System Frequency Dynamic Response of a Novel, Self-Synchronizing Inverter in a High Renewable Penetration Grid

Abstract

In this thesis, a controller achieving current tracking objective without knowledge of the grid parameters is developed. An estimated rotating reference frame (γδ-frame) is utilized. Within the control scheme, adaptive compensation terms facilitate the current tracking objective and, simultaneously, accounts for the unavailable grid voltage magnitude, grid frequency, and grid phase, hence eliminating the need for an additional measurement and feedback system for synchronization, such as a Phase-Locked Loop (PLL). System frequency behavior using the controller in a high-renewable (low-inertia) grid indicates that the monitored performance metrics are significantly improved when compared to PLL-controlled, inverter-dominated grids. v Table of Contents Acknowledgements .

Nonlinear Self-Synchronizing Current Control for Grid-Connected Photovoltaic Inverters

“…Motivated by the subsequent stability analysis and using the open loop error dynamics for the current in (20), the following duty cycle control inputs are defined as follows:…”

“…where k d i ∈ R + is a positive estimation gain. The closed loop error dynamics of the current are obtained by substituting (21) into the open loop error dynamics in (20) as follows:…”

“…Many approaches have been proposed in the literature to improving the performance of the PLL schemes to address any potential instability issues resulting from the interaction between the PLL schemes and current control loop [17,18]. These challenges have motivated researchers to develop control schemes for grid-connected inverters that do not require a synchronization system such as PLLs [19][20][21][22]. For instance, the authors in [23] proposed a direct power controller for a single-phase grid-connected inverter without a PLL scheme.…”

“…Although these methods do not need a PLL scheme, they do not consider a grid-connected PV system or the additional dynamics this would entail. Previous studies [19][20][21][22][23][24] have considered a fixed dc voltage as an input. Hence, the dynamic of the PV panels, dc voltage regulator, and maximum power point tracking algorithm are not included in their control schemes.…”