Improved Passivity-based Control Method of Grid-connected PV Inverter in Weak Grids

With the continuous increase in the penetration rate of photovoltaics (PV), the operating environment of the power grid becomes more and more complex. Weak grids usually present electrical characteristics like high harmonic content, high grid impedance and fluctuating voltage. When a grid-connected PV inverter is connected to weak grids, the traditional control method shows its limitation. In view of the nonlinearity of the mathematical model of the PV inverters, the algorithm derived from passive-based control (PBC) theory can be used to control the PV inverter, enabling the inverter to have better performance in weak grids. Firstly, this paper establishes the Euler-Lagrange (EL) mathematical model of the inverter based on energy method, and proves the passivity of the inverter system. Secondly, passivity-based control is applied to design the traditional passivity-based controller of the inverter system by injecting damping; then an improved passivity control method based on quasi-PR control method is proposed, namely, the error energy is first sent to the quasi-PR controller to change the damping coefficient of the system, then the coefficient is send to a conventional passivity-based controller to achieve the improved passivity-based control method. Finally, experimental comparison of the two methods show that the improved passivity-based control method is more suitable for weak grids with voltage instability and large impedance. The experimental results verify that the improved passivity-based control has strong robustness when the voltage fluctuates.