Parallel-connected Inverters Power System Harmonic Suppression Technology Based On Decentralized Control

In recent years,new energy power generation technologies based on renewable energy such as wind power and solar energy have been greatly developed.The proportion of new energy power in energy structure is increasing,which provides conditions for large-scale construction of distributed power generation systems.In the multi-inverter parallel grid-connected application,the power electronic device introduces many power harmonics to the grid,and the control parameter differences of each distributed power generation system,the line impedance difference,and the geographical difference will access the grid point.Power quality has a large impact,and even leads to system instability.When optimizing for a single distributed generation system,further cost control,efficiency improvement and reliability optimization are very difficult,and carrier-interleaved multi-inverter parallel control has certain advantages compared with traditional methods,including: low cost(Removal of ripple reduction requirements for passive filters),high reliability(large-capacity capacitors used in filters are considered to be reliability bottlenecks),and modularity(systems can work with multiple low-power modules).The lumped control technology of multimachine parallel connection is greatly constrained by environment and cost in practical applications,and the long communication line will reduce the reliability of system operation.This paper takes parallel inverter system as the research object,based on carrier phase shift control.The technology proposes a multi-inverter parallel harmonic suppression method under autonomous control.The research contents and innovations of this paper are summarized as follows:In view of the low switching frequency of high-power inverters,it is necessary to use high-capacity capacitors to absorb higher harmonics.Based on the advantages of carrier phase shift control technology in controlling the high order harmonics of inverters,the carrier phase shifting technology is applied to high power converter.In the grid-connected scenario where the inverter is connected in parallel,the original lumped control or high-bandwidth communication control strategy is improved,and the global carrier synchronization signal is designed according to the inherent synchronization characteristics of the system.Under the decentralized control,the phase of each inverter carrier is adaptively adjusted with a relatively low frequency to realize carrier interleaving control between multiple inverters.The controller monitors the inverter carrier phase in real time,and sets the relevant carrier phase difference according to the actual operating conditions of each inverter,thereby achieving efficient suppression of the inverter switching times and above,and reducing the capacity of the filtering capacitor.For the island operation mode,the accurate power shared control of the parallel connected converters,according to the physical parameters of the system,based on the droop control power sharing,set the matching fundamental frequency virtual impedance to achieve the converter accurate power sharing.Aiming at the problem of low-order harmonic voltage caused by nonlinear loads,a control method using harmonic frequency virtual impendance to suppress low-order harmonic voltage is proposed.According to the inherent synchronization characteristics of the droop control system,combined with carrier phase shift control,the global carrier synchronization signal under the decentralized control of the island system is designed to realize interleaving PWM between multiple inverters,and the power harmonic suppression of the island system is achieved.Finally,a multi-inverter parallel experimental platform is built,and the correctness and effectiveness of the control and modulation strategies proposed in this paper are verified by experiments.