Analysis And Modeling Of Nonideal Converters For Power Conditioning Unit

The power supply system is very crucial for the stability of spacecraft system.Hence,the power conditioning unit(PCU)is very important as the control unit of the power supply system.In high power system,control strategy with regulated bus voltage under Solar Array-Battery(SA-B)system is widely used.In power system using sequential switching shunt regulator(S3R)technology,the bus voltage is regulated by PCU with sequential shunt,battery charging regulator(BCR)and battery discharging regulator(BDR).Typical non-isolated step-up and step-down converters are discussed in this paper for BCR and BDR application.This paper takes Superbuck converter as BCR topology and HE-Boost converter as BDR topology for spacecraft power system application.The frequency responses of both converters are analyzed and the small-signal models are established to ensure the stability and reliability of the power system.There exist non-ideal parameters in practical circuits,such as the nonlinearity of inductors,equivalent series resistor of power devices and transformer leakage inductor.Non-ideal parameters will influence the working condition of practical converter.To optimize the control system parameter and improve converter performance,the primary non-ideal effects are analyzed.As to Superbuck converter,damping network is introduced to avoid right half plane(RHP)zero.In the meantime,the small-signal model of Superbuck converter is derived considering the inductance nonlinearity and equivalent series resistor(ESR).The existence of transformer leakage inductor as well as the nonlinearity and ESR of input inductor influences the working principle and frequency response of HE-Boost converter.In this paper,the leakage inductor current freewheeling mode is analyzed and small-signal model of non-ideal HE-Boost is established.Working in the battery charging domain,Superbuck converter has three status:1.constant current charging in sufficient sunlight condition 2.restricted current charging in insufficient sunlight condition.3.constant voltage charging with battery fully charged.Working in the battery discharging domain,HE-Boost converter aims to maintain bus voltage.The control strategy is determined based on the working status of both converters.The parameter design results are given in this paper,and a 1.8kW BDR/3A BCR prototype is built to verify the theoretical analysis and derived small-signal models.For Superbuck converter,theoretical model proves to be accurate with deviation less than 1dB in amplitude and 10 degree in phase while the deviation is less than 2dB and 20 degree for HE-Boost converter.And the design of control system meets the design requirements.