Quasi-Eight-Level Inverter with Output-Side Transformers for Single-Phase Off-Grid Electrical Energy Supply

Kayhan Ince

Research output: ThesisDoctoral Thesis

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Abstract

Renewable energy resources available locally are ideally suited for providing electricity supply in remote areas. This work describes design and layout of a special single phase supply system with high voltage quality and low power electronics expenditure through application of a special quasi-eight-level inverter output voltage shape with H-bridge circuit configuration. The task is to minimize the number of stochastic and unknown parameters influencing the device functionality. First, the different possibilities to implement a multilevel inverter for grid and its power supply are explored, pointing out the advantages and disadvantages of each solution. Then, a H-bridge-module is designed and built. With these modules and together with some innovative concepts a model of a multilayer inverter is developed and a set of preliminary measurements are gained. The few loads requiring three-phase voltage are motors which shall be driven individually by demand-controlled inverters at corresponding various frequencies and voltages. For the intended application, simplicity is more important than the common approach of higher power transfer capability of three-phase systems. Ideally, the voltage at output side is sinusoidal without harmonics. Practically, we have to find a compromise between voltage quality (that still must fulfill common standards for voltage sags from commutation or switching, and harmonics) and on other side investment in hardware, amount of losses, and robustness. In order to obtain a good voltage shape we may use either high switching frequencies and filter circuits (less than optimum because of additional losses, extra cost and possible resonances to loads), or suitable multi-level inverters which can be realized without filters. Any deviation between ideal sinusoidal shape and actual switched voltage creates a current rate of rise or fall differences to ideal purely sinusoidal current waveform. For a certain current difference the integral of switched minus actual voltage over time is decisive. Finally, the model is validated by practical measurements indicating its correctness.
Translated title of the contributionQuasi-Acht-Level-Wechselrichter mit Ausgangsseitigen Transformatoren für Einphasen-Off-Grid Elektrische Energieversorgung
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Lorber, Karl, Assessor B (internal)
  • Weiß, Helmut, Assessor A (internal)
Publication statusPublished - 2010

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