Research On High Power Density Modular Digital Control Inverter

400Hz inverter is widely used in the field of aviation.This paper focuses on improving the inverter power density,modular function and reliability under short circuit condition.Dual buck full bridge inverter(DBFBI)solves the problem of shoot through and reverse recovery of parasitic diode.It is suitable for medium frequency inverter application because it makes the Si MOSFET working at higher switching frequency in inverter applications possible.Firstly,the article designs a filter inductor from the view of optimizing system loss.The method of carrier phase shifted SPWM(CPS-SPWM)and inductor coupling can both introduce circulation current.This article analyzes the reason in detail and brings out a design guideline of DC and AC inductors.In order to improve the control bandwidth of the system and meet the need of modular functionavoid,the hybrid control of the digital voltage outer loop and analog inductor current inner loop is adopted.It also avoids the delay characteristic of digital control affecting the system stability.And the method of control parameter design is summarized.The relevant standard requires that the aeronautical static inverter(ASI)can output twice the rated current at the short circuit condition without damage at least 5s.When short circuit happens,the large current will cause a huge loss on the power device and has an impact on the reliability of system.This paper analyzes the operating mechanism of the control circuit when single phase short circuit to ground and phase-to-phase short circuit.A method of switching frequency reduction control is proposed.It remarkably reduces the loss of the system during single-phase short circuit and improves the reliability of the system under severe working conditions.To meet the demand of three-phase or large capacity power supply,improving the expandability of the module is necessary.The CAN bus and the current sharing bus are added into the single-phase inverter system,which reduces the complexity of the connection between modules.The CAN bus realizes the phase synchronization and the setting of the main module democratically.Besides,accurate phase control between modules is achieved by the time stamping function provided by the microprocessor 28335.Finally,two 1500 VA inverter modules have been developed,and the experiment verifies the correctness of the theoretical analysis.