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Power Conditioning Systems for Renewables, Storage, and Microgrids


The introduction of variable renewables, storage and microgrids into today's electrical grid requires conversion of electric power from one form to another (AC to/from DC and/or conversion between different voltage levels), and requires conditioning the power quality to what is needed by the subsystems being integrated. These functions are performed by Power Conditioning Systems (PCSs) that are a key enabler to utilizing renewables, storage and microgrids on a large scale. This project develops measurement methods for PCSs and associated high-megawatt power electronics technologies needed for these applications, and supports PCS performance standards development to provide smart grid interactive interfaces for these devices. The PCS grid applications supported include smart grid interfaces for individual renewable/clean energy and storage systems including plug-in vehicles used as storage, as well as microgrids, and DC circuits. A long term goal of this project is to demonstrate the interoperability of these devices in a building and campus scale microgrid demonstration at NIST.


Objective:  Establish standards and measurement methods for smart grid and microgrid PCSs and associated component technology needed to transition from today's low penetration of non-dispatchable intermittent renewable energy sources to the future high penetrations of dispatchable smart grid interactive distributed generators, storage, and microgrids by 2017.

What is the new technical idea? The term Power Conditioning System (PCS) refers to the general class of devices that use power electronics technologies to convert electric power from one form to another; for example, converting between direct current (DC) and alternating current (AC), and/or converting between different voltage levels, and/or providing specific power qualities required by the subsystems being interfaced by the PCS. Power electronics technologies and PCS applications have continuously progressed since the invention of the power transistor (the key enabling technology) and are transforming the way electricity is generated, stored, delivered, and used, as well as the way mechanical systems are actuated.

Many "loads" on the power grid today are already interfaced through PCSs that provide the type of electricity needed by the load and also provide valuable grid interface characteristics such as unity power factor (phase of AC current draw is aligned with AC voltage) and reduced waveform harmonics(reduced sinusoidal distortion of load current). The transition to PCS-based loads occurred over the last three decades, starting with low power loads and evolving toward high power loads such as today's large variable speed electric motor drives (up to 100 MW). The grid "power delivery system" itself has also begun to use PCSs such as Flexible AC Transmission System (FACTS) devices that inject corrective power waveforms into the grid, and High Voltage DC Transmission (HVDC) stations that convert between AC and DC for long distance transmission (at 1000 kV, 1000 MW levels).

On the other hand, only a fraction of power generators on the grid today are PCS-based (<<1% overall),but we are on the verge of a transformation to much higher penetration levels of PCS-based generators(>10%) that will occur over only a few years. The transformation is partially due to the addition of renewable/clean energy sources that produce DC (photovoltaic and fuel cell) or variable AC (wind turbines) and thus require a PCS to convert to regulated AC meeting grid interconnection requirements. The distributed nature of solar energy also poses unique challenges in simultaneously meeting the requirements to provide grid stability by remaining connected during abnormal grid conditions, while also ensuring safety by de-energizing or separating into a microgrid island when the distribution grid goes down. Microgrids also provide resiliency and power quality advantages to consumers and can contribute to overall stability of the grid. Advanced smart grid-interactive PCS-based generator and microgrid functions developed as a result of this project enable solutions to these and many other issues and will enable distributed generators to provide grid interactive functions that increase their value proposition.

Future grid architectures involving fleets of stationary microgrids plus tactical mobile microgrids can playa critical role during disaster response involving wide-area electricity outages by enabling individual microgrids to continue to operate or to be brought back up before transmission lines and substations are restored. (An example of the benefit of this technology during a natural disaster is the microgrid in Sendai, Japan, after the Great East Japan Earthquake. Connecticut, for example, is actively pursuing microgrid technology and has established a microgrid grant and loan pilot program.) In the future, tactical mobile microgrids consisting of compact, lightweight PCS units on trucks might be used to rapidly integrate diverse types of generators, storage, loads and feeders during wide area disaster recovery efforts. Disaster-recovery capability might also be integrated intrinsically within power conditioning units of critical infrastructure equipment such as nuclear power plant cooling systems or municipal flood pump stations so that they can rapidly interface to alternate electricity sources during disaster recovery. The interagency coordination of PCS, Distributed Energy Resources (DER) and microgrid technology and standards development performed by this project will aid in more rapid adoption of advanced disaster recovery strategies.

What is the research plan? This NIST project addresses the critical standards, metrology, and technology gaps needed to support the transformation to high penetration levels of PCS-based distributed generators, storage and microgrids. The project will enable DER to be used by entities, such as utilities and industrial parks, as multi-functional operational assets to manage local and regional grid operations including the ability to island into resilient self-sustainable microgrids. Microgrids will be treated as resources to the grid, as initiated by either the grid operator or a third party; which can run as either single entities or in aggregate (including clusters).The project plan has three tasks that address: 1) metrology and standards for advanced interface functionalities of PCS-based generators, storage, and microgrids, 2) advanced PCS technologies and metrology needed to support these applications, and 3) application integration through conformity and interoperability testing and transition to demonstrations. The first two Tasks are accomplished by leveraging the Smart Grid Interoperability Panel (SGIP) Distributed Renewables, Generators and Storage(DRGS) Domain Expert Working Group (DEWG) led by this NIST project, the NIST High Megawatt PCS Technology Roadmap Workshop series led by this project, and the existing NIST High-Voltage High-Frequency power semiconductor device characterization and modeling laboratories.

To accomplish the third task, the project is designing and constructing the Microgrid/PCS Interoperability Lab within NIST Smart Grid Testbed. The new lab will enable testing interoperability of PCS-based devices and controllers in microgrid scenarios. The lab will also include electrical interconnection and information exchange with devices and systems from other Smart Grid Projects located in adjacent labs. The Microgrid/PCS Interoperability lab is being configured to support four different scales of microgrids:

  • Thrust A (residential customer microgrid)
  • Thrust B (light commercial facility microgrid)
  • Thrust C (DC microgrids)
  • Thrust D (distribution feeder segment microgrid)

Each Thrust will consist of the following four phases:

  • Phase 1: power equipment configuration and safety
  • Phase 2: microgrid equipment configuration and testing
  • Phase 3: satellite lab equipment interconnection and testing
  • Phase 4: transition microgrid/PCS equipment to demonstrations, eg.,microgrid equipment and smart inverters in netzero house

Major Accomplishments:

Technology Transfer Outcomes: :  

  • Several standards in the IEEE 1547 family and UL1741 have been developed and published, forming a technical foundation to support increased utilization of smart grid-interactive distributed energy resources (DER), and increased use of these standards is anticipated. Public rulemaking proceedings are also being conducted by FERC, the California Public Utility Commission and others referencing the need for the new functionalities of these standards. 
    • IEEE 1547.4 for grid islanding applications and IEEE 1547.6 for secondary networking were published. (FY11) 
    • UL 1741 Certification Requirements Document (CRD) “Special Purpose Utility Interactive Product Requirements” was published. (FY13) 
    • IEEE P1547.8 for advanced grid-interactive DER functionalities is on track for publication this year. (FY13) 
    • IEEE 1547a (Amendment 1 to IEEE 1547) is on track for publication this year, with modifications to address voltage regulation and frequency ride-through based on new functionalities needed to support interconnection of distributed energy resources. (FY13) 
    • IEC 61850-7-420 new edition is on track for publication in FY13 including the multifunctional electric storage, distributed energy resources operational interface of IEC 61850-90-7 (published this year) and harmonization and mapping with other standards. (FY13)