Adaptive PWM Control and Dynamic Switching Frequency for Leakage Current Suppression and THD Control in 3-Level NPC Inverters

This paper presents an adaptive operation algorithm for 3-level NPC grid-connected inverters that simultaneously addresses leakage current suppression and total harmonic distortion (THD) control in transformerless photovoltaic systems. The proposed approach integrates intelligent PWM method selection with dynamic switching frequency optimization to achieve optimal inverter performance under varying operating conditions. The algorithm employs a hierarchical control structure where high-level decisions regarding PWM method selection between Phase Disposition (PD) and Phase Opposition Disposition (POD)PWM are made based on real-time leakage current measurements, while low-level switching frequency adjustments using perturbation and observation (P&O)technique maintain acceptable THD levels. Comprehensive PSIM simulation validation demonstrates that the algorithm achieves up to 40% reduction in leakage current under fault conditions while maintaining grid current THD below 3.5%, meeting international safety and power quality standards. The algorithm’s response time of 0.5 seconds for leakage current threshold violations and convergence within 1.5-2.0 seconds for THD optimization provides adequate protection for safety applications. The software-based solution requires no additional hardware components, making it suitable for both new installations and retroft applications in commercial inverter systems. The demonstrated performance under realistic fault conditions and grid disturbances confrms the algorithm’s practical viability for transformerless PV inverter applications.