Analysis and control of decentralized PV cascaded multilevel modular integrated converters

Multilevel cascaded photovoltaic (PV) inverters can create interleaved voltage waveforms, allowing for reduced filter sizes and higher efficiencies, whilst still allowing for the maximum power point tracking (MPPT) of individual PV modules. However, unlike the micro inverter, a high gain boost converter is not required due to the series nature of the PV modules. To reduce wiring and installation costs in small scale applications, the compromise is a decentralised approach utilising a restrictive low bandwidth and intermittent communications link between the modular integrated converters (MICs), which limits MPPT. In this paper, a simplified decentralised control algorithm for the MPPT of multilevel cascaded MICs is proposed that covers both individual and global control of the prototype system. The limits of multilevel power sharing distributions are analysed and verified, exploring the fundamental limits of the cascaded topology. Additionally, the necessary communications update rate of the algorithm is analysed as the MPPT speed is varied, focussing on the repercussions that this has on the harmonic current and required global/local operational balance.