Transformerless compensation schemes based on the modular design of the 3-level GTO-inverter

The 3-level inverter topology allows for neutral point operation and simple control over other Static Synchronous Compensation schemes currently in use. Flexible designs in the areas of distribution, transmission and production of electric power provide with superior harmonic performance and reduced switching frequency limitations.; The first of the proposed Static Synchronous Compensator (SSC) schemes uses two 3-level inverters connected in parallel with small current sharing inductors. This compensator is ideal for distribution systems because it yields an output equivalent to a 12-pulse operation, and allows for selective harmonic elimination.; SSCs for high voltage applications (STATCOMs) use GTO-thyristors that have limitations regarding their operating frequency. The inverters switch at fundamental frequency and generate low order characteristic harmonics. In order to overcome this limitation, most STATCOMs operate at a high-pulse number, resulting in characteristic harmonics of higher order. For high voltage applications, however, the magnetic interface and the SSC become too expensive to build and operate.; A different approach is taken for the development of a compensator with harmonic output equivalent to a conventional 48-pulse scheme. The proposed arrangement requires only a small number of 3-level inverters and the magnetic interface has been replaced by small size inductors connected in parallel. The complexity and cost of this SSC can be lower than many conventional schemes, which are based on the 2-level inverter.; A power conditioning unit (PCU) that uses the 3-level inverter topology and combines several poles per phase to achieve high power operation is also developed. Neutral point operation and constant current control are incorporated in the PCU through pulse width modulation, which allows efficient operation without increasing the switching frequency of the inverter valves. A maximum power tracker is employed in order to maximize the efficiency of the interconnected photovoltaic generator, which allows the PCU to supply real and reactive power to the network.