SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  N07-081 (Navy)
Title:  Transient Electrical Power Response Enhancement for Turbine Driven Generators
Research & Technical Areas:  Air Platform, Space Platforms, Weapons

Acquisition Program:  PEO(W) Strike Weapons and Unmanned Aviation (pre-milestone A, ACAT TBD)
  Objective:  Improve the transient response of a lightweight turbine engine serving as the prime mover for an electrical generator which has a relatively large rating compared to the engine’s shaft power output.
  Description:  Airborne electrical power requirements are increasing significantly to support Intelligence, Surveillance, and Reconnaissance (ISR) sensors, electronic attack suites, and possibly directed energy weapons for military applications. For commercial applications, the increase is being driven by passenger comfort and more electric subsystems. One approach to supplying this power is to add a separate propulsion-class turboshaft engine to the platform which is dedicated to driving a lightweight electrical generator. Another approach for some applications is to integrate the generator directly into the propulsion engine. This approach is being considered for high Mach missiles, where any transient effects on the engine cycle have more significant impacts than on other cycles with the luxury of higher operating margins. An issue with these approaches is that the turbine engine cannot respond to load changes as quickly as the generator itself. Effectively, the engine / generator system cannot respond adequately to electrical load changes and this will be exacerbated by the trend toward lighter systems of larger power output. Innovative techniques to enhance the transient response of the turbine engine / generator system for airborne applications are the focus of this topic. Adding inertia to the rotor in the form of a flywheel has been investigated previously and is not the focus. Offerors are strongly encouraged to establish relationships with relevant aerospace system suppliers.

  PHASE I: Investigate approaches to improve the transient response of the turbine engine to rapidly applied electrical loads and analytically estimate possible positive impacts on response as well as negative system impacts. Modeling and simulation to guide the research is encouraged as appropriate.
  PHASE II: Develop and demonstrate technology approaches to the extent allowed by the scope, preferably with an industry partner. Develop a technology transition and/or insertion plan for future systems and commercial ventures.

  PHASE III: Integrate these technologies into an engine driven power generation demonstration and reduce the technologies to a marketable product via licensing or well established relationships with system supplier(s). PRIVATE SECTOR COMMERCIAL POTENTIAL/

  DUAL-USE APPLICATIONS: These methods could be applied on several planned military and commercial platforms requiring significant levels of electrical power as well as commercial microturbines and larger gensets being developed for distributed power installations.

  References:  1. Power System Analysis; Grainger & Stevenson, 1994, McGraw-Hill Publishing ISBN 0-07-061293-5, Chapter 16. 2. Improvement of Power System Transient Stability by Coordinated Operation of Fast Valving and Braking Resistor; Patel, R., Bhatti, T.S., and Kothari, D.P.; IEE Proceedings – Generation, Transmission, and Distribution Vol 150, Issue 3 pp. 311-316, May 2003. 3. Asynchronous Motor Protection Against Dynamic Instabilities; Martinez, Jorge et. al.; IEEE Transactions on Industry Applications, Vol. 36 No 4, Jul/Aug 2000. 4. MIL-STD-704E, “Aircraft Electrical Power Characteristics”, May 1991.

Keywords:  Power, electrical power, turbine engine, turbogenerator, and turbine engine transient response

Questions and Answers:
Q: 1. Do you have a profile of the transient loads or know approximately how much energy is drawn during the transient conditions?

2. How long does it take for the engine to respond to a step load change?

3. Is it OK to slow down the generator while using a power converter to create the correct output frequency and voltage?

4. Does the generator have enough energy stored in inertia to meet the transient energy requirements?
A: 1. No, because this topic does not address a particular application. For any application the electrical load will be based upon which subsystems and payloads supported by the turbine engine are electrically driven. This will be a very different situation for high mach missiles propelled by turbine engines and for aircraft propulsion-class turboshaft engines dedicated to driving electrical generators. The key characteristics for the purposes of this topic are that the transient is rapidly applied (<0.1 second) and large enough in magnitude compared to the engine cycle to cause an impact. In general, a large peak power / small total energy transient would not be expected to cause an impact. A small peak power / large total energy transient would not be expected to cause an impact because the engine would have time to respond to the higher power extraction point.

2. This depends on a number of factors. These include but are not limited to the magnitude of the load change, the operating point of the engine, and the fundamental design of the engine and generator (primarily rotating inertia) and their controls. For purposes of this topic, a typical elapsed time between the point at which a large step load is applied and the point at which the engine cycle reaches steady state operation at the higher extraction point can be assumed to currently be on the order of 2 to 3 seconds.

3. Yes, but the generator and engine are mechanically linked. A DC bus can also be assumed. The key point of the topic is the effect that this potentially rapid speed reduction has on the prime mover and what approaches may be available to improving the engine's response to this situation.

4. For this topic, the assumption is no. If it did, transient response would not be an issue. It should be noted that the engine and generator are mechanically linked so that the generator inertia cannot be separated from the engine inertia.
Q: 1. Do you have a profile of the transient loads or know approximately how much energy is drawn during the transient conditions?

2. How long does it take for the engine to respond to a step load change?

3. Is it OK to slow down the generator while using a power converter to create the correct output frequency and voltage?

4. Does the generator have enough energy stored in inertia to meet the transient energy requirements?
A: 1. No, because this topic does not address a particular application. For any application the electrical load will be based upon which subsystems and payloads supported by the turbine engine are electrically driven. This will be a very different situation for high mach missiles propelled by turbine engines and for aircraft propulsion-class turboshaft engines dedicated to driving electrical generators. The key characteristics for the purposes of this topic are that the transient is rapidly applied (<0.1 second) and large enough in magnitude compared to the engine cycle to cause an impact. In general, a large peak power / small total energy transient would not be expected to cause an impact. A small peak power / large total energy transient would not be expected to cause an impact because the engine would have time to respond to the higher power extraction point.

2. This depends on a number of factors. These include but are not limited to the magnitude of the load change, the operating point of the engine, and the fundamental design of the engine and generator (primarily rotating inertia) and their controls. For purposes of this topic, a typical elapsed time between the point at which a large step load is applied and the point at which the engine cycle reaches steady state operation at the higher extraction point can be assumed to currently be on the order of 2 to 3 seconds.

3. Yes, but the generator and engine are mechanically linked. A DC bus can also be assumed. The key point of the topic is the effect that this potentially rapid speed reduction has on the prime mover and what approaches may be available to improving the engine's response to this situation.

4. For this topic, the assumption is no. If it did, transient response would not be an issue. It should be noted that the engine and generator are mechanically linked so that the generator inertia cannot be separated from the engine inertia.

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