Lifetime Monitoring of Electrolytic Capacitor to Maximize Earnings From Grid-Feeding PV System

Electrolytic capacitors are popularly used in single-phase grid-feeding solar photovoltaic (PV) inverters to suppress the second harmonic and switching frequency voltage ripples. With aging equivalent series resistance (ESR) of capacitor increases and its capacitance value decreases, which lead to increase in dc-link voltage ripple. Oscillations in PV operating point around its maximum power point (MPP), results in reduction of average output power and revenue generated. To address this, frequent replacement of capacitors are required, which may lead to increased cost. Therefore, capacitors must be replaced at an optimal period to ensure maximum earnings. To realize this, a technique for monitoring of power extraction efficiency (PEE) is proposed in this paper. Further, criteria for replacement of capacitor based on the measured values of PEE is suggested. Mathematical model relating the capacitance and ESR values to the PEE is derived. Effect of variation in temperature and solar radiation on PEE is discussed. Detailed simulation studies are carried out using MATLAB-Simulink. A scaled down laboratory prototype of inverter is developed. The proposed technique is implemented in the existing digital processor/controller used for MPP tracking, thereby avoiding additional circuits/sensors. PEE estimated by simulation and experimentation are found to be within 1% of each other.