The Stability Analysis And Optimization Design Of S3R Based On Nonlinear Model

With the increasing requirements for high power and high voltage of the spacecraft, the power system of spacecraft has experienced great development in recent years, and the solar array-battery power supply system has been widely used by far. The sequential switching shunt regulator (S3R) in power conductioning unit (PCU) is used to regulate the current produced by the solar array and maintain the output bus voltage, which is a very important part of PCU. The stability analysis of S3R is very important for the system design. For S3R is formed by power cells in parallel, the control loop of system is parallel hysteresis method, which has strong nonlinear feature. The approximate linearization method has been used for modelling hysteresis by now, but this modelling method ignores many nonlinear characteristics of system, which will lead to an inaccurate stability analysis.The S3R in PCU of100V bus voltage grade with hyateresis control method is the objectof study. To obtain a more accurate stability analysis of S3R, the describing function (DF) method is adopted to model the nonlinear link of S3R in this paper. S3R is analysed by two models, the approximate linearization method and describing function. There are many parameters, like PI parameters and the overlap between two hysteresises, have an effect on the stability analysis with describing function modelling method.The simulation waveforms by PSIM prove that a special operating mode, two power cells in S3R both in the PWM mode, will appear under the critical stable. To analysis of the output characteristic of the system in this special operating mode, an iterative calculation formula for S3R has been deduced. An iterative calculation program is established to describe the bifurcation diagram of the system output voltages phase diagram. The bifurcation diagram can determine the region of this special operating mode.Simulation and experimental results show that the stability analysis by describing function method is exacter than by the approximate linearization method, which means the describing function model is more accurate; and the results also show that the parameters have an effect on the stability, which give a system optimization method; at last, the results show the correctness of the iterative procedure, which give a way to canclulate the region of double section. This paper gives a new method to design S3R and system optimization.