Modeling and analysis of EMI from DC input of photovoltaic systems

• Main Author: Prajapati, Manish
• Other Authors: See Kye Yak
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/106561; http://hdl.handle.net/10220/48131
• Institution: Nanyang Technological University

Electromagnetic compatibility (EMC) is a major technical challenge for solar photovoltaic (PV) systems. As the use of PV systems has increased in recent years, the problems of electromagnetic interference (EMI) from PV systems are becoming more evident. The main source of EMI in PV systems are the power converters, such as dc-dc converters and dc-ac inverters, which use high-frequency switching power electronic devices. The power converters transmit conducted noise emissions at the input side, where PV panels are connected, and at the output side, where loads and ac grid are connected. At the output side, the conducted emissions must comply with relevant EMI regulations to prevent interference to loads or the ac grid. Although similar regulation does not apply to the dc input of a PV system, the high frequency switching converters with its dc input connected to the PV panel causes conducted emissions to propagate along the dc cables. These emissions can then radiate through dc cable and PV panel, which serve as unintentional antennas. Since PV systems are becoming widely accepted in both residential and industrial applications, EMI from these systems must be controlled. In such a task, an EMI model of the system can be a valuable tool as it provides insight into noise generation and propagation mechanisms. Moreover, EMI models are very useful to develop methods to mitigate noise emissions, such as designing EMI filters. However, it is challenging to develop accurate and efficient EMI model of a complex system such as of PV systems. Due to numerous components in power converters, several parasitic components and system specific couplings, conventional methods are inefficient to model such systems. PV systems provide an additional challenge since in addition to different complexity of power converters, noise propagation is influenced by operating condition of PV panel and long dc cables which vary in different systems. Therefore, a simple and efficient method is necessary which can provide a simple yet accurate way to analyze EMI in PV systems. This thesis proposes to develop a measurement-based EMI model of DC input side of PV system. In this approach, the noise source of the system is represented by equivalent Thevenin voltage or Norton current source with equivalent noise source impedance in the frequency domain. Similarly, the noise propagation path is also modeled as equivalent impedance in the frequency domain. To develop an accurate EMI model, the noise source model of the power converters and impedance of PV panels should be extracted at operating conditions. For this purpose, an in-circuit measurement approach is used to extract the noise model at the dc input of a PV system under its actual operating conditions. The dc input side is mainly focused on this research to study the effect of PV panels and dc cables on EMI. The proposed approach provides adequate information for EMI modeling and mitigation purposes without the full knowledge of the internal circuit of the PV system. Using the method, separate noise equivalent models for common-mode (CM) and differential-mode (DM) emissions of a PV system are developed. The model can then be used to study the conducted emissions and radiated emission from the system. The noise source model allows us to estimate noise emissions and evaluate the effectiveness of the filter for EMI mitigation without a trial-and-error process.