again a buck-type feature. Using the SC concept integrated into the CPC cell can make a boosting feature for the inverter's output, while the charging/discharging operation of the involved capacitors can be inherent [32][33][34]. The major drawback of such SCbased topologies is the inrush current problem, which causes an undesirable current stresses for those semiconductor devices integrating into the charging loop of the involved capacitors.…”