A Controller Improving Photovoltaic Voltage Regulation in the Single-Stage Single-Phase Inverter

While substantial research covers current control and synchronization of grid-connected photovoltaic (PV) inverters, issues concerning control of the PV input voltage deserve more attention, as they equally affect the reliable and stable operation of the system. Hence, this article analyses the PV voltage regulation in the single-stage single-phase PV inverter. In contrast to previous work, the PV source influence on the input voltage dynamic is analytically formalized, exposing a potential instability when the PV source is operating in its constant current region. A traditional proportional-integral PV voltage controller fails to ensure a consistent and stable voltage regulation. On the other hand, this issue is resolved by the proposed feedback linearization based controller. The new controller is validated on a test setup comprising of a PV source emulating a 1.2 kW PV array, interfaced to a single-phase inverter connected to a grid emulator. Confirming the issues predicted by the theoretical analysis, the experiments prove two main advantages of the proposed controller. First, PV voltage regulation instability is eliminated when the PV array operates in its constant current region. Second, the PV voltage transient behavior is now independent of the operating point of the PV source.

I. Introduction

The electricity sector is going through a green revolution, powered by the uptake of renewables and retirement of fossil-fuel-based generation. In this scenario, solar photovoltaic (PV) systems are among the largest contributors to the renewable energy mix, thanks to the key role of power electronic converters. Modeling and control of converters is an established yet ever-growing topic among industrial and academic circles, which initially focused on dc–dc converters and then delved into dc–ac converters. Despite the early achievements, small-signal models of dc–dc converters were formally revisited in the presence of a PV input only in the mid 2000s. In [1] and [2], it was found that the dynamic resistance of the PV source heavily affects the converter transient performance and PV voltage regulation. Later, the authors in [3]–[8] revealed stability issues in PV interfacing current-controlled buck converters caused by the variability of dynamic and static resistance of the PV source.