A simple technique linearizing and decoupling dc-link voltage control from source nonlinearity in single-stage photovoltaic inverters

The nonlinear behavior of photovoltaic (PV) sources can deteriorate the performance of PV inverters if their control system is not designed carefully. This article investigates the PV source influence on the dc voltage regulation of single-stage single-phase grid-connected inverters. The analysis reveals two issues: undesired strong coupling between regulation transient performance and PV source operating point, and possible instability arising when the PV source operates on the left-hand side of its maximum power point (MPP). To eradicate these issues, the idea to add the PV power feedforward signal to the output of the dc voltage controller is applied. This action cancels the nonlinearity induced by the source, responsible for poor PV voltage regulation performance, resulting in large-signal linear and stable dc voltage control dynamics. The benefit is twofold. First, the dc voltage transient response is desirably decoupled from the PV source operating condition (left-hand side of MPP, MPP, and right-hand side of MPP). Second, the possible instability occurring at the left-hand side of the MPP is eliminated. The research findings are supported by simulations and experimental results extracted out of a grid-connected inverter fed by a PV emulator. Through this testbed, the proposed controller is compared against conventional and emerging dc voltage control schemes.