Research On Multiphase Interleaved Battery Discharge Regulator For Spacecraft Power Conditioning Unit

The PCU(Power Conditioning Unit)provides electricity for the payload in spacecraft,BDR(Battery Discharge Regulator)modulesare connected battery with power bus to maintain the bus to work properly during insufficient light for heavy load periods.Multi module parallel method is usually used in BDR to realize power expansion.At present,the design and development of PCU are mostly based on the requirements of ESA(European Space Agency).In order to adapt to the complex space environment and guarantee the power supply quality of the spacecraft,ESA puts forward higher requirements on the characteristics of BDR.First of all,ESA electrical and electronic standard demands the phase margin shall be at least 60° and the gain margin 10 d B.Secondly,the bus voltage ripple is taken as the steady requirement and the closed-loop output impedance is taken as the dynamic requirement.Finally,efficiency,power density and reliability are all the key issues to be considered in the design of BDR.The objective of this thesis is to improve the stability margin,power quality and power density of BDR by researching the calculation of output filter capacitor,the selection of topology and the design of controller and control method to apply to multi modules interleaved BDR.The main contents of this thesis are as follows:First of all,this thesis proposes the method to estimate the effect of inductance mismatches on output capacitance selection.Interleaving is a technique that is commonly used to reduce the demand for filter capacitor.However,variations of the filter inductancemay affect the performance of power supply,if the output capacitance is considered under ideal condition,the voltage ripple and dynamic response requirements maybe not satisfied.To solve this problem,the method to calculate output capacitance is presented that ensures the power supply quality of BDR under inductance mismatchby time domain and frequency domain analysis on multiphase interleaved converters.Secondly,in order to meet the requirement of high dynamic response of BDR,a two-phase inverse interleaved coupled inductor Boost converter is proposed.At present,low frequency high-power satellite synthetic aperture radar and the development of communication satellite put forward higher requirements for the dynamic characteristics of BDR.In response to this background,the new converter breaks the energy transfer method between the input and output terminals by coupled inductor,so that the zeros move from the right half plane to the left half plane,the fast dynamic response can be achieved as well as stability.Meanwhile,the input and output inductors in the new converter have been all integrated into one magnetic core,so that the power density is further improved.Thirdly,to reduce the input and output current ripples of the single BDR,a low ripple coupled inductor Boost converter is proposed in this thesis.The more the number of modules is,the better the current ripple cancellation effect in multiphase converters will be.However,the number of parallel BDR is relatively low in low power satellite platform,as a result,the ripple cancellation effect by multiphase is limited.To solve this problem,the operation principle and impact of component tolerances on coupled inductor filteris analyzed,a proper filter design,together with an acceptable attenuation gain under non-ideal factor conditions,is presented.Referring to this method,a low ripple coupled inductor Boost converter composed of a coupled inductor filter and a Boost converter is designed.With only one magnetic core,low-current-ripple in both the input and output terminals is achieved.Finally,in order to ensure that the BDR has sufficient stability margin and good dynamic characteristics to meet the application requirements,a new compensator and loop control method are proposed in this thesis.The proposed compensator can maintain sufficient phase compensation in wide frequency range.Better phase margin,gain margin,module margin and delay margin areachieved by the new compensator in multiphase converter than that of the traditional type II compensator controlled one.In addition,the new control method is also shown to elevate perturbation rejection ability by reducing closed-loop output impedance and audio susceptibility.A further benefit of these methods is that the two can be combined to improve the stability of power supply,and the fluctuation of output voltage can be reduced when the load current or the input voltage changes.