Improving LVRT Overload Performance of Grid-Connected Inverters Through Combined Active Thermal Control

Abstract

Low Voltage Ride Through (LVRT) events impose short-duration but severe overcurrent conditions on grid-connected converters, making the thermally limited overload capability of power semiconductors a key factor for grid support performance. This paper investigates the use of individual and hybrid Active Thermal Control (ATC) strategies to improve the short-time overload capability of grid-connected converters during LVRT operation. Switching frequency reduction, gate voltage variation, and discontinuous PWM are analysed both individually and in combinations within an electrothermal simulation framework that couples loss estimation and a state-space thermal model. The impact of each strategy is quantified in terms of peak junction temperature and maximum admissible fault current under a thermal constraint of ${1 7 5}^{\circ} \mathrm{C}$. Results under Spanish and German grid-code profiles show that hybrid ATC significantly enhances overload capability. The most effective combination, consisting of increased gate voltage and reduced switching frequency, extends the short-time current capability by approximately 25% compared to nominal control, while reducing the peak junction temperature by more than 110°C at 2.2 pu current. These combinations enable converters to survive severe LVRT events and increase their fault current contribution without power module oversizing, thereby improving grid support capability under LVRT operating conditions.