Abstract
For the complex harmonic coupling problem caused by the parallel connection of grid-connected photovoltaic inverters to the grid, the mathematical models of a single three-phase inverter and two three-phase inverters connected in parallel are established in this paper. The transfer function is derived and the resonant characteristics of grid-connected single inverter and parallel grid-connected multi-inverters are analyzed by using Bode diagram. On the basis of the maximum power tracking link, This paper proposes a control strategy which combines the double closed-loop of current by using grid-connected voltage and capacitive current with the proportional feedforward compensation of grid voltage, which maximizes the use of solar energy and has a better harmonic resonance suppression capability at the same time. The effectiveness and correctness of the proposed control strategy are verified by Matlab/Simulink system simulation.
Highlights
Inverter is the core device of photovoltaic power station
It plays an important role in the utilization of solar energy, but it will produce a series of harmonic resonance problems, which will seriously affect the stability of the system[1]
When only the grid voltage acts alone, the other voltage sources can be regarded as short circuit, and the output voltage transfer function is equation (7),of which,Z1 is parallel to R11, sL21 and sC21,Z2 is parallel to R21, sL21 and sC21, Z3 is parallel to Z1, sL12 and Z2, sL22
Summary
Inverter is the core device of photovoltaic power station. It plays an important role in the utilization of solar energy, but it will produce a series of harmonic resonance problems, which will seriously affect the stability of the system[1]. In [3], the resonant coupling characteristics of multi-grid-connected inverter are analyzed, and it is pointed out that the resonant peak value and frequency are related to the number of parallel inverters. The coupled resonance characteristics of the inverter are analyzed according to the Bode diagram drawn, and the current outer loop is constructed by using the grid-connected voltage and current through the quasi-PR controller.
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