Condition monitoring of dc-link capacitor utilizing zero state of solar PV H5 inverter

Single phase direct grid feeding solar photovoltaic (PV) inverters are used to interface with the grid. Aluminum Electrolytic Capacitors (AECs) are used to suppress dc-link voltage oscillation in these inverter. Life of solar PV inverter system is limited due to the use of these capacitors. With ageing its capacitance decreases, which may lead to increased voltage ripple, thereby reduced average power extraction from solar PV and/or damage to semiconductor switches due to overvoltage. Further, prolonged used of aged capacitor could lead to open circuit of the dc-link due to degradation of oxide layer in the AEC. Therefore, to improve the reliability of system, health monitoring of capacitor is desirable. In this paper, a technique for condition monitoring of dc-link capacitor is proposed for the solar PV H5 inverter. Proposed technique estimates capacitance by utilizing the sampled values of solar PV voltage and current during zero states of the inverter. Key advantage is that the existing voltage and current sensors and digital processor/controller are used for estimation of capacitance. Further, the proposed technique is also applicable to other full bridge based, single phase inverters. To validate the efficacy of proposed technique, detailed simulation studies are performed using MATLAB-Simulink. Further, error analysis in the estimation of capacitance values using proposed technique under different levels of solar radiation over the day is provided. Practical aspects of the proposed technique are also discussed in this paper.