三电平NPC逆变器中共模能量分布优化以抑制漏电流

Transformerless photovoltaic (PV) inverters are susceptible to leakage current, which is primarily caused by common-mode voltage (CMV). Most modulation strategies for three-level inverters focus on reducing the amplitude variation of this voltage, but often overlook the impact of its frequency spectrum. Since leakage current flows through a series RLC path defined by the output filter and the parasitic capacitance of the PV panels, shifting the spectral energy of the CMV away from the resonance frequency contributes to attenuate its magnitude. Based on this, two modulation techniques are proposed to not only minimize CMV, but also shape its frequency spectrum for further leakage current reduction. The first concentrates most of the energy around the switching frequency, making it suitable when the resonance frequency is significantly higher than switching frequency. The second redistributes a portion of the energy to higher-order harmonics, making it advantageous when the resonance frequency is close to or below the switching frequency. Both techniques support the full modulation index range and enable neutral-point (NP) voltage control. Simulations and experimental results validate their effectiveness across different resonance conditions. Capacitor voltages remain balanced even under a forced disturbance. In addition, an analysis of leakage current versus modulation index reveals an optimal range in which the current reaches minimal levels.