Research On Parallel Control Of 400Hz Modular Inverters Based On LCL Filtering

400Hz intermediate frequency power supply has a wide range of applications in airports and ships.It provides power for aircraft ground and ship surface power inspection,maintenance and engine startup.It needs to have the ability to provide high quality,high reliability and large capacity power.The use of modular inverters in parallel is an effective way to increase the capacity and reliability of inverter power supplies.In parallel,inverters need to take appropriate technical measures to ensure their steady state and dynamic performance,and to achieve power sharing and circulating current suppression.Compared with inverter modules that use LC filtering in parallel,the LCL filter used in the inverter module can increase the line impedance and change the impedance angle of the inverter’s equivalent output impedance,which is beneficial to reduce the circulating current and use decoupling droop control The power sharing is realized,but the output voltage quality problem of the inverter with LCL filtering will occur when there is a nonlinear load.It is of theoretical significance and practical value to study the parallel connection of inverter modules based on LCL filtering and its voltage quality control technology.Firstly,the advantages of LCL filter in circulating current suppression and power sharing when the inverters are connected in parallel are analyzed.The complex transfer model and parallel model of the inverter are established,and the magnitude of the parallel circulating current is related to the voltage difference,phase difference,and equivalent output impedance of the two inverters.The principle of droop control is analyzed,and the droop control of the inverter is pointed out.When the inverters are connected in parallel,the power sharing degree is related to the impedance angle of the equivalent output impedance of the inverter.The advantages and disadvantages of changing the equivalent output impedance and impedance angle of the virtual impedance technology and using the LCL filter are compared and analyzed.The LCL is also analyzed.The mechanism of filter inverter’s output voltage quality problem under non-linear load.Aiming at the voltage quality problems of LCL filter inverters under non-linear loads,a multi-scale resonant controller and load current feedforward are used to form a virtual negative harmonic impedance to reshape the equivalent output impedance of the inverter at harmonic For small impedance.The parameters of LCL filter and multi-scale resonant controller are designed,and the aforementioned control methods are simulated and experimentally researched.It is verified that the proposed method can improve the output voltage quality of LCL filter inverter with non-linear load.Finally,the droop parallel control strategy of the LCL filter inverter using harmonic impedance remodeling is studied.The dynamic vector method is used to model the small-signal LCL filter inverter parallel system with droop control,and the influence of droop parameters on the stability of the parallel inverter system is analyzed using the Helvetian criterion,and the load-side inductance is also analyzed.Influence on the value of reactive sag coefficient and active sag coefficient.Through simulation and experiments,it is verified that the LCL filter inverter with droop control can achieve better circulating current suppression effect and power sharing effect.