Microgrids and Power Quality Michael Starke, Ben Ollis, Josh Hambrick, Madhu Chinthavali Electrical Engineering Systems Research Division Oak Ridge National Laboratory ORNL is managed by UT-Battelle, LLC for the US Department of Energy ORNL Research TRL 9 • Funded by Department of Energy Systems Test and Deployment TRL 8 – Building technologies Systems Development – Renewable integration TRL 7 – Energy storage TRL 6 Technology – Smart grid and microgrids Demonstration TRL 5 Technology • Target technology readiness at TRL 4 different levels Development TRL 3 – Fundamental science to deployments Feasibility Assessment of technology with industry partners TRL 2 Basic Research TRL 1 What is a Microgrid? “A microgrid is a discrete energy system consisting of distributed energy sources (including demand management, storage, and generation) and loads capable of operating in parallel with, or independently from, the main power grid” – General Microgrids What Makes up a Microgrid? Separation Separation What Makes up a Microgrid? Controllable Controllable Generation Generation PV alone is not a good microgrid asset. What Makes up a Microgrid? Loads Loads What is Needed to Make a Microgrid Successful? • Clear expected functionality of the microgrid Defined Functionality – Should the microgrid be able to island successfully without a blackout? – Blackout ok and blackstart is expected upon that condition? • Enough local and controllable generation and Generation Capacity resource capacity – Standard generators? – Power electronic resources (PV, energy storage, fuel cells?) • Multiple levels of controls Coordinated Control – Devices and controls that support the control and coordination to meet this functionality – Communications to support optimization and device coordination Layers of Controls (Inverters) Primary Control – Secondary Control – – Converter and generation system level controls – Microgrid controller works with assets that are done automatically in response to to ensure voltage and frequency of measurements system are regulated. – Typically fast in nature – Typically slower in nature Typical Structure of Inverter based Devices Controller • Controller – - Measurements I/O – Lowest level is field programmable gate array (FPGA) - Inverter controls or digital signal processors (DSP) - PWM generation – Very fast computation and signal - Fault detection generation in 1-10 us range - System state decision (normal • Interface – conditions) – Real-time layers that support interaction to controller and Interface usually performs the communications interface and - Communication layer state representations - System state decision making – Can be done on the controller (normal conditions) level, but controller is resource - System coordinator limited Main Message: These systems can be complicated! Microgrids Transitioning to Power Electronic Resource Power electronic systems do not have inertia. Need different controls. Power Electronic Resources Fuel Cell Battery Systems PV Systems Power Quality Magnitude • A measurement of the ‘fitness’ of the power Frequency delivered • For US electric grid, usually like to think of a voltage sine IEEE/IEC NFPA/NEMA UL wave operating at 60Hz IEC 61000 NEMA LA 1 UL 96A IEEE 519 NEMA LS 1 UL 1283 • Many standards are available IEEE 1159 NEMA PE1 UL 1449 IEEE 1433 NFPA 70 to support defining power IEEE 1531 NFPA 780 quality and technology IEEE C2 IEEE C62.41 solutions IEEE 1433 IEEE 1564 Theo Laughner, Intro to Power Quality, TVA Presentation, 2017 11 Why is Power Quality Important? • Poor Power Quality Impacts: – Premature failure of devices • Capacitors • Motors • Transformers and cables – Energy efficiency with increased heating and losses • Can Trigger Tripping of Devices – Computers – Relays • Can Lead to Charges from your interconnected utility. 12 Different Electrical Power Quality Signatures Normal Unbalance Interruption Continuity of Service rd 3 Harmonic Sag Frequency th 5 Harmonic Swell Impulse Voltage Magnitude Harmonics Variations 13 Transients Challenges with Power Quality in Microgrids? Ongrid: Offgrid: [ISLANDED MODE] • Voltage support focused • Voltage control and frequency focused o Control reactive power of assets o Control reactive power for voltage to support voltage o Control real power for frequency • Supporting the grid for use cases such • Must deal with system imbalance as o Any imbalance now must be locally o demand reduction supported o local electricity cost reduction. • Power quality issues are generated locally • Power Quality issues can come from main grid 14 What can cause power quality issues within Microgrids? 1. Transient conditions such 3. Increased non-linear loads as that of an islanding event or rectified loads. due to a grid problem. 2. Renewable generation due 4. Changes in local to transient changes in impedance that can impact weather. filtering and power electronic controls. 5. Increased loading on one phase over another during an island. 15 The Connected Community Alabama Power: Neighborhood • 62 Residential buildings (occupied) – HVAC – Water heaters • PV system: 330kW Alabama Power: • Energy storage: 300kW, Microgrid 681kWh • Generator: 400kW 16 Distributed Control Features • Generation assets support multiple control modes (on grid/grid forming/voltage- frequency source) • Energy storage system and generator can detect system issues and transition to grid forming controls • Microgrid control can also coordinate islanding and resynchronization 17 Islanding (Often Observe Short Duration Voltage Surge/Sags) Islanded On-grid 18 Microgrid Island Frequency On-grid On-grid Islanded 19 Waveform distortion following island VOLTAGE CURRENT 20 Voltage Imbalance Voltage imbalance at the microgrid is consistent throughout the day at approximately 0.005 pu. Load imbalance is inconsistent throughout the day but is somewhat balanced amongst phases. 21 Contact: Michael Starke, PhD Electrical Engineering Systems Integration [email protected] 22.