Power Electronics Review Emerging Technology Fund Quarterly Report April 2010 – June 2010

Background The Alaska Center for Energy and Power (ACEP) was conditionally awarded $433,045 from the Denali Commission under the Emerging Technology Fund for testing power electronics devices that could allow wind-diesel systems in Alaska to operate in a diesel-off mode. This is important because by operating in a diesel-off mode, a much greater cost savings can be realized from these systems. The scope of work for this project centered on reconfiguring existing Northwind 100kW inverters (the most common and robust turbine installed in Alaska) to provide frequency, voltage, and VAR support while the diesel generators are shut off (provided adequate wind is available). This option has never been tested in a lab which must first be done, before field testing, due to the high risk of interrupted power to the community. By simply reprogramming existing inverters with new algorithms a low cost solution could be applied to over ten communities which would result in increased power stability with the ability to shut the diesel gen-sets off.

The original proposal requested funding support in the amount of $866,097. Due to funding constraints the Denali Commission only awarded the project $433,045. This required ACEP to rescope the project as the equipment needed for the original project was not able to be purchased.

This is the basis for research on power electronics at the Alaska Center for Energy and Power (ACEP): to simulate operation of the wind diesel systems on a Hybrid Power Test Bed to assist the Alaskan wind industry in developing and improving hybrid power generation systems. Using simulated village loads, researchers can evaluate the interaction of these power sources under realistic conditions at the test bed and work through actual problems the system might encounter in the field.

The key objectives of this project are to:

1. Address technical issues related to high wind penetration as part of the 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. Confirm that an inverter can stabilize power quality in a diesel-off mode.

3. Address issues specifically related to operation of turbines and ancillary equipment in remote locations.

4. Take high penetration systems to the next level by enhancing the rate of success of diesel-off operations.

5. Significantly contribute research which will solidifying Alaska as the leader in wind-diesel technology worldwide and expand employment and economic opportunities in this sector.

In developing the testing protocols, key research questions will be identified and addressed:

1. Impact of increased wind penetration and conditions under which the increased penetration will result in violation of reliability criteria:

a. with concomitant displacement of aged conventional generation; b. without any decrease in existing conventional generation.

2. Assess (and/or develop) control enhancements to fully utilize the reactive power

capability of the machine and the power electronic converters under high penetration with regard to voltage response and stability. Such control enhancements may include

a. grid-side reactive power boost that allows the grid-side converter to inject reactive power into the grid when the rotor is short circuited with a crowbar to protect the rotor-side converter;

b. retrip prevention and dc overvoltage prevention that protect the power electronics and allow maximum utilization of reactive power.

3. Confirm ability of power electronics to meet certain operational technicalities such as low voltage ride through (LVRT), dynamic reactive compensation as per the requirements of FERC1

standards, etc.

4. Overall, since power electronic devices tend to be sensitive to high voltages and currents, the equipment should validate the converters for each aspect of impact of increased wind power penetration on:

• small-signal and transient stability, • frequency stability, • voltage response, and • market operation.

1 The Federal Energy Regulatory Commission is the US federal agency with jurisdiction over high voltage interstate transmission systems, sales, wholesale electric rates, hydroelectric licensing, natural gas pricing, and oil pipeline rates.

Recent Activity

Trip to the National Renewable Energy Lab and Sustainable Automation Billy Muhando and Katherine Keith traveled to Boulder, Colorado in June 2010 to discuss the installation of the Alaska Hybrid Test Bed. A similar unit was installed at NREL when there was a focus on village power systems in the late 80’s early 90’s. This original test bed was used during the design and construction of the Wales High Penetration Wind-Diesel system which was installed in 2002. The ACEP researchers met with Mari Shirazi at NREL who walked us through the layout and design of the test bed, making recommendation for a newer and more modern design. Kat and Billy also met with Jerry Bianchi who provided schematics from the test bed and spent significant amount of time speaking with us about the intricacies of the project. Jerry originally managed the program at NREL and therefore is extremely well qualified to discuss future projects. There also were a couple meetings with Steve Drouilhet, President of Sustainable Automation with discussions revolving around equipment selection, maintenance and warranty of purchased equipment, and modeling software. A tour was also given of the existing testing facilities at Sustainable Automation.

Figure 1: Steve Drouilhet and Billy Muhando

Power Electronics Review The report is on its final iteration and is close to completion. The table of contents is listed below:

1 Wind-Diesel Hybrid Power: Basis for Current Research 1.1 Background

1.2 Overall Objectives 1.3 Research Basis and Scope

1.3.1 Problem Identification 1.3.2 Wind Diesel Research Needs

2 The High Penetration Challenge for Wind-Based Power Systems 2.1 Introduction to Wind Diesel Systems 2.2 Wind Diesel Hybrid Power Plant Classification

2.2.1 Low Penetration 2.2.2 Medium Penetration 2.2.3 High Penetration

2.3 Technical Challenges with High Penetration 3 Power Quality Stabilization

3.1 Power Stability 3.1.1 Grid Connection and Stability 3.1.2 Power Quality Issues

3.2 Converter Systems for Grid Forming 3.2.1 Converter Basics 3.2.2 Converter Control

3.3 Energy Storage Systems 3.3.1 Flywheels 3.3.2 Battery Bank 3.3.3 Flow Battery 3.3.4 Synchronous Condensers 3.3.5 Dumploads

4 Power Electronics: Overview of Technology and Application 4.1 Dispatch and Control Strategy

4.1.1 Conceptual Framework for Diesel-off Mode Operation 4.1.2 Control for Grid Management

4.2 Controller Tuning for the Power Electronics 4.2.1 Linear Controllers 4.2.2 Advanced Control Schemes

4.3 Overview of Converter Technology for Wind Turbine Configurations 4.3.1 Permanent Magnet Synchronous Generators 4.3.2 Doubly Fed Induction Generators 4.3.3 Induction Generators 4.3.4 Synchronous Generators

5 Proposed Hybrid Test Facility for Diesel-Off Mode Operation 5.1 Background and Cross-Reference to Related Work

5.1.1 Diesel-Off Technology and Operation 5.1.2 Existing Wind Diesel Hybrid Test Beds

5.1.3 Lessons Learned from NREL’s HPTB 5.2 Proposed ACEP Wind Diesel Hybrid Test Bed Configuration

5.2.1 Concept and Overall System Layout 5.2.2 The Turbine Simulator: Detailed Description and Schematics

5.3 Suggested Testing Protocols 5.3.1 Looking Ahead to the Test: Procedures 5.3.2 What is Monitored?

5.4 Recommendations 6 Bibliography/Sources of Info.

Equipment Status Initial equipment has been purchased through Sustainable Automation and is expected to be delivered by December 2010. The equipment includes:

1. Model WTS-IG-100-480-60 Wind Turbine Simulator, 100 kW, induction generator, 3-phase 480 VAC input power, 3-phase 480 VAC output power. Includes LabVIEW-based control software.

Figure 2: Sustainable Automation Wind Turbine Simulator

2. Lead-Acid Battery Bank, valve-regulated, maintenance-free, deep cycle, Absolyte GP or equivalent, 336 VDC, 896 Ah nominal capacity. Estimated lifetime = 10 years.

Figure 3: Lead Acid Battery Bank and Inverter Cabinet

3. Grid-Forming Energy Storage Power Converter, 200 kVA, 480 VAC, 60 Hz. Multiple operating modes: grid-forming (voltage and frequency regulation), diesel-parallel (load and VAR sharing), and controlled battery charging. Includes wall-mounted battery disconnect DC circuit breaker. (Does not include grid isolation transformer or battery bank).

Figure 4: Sustainable Automation Inverter

4. Transformer, Isolation, 225 kVA, 480V Delta Primary, 480/277V Wye Secondary

5. Matlab/Simulink/SimPowerSystems model of Diesel Genset, Inverter, Battery, and Primary Load. Models of any future components purchased from Sustainable Automation shall be provided at no charge.

Future Work During the next quarter it is expected that the design drawing for the test bed configuration will be completed along with testing protocols.

Considering the lead time in delivery of the equipment (about 6 months), we shall be making initial preparations - setting up the workspace at the GVEA Bidwell building with e.g., potable water, addressing safety and security concerns etc.

A close collaboration with the installation contractor (Marsh Creek) is deemed necessary, and it is expected he shall be allowed access to the GVEA facility to facilitate layout design, etc.

Data collection is still an ongoing process and we plan to analyze and harmonize all pertinent data from several high penetration areas of Alaska to gauge suitability of the equipment, as well as form a basis for recommendations to the contractor during construction of the test bed for adequate instrumentation. Potential high penetration site visits may be necessary for this task.

We also plan to get the flow battery currently at the ACEP facility in serviceable condition so that we may run high storage capability tests on the hybrid test bed.

Power Electronics Review Emerging Technology Fund Quarterly Report III July 2010-September2010

Recent Activity

Overview of Project Status to the Denali Commission On August 17th, 2010 Katherine Keith made a brief presentation to the Denali Commission during a meeting which included ARPA-E Director Arun Majumdar, Senator Begich, AEA Executive Director Steve Haagenson, and numerous other dignitaries. The briefing provided the group with a broad look at what this project was aiming to achieve and what the current progress was to date.

WiDAC Meeting of Advisory Committee An intensive 3 day web conference was held August 30th – September 2nd, 2010 involving University researchers and the WiDAC Advisory Committee. The meeting was intended to allow the opportunity for industry to provide feedback on the University research work plan. Although this was a preliminary evaluation meeting in preparation for a DOE EPSCoR meeting, time was available to update members on the status of the test bed project funded by the Denali Commission.

DOE EPSCoR Meeting It is apparent that future plans for the project – building research capacity by more faculty and students, and equipment purchase – require additional funding. The DOE EPSCoR Program Manager, Tim Fitzsimmons, led a team of expert reviewers to UAF to examine the work plans pertaining to wind-diesel development. This was intended to justify the request for additional funding for various research projects that are intended to improve the performance, cost, and sustainability of existing and planned wind-diesel systems in Alaska in order to reduce the amount of diesel fuel used for electric power generation, heating, and transportation.

ACEP used this chance to showcase the ongoing research, funded by the Denali Commission, on high-penetration wind-diesel systems which includes this current work of addressing the technical challenges in the areas of power stability and advanced control technologies. In this dialogue, reviewers were able to make valuable suggestions, which hopefully will culminate in future collaborative efforts.

Power Electronics Review

The report has been completed and a copy sent to the Denali Commission on September 21st, 2010 for initial review. The final edited version shall be available for distribution early October 2010. Highlights of the report include:

1. Wind-diesel generation systems and associated high-penetration issues are discussed in detail, with a focus on defined goals and scope for the project. 2. A literature review is given on the various systems and technology available for diesel-off operation and their suitability for the Arctic climate. The report analyzes converter systems for high penetration diesel-off operation and supplementary devices like energy storage (battery banks, flywheels, condensers, dump loads, etc). 3. Proposed test facility – an outline is rendered for the test bed installation, with a brief background on some of the existing laboratories worldwide having similar test bed facilities. Reference is made to the NREL’s Hybrid Power Test Bed in more detail as this serves to provide us with an insight to the installation and operation of high penetration systems, and lessons on what to avoid/what not to do. 4. Test Protocols – this section details the various tests to be conducted as well as the procedures for the trials on the test bed. It covers the systematic performance tests and functional checks/fault diagnostics while analyzing the setup for grid forming functions (voltage and frequency stability). The focus is on the working of the components, viz:

a) Inverter effectiveness for operation of the wind turbine simulator for diesel-off mode strategy

b) Parallel operation of inverter with the diesel gen-set c) Battery charging/discharge and storage

5. Recommendations for contractual obligations and intellectual property are included, to ensure ACEP has the rights to modify converter control software as well as dissemination of information to various stakeholders and the general public. Future plans for extended research on the ACEP test bed are also highlighted, with emphasis on faculty hire, graduate student research, additional equipment purchase, and leveraging for more funding.

ACEP is also considering sending the report to the WiDAC Advisory Committee and NREL for review/comments that may assist in the eventual layout, installation and test trials.

Project Status

Equipment

A 25% down payment has been made toward purchase of initial equipment from Sustainable Automation, Inc. There was a request to adjust the down payment to cover 40% as per the supplier’s terms and conditions, and this matter is being handled internally. The battery bank is ready and shipping for the rest of the equipment is expected in January 2010, however, this is contingent on the installation and working of a similar converter system being developed by the supplier, to be deployed at Kokhanok. The ACEP converter, while being the same as the Kokhanok inverter in terms of rating, will incorporate everything the supplier is learning on that project.

Timeline and Budget

Overall, the project is on schedule and on budget – there have been no major revisions to the scope of the project, and preliminary work is ongoing as planned.

Ongoing and Future Tasks

1. The facility for the test bed at the GVEA Bidwell building has been prepared adequately - potable water, heating/air conditioning, safety equipment etc. As we expect to have streaming data during trials, a local firm is being contracted for internet (+ telephone) connectivity.

2. The design drawing for the test bed configuration will be completed in the next few months; ACEP is still considering the installation contractor (Marsh Creek) for this part of the project.

3. Data collection is ongoing.

4. A mechanical engineering graduate student has been identified for this project and he shall be engaged preliminarily this fall.

5. A flow battery was delivered in September 2010 from Prudent energy for performance testing; though this is a separate project, they shall be housed under the same facility and it is the intention of the research team to conduct advanced storage tests on the hybrid test bed to further gauge the capability of the power electronics for this task.

Power Electronics Review Emerging Technology Fund Quarterly Report IV October 2010-December 2010

Recent Activity

Power Electronics Report The Power Electronics Review – a prerequisite for Phase I of the Project – was completed in September 2010. The report was circulated to AEA, NREL, and the Denali Commission, for feedback and general observations/recommendations prior to final edit. The final, edited version is now available in electronic form; it is expected that this will be posted online at the ACEP site for ease of access. Hard copies shall be available soon (if/when required).

The table of contents for the final report is as follows:

1 Wind-Diesel Hybrid Power: Basis for Current Research 1.1 Background 1.2 Research Basis and Scope

1.2.1 Problem Identification 1.2.2 Wind-Diesel Research Needs 1.2.3 Overall Objectives

2 Diesel-off Mode Operation for High Penetration Power Systems 2.1 Introduction to Wind-Diesel Systems 2.2 Wind-Diesel Hybrid Power Plant Classification

2.2.1 Low Penetration 2.2.2 Medium Penetration 2.2.3 High Penetration

2.3 High Penetration Challenges 2.4 Dispatch with Diesel-off Technology

3 Technology for Enhancing Power Quality in Wind-Diesel Systems 3.1 Power Stability

3.1.1 Grid Connection and Stability 3.1.2 Power Quality Issues

3.2 Converter Systems for Grid Forming 3.2.1 Converter Basics

3.2.2 Frequency and Voltage Regulation in Wind-Diesel Systems 3.2.3 Algorithmic Tuning for Power Electronics

3.3 Energy Storage Systems 3.3.1 Flywheels 3.3.2 Battery Energy Storage System (BESS) 3.3.3 Flow Battery 3.3.4 Synchronous Condensers 3.3.5 Dump Loads

4 Proposed Hybrid Test Facility for Diesel-Off Mode Operation 4.1 Background and Cross-Reference to Related Work

4.1.1 Existing Wind Diesel Hybrid Test Beds 4.1.2 NREL Hybrid Power Test Bed (HPTB) 4.1.3 Lessons Learned from NREL’s HPTB

4.2 Proposed ACEP Wind-Diesel Test Bed Configuration 4.2.1 Concept and Overall System Layout 4.2.2 The Wind Turbine Simulator

4.3 Recommended Testing Protocols 4.3.1 Functionality Checks 4.3.2 Test Procedures with the Wind Turbine Simulator 4.3.3 Parallel Operation of Inverter with Diesel Gen-set 4.3.4 Battery Charging

4.4 Instrumentation and Monitoring 4.5 Recommendations 4.6 Future Plans for Extended Research on the ACEP Test Bed

5 Bibliography/Sources of Info.

Project Status Budgetary Issues Funds committed to the first round of equipment purchase has either been paid or in the process of being disbursed to the supplier. The balance of the funds ($110K) has been earmarked for purchase of additional components that are necessary for complete functionality of the test bed. Of essence are a Hybrid System Supervisory Controller (HSSC) and a secondary load controller, since it would be a challenge to perform pertinent tests with only the WTS and inverter. The HSSC is to effect automatic monitoring and supervisory control of the WTS as well as data-logging and historic data visualization. It also allows for a thermal storage unit to be incorporated in the system. Initial quotations received indicate that these components will cost about $275K, and we are still sourcing for incremental funding to meet the difference of $165K. The Hybrid System

Supervisory Controller is the most critical additional component and costs $160,000. The next most critical component is a Secondary Load Controller which costs $85,000. Of additional interest is the Synchronous Condenser and Controller which will cost $85,000. Each component has an added expense of 10% for a support contract.

Ordered Equipment

The 100kW Wind Turbine Simulator ordered from Sustainable Automation Inc is progressing well: the skid assembly is complete, with the motor and generator precision aligned; all major parts for the control cabinet are on ground; and company technical staff are making some improvements to the control software. It is expected that once the controls are fully assembled, testing and debugging will commence for a period of about 2 weeks prior to shipping.

Fig. 1: Part of the skid assembly, October 2010.

It is highly anticipated that the ordered parts, namely:

1. Wind turbine simulator (WTS)

2. Lead-acid battery bank 3. Grid-forming energy storage power converter, 4. Transformer (and isolation)

shall be delivered in the first quarter of 2011.

Test Bed Facility and Installation

The premises to house the test bed at the GVEA Bidwill Avenue facility have been set up accordingly (power, telephone/internet, potable water, etc).

Timeline and Schedules

Overall, the project is on schedule. The logistics for installation now include initial testing and commissioning by Marsh Creek in Anchorage (this is the contractor that shall perform the installation).

Power Electronics Review Emerging Technology Fund Quarterly Report I (2011) January 1st 2011-March 31st 2011

Project Status

The focus of Q1, 2011, has been on acquiring remaining test bed components, selecting the manufacturer of the supervisory controller, and developing an installation plan. All equipment from Sustainable Automation is due to arrive in Anchorage mid-April and Marsh Creek has begun uncrating the equipment and creating a space in their warehouse facility where the test bed can be housed until Fall. The Energy Lab in Fairbanks is scheduled to be completed in October 2011. The Hybrid Test Bed will be relocated at the Energy Lab at that time.

All of the hardware components have been purchased and mostly delivered to the Marsh Creek facility in Anchorage. The suppliers of this existing equipment to date includes: Sustainable Automation (Wind Turbine Simulator, Grid Forming Inverter, and Battery Bank) and Marsh Creek (Gen-sets). We still need to acquire the Controller in order to commission the Hybrid Test Bed. The Controller needs to manage and automate the operation of the hardware components. It is also responsible for the grid integration of renewable and conventional generation. The suppliers of this technology worldwide, willing to distribute to America, include Sustainable Automation and Powercorp. Numerous components have already been supplied by Sustainable Automation and to date have failed to be delivered in a timely fashion. In order to commission the test bed and remain on schedule for final reporting to the Denali Commission it is critical that the Distributed Control System be delivered on schedule. Powercorp’s DCS utilizes ethernet for communication and does not have a master automation controller, as is typically seen in Alaskan communities, which has the potential to fail and force manual operation. The unique and secure software architecture has been developed at Powercorp and allows for remote access. The Hybrid Test Bed is well suited to testing and demonstrating technology new to Alaska in order to increase comfort and reduce risk for our smaller developers. Sustainable Automation’s controller is a master supervisory controller which has been deployed in Selawik, Wales, and Kokhanok. Powercorp’s controller is a distributed control system, which has yet to be utilized in Alaska, but one which provides success in numerous other installations worldwide. In order to secure a multi-vendor test bed-we would like to sole source the purchase of the DCS to Powercorp-the only developer of this distributed control technology.

During the next month it is expected that we will have a purchase order in place with Powercorp and a Service Agreement in place with Marsh Creek. The expected commissioning date is now August 1st which will allow for five month of debugging and testing.

Budgetary Issues

To date Billy Muhando has charged 784 hours of time and Katherine Keith has charged 98 hours for a total of $56,298. This leaves the project with about $23,000 for remaining personal services and staff benefits. With respect to equipment there is $110,675 in remaining funds which will be used to purchase the Distributed Control System from Powercorp. In order to accommodate the lateness of equipment delivery and recent project developments a budget revision will soon be requested from the Denali Commission.

Ordered Equipment

The 100kW Wind Turbine Simulator has arrived at Marsh Creek but has not yet been installed or commissioned.

The Lead-Acid Battery Bank is in Anchorage and is waiting for Marsh Creek to have room in their warehouse before it is delivered to that facility.

The Grid-Forming Power Converter has shipped and will arrive in Anchorage approximately May 1st.

The Transformer has arrived damaged at the Marsh Creek facility. Pictures were taken but the damage is superficial and will not impact the functionality of the transformer.

Timeline and Schedules

The logistics for installation now include initial testing and commissioning by Marsh Creek in Anchorage (this is the contractor that shall perform the installation). It is intended that initial testing will begin on August 1st.

Wind-Diesel Hybrid Test Bed Emerging Technology Fund Quarterly Report II (2011) April 1st 2011-June 30th 2011

Project Status

The focus of Q2, 2011, has been on getting all the crucial equipment to Marsh Creek in readiness for commissioning and start of trials. All the hardware components that were ordered from Sustainable Automation Inc. have been delivered at the Marsh Creek facility in Anchorage, including the Wind Turbine Simulator, Grid Forming Inverter, Transformer, and Battery Bank. Delivery of the simulation models was made in June 2011. The Wind Turbine Simulator has been commissioned by Sustainable Automation.

Not yet delivered but already ordered from Powercorp is the Controller needed to commission the Hybrid Test Bed. The Controller needs to manage and automate the operation of the hardware components. It is also responsible for the grid integration of renewable and conventional generation. In line with securing a multi-vendor test bed, the controller was sole-sourced to Powercorp as they are the only developer of this distributed control technology. Powercorp’s Distributed Control System (DCS) utilizes ethernet for communication and does not have a master automation controller, as is typically seen in Alaskan communities, which has the potential to fail and force manual operation. The unique and secure software architecture has been developed at Powercorp and allows for remote access. The Hybrid Test Bed is well suited to testing and demonstrating technology new to Alaska in order to increase comfort and reduce risk for our smaller developers. Powercorp’s controller is a distributed control system, which has yet to be utilized in Alaska, but one which provides success in numerous other installations worldwide. In order to secure a

A Service Contract between UAF and Marsh Creek is expected to be in place in July 2011; this spells out the scope of work, warranty, and terms of payment, among other pertinent issues.

Equipment & Budget

The Distributed Control System (DCS) ordered from Powecorp is expected to be delivered in July, with subsequent commissioning thereafter. The quoted price of this unit is 119,243.27 $AUD.

Marsh Creek has indicated that they shall loan us some resistive load banks as we try to source for our own.

Plans are underway for AVEC to allow us use of two diesel generators for initial trials, and indications are that one needs to be returned in early 2012 while the other may provisionally be used for the duration of the project.

Timeline and Schedules All commissioning work should be done by early August, after which performance trials will begin. A MS graduate student who is undertaking research on control for distributed generation in high penetration systems will stationed in Anchorage for the next three months for the equipment trials at Marsh Creek. Preliminary test procedures are in place for the student to perform the research in accordance with the funding objectives, namely, diesel-off operation in high penetration systems.

Wind-Diesel Hybrid Test Bed Emerging Technology Fund Quarterly Report III (2011)

July 1st 2011-September 30th 2011

Overview

The defining theme for this task is development of transformative and efficient energy technologies to address high penetration challenges in Alaska, with a focus on integration of intelligent control systems, power electronics, and advanced storage for overall power quality generation, with the added benefit of reduced diesel consumption. A test bed consisting of a wind-turbine simulator, power converter, battery bank, diesel gensets and load bank is the backbone of this Task; control of these integrated systems is via a supervisory control and data acquisition (SCADA) system that acquires real time data from all parts of the system. The SCADA with the associated controller manage the economic and reliable distribution of the generation sources to the loads and turns off (or on) the diesel generators using specified control algorithms. In this way a number of generation sources can be simulated to distribute power to electric loads and some of the loads can potentially inject electric power back into the grid.

Part of the research on the test bed will be devoted to energy storage systems. Initially the functional operation of the wind-diesel system will incorporate lead acid battery bank (336VDC, 896 Ah nominal capacity). ACEP has been performance testing a 5kW, 20 kWh Prudent Energy Vanadium Redox (VRB) flow battery, and this module is to be integrated with the rest of the test bed components for storage and ancillary services research.

Project Status

Equipment

Q3 saw a significant attainment of some of the milestones for the project. UAF entered into a service contract with Marsh Creek LLC of Anchorage for the latter to provide a conducive environment for commissioning and troubleshooting of the test bed equipment to ensure all components run as required prior to final installation at UAF.

Most of the test modules were in place for staggered commissioning while orders and/or acquisition of supplementary equipment (supervisory controller, diesel gensets, etc) were in progress. The functionality of the test bed system has since been demonstrated where the components are able to ‘see’ each other during dynamic simulations.

The main equipment vendor – Sustainable Automation Inc. – made available the distributed power system models (diesel genset, induction generator wind turbine, grid-forming inverter, battery bank and load bank) to be used for exercises by students undertaking research involving the test bed equipment.

Data Collection

Data collection has been ongoing, and of the Alaska Energy Authority (AEA) has been helpful in assisting with access to operational data of wind-diesel systems from selected projects. There are indications that high resolution data may be obtained to enhance transient studies at the test bed. The ACEP data management team has been busy formatting these data for ease of use and analysis. Q3 saw ACEP try to streamline and coordinate the data management efforts with UAA's ISER (since this is similar to what ISER is doing for the DOE EPSCoR project). ACEP has been interested in data formats for village power systems including fuel consumption, generation levels for both diesel gen-sets and turbines, costs of installation and O&M, electrical data (voltage, current, power, power factor, etc), thermal and flow rate data (fuel flow rates, etc). The data can be obtained from village generation and load dynamics, and may be categorized as: 1) Utility data; 2) Economic data; and 3) Energy research data. The data is limited due to storage capabilities in the communities and the lack of good remote data collection systems. The simple bottom line energy cost data is really what is important. How much does the energy cost the end consumer ($/kWh) and what savings ($/year) in fuel displacement can be garnered from the implementation of 1) energy efficiency improvement measures, and 2) introduction of renewable/alternative energy sources that are locally viable in that specific order.

New Lab Facility

The building that will house the test bed lab equipment is nearing completion; the ACEP team has been involved in layout design to ensure the civil works are completed with due regard to expected placement of the modules (with corresponding electrical network/switchgear, exhausters, fuel supply bays, drainage, etc). It is expected that the test bed system shall be installed by the end of the year. A MS graduate student who is undertaking research on control for distributed generation in high penetration systems will continue with performance trials in accordance with the funding objectives, namely, diesel-off operation in high penetration systems.

1

Wind-Diesel Hybrid Test Bed Emerging Energy Technology Fund Quarterly Report IV (2011)

October 1st 2011-December 30th 2011

Project Status

Research Overview

The defining theme for this research project is development of transformative and efficient energy technologies to address high penetration challenges in Alaska, with a focus on integration of intelligent control systems, power electronics, and advanced storage for overall power quality generation, with the added benefit of reduced diesel consumption. A test bed consisting of a wind-turbine simulator, power converter, battery bank, diesel gensets and load bank is the backbone of this project; control of these integrated systems is via a supervisory control and data acquisition (SCADA) system that acquires real time data from all parts of the system.

A MS graduate student who is undertaking research on control for distributed generation in high penetration systems has continued with performance trials in accordance with the funding objectives, namely, diesel-off operation in high penetration systems.

Modeling and Simulation

The distributed power system models that were delivered by Sustainable Automation Inc. in Q3 continued to be used for simulation in anticipation of the test bed installation; these included the Matlab-SimPowerSystems models of diesel genset, inverter, battery, and primary load. Primarily, research work has involved use of wind speed data from select wind-diesel installations in Alaska to analyze various load-dispatch scenarios. Some of the objectives have been to test the power electronic components for voltage and frequency regulation, devise alternate and more robust control algorithms in lieu of those supplied with the equipment, and to investigate the capability of the system for diesel-off operation.

Data collection has been ongoing, with strong input from the Alaska Energy Authority (AEA) in accessing operational data of wind-diesel systems from selected projects. Data formats for several power systems including fuel consumption, generation levels for both diesel gen-sets and turbines, costs of installation and O&M, electrical data (voltage, current, power, power factor, etc), thermal and flow rate data (fuel flow rates, etc) have been obtained from village generation and load dynamics.

Wind-turbine Simulator

Inverter System

2

Equipment

The following equipment that was crucial in implementing the project was delivered by Sustainable Automation Inc., who subsequently provided their engineer for commissioning of the system at the Marsh Creek LLC facility in Anchorage:

1. Model WTS-IG-100-480-60 Wind Turbine Simulator, 100 kW, with induction generator, 3-phase 480 VAC input power, 3-phase 480 VAC output power;

2. Lead-acid battery bank, valve-regulated, maintenance-free, deep cycle, Absolyte GP, 336 VDC, 896 Ah nominal capacity;

3. Grid-forming energy storage power converter, 200 kVA, 480 VAC, 60 Hz with multiple operating modes: grid-forming (voltage and frequency regulation), diesel-parallel (load and VAR sharing), and controlled battery charging; and

4. Transformer and isolation, 225 kVA, 480V Delta Primary, 480/277V Wye Secondary.

Marsh Creek LLC made available some of the accessories needed for commissioning, including switchgear and a diesel gen-set, and provided a conducive environment for troubleshooting of the test bed equipment to ensure all components run as required prior to final installation at UAF.

Part of the research on the test bed will be devoted to energy storage systems. Initially the functional operation of the wind-diesel system will incorporate lead acid battery bank (336VDC, 896 Ah nominal capacity). ACEP has been performance testing a 5kW, 20 kWh Prudent Energy Vanadium Redox (VRB) flow battery, and this module is to be integrated with the rest of the test bed components for storage and ancillary services research.

3

New Lab: Energy Technology Facility

The new building that will house the test bed equipment – the Energy Technology Facility – was completed and handed to UAF/ACEP in December 2011. The ACEP team has been involved in layout design to ensure the civil works are completed with due regard to expected placement of the modules (with corresponding electrical network/switchgear, exhausters, fuel supply bays, drainage, etc). Pending work includes installation of exhaust systems/mufflers – ACEP is working with the contractor to have these in place. Additionally, fuel tanks are yet to be installed – specifications have been submitted to the University and approval is pending. Further, diesel gen-sets are needed to conduct the various research themes: high penetration wind-diesel operations, diesel engines’ exhaust testing, waste heat recovery, etc. On this front ACEP has been sourcing for these items and so far AVEC has indicated they shall provide a Detroit 60-Series, while AEA will loan ACEP a Cummins L10. It is expected that the test bed system shall be delivered and installed in January 2012.

Albeit the functionality of the test bed system has been demonstrated during commissioning, more rigorous testing shall be undertaken once the equipment is installed to check, among others: that components are able to ‘see’ each other during dynamic simulations, capability for diesel-off mode, and controls development and energy storage for voltage and frequency stability.

Wind-Diesel Hybrid Test Bed Emerging Energy Technology Fund Quarterly Report I (2012)

January 1st 2012-March 31st 2012

Project Status

Research Overview

The defining theme for this research project is development of transformative and efficient

energy technologies to address high penetration challenges in Alaska, with a focus on integration

of intelligent control systems, power electronics, and advanced storage for overall power quality

generation, with the added benefit of reduced diesel consumption. A test bed consisting of a

wind-turbine simulator, power converter, battery bank, diesel gensets and load bank is the

backbone of this project; control of these integrated systems is via a supervisory control and data

acquisition (SCADA) system that acquires real time data from all parts of the system.

Preliminary research work has focused on modeling and simulation of distributed generation in

high penetration systems, with the main objective being control performance. This forms the

basis for the trials to be conducted on the physical system at the test bed facility. Overall, the

project is on track and on schedule, and it is expected that once all the equipment is installed then

testing will commence in accordance with the funding objectives, namely, diesel-off operation in

high penetration systems.

Modeling and Simulation

The distributed power system models that were delivered by Sustainable Automation Inc. in

2011 continued to be used for simulation in anticipation of the test bed installation; these

included the Matlab-SimPowerSystems models of gensets, inverter, battery, and primary load.

Research work has involved use of wind speed data from select wind-diesel installations in

Alaska to analyze various load-dispatch scenarios. Some of the objectives have been to test the

power electronic components for voltage and frequency regulation, devise alternate and more

robust control algorithms in lieu of those supplied with the equipment, and to investigate the

capability of the system for diesel-off operation. ACEP has accessed wind speed data and other

operational information from the Ugashik power system which is being used in the analysis of

the models. The data primarily gives aspects of field performance including fuel consumption,

generation levels for both diesel gen-sets and turbines, costs of installation and O&M, electrical

data (voltage, current, power, power factor, etc), thermal and flow rate data (fuel flow rates, etc)

have been obtained from village generation and load dynamics.

Wind-turbine

Simulator

Diesel Gen-set

Inverter System

2

Equipment and Test Bed Status

Ongoing assembly at ACEP’s ETF: the lead-acid battery bank, wind turbine simulator with

grid form inverter, and CAT diesel engine.

Most of the equipment crucial in implementing the project has been received, and ACEP is in the

process of assembling the test bed. The components on ground include the 100 kW Wind

Turbine Simulator with induction generator, 3-phase 480 V output power; the lead-acid battery

bank, 336 VDC, 896 Ah nominal capacity; the Grid-forming energy storage power converter;

and transformer and isolation, 225 kVA, 480V Delta Primary, 480/277V Wye Secondary. ACEP

is still exploring ways to acquire a diesel engine (150~350 Kw range) to complete the

installation. Part of the research on the test bed will be devoted to energy storage systems.

Initially the functional operation of the wind-diesel system will incorporate lead acid battery

bank, and later the 20 kWh Prudent Energy Vanadium Redox (VRB) flow battery will be

integrated in the test bed platform for further storage and ancillary services research.

Wind-Diesel Hybrid Test Bed

Emerging Energy Technology Fund

Quarterly Report II (2012)

April 1st

2012-June 30th

2012

Project Status

Background

The Alaska Center for Energy and Power (ACEP) was conditionally awarded $433,045 from the

Denali Commission under the Emerging Technology Fund for testing power electronics devices

that could allow wind-diesel systems in Alaska to operate in a diesel-off mode to realize greater

cost savings from these systems. The scope of work for this project centers on use of grid-form

power electronic converters to provide frequency, voltage, and VAR support while the diesel

generators are shut off (provided adequate wind is available). This option has never been tested

in a lab which must first be done, before field testing, due to the high risk of interrupted power to

the community. Part of the research involves design of advanced control paradigms that may be

integrated into the system by reprogramming existing inverters with new algorithms to evolve a

low cost solution that can be applied to over ten communities, with the anticipated result of

increased power stability with the ability to shut the diesel gen-sets off.

Research Overview

The basis for research on power electronics is to simulate operation of the wind diesel systems

on a Hybrid Power Test Bed to assist the Alaskan wind industry in developing and improving

hybrid power generation systems. Using simulated village loads, researchers can evaluate the

interaction of these power sources under realistic conditions at the test bed and work through

actual problems the system might encounter in the field.

The defining theme for this research project is development of transformative and efficient

energy technologies to address high penetration challenges in Alaska, with a focus on integration

of intelligent control systems, power electronics, and advanced storage for overall power quality

generation, with the added benefit of reduced diesel consumption. The recently installed test bed

consisting of a wind-turbine simulator, power converter, battery bank, diesel gensets and load

bank is the backbone of this project; control of these integrated systems is via a supervisory

Wind-turbine

Simulator

Diesel Gen-set

Inverter System

control and data acquisition (SCADA) system that acquires real time data from all parts of the

system.

Equipment and Test Bed Status

Most of the equipment crucial in implementing the project has been received, assembled,

commissioned, and ACEP is in the process of analyzing various simulation scenarios on the test

bed.

The components on ground include the 100 kW Wind Turbine Simulator with induction

generator, 3-phase 480 V output power; the lead-acid battery bank, 336 VDC, 1000 Ah nominal

capacity; the Grid-forming energy storage power converter; transformer and isolation, 200 kVA,

480V Delta Primary, 480/277V Wye Secondary; and a 300kW Caterpilar diesel gen-set.

Part of the research on the test bed will be devoted to energy storage systems. Initially the

functional operation of the wind-diesel system will incorporate lead acid battery bank, and later

the 20 kWh Prudent Energy Vanadium Redox (VRB) flow battery will be integrated in the test

bed platform for further storage and ancillary services research.

Ongoing Work

Preliminary research work has focused on computer-based modeling and simulation of

distributed generation in high penetration systems, with the main objective being control

performance. Ongoing work involves testing the power electronic components for voltage and

frequency regulation under various wind data and load conditions, as well as simulating

performance with individual generation components.

The manufacturer of the grid-form inverter was on-site for final development of the equipment at

full power levels, which were not available at their own facility. Upon eight days of development

and testing the unit underwent a through commissioning test. The proper operation of the

inverter-battery system was confirmed. Commissioning included operation in parallel with the

diesel gen-set and wind turbine simulator; transition to diesel-off mode and operation in this

mode (grid-form inverter and wind turbine simulator only) under varying load and wind power

levels. Operation in diesel-off mode was confirmed with the caveat that this mode is available

only if the wind generator is spinning to provide the basic grid. It was pointed out earlier by the

manufacturer that the grid-form inverter cannot support a grid stand-alone, but does require an

electrical machine (synchronous condenser) to be online in parallel. Aside from this caveat the

unit performed to expectations and produce power within parameters of industry standards.

The other customer in the state (Marsh Creek, LLC) was present for commissioning and their

request regarding test scenarios were accommodated where ever possible during commissioning.

Immediate focus is going to be on power system performance including fuel consumption,

generation levels for both diesel gen-sets and turbine (WTS), and overall efficiency. The data

collected in the commissioning process is currently assessed to plan further testing scenarios. A

distributed control system is being installed to automate the interaction of components on the

testbed.

The photo shows the fully assembled wind-diesel testbed at the ACEP Energy Technology

Facility in Fairbanks, AK. To the far left, the wind turbine simulator. To the right, the grid

forming inverter, and the battery bank in the background.

ACEP Quarterly Report III (2012)

Wind-Diesel Hybrid Test BedEmerging Energy Technology Fund

Marc Mueller-Stoffels

Reporting Period: July 1, 2012 to September 30, 2012Grant number: Denali Commission: 01233; UAF: G6249.

October 2012

©2012 Alaska Center for Energy and Power, Fairbanks, AK, USA.All rights reserved.

Alaska Center for Energy and PowerInstitute of Northern EngineeringUniversity of Alaska FairbanksPO Box 755910Fairbanks, AK 99775-5910

Gwen Holdmann, Directorgwen.holdmann@alaska.edu

Dr. Marc Mueller-Stoffelsmmuellerstoffels@alaska.edu

Project Status

BackgroundThe Alaska Center for Energy and Power (ACEP) was conditionally awarded $433,045from the Denali Commission under the Emerging Technology Fund for testing powerelectronics devices that could allow wind-diesel systems in Alaska to operate in adiesel-off mode to realize greater cost savings from these systems. The scope of workfor this project centers on use of grid-form power electronic converters to provide fre-quency, voltage, and VAR support while the diesel generators are shut off (providedadequate wind is available). This option has never been tested in a lab which must firstbe done, before field testing, due to the high risk of interrupted power to the commu-nity. Part of the research involves design of advanced control paradigms that may beintegrated into the system by reprogramming existing inverters with new algorithmsto evolve a low cost solution that can be applied to over ten communities, with the an-ticipated result of increased power stability with the ability to shut the diesel gen-setsoff.

Under this project, a GRIDFORM inverter was purchased from Susitainable PowerSystems, LLC, to assess: 1) the general viability of inverter technology to providediesel-off mode in hybrid micro-grids when tied to energy storage; 2) And to assessthe performance of the particular product for use in rural Alaska.

3

ACEP Hybrid Applications TestbedAt a glance:

• ACEP operates an isolated micro-grid laboratory at similar scale as rural Alaskanpower systems.

• The grid consists of a 320 kWe diesel genset, a 100 kW wind turbine simulator,and a 250 kW load bank.

• The system is setup for 480 VAC operation.

ACEP has developed a Hybrid Applications Testbed with the aim to emulate typi-cal rural Alaskan wind-diesel systems up to power levels of 500 kW. The philosophy ofthe testbed is to be able to test technologies meant to increase power plant efficiency,as measured by the amount of diesel consumed per unit of energy produced, in a con-trolled setting which is readily accessible by road. Through this, the risk of acquiringsub-optimal equipment for rural Alaskan utilities is to be reduced by demonstratingand testing equipment designed/destined for rural Alaska before it is deployed.

The testbed setup utilized for the test of a particular piece of equipment can beadjusted depending on the equipments typical and rated power levels, or based on thepower levels of a given rural power plant.

For the test regiment described in Section the testbed was configured with a320 kWe Caterpillar diesel genset, a 100 kW wind turbine simulator and a250 kW/187.5 kvar variable load bank. The nominal grid voltage is 480 VAC, three-phase.

The wind turbine simulator, a product of Sustainable Power Systems LLC, con-sists of two mechanically coupled induction machines, a motor and a generator. Themotor is controlled by a variable frequency drive (VFD) and its output torque can becontrolled via torque, power, or wind speed and wind turbine power curve time series,or set point inputs. The generator connects directly to the main grid bus. The poweroutput is not conditioned.

The 250 kW/187.5 kvar variable load bank is a product of Load Technology, Inc.Load can be controlled in 5 kW and 3.5 kvar steps, independently of each other. Thenominal voltage of the load bank is three phase 208 VAC, and it is connected to the gridthrough a Delta-Wye-connected transformer (Delta on 480 VAC, Wye on 208 VAC,300 kVA). The lab setup for this test is shown in Fig. 1.

4

SG

L1

L2IGIMVFD

ACDCBattery

WTS

T2

T1

Figure 1: Single line drawing of Hybrid Applications Testbed setup for the GRID-FORM inverter test. The GRIDFORM inverter is shown in green, connected to thebattery and the isolation transformer (T2). The components of the wind turbine sim-ulator (WTS) are shown on gray background. The induction motor (IM) drives the in-duction generator (IG) based on control signals transmitted to the variable frequencydrive (VFD). Only the IG of the WTS is electrically connected to the hybrid grid,the VFD and IM receive external grid power. The main load bank (L1) is connectedto the hybrid grid through a voltage transformer (T1). The load bank (L2) was usedto simulate slight phase imbalances. The load bank connection and the connectionto the synchronous generator (SG, diesel genset) were instrumented with WattsOnmeters (blue dots). A Fluke 435 II Power Quality and Energy Analyzer (red dot) wasconnected to the load bank transformer for most test. The exception is the inverterefficiency test, where the Fluke 435 II was connected to the grid side of the isolationtransformer and the DC link of the GRIDFORM inverter.

5

GRIDFORM Inverter TestAt a glance:

• GRIDFORM Inverter is IGBT-based, rated at 200 kVA/160 kW.

• As per manufacturer, additionally, a synchronous condenser is required for fullfunctionality.

The inverter-battery setup tested is a product of Sustainable Power Systems LLC,Boulder, CO1 (SPS). The GRIDFORM inverter is a new product developed by SPS,with an American Superconductor PM3000 IGBT-based inverter module at its core.The inverter tested is accompanied by an Absolyte® GP flooded lead-acid batterybank, sized by SPS. The grid connection is made through a Delta-Wye isolation trans-former (Wye on grid-side, Delta on inverter-side). The GRIDFORM inverter suppliedfor the lab is serial number 2, with serial number 1 being deployed at Kokhanok, AK,and a smaller development unit exiting at SPS facilities.

The specifications given by SPS for the GRIDFORM inverter are shown in Table 1.

Table 1: GRIDFORM inverter specifications as per ’Energy Storage Inverter UserManual’, Rev. 1, June 2012, provided by SPS.

Electrical CharacterisiticsRated AC power 200 kVARated AC current 240 AAC line-to-line voltage 480 VACNominal battery voltage 336 VDCRated DC current 500 ANominal DC link voltage 750 VDCSwitching frequency 3 kHz

Environmental CharacteristicsStorage temperature -40 ◦C to 85 ◦CAmbient operating temperature -25 ◦C to 40 ◦CHumidity 0 to 95% non-condensingAltitude <1000 m without derating

1The unit was supplied by the precursor company, Sustainable Automation LLC.

6

The GRIDFORM inverter cannot support a grid without an inertial machine (genset,wind turbine, synchronous condenser, or similar) being online. The manufacturer sug-gests a combination of GRIDFORM inverter and a synchronous condenser if diesel-off mode is desired. In this case, the synchronous condenser can provide reactivepower support, and be the back-up inertial machine, should the wind turbine(s) sud-denly drop offline. This requirement is not an concern in the laboratory setting wherepermanent grid stability is not an issue; a synchronous condenser was not part ofthe test setup. By some definitions, this renders the GRIDFROM inverter a grid-supporting inverter, as the synchronous condenser can be considered a source of reac-tive power on the grid with which the GRIDFORM inverter shares load via voltagecontrol.

During the third quarter of 2012 testing of the GRIDFORM inverter continuedunder various scenarios to assess its viability as a solution to diesel-off mode in a windpowered micro-grid. The inverters efficiency was also assessed, which is an importantcornerstone to make economic assessments possible. In addition, ACEP engineersreviewed the inverter design, with respect to usability, operator safety and hardinessfor use in rural Alaska. Initial data processing tasks were performed.

7

ACEP Quarterly Report IV (2012)

Wind-Diesel Hybrid Test BedEmerging Energy Technology Fund

Marc Mueller-Stoffels

Reporting Period: October 1, 2012 to December 31, 2012Grant number: Denali Commission: 01233; UAF: G6249.

January 2013

©2013 Alaska Center for Energy and Power, Fairbanks, AK, USA.All rights reserved.

Alaska Center for Energy and PowerInstitute of Northern EngineeringUniversity of Alaska FairbanksPO Box 755910Fairbanks, AK 99775-5910

Gwen Holdmann, Directorgwen.holdmann@alaska.edu

Dr. Marc Mueller-Stoffelsmmuellerstoffels@alaska.edu

Project Status

BackgroundThe Alaska Center for Energy and Power (ACEP) was conditionally awarded $433,045from the Denali Commission under the Emerging Technology Fund for testing powerelectronics devices that could allow wind-diesel systems in Alaska to operate in adiesel-off mode to realize greater cost savings from these systems. The scope of workfor this project centers on use of grid-form power electronic converters to provide fre-quency, voltage, and VAR support while the diesel generators are shut off (providedadequate wind is available). This option has never been tested in a lab which must firstbe done, before field testing, due to the high risk of interrupted power to the commu-nity. Part of the research involves design of advanced control paradigms that may beintegrated into the system by reprogramming existing inverters with new algorithmsto evolve a low cost solution that can be applied to over ten communities, with the an-ticipated result of increased power stability with the ability to shut the diesel gen-setsoff.

Under this project, a GRIDFORM inverter was purchased from Susitainable PowerSystems, LLC, to assess: 1) the general viability of inverter technology to providediesel-off mode in hybrid micro-grids when tied to energy storage; 2) And to assessthe performance of the particular product for use in rural Alaska.

New LoadTec Load BankThis project was extended beyond its initial termination date due to delays regardingthe receipt of a new load bank. A 255 kW/187.5 kvar, 480 VAC, 3-phase reactive loadbanks was ordered in 2011. Due to problems in the supply chain, the manufacturer wasunable to meet the initial delivery date (June 2012). Several later delivery dates weremissed as well.

ACEP received this load bank in late December, 2012. Currently, this piece of

3

equipment is being installed into the Hybrid Applications Testbed.

4

GRIDFORM Inverter Test - Data Analysis and FinalReportAfter initial testing in QII and QIII several smaller additional tests were performedon the Hybrid Applications Testbed. The data from these tests were used to: 1) facil-itate model development by a new PhD graduate student, and 2) to gain some moreinformation on the operation of the GRIDFORM inverter.

In parallel, the data collected from various tests of the hybrid system were pro-cessed with regards to the performance of the GRIDFORM inverter. Performanceassessment includes:

• Inverter design review.

• Inverter-battery interaction.

• Power quality during load and operational mode changes.

• Diesel-off mode.

• Inverter efficiency (see Fig. 1).

A final report regarding the GRIDFORM inverter is under final internal review,and has been independently reviewed by Philip J. Maker, a remote hybrid systemsspecialist of Darwin, Australia. In addition, Mr. Maker has reviewed the ACEP HybridApplications Testbed.

5

10 20 30 40 50 60 70 80 90 10065

70

75

80

85

90

95

100

Active Power [kW]

Effi

cien

cy [%

]

GFI Supplying EnergyGFI Absorbing Energy

Figure 1: Efficiency vs active power. The GRIDFORM inverter exhibits up to 95%efficiency when absorbing power into the battery (black dots), and up to 91% efficiencywhen supplying power to the grid (blue dots). At low power levels efficiency is generallymuch reduced. Efficiency was assed using the inverter efficiency mode of the Fluke®

435 Series II Power Quality and Energy Analyzer with the DC measurement performedat the battery to GRIDFORM inverter connection and the AC measurement taken onthe grid-side of the isolation transformer. The GRIDFORM inverter was in kW/kvarmode during this test with the kvar set-point constant at 35 kvar. The diesel was online.

6