Control and Performance of 240°-Clamped Space Vector PWM in Three-Phase Grid-Connected Photovoltaic Converters Under Adverse Grid Conditions

This article evaluates the performance of a relatively new pulsewidth modulation (PWM) method i.e., 240-clamped space vector PWM (240CPWM), in three-phase grid-connected photovoltaic (PV) converters under various grid voltage conditions. 240CPWM is a minimum switching loss PWM method that reduces the switching loss by 85% at unity power factor and has better total harmonic distortion (THD) as compared to conventional space vector PWM. A unique six-pulse dynamically varying dc-link voltage is required for 240CPWM. Typically, a three-phase grid-connected PV system consists of a dc-dc stage followed by a dc-ac stage. In this article, the dc-dc stage is operated in closed-loop control to shape the dynamic dc-link voltage required for 240CPWM. The dc-ac stage is operated in the current control mode using a proportional-integral controller along with a harmonic compensator to ensure sinusoidal grid currents along with maximum power point tracking. The modulation index of the dc-ac stage is uncontrolled and fixed at the maximum value, and the primary control mechanism changes the magnitude, phase, and wave shape of the dc-link voltage. The coordinated control of dc-dc and dc-ac stages is ensured for better dynamic performance and grid support functions. Finally, the performance of the grid-connected PV converter with 240CPWM is validated using a three-phase 3-kW 208-V hardware prototype under nonunity power factors, voltage unbalance, and voltage sag/swell conditions for the first time. The implemented control with 240CPWM achieves smooth operation under nonunity power factor and grid voltage disturbance conditions with THD as low as 3.5% and peak combined efficiency of dc-dc and dc-ac stages as 96.4%.