Research On Module-Combined 400Hz Inverter And Its Control Technologies

400Hz inverters are widely used in aviation,ship and other fields.In order to achieve the modular three-phase inverters with high efficiency,simple connection,high output voltage quality and strong ability for imbalance loads,the single-phase 400 Hz inverter module based on three-level half-bridge inverter topology and the control technologies for simply combining three modules to a three-phase inverter are studied.Firstly,the principles of 3L-NPC half-bridge inverter and T-NPC half-bridge inverter are introduced.The loss analysis model for NPC inverters based on MOSFETs is established.The losses of power devices between the two topologies have been analyzed and compared.The influence of the switching frequency on the losses is clarified,which provides a theoretical basis for selecting the power circuit and switching frequency.The filter structure optimization of the inverter module has been studied.The passive damping and subharmonic traps are used to reduce the filter volume.To achieve high quality output at the steady state and dynamic state,the control technologies and the design procedure of the regulators of the inverter based on the output voltage RMS outer loop,instantaneous output voltage loop and instantaneous inductor current loop are analyzed.The method of combining three modules to a three-phase inverter based on single-phase inverter module is studied.In order to solve the problem of symmetry of output voltage when combining three modules to a three-phase inverter with the method of decentralised control,a phase closed loop control scheme of three-phase output voltage has been proposed.With this scheme,the output voltage symmetry of the combined three-phase inverter is ensured under various imbalance load conditions.A 3.3kVA single-phase T-NPC inverter module and a combined inverter prototype consisting of three single-phase modules are developped based on the theoretical analysis.The experimental results verify that the single-phase inverter module designed in this paper has excellent steady state and dynamic performance,and the three-phase inverter can be directly combined by three single-phase inverters without the need of an external combination controller,and the combined inverter has a strong ability for imbalance loads.The output voltage symmetry is satisfying under imbalance load conditions.The output characteristics of the 10 kVA combined three-phase 400 Hz inverter prototype based on three 3.3kVA modules are in line with the relevant standards.