Técnicas de modulação vetorial baseadas na distribuição da energia de modo comum para atenuação da corrente de fuga em inversores fotovoltaicos de três níveis

Abstract

Transformerless photovoltaic inverters are susceptible to leakage current, predominantly caused by the common-mode voltage. Modulation strategies typically focus on reducing the amplitude of this voltage, while its frequency spectrum is often neglected. Since the leakage current flows through an RLC loop formed by the output filter and the parasitic capacitance of the photovoltaic modules, the distribution of the common-mode voltage frequency spectrum relative to the circuit resonance frequency has a direct impact on its magnitude. Therefore, shifting the energy of its frequency components away from the resonance region constitutes an effective leakage current mitigation strategy. Based on this premise, this work introduces a modulation approach grounded in the spectral distribution of common-mode energy. To validate this approach, two modulation techniques are proposed. The first concentrates most of the energy around the switching frequency, making it more suitable when the resonance frequency is significantly higher. The second redistributes part of the energy to higher-order harmonics, making it more advantageous when the resonance frequency is close to or lower than the switching frequency. The proposed techniques operate over the entire modulation index range, enable DC-link capacitor voltage balancing, and exhibit low harmonic distortion and switching losses, as confirmed by both simulation and experimental results. In addition, the analysis of leakage current as a function of the modulation index reveals an optimal operating region in which the leakage current is minimized.