Research On Stacked Boost Converters For The Primary Power Systems Of Spacecraft

Power Conditioning Unit (PCU) that allocates the energy among solar array, battery and primary load in a rational way plays an important role in the primary power system of spacecraft. According to the standards specified by the European Space Agency (ESA), the input and output of modules in PCU should have the like-polarity voltage and continuous current. As the traditional DC/DC converters are hard to meet these requirements, they are not suitable for PCU.Stacked Boost Converter (SBC) consists of a stacked branch and an isolated DC/DC converter in parallel at input and in series at output. It belongs to non-isolated boost DC/DC converter with continuous current. When the voltage gain is less than3, SBC is suitable for aerospace applications as a result of the merits of high efficiency, continuous input and output current and easily controlled system.In this paper, the topologies of SBC, the effect of leakage inductor and the improvements of system stability will be focused.By combining the stacked branch and isolated DC/DC converter in different ways, the structures and generation rules of three kinds of standalone-inductor SBC are proposed, which are named as V-SBC1, C-SBC1and C-SBC2respectively. Then, several standalone-inductor SBC topologies are derived, including not only the proposed topologies that can’t realize low-ripple input current and high voltage gain but also some new SBC topologies with excellent performance.Further research on standalone-inductor SBC indicates that the standalone inductor in standalone-inductor C-SBC1and C-SBC2can be substituted by coupled inductor. By changing the two windings of coupled inductor in different branches, the structures and generation rules of two kinds of coupled-inductor SBC are proposed, which are named as C-SBC1and C-SBC2respectively. Compared with standalone-inductor SBC, the total volume and weight of inductor are reduced, the voltage gain and current ripple can be regulated either by the turn ratio of transformer or coupled-inductor to meet the application requirements. Coupled-inductor SBC has many unique advantages comparing with standalone-inductor SBC.In order to avoid the short circuit at the input terminal, SBC contains a transformer. Usually, the analysis of operating modes is simplified by neglecting the leakage inductor. If the leakage inductor is considered, the operating modes will be very complicated. Therefore the steady state performance is affected. With push-pull SBC, the topologies are divided into four kinds according to the different characteristics of current spike which is introduced by the leakage inductor. Three representative topologies with positive spike, negative spike and positive&negative spike are analyzed to investigate the effect of leakage inductor on the transient switching procedures. After this, Equivalent Current Sampling Method (ECSM) which eliminates the sampling time delay and achieves excellent dynamic performance is adopted to prevent the spike disturbance on current sampling. However, ECSM reduces the sampling accuracy due to neglecting the spike. So the current sampling error is analyzed in quality and quantity, which provides the foundation for offsetting and enhancing the sampling accuracy.The operating modes of PCU are complicated. The DC/DC converters in PCU operate in parallel or in cascade. So the stability of PCU is not only depended on the loop gain of single converter, but also influenced by the coupling relationship between converters. If SBC is chosen as the load converter, the input voltage ripple can’t be neglected. Besides the loop gain, audio susceptibility and input impedance should be taken into account. The audio susceptibility and input impedance can be optimized by improving the control strategy which needs additional components and makes the control system hard to design. Based on the proposed three-capacitor structure, this paper analyzes the effect of the output capacitors and parasitic parameters, then proposes the single-capacitor structure. Considering the parasitic parameters, the small-signal models of push-pull SBC with single-capacitor and three-capacitor are set up to compare the loop gain, output impedance, audio susceptibility and input impedance. Compared with three-capacitor structure, two capacitors are spared to enhance the power density for single-capacitor structure. The output capacitor can be designed without considering the audio susceptibility and input impedance. Moreover, the audio susceptibility and input impedance can be obviously improved under single-capacitor structure.