A Differential-Mode Current-Sourced High-Frequency-Link Photovoltaic Inverter
Thirumalai Sivasubramanian, Priyadharshini
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Photovoltaic-inverter architectures include a dc/dc stage followed by a dc/ac conversion stage and a transformer. Some architectures employ a bulky 60 Hz line transformer while most other inverter designs are based on High-Frequency-Link (HFL) architectures. The HFL architecture employs the high-frequency transformer either in the dc/dc stage or in the dc/ac stage. The HFL architectures have higher power density than the inverters that uses a line transformer. As a step ahead, single–stage inverters are a definite solution to achieve a more compact Power-Electronics-Interface, Current-source inverters, in particular, have an inherent boosting capability, thereby reducing the need for a transformer with higher turns ratio. Also, a current-sourced topology eliminates the need for a bulky and expensive bus capacitor. A differential-mode current-fed Zero-Current-Switching (ZCS) voltage-doubling PV inverter has been designed. This inverter has two modules of dc/dc converters that are connected differentially to the PV source. This inverter does not require a) 60-Hz transformer, b) front-end dc/dc converter, and c) can boost a low-voltage (30-60V) input to a 120V/60 Hz output using a unity-turns-ratio transformer because of the added voltage gain of the topology. Main switches are switched using ZCS. The inverter requires a smaller high-frequency transformer because of a) 100-kHz switching, b) bipolar transformer current and voltage in every switching cycle, and c) the transformer sees only half of the input current at any given instant. The modularity of the inverter extends the scope of the topology to be used as a dc/dc converter, single-phase inverter and also the possibility of extending the topology to both split-phase and three-phase. A harmonic compensation control is designed and implemented, to reduce the THD at the load, using a Proportional Resonant (PR) controller. The design and analysis of the inverter has been validated using SABER.