A new class of PV inverters: Series partial resonant converters

This paper proposes a novel single stage Photovoltaic (PV) inverter which fulfills all the system requirements (i.e. inverting dc voltage to proper ac, stepping up or down the input voltage, maximum power point tracking (MPPT), generating low harmonic ac current and input/output isolation). This three-phase inverter is a new class of partial resonant ac link converters in which the link is formed by a series ac inductor/capacitor (LC) pair having low reactive ratings. The ac capacitor is the main energy storage element and the inductor is merely added to facilitate the zero current turn-off of the switches. Unlike other common PV inverters, no bulky low frequency transformers or electrolytic capacitors are required in this inverter. Electrolytic capacitors cause the most severe reliability issues in the PV inverters. Therefore, their absence will improve the reliability of the whole system noticeably. This will consequently increase the consumers´ confidence in renewable technology as the PV inverters reliability is currently one of the major issues hindering broad PV penetration. The switches employed in this converter can be of any type and even thyristors can be used. Thyristors are more efficient than the other types of switches, they are available at both high current/high voltage ratings, and they are inexpensive and reliable. Considering the aforementioned features, the proposed inverter is believed to overcome most of the shortcomings associated with the currently available PV inverters as it is more reliable, more compact, more efficient, and it offers longer life-time. The performance of this inverter will be verified in this paper.