EE362G Smart Grids: Architecture Ross Baldick, Department of Electrical and Computer Engineering Spring 2019 Copyright © 2019

Outline Conceptual smart grid architecture. Generation and transmission. Distribution automation and end-use. Copyright © 2019

Conceptual architecture. Key definition of smart grid is communications and control overlaid on existing power grid. Additional aspects of smart grid relate to: Need to accommodate renewables and distributed generation, and Integrating end-user more explicitly into grid decision-making. Copyright © 2019

Conceptual architecture. Bulk generation Distribution substations Distributed generation Transmission system Distribution automation Supervisory Control and Data Acquisition End-use Information and communications technologies (ICT) providing interface to markets, ISO operations, end-users Electrical connection supporting power flow Communication connection Copyright © 2019

Generation and transmission. Previous lectures have shown that the generation and transmission system is “smart” and continues to get smarter: Improve efficiency of operation, Increase integration of renewables, Better utilize (and compensate for shortcomings of) human skills. Information and communication technologies (ICT) already heavily utilized. Copyright © 2019

Generation and transmission. Relatively small number of elements to be telemetered and controlled: ERCOT has around 600 bulk generating units, Approximately 6,000 transmission lines, Many hundreds of distribution substations. ERCOT Independent System Operator models, telemeters data, and issues dispatch instructions for these components. Copyright © 2019

Distribution automation and end-use. Focus of lectures will now shift towards: Distribution system, and End-use of electricity. Despite efforts beginning at least as early as 1980s, ICT only more recently utilized in: Distribution automation, and End-use. Copyright © 2019

Distribution automation and end-use. One-way versus two-way flow of power on distribution system. Centralized versus hierarchical versus autonomous/decentralized monitoring and control. Communications. Copyright © 2019

One-way vs two-way flow of power. Historical design of distribution system has generally assumed one way flow of power from single source at transmission bus to loads. Generation sources in distribution system, such as rooftop solar, pose a particular challenge because power flow can reverse at high penetrations: Power could flow in either direction on distribution feeder. Copyright © 2019

One-way vs two-way flow of power. Two-way flow of power complicates: Voltage control: historical design assumes that voltage magnitude decreases towards ends of feeders, with distributed resources, voltage magnitude may increase towards ends of feeders, Protection (fuses): historical design assumes that current decreases towards ends of feeders, with distributed resources, current may be higher towards end of feeders. Copyright © 2019

One-way vs two-way flow of power. Distribution system protection, monitoring, and control is likely to require significant redesign and rebuild to accommodate significant penetration of distributed renewables and dispatchable demand. Copyright © 2019

Centralized vs hierarchical vs autonomous. Huge number of distribution elements and end-use components: Historically distribution elements mostly autonomous or under decentralized control, Challenge for a single entity such as ISO to monitor and control/dispatch a large number of relatively smaller components, Alternative of hierarchical control where, for example, “Distribution System Operator” (DSO) monitors and controls distribution system, and interfaces with ISO. Copyright © 2019

Autonomous and decentralized control. End-use consumers have historically almost all been autonomous! I switch on a light when I choose without consulting utility, ISO, DSO… But collective behavior of a large number of consumers is relatively predictable, given weather information, So, eg, short-term planning of generation could be based on relatively accurate forecast of distribution loads tomorrow. Copyright © 2019

Centralized or hierarchical control. Ceding some end-use decisions to ISO or DSO can provide value: “loads acting as resources” (LaaR) in ERCOT provide reserves for cases of generation outage, LaaRs typically provided by a relatively small number of large, industrial loads, Have been utilized for decades. Copyright © 2019

Centralized or hierarchical control. Increasing amount of renewables increases uncertainty of supply. Increasing amounts of controllable distribution system load can potentially help to cope with this uncertainty: Larger number of smaller end-users, Utilizing flexibility of timing of end-use consumption can help with integrating renewables, Controlled electric vehicle charging, See in exercise. Copyright © 2019

Centralized or hierarchical control. Should controllable distribution system load be directly represented into ISO model? Such “level jumping” (between distribution and transmission) is acceptable with only a few, large dispatchable loads, But will pose problems with high participation: What is meaning of distribution feeder forecast load if a large fraction of load is controllable? The need to have a well-defined interface between transmission and distribution may be driver of need for DSO. Copyright © 2019

Autonomous and decentralized control. Distribution system elements such as switched capacitors and regulating transformers have historically been autonomous: Controlled on the basis of time or local voltage measurement. Copyright © 2019

Centralized or hierarchical control. Increasing amount of distributed renewables increases complexity of operation of distribution system: DSO monitoring and coordinated control of capacitors and regulating transformers may improve ability to regulate voltage, In practice, capacitors and regulating transformers will have “fast” autonomous response to large changes together with slower update of “set-points” based on more centralized decisions. Copyright © 2019

Centralized or hierarchical control. Protection in distribution system has historically been autonomous and designed assuming one-way flow of power: Considerable use of fuses, requiring truck roll to restore, Sized based on the assumption that current decreases towards end of feeder. Copyright © 2019

Centralized or hierarchical control. Automated protection with circuit breakers together with communication can improve response to outages: “Fault location, Isolation, and Service Restoration” (FLISR) can improve reliability of delivery by reducing outage time. More sophisticated monitoring and protection also likely to be necessary to support two-way flow of power in distribution system: Distribution system SCADA, DSO. Copyright © 2019

Communications. Key aspect of smart grid architecture is establishing secure, encrypted, comprehensive communication fabric that accommodates current and future applications: Unified communications backbone to support all distribution system SCADA functions, Additional “special cases” such as wireless mesh for short-distance communications to gather revenue meter data before transmitting on backbone. Copyright © 2019

Communications. Recognition that there are synergies between various functions: Revenue meter can provide “last gasp” information about outage to help inform restoration after faults, Additional metering can help to detect electricity theft (“non-technical losses.”) Copyright © 2019

Summary Conceptual smart grid architecture. Generation and transmission. Distribution automation and end-use. Copyright © 2019

Homework Exercises: Due 2/21. See homework download. Copyright © 2019