Title: | Suuritehoisten aurinkosähkösuuntaajien verkkosuodinratkaisut Different line filter topologies in high power solar inverters |
Author(s): | Luoma-aho, Jere |
Date: | 2017-05-08 |
Language: | fi |
Pages: | 80+8 |
Major/Subject: | Electrical Power and Energy Engineering |
Supervising professor(s): | Hinkkanen, Marko |
Thesis advisor(s): | Viitanen, Tero |
Keywords: | verkkosuodin, pulssinleveysmodulointi, muuntaja, aurinkosähkösuuntaaja |
Location: | P1 | Archive number: |
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Abstract:The purpose of this study is to compare different line filter topologies and to see how well they can be applied in two-level high power solar inverters. The most relevant modulation strategies are introduced, and for solar inverters, a typical wide-range modulation index is considered. The examined filter topologies are LCL, LC and LLC filters. Medium voltage (MV) transformers and their impedances are an essential part of the study. Thus, the impedances are included in the examined cases. Filter comparison is implemented with analytically calculated transfer functions and time domain simulations. Transfer functions are calculated from single-phase equivalent filter models. Also, analytically produced grid current spectrums are studied. In the time domain simulations, grid current is simulated and the magnitudes of the harmonic currents in the grid current are compared to the limits of the standard. In addition, one grid disturbance and one fast-power reference variation are simulated. According to the results, modulation strategy and modulation index affect the filtering demand. The MV transformer impacted the filtering capability of the LC and LLC filters. However, the MV transformer did not significantly influence the LCL filter. Little differences between the filter topologies were detected when nominal power of the transformer was close to the nominal power of the examined inverter. However, differences between filter topologies were greater when nominal power of the transformer was much greater than the nominal power of the examined inverter. In that case, with LC and LLC filters, high harmonic currents were seen in the grid currents – especially at resonance and modulating frequencies. The filters also did not pass the standard limits. |
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