EETG: High Penetration Hybrid Power System

Project Overview

Diesel-off hybrid power systems represent the next generation wind diesel systems. In traditional systems, the diesel gen-set regulates both the voltage and frequency of the grid. In order to maximize fuel savings, it is desirable to be able to operate the system with the diesel engines shut off when other renewable power sources, such as wind, are available. However, in order to do so power electronics must be advanced enough to meet the power quality needs for the grid and customers. The Alaska Wind-Diesel Application Center proposes to analyze state-of-the-art power electronics to assess options for operating in a diesel-off mode. The review will be broad, incorporating both a systemic analysis of diesel-off technology as well as a component analysis, which will look in-depth at flywheel, energy storage, and inverter dynamics.

Project Objectives

Diesel-off hybrid power systems represent the next generation wind-diesel systems. In traditional systems, the diesel gen-set regulates both the voltage and frequency of the grid. In order to maximize fuel savings the diesels need to shut off when other renewable resources are available, but to do so the power electronics must be advanced enough to meet the needs of the grid. Further development of large hybrid inverters is needed to advance this technology. WiDAC will analyze state of the art inverters to control the systems in a diesel-off mode. Being able to do so will save significantly on the capital cost of installed projects and increase the overall simplicity of hybrid power systems.

Work Plan

This project incorporates two phases, as follows

  1. A detailed literature review of inverter technology, including a background study of power electronics and an in-depth power quality analysis of high penetration systems. A list of key research questions will be identified and a testing protocol will be designed for each topic.
  2. The construction of the testbed and hardware testing. WIDAC has several designs for testbeds that require components of varying costs; final design is pending selection of hardware in Phase I.

The final decision on what hardware to test will depend on the results from the Phase I review. In addition, a go/no-go decision point will be included at the end of Phase I that will take into account whether appropriate hardware has been identified and if it can be procured and tested within the constraints of the remaining budget. Key research questions and testing protocols will also be developed at the end of Phase I, based on final equipment selection.


  1. Address technical issues related to higher penetration of wind as part of overall generation portfolio in order to reduce the amount of diesel fuel used and improve the economics of existing and planned wind-diesel systems.
  2. Address issues specifically related to operation of turbines and ancillary equipment in remote locations.
  3. Take high penetration systems to the next level by enhancing the rate of success of diesel-off operations.
  4. Solidify Alaska as the leader in wind-diesel technology worldwide and expand employment and economic opportunities in the sector.


Voltage instability problems have been attracting significant attention as Alaskan wind farms increase their level of penetration on isolated diesel grids. Currently, in hybrid power systems, the diesel gen-set regulates both voltage and frequency of the grid as well as provides the needed VAR support. One of the considerations with high-penetration wind-diesel systems is that, ultimately, the diesel needs to be shut off in order to realize maximum fuel savings. To supply the required power quality without using diesel, other equipment is needed to provide VAR support, such as a switchable capacitor bank, static converter or synchronous condenser (rotary converter). The system total reactive powers needs are balanced at all times with these devices to maintain voltage stability. This function can also be accomplished through power electronics such as inverters, which in fact could be the inverters already in use in modem wind turbines. The concept of using the inverter system built into the wind turbines themselves to provide voltage and VAR stability is the main thrust of this project.

Sudden changes in load or generation can cause oscillation and instability in rural isolated power systems. This is a bigger issue in isolated wind-diesel power plants and becomes a dominant issue when trying to operate in wind-only mode. In order to understand the importance of this technology, it is important first to understand how wind-diesel systems operate in a diesel-off mode. To do this it is best to evaluate an existing functional system on St. Paul Island. While the diesel gen-sets are producing power the system voltage and frequency are controlled by the gen-sets. When the wind is blowing in a diesel-on mode, the wind turbines produce variable AC power through the generator and are balanced by the dispatchable thermal loads and variations in diesel gen-set output. The St. Paul system has an additional issue in wind-only mode as the wind turbine generator is an induction generator. This means that with the diesel generator turned off there would be no other source of VARs to stabilize the system. To handle this issue, a synchronous converter has been integrated into the system on St. Paul that allows for stable control in the wind-only mode.

Funding and Partnerships

Recipient Alaska Wind-Diesel Application Center
Project Title High Penetration Hybrid Power System
Funding Source(s) Denali Commission EETG Program
Funding Sponsor(s) Denali Commission
Grant Manager(s) Alaska Center for Energy and Power
Funding Amount $433,045.00
Match Funding $0.00
Project Timeline 01/01/2010 - 03/31/2011

Grant Sponsor

This project is a Denali Commission EETG Program project. The funding goal of the EETG program is to develop emerging energy technology that has the potential of widespread deployment in Alaska and has the long-term goal of reducing energy costs for Alaskans.

Project Recipient

The Alaska Wind-Diesel Applications Center (WiDAC) is a center of excellence in wind-diesel technology that analyzes technology options, tests state-of-the-art hardware and control software, educates engineers, trains operators, and provides technical assistance to wind–diesel stakeholders both within and outside the State of Alaska. The purpose of WiDAC is to support the broader deployment of cost-effective wind-diesel technologies to reduce and/or stabilize the cost of energy in Alaska ’s rural communities.

Grant Management


The Alaska Center for Energy and Power (ACEP), an energy research group housed under the Institute of Northern Engineering at the University of Alaska, Fairbanks, is serving as the program manager of the EETG solicitation. As the projects deal with emerging energy technology and by nature are high risk, high reward, ACEP’s technical knowledge and objective academic management of the projects, specifically for data collection, analysis, and reporting, is a vital component to the intent of the solicitation, i.e., providing lessons learned and recommendations.

Project Partnerships


WiDAC was established by ACEP, together with its partners the Alaska Energy Authority and the National Renewable Energy Laboratory.

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Project Information

Supplementary Information


Data and Analysis

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