Research On Multi-output Isolated DC Power Supply

With the continuous improvement of the electrification of multi-electric aircraft and airborne electrical equipment,the demand for multi-output DC power supplies continues to increase.The traditional multi-output DC power supply often realizes the expansion of multiple outputs by using transformer with multiple secondary windings,but the following problems exist: 1)limited output channels;2)low accuracy for auxiliary outputs;3)no independent fault protection.In-depth study of the above issues will help broaden the application range of multi-output DC power supplies.In this thesis,a two-stage multi-output power supply is studied.The LLC resonant circuit at the front stage realizes voltage isolation conversion and stable output voltage.The back stage uses multiple power switches to realize the expansion and the independent control of the multiple outputs.The control strategy based on feedback capacitor is adopted to reduce the current peak when the capacitive load is turned on.The variation law of voltage and current of the switch under different loads is derived and the design method of main circuit parameters is given.To improve the fault protection capability,the transformer with variable magnetizing inductance is studied to increase the hold-up time.And independent overload protection circuit is designed for each output.In addition,a compensation circuit is studied to effectively solve the problem of increased load regulation due to the introduction of the back-stage circuit.For the back-stage power switch,different mission profiles are discussed and the corresponding junction temperatures are extracted.The physical model of the power switch is established to maintain the distribution of thermal stress by finite element simulation.Based on the failure mechanism analysis,the life model is established to realize the life prediction of the power switch.A prototype of 5-output 75 W power supply with 28 V input and 15 V output is built to verify the operating characteristics and fault protection functions.The hold-up time can be increased to about three times by controlling the magnetizing inductance.The overload fault for each output can be protected independently.And a prototype of 175 W power supply with 28 V input,5-channel 15 V outputs,5-channel-15 V outputs and 5-channel 5V outputs is modular integrated built based on thermal structure analysis.The compensation effect of the load regulation compensation circuit is verified.