Self-Bootstrapping Isolated Power Converter
Electrical and Electronics
Self-Bootstrapping Isolated Power Converter (GSC-TOPS-374)
Safe, Reliable, and Efficient Compact Self-Starting Bi-Modal Operating Isolated Converters
Overview
Isolated power converters (IPCs) provide safety and performance benefits like noise reduction by separating current flow between a circuit’s input and output. Existing IPCs require bootstrapping the main converter on startup by using a dedicated converter to supply isolated power from the output to the input. The need for two converters decreases efficiency, increases size, weight, and power (SWaP) requirements, and adds complexity to the overall power converter. The bootstrapping problem is significant in space flight applications where SWaP considerations are critical.
In response, engineers at NASA's Goddard Space Flight Center developed the Self-Bootstrapping IPC to eliminate the need for an isolated bootstrap converter by allowing bi-modal operation of a single converter. Specifically, the invention operates in transition mode for bootstrapping and then migrates to fixed frequency mode via closed feedback. This bi-modal converter allows users to benefit from reduced mass and volume, increased power density, and improved efficiency (91-94%).
The Technology
NASA’s Self-Bootstrapping IPC operates in either transition mode for bootstrapping or fixed frequency mode for a regulated output via closed feedback. The transition mode is initially turned on via the input (i.e., primary) voltage control of the main switch and acts as a bootstrap converter utilizing a Gallium Nitrate transistor to control peak primary inductor current. That peak current can be varied via the sensor gain and/or a precise artificially generated offset and controls the switching frequency together with the secondary load (i.e., output). The IPC operates in transition mode until the Pulse Width Modulator (PWM) Under Voltage Lockout threshold is reached and fixed frequency mode begins. Fixed frequency operation is controlled by the PWM and the normal operation mode of the converter maintains a frequency while varying the duty cycle as needed. The PWM is secondary ground referenced and controls primary switching via galvanic isolation. The peak current in transition mode is set higher than the peak current in fixed frequency operation to prevent interruption or instability while in fixed frequency operation after bootstrap is completed. However, the transition mode control can serve as the overall peak current limiter. This invention is applicable to both flyback and buck-derived topologies with similar efficiency and size advantages.
While NASA originally developed the Self-Bootstrapping IPC for CubeSats and space-based electronics with strict SWaP requirements, it may also be useful for safety-critical industries (e.g., aerospace and defense) to allow for high reliability power supplies and more favorable SWaP than existing state-of-the-art high-power dc-dc converters. The reliability, efficiency, and SWaP advantages of this NASA invention could also benefit medium- and high-power commercial power supplies.
Benefits
- Efficiency: Lower operating power consumption than separate bootstrap and main converters.
- High power density: Processes more power per volume unit than state-of-the-art high-power dc-dc converters.
- Small footprint: Combining two converters requires less physical space than separate ones.
- Simplicity & reliability: Use of a single converter reduces technical complexity and redundancy.
Applications
- CubeSats and space-based electronics: NASA’s Self-Bootstrapping IPC is small for factor, lightweight, and efficient, making it ideal for SWaP-conscious space electronics.
- Aerospace and defense industry: High-reliability power supply improves safety and performance of critical aerospace and defense electronics.
- Commercial electronics: Potential to increase the reliability and performance of medium- and high-power commercial power supplies.
Technology Details
Electrical and Electronics
GSC-TOPS-374
GSC-18988-1
Similar Results
Power Processing Unit (PPU) for Small Spacecraft Electric Propulsion
Key subsystems of a scalable PPU for low-power Hall effect electric propulsion have been developed and demonstrated at NASA GRC. The PPU conditions and supplies power to the thruster and propellant flow control (PFC) components. It operates from an input voltage of 24 to 34 VDC to be compatible with typical small spacecraft with 28 V unregulated power systems. The PPU provides fault protection to protect the PPU, thruster, PFC components, and spacecraft. It is scalable to accommodate various power and operational requirements of low-power Hall effect thrusters. An important subsystem of a PPU is the discharge supply, which processes up to 95% of the power in the PPU and must process high voltage to accelerate thrust generating plasma. Each discharge power module in this PPU design is capable of processing up to 500 W of power and output up to 400 VDC. A full-bridge topology operating at switching frequency 50 kHz is used with a lightweight foil transformer. Two or more modules can operate in parallel to scale up the discharge power as required. Output voltage and current regulation controls allow for any of the common thruster start-up modes (hard, soft or glow).
Next Generation “Closed Strayton” Engine Design
The core “Strayton” generator technology consists of a gas turbine engine with short, axial pistons installed inside the hollow turbine shaft. These pistons form a Stirling engine that cycles via thermo-acoustic waves, transferring heat from the turbine blades to the compressor stage, which improves overall engine performance. Power to an alternator is, thus, delivered from both turbine shaft rotation and the oscillation of the internal pistons.
This synergistic relationship is markedly enhanced in a closed-cycle system, where the sealed turbine engine recirculates a working fluid heated via an external source, such as a hydrogen fuel cell and combustor. This system supports higher compression ratios, reduces the turbine diameter to less than 4”, and eliminates the need for large recuperators. Operational efficiency is projected to extend into the low temperature range (750° C), reducing the need for advanced materials and providing cleaner combustion for hydrogen-based applications. Pressurized, inert working fluids also replace mechanical bearings and gearboxes, enabling years of maintenance-free operation.
The fuel cell and Stirling cycle produce 10% of the total system energy, while the Brayton cycle produces 90%. Other external heat sources could include nuclear, solar, or biogas. Conservative estimates for the hydrogen fuel-cell configuration lifetime are in the 100,000 hour range.
High-Voltage Power System for Hybrid Electric Aircraft Propulsion
Glenn's novel system supports the NASA Aeronautics Research Mission Directorate (ARMD) strategic plan to leverage advancements in technologies over the next 25 years and beyond, leading to new aircraft configurations with enhanced performance, improved energy efficiency, and reduced CO2 emissions. The electric system is a multi-megawatt micro-grid that converts mechanical energy to electric via generators, and electric energy to mechanical via motor-driven fans. This innovation would use the variation in aircraft throttle settings to produce a high-voltage (20 kilovolts), variable-frequency 9-phase AC distribution system. Using doubly fed electric machines (generator, propulsor, and flywheel) allows for field excitation that can cause variable-frequency or variable speed operation around the commanded throttle setting. The flywheel enables an energy storage system that recovers and reuses energy, while the flywheel slews with the throttle control using the electromagnetic torque produced by the doubly fed electric machine. This design permits both sub-synchronous and super-synchronous operation using limited field excitation power provided through power converters. Finally, the reduced switchgear mass facilitated through the use of a high-frequency AC system, setting-less protection zones, and simplified switches for fault clearance provides enhanced operational capability. This system can be controlled so that fault energy is minimized, preventing collateral damage to aircraft structures even with high voltage distribution. Glenn's innovative system adds performance, efficiency, reliability, and cost savings to cutting-edge hybrid electric technology.
This is an early-stage technology requiring additional development, and Glenn welcomes co-development opportunities.
Enhancing Fault Isolation and Detection for Electric Powertrains of UAVs
The tool developed through this work merges information from the electric propulsion system design phase with diagnostic tools. Information from the failure mode and effect analysis (FMEA) from the system design phase is embedded within a Bayesian network (BN). Each node in the network can represent either a fault, failure mode, root cause or effect, and the causal relationships between different elements are described through the connecting edges.
This novel approach can help Fault Detection and Isolation (FDI), producing a framework capable of isolating the cause of sub-system level fault and degradation.
This system:
Identifies and quantifies the effects of the identified hazards, the severity and probability of their effects, their root cause, and the likelihood of each cause;
Uses a Bayesian framework for fault detection and isolation (FDI);
Based on the FDI output, estimates health of the faulty component and predicts the remaining useful life (RUL) by also performing uncertainty quantification (UQ);
Identifies potential electric powertrain hazards and performs a functional hazard analysis (FHA) for unmanned aerial vehicles (UAVs)/Urban Air Mobility (UAM) vehicles.
Despite being developed for and demonstrated with an application to an electric UAV, the methodology is generalized and can be implemented in other domains, ranging from manufacturing facilities to various autonomous vehicles.
Novel, Solid-State Hybrid Ultracapacitor Battery
The subject technology is an extension of closely related, solid-state ultracapacitor innovations by the same team of inventors. The primary distinction for this specific technology is the addition of co-dopants to affect the dielectric behavior of the barium titanatebased perovskite materials. These co-dopants include lanthanum and other rare earths as well as hydroxyl ions. The materials are processed at the nano scale, and are subjected to carefully designed thermal treatments as well.
The presence of the hydroxyl ions has been shown to provide several orders of magnitude increase in the capacitance of the dielectric material. Additionally, these high capacitance values are obtained at relatively low voltages found in current consumer and industrial electronics.
The capacitors tested to date are simple, single-layer devices. Ultimately, a range of manufacturing methods are possible for making commercial devices. Features of the technology enable manufacturing via traditional thick-film processing methods widely used in the capacitor industry, or via advanced printing methods for state-of-the-art printed electronics.
Future efforts will be made to advance the manufacturing and packaging processes to increase device energy density, including multilayer devices and packages
