Electromagnetic Interference From Photovoltaic Inverter Conduction System

With the development of the PV industry still continuing, the off-grid inverter devices are receiving ever growing wider range of applications, also the EMC issues aroused more attention. This paper gives an investigation into related issues of conductive EMI, mainly including the design of off-grid inverter system and laboratory platform construction, also the calibration and compensation for AC and DC line impedance stable networks, and the mechanism analysis of conductive EMI as well as the noise suppression of conductive EMI.This paper firstly illustrates the standards of EMC, mainly focused on mechanism and suppression research of conductive EMI in off-grid inverter systems, the illustration of required standards on off-grid systems and EMC are also included in this paper. Selecting the conventional two stage inverter structure, constructed single phase off-grid inverter systems based on BOOST circuit, analysis the basic principle of SPWM control. An integral conductive EMI platform is built with the combined testing equipments of Spectrum Analyzer、AC-LISN、DC-LISN、noise separating networks. It can measure the DC-DC transforming module noises、DC-AC output ports module noises and load noises, which makes it convenient to compare and analysis the mechanism features of noises.This paper mainly focused on the calibration technology of line impedance stable networks(LISN), AC-LISN is generally used in AC noises measurements, according the national standard GB/T6113.102-2008, the AC-LISN functionalities are illustrated and features parameters of AC-LISN be presented, the high frequency models of four main parameters in AC-LISN are obtained with the aid of MATLAB simulation, and the calibration methods of the corresponding parameters measure are given, also the process mode in specific case like interference caused by metal plate are given. DC-LISN is generally used in DC side noises measurements, systematic introduce the measuring methods of DC noises in off-grid inverter systems, analysis the corresponding influences possibly induced by the measuring equipments used in DC noises measurements, The DC-LISN measuring calibration technology is studied combined with the theory of waves reflection and S parameters, analysis the calibration methods of DC-LISN in measuring the insert losses、internal impedance, the secondary reflection effect of waves is analyzed and yields the corresponding calibration and compensation at the same time.Moreover,the paper separately researched the mechanism of noise generated in DC-DC and DC-AC systems, and yields the corresponding noise model.Study on the filtering and suppressing technology of the PV off-grid inverter systems, analysis the high frequency features of resistor、capacitor、inductor, illustrates the functions of common mode choke、magnetic bead、ferrite-oxide magnetic rings in noises suppression, mainly illustrate effect of filter and buffer circuit design in noise suppression. AC and DC EMI filter are properly designed for the off-grid system noise suppression to make the noise level satisfying the requirements of GB9254-2008.