Comparative analysis of PWM techniques: An electromagnetic compatibility study on the inverter operation within photovoltaic systems

The stepped common mode voltage generated in the normal operation of a PWM inverter, applied over the distributed capacitive couplings between the electric system devices and the ground, produces high-frequency transient currents that flow through the system earth return path, leading to electromagnetic compatibility problems. In this context, this paper addresses specifically the inverter switching, focusing the generated common-mode voltage and the resulting undesired common mode currents that flow within a photovoltaic installation. Several different PWM techniques are analyzed and compared regarding the corresponding common mode voltage pattern and the correlated ground current. The studied modulation strategies are fully described and latter implemented in the Matlab/Simulink software, being the inverter placed within a detailed representation of the whole photovoltaic system, appropriately modeled for high-frequency studies. The advantages and limitations of the analyzed switching techniques are then pointed out and ranked, with special attention to the common mode quantities generation.