Flying-capacitor topology for grounding of single-phase transformer-less three-level photovoltaic inverters

Abstract

This paper presents a new inverter topology named after its operating principle based on a flying capacitor. The inverter uses neither a grid transformer (50/60 Hz) nor a high frequency transformer and therefore does not provide a strict galvanic isolation. However, its innovative circuit has been designed in order to allow grounding one pole of the photovoltaic (PV) generator which is not feasible with common transformer-less PV inverters. The slight drop in efficiency and increase in size and costs due to the use of more numerous semiconductors and additional passive components is well below that of inverters using high or low frequency transformers and is fully compensated by decisive technical advantages. Indeed, the ability to ground the DC side of the inverter can be of a great interest for certain PV generators but also for other kinds of applications such as batteries

Novel multi‐level inverters with flyback high frequency link

“…However, these MLIs lack of electrical isolation. Once the input power supply has an accident, the electrical equipment of the load side is affected directly, even suffers fatal damage [6]. For this reason, such as solar power generation [7, 8] and high‐voltage DC (HVDC) transmission [9], isolation requirements are put forward for user‐side inverters.…”

A multi-string photovoltaic inverter for thin-film or back-side contacted solar modules

“…The diode D8 protects the transistor T3 from overvoltage, if T3 switched off, before i L2 has reached zero [4]. Due to parasitic resistances in the charging path, the current i L2 is a damped sine half-wave (see also [7,8]). Note, that the energy for the positive half-wave of u A is taken from X2 / X3, while the energy for the negative half-wave is taken from X1 / X3 [4].…”