Optimized Selection and Utilization of DC-Link Capacitor in a Single-Phase PV Grid Inverter System

Single-phase PV grid inverters usually require large reservoir capacitors on the DC-Link to absorb 2^nd order harmonics. This paper shows in a design how to improve the utilization of metalized polypropylene film capacitor (MPFC) specifications in multiple dimensions simultaneously: breakdown voltage rating, capacitance, ripple current capability and warranted reliability performance. As a result, the system size and cost can be reduced, while the overall energy capturing efficiency is guaranteed. Under low-capacitance conditions the DC-Link voltage varies within a fundamental cycle; a boost converter is placed between the PV panel and the DC-Link to provide MPPT (maximum power point tracking). The modulation index of the output inverter can be dynamically varied for waveform compensation. Comparison is made with electrolytic capacitors and it is found that when using an optimized capacitor selection strategy, it is possible to mitigate the increased size and cost implications of film capacitors. Simulation demonstrates the design of a 2.5kW system, while experiment is conducted to prove the design concept.