Development of Modulation Strategies for NPC Inverter Addressing DC Link Balancing and CMV Reduction
Authors
Boian, Daniela ; Biris, Ciprian
Term
4. term
Education
Publication year
2012
Pages
110
Abstract
To-niveaus-vekselrettere kan skabe fællesmodespænding (CMV) i motorviklinger, hvilket driver lejestrømme og kan give motorfejl. De medfører også lækstrømme gennem stator og motorhus, som skaber fællesmode elektromagnetisk interferens (EMI). Flerniveaus-vekselrettere giver lavere total harmonisk forvrængning (THD) og kan med passende modulationsstrategier reducere CMV. Tre-niveaus-topologien giver et godt kompromis mellem ydeevne og kompleksitet, men fordi udgangen dannes fra seriekoblede DC-link-kondensatorer, er det en udfordring at holde neutralpunktet i balance; ubalance kan give spændingsbelastning af halvledere. Dette projekt udvikler modulationsstrategier, der både holder DC-link-spændingerne i balance og reducerer CMV. Fire strategier blev udviklet og valideret i simulation, og til eksperimentel afprøvning blev en Neutral Point Clamped (NPC) tre-niveaus-vekselretter designet og bygget. For hver strategi blev CMV, EMI og neutralpunktbalance analyseret. Alle de foreslåede strategier viste forbedrede CMV- og EMI-spektre sammenlignet med klassiske metoder (NTV og ZCM).
Two-level inverters can create common-mode voltage (CMV) across motor windings, which drives bearing currents and can cause failures. They also produce leakage currents through the stator and motor frame, leading to common-mode electromagnetic interference (EMI). Multilevel inverters improve output quality by lowering total harmonic distortion (THD) and, with suitable modulation strategies, can reduce CMV. Among these, the three-level topology offers a good balance between performance and complexity. However, because it synthesizes the output from series-connected DC-link capacitors, keeping the neutral point (midpoint) balanced is challenging and can overstress semiconductor devices if not managed. This project develops modulation strategies that simultaneously maintain DC-link voltage balance and reduce CMV. Four strategies were created and validated in simulation, and a Neutral Point Clamped (NPC) inverter was designed and built for experimental tests. For each strategy, we analyzed CMV, EMI, and neutral-point balance. All proposed strategies showed improved CMV and EMI spectra compared with classical methods (NTV and ZCM).
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