Modified Synchronous Pulsewidth Modulation of Current-Fed Five-Level Inverter for Solar Integration

Abstract

Large-scale photovoltaic (LSPV) energy conversion systems have been installed at many places across the world. The essential component of LSPV system is the dc-ac conversion stage. The usage of multilevel converters is one of the recent advances in the dc-ac conversion stage of LSPV system to enable transformer-less inversion. Current-fed multilevel inverter has been chosen in this paper as it provides high power inversion with inherent voltage boosting and thus avoids the usage of transformer. High power conversion necessitates low device switching frequency operation in order to satisfy thermal constraint of semiconductor devices and also to improve efficiency. However, low device switching frequency operation leads to higher harmonic distortion of inverter output currents. Synchronous optimal pulse-width modulation (SOP) technique is an emerging low device switching frequency modulation technique which has been successfully implemented for voltage source multilevel inverters. However, state-of-the-art SOP technique cannot be directly applied to modulate current source multilevel inverter topologies due to additional constraints on the switching commutations. Therefore, the purpose of our study was to propose modified SOP technique to achieve : low device switching frequency and minimal harmonic distortion of inverter output currents. The topology of current-fed five-level inverter was used for demonstrating the performance of proposed technique. A generalized conversion method was introduced in the modified SOP technique for including switching constraints of current-fed inverter. In addition, a state-sequencing machine was developed by utilizing redundant inverter states to produce equal switching commutation among all semiconductor devices at minimal switching frequency of 350 Hz. The experimental results obtained from five-level current source inverter of 1.2 kW demonstrated the effectiveness of proposed SOP technique. Index TermsSynchronous optimal pulsewidth modulation (SOP), current-fed multilevel inverter, low frequency modulation, solar power integration. Manuscript

FPGA Digital Architecture for Multilevel Synchronous Optimal PulseWidth ModulationWith Seamless Pulse Pattern Transitions

“…While the main references [19]- [21] in the fields of SOP and SHE modulations put emphasis on the process of optimizing switching angles and its harmonic distortion performance in steady state, there are few studies that address the practical difficulties of implementing this type of modulation. In [22] the modulation is implemented in a Digital Signal Processor (DSP), purely via software, which limits the number of switches per cycle as well as the resolution of switching angles due to the inherent time constraints of computational loops. A more elaborate approach based on the translation of the optimized angles table into comparisons performed by PWM modules of a DSP is used in [23].…”

A new tri-source symmetric cascaded multilevel inverter topology with reduced power components

“…MLIs use isolated dc sources and small capacitors to synthesize output voltage in small steps through the cascading connection of H-Bridge (HB), half leg structure with clamping diodes and flying capacitors (Rodriguez et al , 2002). Several remarkable achievements have been registered in developing topological structures (Trabelsi et al , 2021; Mhiesan et al , 2020; Bhaskar, 2020) and modulation strategies (Gnanasambandam et al , 2017; Meraj et al , 2019; Shukla et al , 2007). A new MLI topology is based on multilevel dc-link and an HB inverter to reduce the switching devices, dc sources and clamping capacitors/diodes to offer more voltage levels.…”

Three‐phase two‐leg buck‐boost DC‐AC inverter with differential power processor unit

“…The current source inverter (CSI) has been utilized in different applications as it can perform as single‐stage boost inverter which is needed in various renewable energy applications 4,12–15 . The CSI offers, in addition, only boosting capability in DC/AC power conversion compared to VSIs.…”

“…The current source inverter (CSI) has been utilized in different applications as it can perform as single-stage boost inverter which is needed in various renewable energy applications. 4,[12][13][14][15] The CSI offers, in addition, only boosting capability in DC/AC power conversion compared to VSIs. CSIs suffer from several demerits as high cost, size, and hardware component count due to the presence of a bulk DC-link inductor and output C-L filter that are mandatory for DC-link current smoothing and output voltage filtering, respectively.…”