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This paper proposes a megawatt (MW)-scale high-voltage (HV) electrical power-conversion element for large-spacecraft electric propulsion (EP) systems. The proposed scheme is intended for long-term and crewed missions, and it is driven by a nuclear electric propulsion (NEP) that acts as a heat source. The scheme includes (i) A two-rotor generator (TRG), (ii) A rectification stage, and (iii) An isolated dual output DC-DC (iDC2) converter. The TRG is a high-reliability electric machine with two rotors, a permanent magnet rotor (PMR), and a wound field rotor (WFR). The PMR has a fixed flux and hence back-EMF, while the back-EMF due to the WFR is controlled by injecting a direct current (DC) into the WFR winding. The total TRG output voltage, which is the sum of voltages due to the PMR and WFR, is controlled over a prescribed region of spacecraft operation. The output of the TRG is rectified and connected to the input of the iDC2 converter. The iDC2 converter uses a three-winding transformer, where the primary winding is fed from the rectified output of TRG, the secondary winding processes the propulsion power to an electric thruster via a high-voltage DC (HVDC) link and a tertiary winding that is connected to the spacecraft's low-voltage DC (LVDC) power system. Three controllers are proposed for the system: an HVDC voltage controller, an HVDC current controller that controls the voltage and current processed to the thruster, and an LVDC controller that adjusts the current to the LVDC system. Detailed analytical models for the TRG, iDC2 converter, and controllers are developed and verified via simulations under different conditions. The analytical studies are further validated via results from a laboratory prototype. [ABSTRACT FROM AUTHOR]

Timed Failure Propagation Graphs (TFPGs) have been widely used for the failure modeling and diagnosis of safety-critical systems. Currently most TFPGs are manually constructed by system experts, a process that can be time-consuming, error-prone, and even impossible for systems with highly nonlinear and machine-learning-based components. This letter proposes a new type of TFPGs, called Real-Valued Timed Failure Propagation Graphs (rTFPGs), designed for continuous-state systems. More importantly, it presents a systematic way of constructing rTFPGs by combining the powers of human experts and data-driven methods: first, an expert constructs a partial rTFPG based on his/her expertise; then a data-driven algorithm refines the rTFPG by adding nodes and edges based on a given set of labeled signals. The proposed approach has been successfully implemented and evaluated on three case studies.

With the development of space exploration, high-power and high-voltage power systems are essential for future spacecraft applications. Because of the effects of space radiation such as single event burnout (SEB), the rated voltage of power devices in converters for a spacecraft power system is limited to a level much lower than that for traditional ground applications. Thus, multi-level DC/DC converters are good choices for high-voltage applications in spacecraft. In this paper, a fault-tolerant strategy is proposed for a three-level flying capacitor DC/DC converter to increase the reliability with minimal cost. There is no extra hardware needed for the proposed strategy; the fault tolerance of the converter is only achieved by changing the software control strategy. A stage analysis of the proposed strategy is provided in detail for different fault locations and ratios between the input and output voltage. Finally, a simulation model and prototype are built to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Simplified modeling of a spacecraft power system is proposed to predict the conducted electromagnetic compatibility (EMC) environment. A key element of the spacecraft conducted environment is the electrical power subsystem, which corresponds to the power source. Since the impedance of the power source has a significant effect on conducted interference, the assessment of power bus impedance is essential to control and manage spacecraft EMC. In the proposed model, all components inside the power system were modeled as simple equivalent circuits with lumped elements. The advantage is that it simplifies the complex power system so that its impedance can be quickly obtained at the early stage of spacecraft system design and development. The model is validated by comparing the calculated results with experimental data. The comparison results between simulation and experiment showed good agreements.

With the development of space exploration, high-power and high-voltage power systems are essential for future spacecraft applications. Because of the effects of space radiation such as single event burnout (SEB), the rated voltage of power devices in converters for a spacecraft power system is limited to a level much lower than that for traditional ground applications. Thus, multi-level DC/DC converters are good choices for high-voltage applications in spacecraft. In this paper, a fault-tolerant strategy is proposed for a three-level flying capacitor DC/DC converter to increase the reliability with minimal cost. There is no extra hardware needed for the proposed strategy; the fault tolerance of the converter is only achieved by changing the software control strategy. A stage analysis of the proposed strategy is provided in detail for different fault locations and ratios between the input and output voltage. Finally, a simulation model and prototype are built to verify the effectiveness of the proposed strategy.

The solar arrays of space stations, communication satellites and lunar/Mars rovers, are occasionally partially shaded by the vehicles themselves. The shading can cause the output power of the solar array to significantly decrease even when the shaded area is quite small. This effect is stronger in direct energy transfer power systems, which are widely used in space applications because of their simplicity and reliability. In this study, we develop a model of solar arrays to evaluate their power performance under partially shaded conditions. Our analysis considers the various impacts of irradiation, partial shading, and layout of the solar array. Two objective functions that can be used to assess the overall power performance of solar arrays under various conditions are proposed. A multi-objective genetic algorithm with a small population is also proposed to optimize the layout of the solar array. The experimental results on a scaled-down equivalent model verify the effectiveness of the proposed method, and demonstrate that the magnitude of the power reduction and variation under partially shaded conditions decreases without increasing the system complexity. [ABSTRACT FROM AUTHOR]

This paper proposes a novel electrical power supply system architecture (power conditioning and processing unit, PCPU) for high-power all-electric propulsion spacecraft platform with high-voltage power bus (HVBUS) powering thrusters and regulated power bus (VBUS) powering onboard payloads, respectively. The design principle of function modules in PCPU has been analyzed. Besides, the test on electrical characteristic of VBUS and HVBUS in prototyped system proves the stable and reliable work of buses in PCPU. [ABSTRACT FROM AUTHOR]

In this paper, a pulsewidth modulation (PWM) plus secondary-side phase-shift (SSPS) controlled full-bridge three-port converter (FB-TPC) is proposed for a renewable power system, which is derived by integrating two interleaved buck/boost circuits (IBBC) and a SSPS full-bridge converter (FBC), to interface the energy source, energy storage element, and output load simultaneously. The two switching legs are shared by the IBBC and FBC, which improves the active devices sharing ratio and power density. With PWM plus SSPS control scheme, decoupled power control can be realized and the converter can achieve wide input voltage range power conversion. In addition, zero-voltage switching (ZVS) of both the primary and secondary switches are achieved in a wide range. Furthermore, the circulating current can be greatly eliminated, which helps to reduce conduction losses. Moreover, the voltage stresses on the secondary rectifier are effectively suppressed since the power switches and diodes are clamped to output voltage. The operation principles, output characteristics, ZVS performances, and control strategy are analyzed in detail. Experimental results of a 600-W prototype are provided to verify the effectiveness and the advantages of the proposed converter. [ABSTRACT FROM PUBLISHER]

This paper presents some rigorous arguments on a chaotic strange attractor in a spacecraft power system, which is a 3D system with hysteresis switching. By carefully picking a suitable cross-section with respect to the attractor, we find a topological horseshoe of the corresponding third-returned Poincaré map, thus giving a rigorous verification of the existence of chaos in this system. Numerical computation shows that the two Lyapunov exponents of the Poincaré map are both positive and that there exists a two-directional expansion in this horseshoe, suggesting that this attractor is hyperchaotic in nature. [ABSTRACT FROM AUTHOR]