By Gordon Lum
Traditionally, electric utilities have supplied energy based on predicted demand. This paradigm is rapidly changing as an increasing number of less-predictable Distributed Energy Resources (DER), particularly solar, come online. DER have intermittent and currently uncontrolled effects on the grid, leading to stability issues, including blackouts, which ironically are due to over-production of energy.
California, along with many other states, has made great strides in recent years to define a solution that mitigates the problems associated with increased penetration of rooftop solar. This has culminated in the June 2016 Rule 21 decision by the California Public Utilities Commission (CPUC) requiring smart inverters to be managed by utilities or DER operator/aggregator to maintain grid reliability. This article provides a brief update on the status of California Rule 21 implementation.
California Rule 21
The Rule 21 decision was based on the recommendations of the Smart Inverter Working Group (SIWG) and consists of three phases of implementation: Phase 1 – Implementation of mandatory autonomous smart inverter functions; Phase 2 – Adds communications requirement for smart inverters; and Phase 3 – Recommendations for advanced smart inverter functions.
In Phase 1, smart inverters are configured with settings that conform to each utility’s Interconnection handbook. Once configured, they operate autonomously (i.e. without the need for communications) by adjusting their output to local conditions, thus helping maintain grid reliability and power quality. The seven Phase 1 functions are:
- Anti-Islanding: Trip off under extended anomalous conditions
- Low/High Voltage Ride-Through: Ride through voltage excursions beyond normal limits Low/High Frequency Ride-Through: Ride through frequency excursions beyond normal limits
- Volt-VAr: Dynamic reactive power injection through autonomous responses to local voltage measurements
- Ramp Rate: Define default and emergency ramp rates as well as high and low limits
- Fixed Power Factor: Provide reactive power by a fixed power factor
- Soft Reconnect: Provide “soft-start” methods
In Phase 2, a bi-directional communications requirement between the utility and the smart Inverter or aggregator is mandated. Although the Phase 1 functions can operate autonomously, they cannot be modified without communications. As the network or solar conditions change, their parameters and software cannot be updated. Furthermore, most, if not all the proposed Phase 3 functions, require communications. Communications allows functional and security updates to be issued to the smart inverter without the need to physically go to each site.
A selected communications protocol must: operate over different media interfaces; operate over the TCP/IP internet protocols; use the international standard IEC 61850 as the information model; provide cybersecurity at the transport and application layers; and provide cybersecurity for user and device authentication.
CA Rule 21 has selected the IEEE 2030.5 standard (also known as Smart Energy Profile 2.0) as the default communications protocol as it satisfies all the listed selection criteria. IEEE 2030.5 is a secure, scalable, and consumer-friendly application-layer protocol built upon standard Internet protocols. The standard contains DER object models based on IEC 61850, direct controls, autonomous curves, and status and metrology information. These features ensure the utility has the tools necessary to maintain grid stability and reliability.
Additionally, the Rule 21 decision directs the California investor-owned utilities (IOUs) to publish any agreed-upon technical requirements for implementation of the Phase 2 protocol. On August 31, 2016, the California Smart Inverter Implementation Working Group published version 1.0 of the “IEEE 2030.5 Common California IOU Rule 21 Implementation Guide for Smart Inverters,” which defines the Common Smart Inverter Profile (CSIP) for California. CSIP creates a common communication profile for inverter communications that could be relied on by all parties to foster “plug and play” communications. Some guiding principles of CSIP include:
- Using IEEE 2030.5 to achieve interoperability by defining a complete profile including a data model, messaging model, communication protocol and security
- Restricting and/or eliminating some IEEE 2030.5 options to enhance interoperability
- Using existing IEEE 2030.5 resources and methods instead of inventing new ones
With the CSIP Implementation Guide, the IEEE 2030.5 specification, and each IOU’s Interconnection Handbook, smart inverter manufacturers, aggregators, and others can start implementing all the Phase 2 requirements.
The use of smart inverter systems can increase the life of distribution equipment by minimizing their operations, while at the same time improving the power quality for customers. Advanced functions will permit smart inverter systems to play an even more active role in distribution system stabilization, power system reliability, and overall energy efficiency. In March 2016, the SIWG completed technical analysis on the following candidate advanced smart inverter functions:
- Monitor DER Data – Ability to provide status information and metrology data
- Disconnect/Reconnect – Ability to provide a “cease to energize” state
- Limit Maximum Real Power – Ability to set a maximum limit on real power output
- Set Real Power Output – Ability to set the real power output level
- Frequency-Watt Mode – Ability to counteract frequency excursions by increasing or decreasing real power output
- Volt-Watt Mode – Ability to counteract voltage excursions by increasing or decreasing real power output
- Dynamic Reactive Current – Ability to provide reactive current support in response to dynamic variations in voltage
- Scheduling Controls – Ability to schedule DER controls for specific time periods
In the future, power engineering analysis, testing results, economics, tariffs, and other considerations will ultimately determine which advanced functions the utilities will use to achieve these goals.
Current State of Affairs
The Rule 21 decision mandates the implementation of the Phase 1 functions for all interconnecting smart inverters one year from the approval of UL 1741 Supplement SA. UL 1741 SA was balloted on September 8, 2016 and approved, and UL has indicated they are ready to start certification. On September 2017, all inverters will need UL1741SA certification for an interconnection permit.
The Rule 21 decision directs the California IOUs to file an advice letter pertaining to any agreed-upon technical requirements for communications within six months of the decision. Version 1.0 of the CSIP Implementation Guide is complete and the IOUs are currently working on their Interconnection Handbooks.
In the meantime, utilities, aggregators, smart inverter manufacturers, and other parties have been actively testing Phase 2 communications in lab and field conditions. Larger scale field trials are in the planning stage.
The Rule 21 decision directs the California IOU’s to file an advice letter pertaining to advanced smart inverter functions within six months of the decision. Utilities and other stakeholders are currently working on finalizing the list of advanced inverter functions for Phase 3.
Gordon Lum, an IEEE member, leads Kitu Systems' engineering team with overall responsibility for taking the G2H SE2 Software to production holds. After obtaining a bachelor's degree in electrical engineering from MIT and a master's degree in electrical engineering from the University of California, San Diego, he spent his first five years working in defense communications at Linkabit. Later, Gordon’s career was dedicated to the early stages of digital satellite TV communications. In the mid-90s, he founded and acted as Vice President of Engineering at Corelent (FKA TurboNet), which developed the first certified DOCSIS cable modem, and he remained at the company for 15 years. He has over 23 years experience in the design, development, and deployment of all types of digital communications equipment.
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