Novel control approach for enhancing multi-performance of two-stage converter during power transfer from solar photo-voltaic array to AC grid

Abstract

Abstract This paper presents a nonconventional control approach for augmenting various performances of two-stage power converter (DC-side boost converter and three-phase voltage source inverter (VSI)) during power transfer from solar photo-voltaic array to AC grid. In the application, intermediate DC link voltage is traditionally regulated to settle at a constant and high value. This fixed value is not optimum in respect of various performances of the converters under variable power transfer scenarios. In this respect, variable values of DC link voltage under different power transfer conditions are necessary, which is absent in conventional scheme. For achieving the control flexibility, two modifications of traditional control scheme are proposed as, omission of intermediate DC link voltage regulating loop and controlling of modulation index of current loop between 0.98 and 1 for VSI. In effect, significant multi-benefits are obtained as, (i) reduction of voltage stress on power switches to enhance their life span, (ii) reduction of size, cost and enhanced lifetime of DC link capacitor, (iii) improved efficiency of conversion system and (iv) reduction of total harmonic distortion (THD) during maximum power injection from solar photo-voltaic (PV) array to connected AC system. First three benefits are produced due to reduction of DC link voltage for achieving required power transfer and fourth benefit is achieved due to high valued modulation index (between 0.98 and 1). Both simulation and experimental studies verify superior performances of two-stage converter with the help of proposed logic under variable solar power conditions. Derived mathematical condition on interplay between DC link voltage value and power transfer amount at different power factors (unity and leading) provides insight of proposed control approach.