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Electrified aircraft propulsion (EAP) is a prospective advanced propulsion concept to reduce aircraft noise, NOx emissions and aircraft fuel burn. In its most primitive definition, EAP refers to concepts that utilize electrical power in propulsion of the aircraft. This includes hybrid electric, such as the Boeing-General Electric (GE) “Sugar Volt” and turboelectric concepts, such as STARC-ABL, featuring two main engines and an electrically powered aft thruster for boundary layer ingestion. It also includes electric vertical takeoff and landing (eVTOL) vehicles such as NASA's revolutionary vertical lift technologies (RVLT) concepts. The images below show renderings of the Sugar Volt, STARC-ABL, and RVLT EAP concept vehicles.
Hybrid electric and turboelectric concepts utilize an electrical power system to deliver power from an electrical source, e.g. battery or generator, to a motor which drives a propulsor (or aids a turbine) that provides thrust for the vehicle. The electrical power system impacts the overall weight, thermal system requirements, and efficiency of the propulsion system and these tradeoffs need to be considered to meet the design objectives, especially in an optimized fashion. More specifically, this requires the power system to be included in the conceptual design phase of the propulsion system. One of the most widely used tools for conceptual design of propulsion systems is the Numerical Propulsion System Simulation (NPSS).
This repository, the NPSS Power System Library (PSL), is designed to enable NPSS to address these needs for modeling EAP systems. Further, this documentation describes the library, how to use it, and the components, tools, and other files that it contains.
This library contains a set of power system and circuit components, as well as an interpreted electric port component designed to connect power system components. The electric port is included in all power system components and passes voltage, current, and electrical power information back and forth using complex numbers (phasors) implemented via a complex number class. The components are designed to work in a manner analogous to baseline NPSS components like compressors, turbines, ducts, and others which communicate via their inherent fluid ports. Electric machine components, being the motors and generators, have performance (efficiency) maps that work like traditional NPSS compressors and turbines.
The library also contains simplified thermal management system (TMS) components designed to be connected to the library's power system blocks. These are similar to base NPSS components that can be used to represent TMSes, such as ducts and heat exchangers, but are set up to be convenient to integrate with power blocks.
The electric port serves the purpose of connecting pairs of power system components to form a network. In the present implementation of the Power System Library, components will carry either voltage or current (i) information to be communicated via their electric port(s). A component that carries voltage information is denoted a node or containing an internal node and will have no information on the currents (i) going through its ports when beginning an NPSS solver iteration. Conversely, components that do not contain nodes (nodeless) will not have voltage information but instead populate their electric ports with current (i) information.
For an NPSS Power System Library model to function, nodal components must thus be linked with nodeless components to properly populate the network with voltage and current (i) values. The Power System Library accomplishes this by defining NPSS solver indepedent variables to represent node voltages in power transforming components. Power transform components may then be linked to other nodal components using nodeless transmission components (e.g. cables, breakers, etc.) to transmit current (i) information between the nodes. The NPSS solver subroutine will then balance the net current (i) at a node to 0 to preserve Kirchoff's Current Law (KCL) by perturbing on the node voltages.
Most power transmission components presently do not contain NPSS solver independents for their currents (i). Those that do (e.g. AeroCable & Breaker) are only run on-design to help size the component to the correct ampacity.
For an NPSS Power System Library model to presently work, nodeless (i.e. power transmission) components like cables and breakers must be explicitely defined at the beginning of the solver execution sequence (before any nodal component). This is due to the fact that nodal components do not initially know their port currents (i) when beginning an iteration. The prePass() function is defined for all nodal components to populate their ports with voltage values before model iteration. Nodeless components are then the first components to run so thaty they may populate current (i) values. THis results in all network ports becoming populated with both voltages and currents (i). In short: voltage propagates on a network by the nodal components' prePass() function; current (i) propagates by executing nodeless components first in the solver sequence.
--describe things people need to know about how to use power blocks in assemblies, depends on
Once model components have been defined, a user may connect them to each other using the linkPortsI() function. This works almost identically to the NPSS linkPorts() for fluid connections. All Power System Library electrical components will contain at least one electric port (input or output) to connect to.
Consider a Battery object B1 with ElectricPort EP_O and Cable object C1 with ElectricPort EP_I. We may simply connect these components using linkPortsI like so:
linkPortsI(B1.EP_O, C1.EP_I);
(not technically true right now but maybe future addition?) An electric input port can only be connected to an electric output port and vice versa.
The Power System Library is capable of modeling networks with both Direct Current (DC) or Alternating Current (AC) electric power types.
--describe the electric power types, and how they affect the solver setup. Describe the power propagation logic once it is completed
--describe common issues people have when building models, running models, and anything else we can think of.
To continue reading, see Items Within Library.