Condition Monitoring of Aluminum Electrolytic Capacitors

Indian patent, Appl. No. 201611008693, 2016

Existing single phase direct grid feeding solar PV inverter are based on voltage source inverter topologies. Aluminum electrolytic capacitors (AEC) are used as an energy storage element in these inverters, to limit second harmonic voltage ripple to a low value and to maximize the PV power extraction efficiency (PEE). AECs are popularly used due to their high energy density as compared to other capacitors. However, AEC degrades due to its electrolyte loss with time, which leads to rise in equivalent series resistance (ESR) and fall in capacitance value. Further, the rate of loss in electrolyte increases with temperature. This leads to increase in magnitude of ripples in PV voltage with ageing. This reduces the PEE, which results in less power availability from solar PV system. Increase in voltage ripple could also lead to failure of inverter.

To avoid this, we have developed online techniques to monitor the health of AEC in solar PV inverters. These techniques would provide timely indication of the capacitor (AEC) failure, thereby avoiding downtime of the solar PV system.

Dynamic Voltage Restorer

Technology Transferred to Emerson Network Power (I) Pvt. Ltd.

Dynamic Voltage Restorer (DVR) is a custom power device used in electrical distribution system for power quality improvement. The main application of DVR is for voltage compensation of sensitive loads against voltage disturbances like sag and swell in distribution lines. A 5kVA, IGBT based, digitally controlled single phase DVR is designed and developed. It is capable of regulating the load voltage within 2% of its nominal value (230V) for grid voltage variation of 185V to 265V.

High Reliable Solar Inverter

Indian Patent, Appl. No. 2912/MUM/2011

Life of solar PV panels is more than 20 years. However, inverters are less reliable and typically have 3-7 years of life span, beyond which high failure rate of inverters is expected. Failures of power electronic converters are mainly due to the following components: (i) Aluminum Electrolytic Capacitors (AEC), and (ii) Switching semiconductor devices.

We have proposed a high reliable solar inverter topology. It is based on current source converter, which uses inductors to store energy instead of AEC, thereby increasing the operational life. The proposed inverter is a transformer-less pulse width modulated (PWM) current source inverter. Further, this inverter offers inherent voltage boost feature, which avoids the use of additional dc-dc converter in case of low voltage solar PV string. This improves the conversion efficiency due to single stage conversion.

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