Microgrid Full PPT Upto Unit 5 PDF

Microgrid (Professional Elective- VI) – IV B.Tech EEE A & B Course Instructor: Dr. VSB Chaitanya Duvvury, B.Tech, M.Tech (Honours IIT BHU Varanasi), Ph.D. (IIT Kharagpur). Assistant Professor, Department of EEE, Dr. BV Raju Institute of Technology (UGC Autonomous), Narsapur, Telangan...

Microgrid (Professional Elective- VI) – IV B.Tech EEE A & B Course Instructor: Dr. VSB Chaitanya Duvvury, B.Tech, M.Tech (Honours IIT BHU Varanasi), Ph.D. (IIT Kharagpur). Assistant Professor, Department of EEE, Dr. BV Raju Institute of Technology (UGC Autonomous), Narsapur, Telangana Ph. No: 9933670003 Email: [email protected] Dr. V S B Chaitanya Duvvury UNIT 1 Introduction to Microgrid 1) Microgrid Definition. 2) Typical structure and configuration of a Microgrid. 3) Significance of Microgrids. 4) Types of Microgrids AC, DC and hybrid Microgrids. Reference Books: 1). Microgrids, Architectures & Control, Wiley, Edited by Prof. Nikos Hatziargyriou, National Technical University of Athens, Greece. 2). Microgrids Design and Implementation, Springer, Antonio Carlos Zambroni de Souza Miguel Castilla. Dr. V S B Chaitanya Duvvury Microgrid Definition Dr. V S B Chaitanya Duvvury Microgrid Definition  Electrical distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way, either while connected to the main power network and/or while islanded”.  Microgrid is Capable of operating in both modes : i). Grid-connected mode. ii). Stand-alone or islanded mode.  The capability of Microgrids to switch into the islanded mode in case of faults in the upstream network (Main grid) increases the reliability of customer supply and the resilience of the distribution networks. Dr. V S B Chaitanya Duvvury Typical structure and configuration of a Microgrid  Figure shown in typical Microgrid structure consists of two feeders and an energy storage device are connected to the low-voltage (LV) side.  As the structure considered for the Microgrid transmits power through AC, power electronic converters are used to adjust the DC sources and perform the DC/AC transformation. Typical Microgrid structure Dr. V S B Chaitanya Duvvury Typical structure and configuration of a Microgrid  Connection to the main grid in the medium voltage (MV) side is made through the point of common coupling.  A circuit breaker allows decoupling the Microgrid to the main grid in cases of disturbances, changing the operation to islanded mode.  Microgrid controller functions are listed below: i) MGCC (Microgrid Central Controller) ii) MC (Microsource Controller) iii) LC (Load Controller) Typical Microgrid structure Dr. V S B Chaitanya Duvvury Typical structure and configuration of a Microgrid Microgrid Central Controller: Performs centralized control and is responsible for managing the energy bought/sold and provide islanding logic or supply restoration via electrical power utility. It is also responsible for maintaining the voltage and frequency within a range of specified values. Optimal operation is achieved by sending control signal settings to MCs and LCs. Microsource Controller: MC should be able to control the voltage and power flow in response to load changes or disturbances. Quickness in response and the ability to adjust regardless of source connected type are other main features. Load Controller: Perform control in controlled loads by connection/disconnection of certain equipment in certain predetermined periods. LC also relieves unfavorable operating condition of Microgrid. Dr. V S B Chaitanya Duvvury Significance of Microgrids Enhanced Resilience: Microgrids can operate independently of the main grid, ensuring a continuous power supply even during grid outages or natural disasters. This is particularly crucial for critical infrastructure such as hospitals, military bases, and remote communities. Improved Energy Efficiency: Microgrids facilitate localized generation and distribution of electricity, reducing transmission and distribution losses that occur in traditional centralized power systems. Integration of Renewable Energy: Microgrids play a vital role in integrating renewable energy sources, such as solar panels, wind turbines, and battery storage, into the grid. It also provide a platform for efficient management and utilization of distributed energy resources (DERs). Empowering Local Communities: Microgrids empower local communities by enabling them to take control of their energy supply. They encourage decentralized energy production, allowing individuals, businesses, and communities to generate their own power and become more self-reliant. Dr. V S B Chaitanya Duvvury Significance of Microgrids Load Management and Demand Response: They allow for real-time monitoring and control of electricity consumption, enabling optimized energy usage and demand response programs. This can lead to more efficient utilization of energy resources, cost savings, and reduced strain on the overall grid during peak demand periods. Integration of Electric Vehicles (EVs): Microgrids provide the infrastructure for EV charging stations and can manage the charging and discharging patterns of the vehicle batteries. This helps to lessen the strain on the grid caused by EV charging and allows for better utilization of renewable energy sources for vehicle charging. Market Opportunities and Energy Trading: Microgrids create opportunities for localized energy markets and peer-to-peer energy trading. Participants within a Microgrid can trade surplus energy directly with each other, promoting energy sharing, reducing costs, and supporting the growth of a decentralized energy economy. Dr. V S B Chaitanya Duvvury Types of Microgrids AC, DC and hybrid Microgrids PEC – Power Electronic Converter DC Loads AC Loads Dispersed generation in DC Microgrid Dispersed generation in AC Microgrid Dr. V S B Chaitanya Duvvury DC Vs AC Microgrids In an DC Microgrid, Distributed generation sources such as photovoltaic panels, fuel cells, and battery banks operate in DC mode and are located near the loads. Various loads such as computers, TVs, and LED bulbs are supplied with direct current. In an AC Microgrid, DC sources such as PV and fuel cells are converted to AC using DC/AC converters while AC sources are coupled directly using power electronics interfaces. DC loads are connected via AC/DC converters. In DC Microgrids, AC generating sources and loads are converted to DC using DC/AC converters. However, the conversion process results in losses. The DC/AC inverter is approximately 85% efficient, AC/DC rectifier 90%, and DC/DC converters 95%. At first, these previous data indicate that the fewer conversions type AC/DC better is the use of energy. Dr. V S B Chaitanya Duvvury Hybrid Microgrid Hybrid Microgrid Dr. V S B Chaitanya Duvvury Hybrid Microgrid  An intermediate solution is the formation of hybrid Microgrids.  The main objective is to develop networks minimizing the number of converters, i.e., reducing the losses associated with conversion.  In hybrid networks, AC generation sources and loads are connected to the AC side of the network.  DC generation sources and loads are connected to the DC side.  The connection between the AC and DC sides of the network is made through a bidirectional converter, which can act both as an inverter drive and as a rectifier relying on the power flow direction. Dr. V S B Chaitanya Duvvury UNIT 2 Microgrids Control Issues 1) Introduction of Control Function. 2) Role of Information and Communication Technology. 3) Microgrid Control Architecture. 4) Centralized and Decentralized control Reference Book: Microgrids, Architectures & Control, Wiley, Edited by Prof. Nikos Hatziargyriou, National Technical University of Athens, Greece. Dr. V S B Chaitanya Duvvury Introduction of Control Functions  Control functions in a Microgrid is categorized into three groups, i). Upstream Network Interface. Microgrid actions to import or export energy following the decisions of the ESCO (energy service provider/company). ii). Microgrid Control. All the functionalities within the Microgrid… iii). Local Control & Protection All the functionalities that are local and performed by a single DG, storage or controllable load Dr. V S B Chaitanya Duvvury Introduction of Control Functions  Decision for island/interconnected mode.  Market Participation. Upstream Network Interface  Upstream Coordination  Voltage/frequency control.  Active/reactive power control. Microgrid Control  Load consumption/shedding.  Black start.  Primary Voltage/frequency control.  Primary Active/reactive power control. Local Control & Protection  Battery Management.  Protection. Dr. V S B Chaitanya Duvvury Role of Information and Communication Technology (ICT) ICT enables the integration and coordination of these diverse energy resources to enhance the efficiency, reliability, and sustainability of the Microgrid.  Monitoring and Control Smart sensors and meters gather data on energy generation, consumption, storage levels, and grid conditions. This data is processed and analyzed to optimize the operation of the Microgrid, balance supply and demand, and prevent overloads or blackouts.  Energy Management Systems It can predict energy demand patterns, prioritize energy sources, and automate switching between different resources for optimal efficiency and cost savings.  Demand Response By providing consumers with real-time information on energy prices and consumption patterns, they can adjust their energy usage to avoid peak demand periods and reduce overall energy costs. Dr. V S B Chaitanya Duvvury Role of Information and Communication Technology  Grid Stability and Resilience ICT helps maintain grid stability by continuously monitoring system parameters and quickly responding to any faults or anomalies. This can involve reconfiguring the Microgrid, isolating faulty components, and restoring normal operation.  Integrating Renewable Energy Microgrids often incorporate renewable energy sources, which are inherently intermittent. ICT can predict the availability of solar or wind energy and adjust the Microgrid’s operation to accommodate these fluctuations seamlessly.  Energy Storage Management Energy storage is a critical component of Microgrids, helping to store excess energy during periods of high generation and release it when demand is high or generation is low. ICT optimizes the charging and discharging cycles of energy storage systems to ensure efficient use of stored energy. Dr. V S B Chaitanya Duvvury Role of Information and Communication Technology  Market Integration and Peer-to-peer Trading ICT can enable peer-to-peer energy trading within Microgrids. Prosumers (consumers who also produce energy) can directly trade surplus energy with others in the Microgrid, creating a more decentralized and dynamic energy market.  Predictive Maintenance ICT allows for predictive maintenance of Microgrid assets. By analyzing data from sensors and monitoring systems, maintenance needs can be anticipated, reducing downtime and improving the overall reliability of the Microgrid.  Cyber security As Microgrids become more connected and dependent on ICT, cyber security becomes a critical concern. Implementing robust cyber security measures ensures the protection of data and the resilience of the Microgrid against potential cyber threats. Dr. V S B Chaitanya Duvvury Microgrid Control Architecture  Figure shown in typical Microgrid structure consists of two feeders and an energy storage device are connected to the low-voltage (LV) side.  As the structure considered for the Microgrid transmits power through AC, power electronic converters are used to adjust the DC sources and perform the DC/AC transformation. Microgrid architecture Dr. V S B Chaitanya Duvvury Microgrid Control Architecture  Connection to the main grid in the medium voltage (MV) side is made through the point of common coupling.  A circuit breaker allows decoupling the Microgrid to the main grid in cases of disturbances, changing the operation to islanded mode.  Microgrid controller functions are listed below: i) MGCC (Microgrid Central Controller) ii) MC (Microsource Controller) iii) LC (Load Controller) Dr. V S B Chaitanya Duvvury Microgrid Control Architecture Microgrid Central Controller: Performs centralized control and is responsible for managing the energy bought/sold and provide islanding logic or supply restoration via electrical power utility. It is also responsible for maintaining the voltage and frequency within a range of specified values. Optimal operation is achieved by sending control signal settings to MCs and LCs. Microsource Controller: MC should be able to control the voltage and power flow in response to load changes or disturbances. Quickness in response and the ability to adjust regardless of source connected type are other main features. Load Controller: Perform control in controlled loads by connection/disconnection of certain equipment in certain predetermined periods. LC also relieves unfavorable operating condition of Microgrid. Dr. V S B Chaitanya Duvvury Microgrid Control Architecture Microgrid Central Controller: Performs centralized control and is responsible for managing the energy bought/sold and provide islanding logic or supply restoration via electrical power utility. It is also responsible for maintaining the voltage and frequency within a range of specified values. Optimal operation is achieved by sending control signal settings to MCs and LCs. Microsource Controller: MC should be able to control the voltage and power flow in response to load changes or disturbances. Quickness in response and the ability to adjust regardless of source connected type are other main features. Load Controller: Perform control in controlled loads by connection/disconnection of certain equipment in certain predetermined periods. LC also relieves unfavorable operating condition of Microgrid. Dr. V S B Chaitanya Duvvury Centralized and Decentralized control Centralized control and decentralized control are two different approaches for Microgrid control. DSO  distribution system operator ESCO  energy service provider/company RES  Renewable energy sources centralized control Dr. V S B Chaitanya Duvvury Centralized control In a centralized control system, decision-making authority and control are concentrated in a single location or entity. A central controller or management system is responsible for collecting data from various sources, processing information, and making decisions that govern the entire system. The central controller has a comprehensive view of the system and can implement global optimizations and strategies. Drawbacks of Centralized control Single point of failure: If the central controller malfunctions or becomes unavailable, the entire system may be affected. Scalability challenges: As the system grows in size and complexity, the centralized approach may become less efficient and more difficult to manage. Dr. V S B Chaitanya Duvvury Centralized and Decentralized control DSO  distribution system operator ESCO  energy service provider/company RES  Renewable energy sources IC  Individual controller Decentralized control Dr. V S B Chaitanya Duvvury Decentralized control In a decentralized control system, decision-making authority is distributed among multiple independent entities or subsystems. Each entity has its own local control capabilities and makes decisions based on local information and objectives. There is no single point of control, and each entity operates autonomously within its predefined scope. Drawbacks of Decentralized control Lack of global coordination: Each entity operates independently, which may lead to suboptimal global performance. Complexity: Designing decentralized control systems can be more complex and require careful coordination mechanisms. Dr. V S B Chaitanya Duvvury UNIT 3 Power Electronic Converters for Microgrids 1) Modes of Operation of Microgrid Converters. Up to Mid 1 Syllabus 2) Converter Topologies. 3) Modulation Strategies. 4) Control and System Issues. Mid 2 Syllabus 5) Future Challenges and Solutions Reference Book: Power Electronic Converters For Microgrids, Wiley, Suleiman M. Sharkh University of Southampton, United Kingdom. Dr. V S B Chaitanya Duvvury Modes of Operation of Microgrid Converters  Power electronic converters convert DC (from photovoltaic cells, batteries, fuel cells or variable frequency AC (wind) into 50/60 Hz AC power that is injected into the grid and/or used to supply local loads.  Converters connected to batteries or other storage devices will also need to be bidirectional to charge and discharge these devices. A schematic diagram of a Microgrid Dr. V S B Chaitanya Duvvury Modes of Operation of Microgrid Converters  In this mode, the Microgrid operates in synchronization with the utility grid. Grid- The converter allows bidirectional power flow, enabling the Microgrid to import or Connected export power to and from the grid as needed. Mode  The converter output current or voltage needs to be synchronized with the grid, which is usually achieved by using a phase-locked loop (PLL) or grid voltage zero crossing detection.  In this mode, the Microgrid is disconnected from the main grid, where two or Stand- more power electronic converters switch to stand-alone mode to supply a critical load. Alone In this case, these converters need to share the load equitably. Mode  Equitable sharing of load by parallel connected converters operating in stand-alone mode requires additional control. Dr. V S B Chaitanya Duvvury Modes of Operation of Microgrid Converters  There are several methods for parallel connection, which can be broadly classified Stand- into two categories: Alone (i) frequency and voltage droop method and Mode (ii) master-slave method, whereby one of the converters acts as a master, setting the frequency and voltage, and communicating to the other converters their share of the load.  The battery charging mode ensures that the energy storage system optimally Battery stores energy from different sources and makes it available for later use, either to Charging meet load demand or to provide grid support services. Mode  The power electronic converter could then be used as a battery charger. The charging mode is typically managed by a battery management system (BMS) that monitors and controls the charging process. Dr. V S B Chaitanya Duvvury Converter Topologies Two level grid-connected inverter with LCL filter  A two-level grid-connected inverter with an LCL, particularly in applications like photovoltaic (PV) systems and wind energy converters.  This setup is designed to convert the DC power generated by sources into AC power that can be synchronized and injected into the utility grid. Grid-Connected Inverter LCL Filter Controller Grid Synchronization Dr. V S B Chaitanya Duvvury Converter Topologies Multi-level voltage source inverter (a) NPC and (b) cascaded  The Neutral-Point-Clamped (NPC) inverter is a multilevel voltage source inverter (VSI) topology provides improved waveform quality and reduced harmonic distortion compared to conventional two-level inverters.  A Cascaded Multi-Level Voltage Source Converter (Cascaded MLVSC) is a type of multilevel inverter topology that generates a high-quality AC output voltage waveform by stacking multiple H- bridge cells in a cascaded fashion. Dr. V S B Chaitanya Duvvury Converter Topologies Interleaved converter with two channels  In an interleaved converter with two channels, two individual power converter channels are designed and connected in parallel to share the load.  The switching devices and control circuitry for each channel are designed to operate out of phase with each other, creating an interleaving effect. This means that while one channel is in an ON state, the other channel is in an OFF state, and vice versa Dr. V S B Chaitanya Duvvury Converter Topologies (a) Three-phase current source converter and (b) matrix converter  A basic three-phase current-source inverter consists of six controlled switches, arranged in a bridge configuration.  The inverter is connected to a DC current source, and a three-phase AC load. The switches are controlled to modulate the output current waveform.  A three-phase matrix converter is a specialized type of power electronic device that provides bidirectional three-phase AC-to-AC power conversion without the use of bulky energy storage components like capacitors or inductors.  The matrix converter typically contains a total of nine bi-directional switches (3x3 matrix) for a three-phase system. Dr. V S B Chaitanya Duvvury Modulation Techniques Modulation techniques used to control the switching of power semiconductor devices and help in shaping the output voltage and current waveforms. PWM (Pulse Width Modulation) Hysteresis modulation, and Pulse density modulation (PDM). Hysteresis modulation continuously compares a reference signal (desired value) with a feedback signal (actual value) and making control decisions based on the error between these signals. The goal is to keep the actual value within a predefined hysteresis band around the reference value. Not preferred for microgrid inverters where high quality output current and good transient response are essential requirements. Dr. V S B Chaitanya Duvvury Modulation Techniques Most grid connected converters use Pulse Width Modulation (PWM). It involves varying the width of the pulses in a high-frequency carrier waveform while keeping the carrier frequency constant. By adjusting the duty cycle (the ratio of the on-time to the total period), the average output voltage can be controlled. Pulse density modulation (PDM) is another possible modulation technique. It is not commonly used in conventional converters but it has been used in high-frequency (150 kHz) converters used for induction heating. The potential for this modulation strategy is yet to be explored in the context of converters for grid connection applications. Dr. V S B Chaitanya Duvvury Control and System Issues key control and system issues related to microgrid converters Voltage and Frequency Regulation:  Microgrid converters must maintain voltage and frequency within specified limits to ensure grid stability. Voltage and frequency control becomes especially challenging in islanded (standalone) mode when the microgrid operates independently from the main grid. Islanding Detection and Synchronization:  Ensuring proper islanding detection is crucial to protect utility workers and equipment during grid outages.  Microgrid converters need to synchronize their output with the grid when connected and autonomously when in islanded mode. Dr. V S B Chaitanya Duvvury Control and System Issues Power Quality and Harmonics:  Microgrid converters should minimize harmonic distortion and ensure power quality to prevent damage to sensitive loads and other connected equipment. Load and Generation Management:  Control algorithms are needed to manage the interaction between variable DERs like solar and wind with energy storage systems.  Load shedding and demand-side management may be necessary to match generation with demand. Energy Storage Integration:  Proper control of energy storage systems (e.g., batteries) is essential for efficient energy dispatch, peak shaving, and grid support functions.  State-of-charge (SoC) and state-of-health (SoH) management are important for prolonging battery life. Dr. V S B Chaitanya Duvvury Control and System Issues Grid Interconnection Standards:  Microgrid converters must adhere to grid interconnection standards and codes to ensure safe and reliable operation when connected to the main grid. Communication and Control Networks:  Robust communication networks are needed for real-time monitoring and control of microgrid components.  Redundancy and cyber security measures are essential to protect against communication failures and security threats. Protection and Fault Management:  Microgrid converters should have protection schemes to detect and mitigate faults within the microgrid.  Fast fault detection and isolation are crucial for preventing cascading failures and ensuring system reliability. Dr. V S B Chaitanya Duvvury Control and System Issues Grid Support Functions:  Microgrid converters can provide grid support functions, including voltage regulation, reactive power control, and grid frequency support.  These functions are important for stabilizing the local grid and improving its resilience. Energy Management and Optimization:  Advanced control strategies and energy management systems (EMS) optimize the dispatch of DERs to maximize self-consumption of renewable energy and minimize energy costs. Dr. V S B Chaitanya Duvvury Future Challenges and Solutions  The cost and size of the converter and filter components remain an issue. It may be addressed by increasing the frequency and using either multilevel or interleaved topologies. Further research is needed to establish the optimum trade-off between power electronic devices and filter components.  It may be beneficial to take an overall system approach when designing the converter, rather than considering the design of the converter in isolation. For example, a cascaded multilevel converter requires multiple isolated DC-links, which requires a multi-tap transformer or complex schemes using flying capacitors.  The rapid increase of inverter interfaced DG units is already raising issues related to coordination of protection relays, both in grid-connected and stand-alone modes  The standards governing these converters are still evolving and practical implementation is continuously giving rise to new issues that need to be thought about and regulated. Dr. V S B Chaitanya Duvvury UNIT 4 Microgrid Protection 1) Introduction. 2) Key Protection Challenges. 3) Possible Solutions to Key Protection Challenges. 4) Case Study Reference Book: Power Electronic Converters For Microgrids, Wiley, Suleiman M. Sharkh University of Southampton, United Kingdom. Dr. V S B Chaitanya Duvvury Introduction to Microgrid Protection  The integration of distributed generation (DG) within Microgrids into distribution networks (DNs) requires rethinking of traditional protection practices.  For example, fault current’s magnitude and its direction can change when DG is introduced into a distribution network. Dr. V S B Chaitanya Duvvury A simple MG structure Key Protection Challenges relay situated upstream of the DG unit 1) Fault Current Level Modification Fault Fault current contributions from grid and DG  The relay situated upstream of the DG unit will only measure the fault current supplied by the upstream source.  As this is only one part of the actual fault current, the relays, especially those with inverse time characteristics, may not function properly, resulting in coordination problems. Dr. V S B Chaitanya Duvvury 2) Reduction in Reach of Impedance Relays Z=V/I ** The risen fault distance is because of the voltage increase caused by extra infeed Fault at the common bus. In other words, the DG with the main source contributes to the fault current. A line to ground fault take place at point F2. The impedance measured by distance relay is ZF and the setting of relay is Z (say). In some cases, it may happen that line impedance ZF measured by relay due to fault at F may exceed the setting value Z i.e. ZF > Z. What will happen then? The relay will not actuate to clear the fault even though point F is within the protected zone. This scenario is called under reach of relay. Dr. V S B Chaitanya Duvvury  3) Bidirectionality and Voltage Profile Change BVRIT Campus Grid Power in kW  The power flow changes its direction in the case of distribution networks with embedded DG when local generation exceeds the local consumption.  The reverse power flow may hinder the working of directional relays as, traditionally, radial distribution networks are designed for unidirectional power flow.  Moreover, reverse power flow also means a reverse voltage gradient along a radial feeder. This can cause power quality problems, result in violation of voltage limits, and cause increased equipment voltage stress. Dr. V S B Chaitanya Duvvury 4) Islanding  DG can create severe problems when a part of a distribution network with a DG unit is islanded. This phenomenon is described as loss of mains (LOM) or loss of grid (LOG).  In the case of LOM, the utility supply neither controls the voltage nor the frequency of isolated network.  If the embedded generator continues supplying power despite the disconnection of the utility, a fault might persist as it will be fed by a DG.  The voltage magnitude gets out of control in an islanded network as most of the small embedded generators and grid interfaces are not equipped with voltage control. This can lead to unexpected voltage levels in the case of island operation.  Frequency instability may be another result of the lack of voltage control that poses a risk to electric machines and drives. Dr. V S B Chaitanya Duvvury 5) Effect on Feeder Reclosure  The role of an autorecloser is very important in restoring the system after a fault that lasts for a very short interval.  The automatic recloser attempt may fail as a result of feeding of a fault from a DG.  Due to active power imbalance, a change in frequency may occur in the islanded part of the grid. In this scenario, an attempt at reclosing the switch would couple two asynchronously operating systems.  Moreover, conventional reclosers are designed to reconnect the circuit only if the substation side is energized and the opposite side is unenergized. However, in the case of DG, there would be active sources on both sides of the recloser, thus hampering its working. Dr. V S B Chaitanya Duvvury Possible Solutions to Key Protection Challenges 1) Interlocking Main Relays: The main relay of the feeder with DG is equipped with an interlocking system. When a short circuit is detected, a locking signal is sent to the main relay of the feeder with DG. This prevents maloperation, even in the presence of back feeding from the DG to the fault. 2) Use of Directional OC Relays: Using directional Over current (OC) relays instead of OC relays can solve Bidirectionality issues. However, this method has its limitations. 3) Relay Readjustment: Adjusting relay settings in terms of time can help. Feeders without DG can have faster relay settings than feeders with DG. Care must be taken to ensure coordination with downstream protection devices. 4) Disconnection of DG: Ensuring disconnection of DG from the network before reclosing the feeder breaker is essential. Dr. V S B Chaitanya Duvvury Possible Solutions to Key Protection Challenges 5) Synchronization with Grid: For cases where DG is allowed to carry islanded loads, a Synchro-check relay on the circuit breaker or recloser can coordinate synchronization with the grid before reclosing the feeder breaker. 6) Reclosing Speed vs. Power Quality: There is a trade-off between the speed of reclosing and power quality. Faster reclosing improves power quality, but to ensure successful reclosing, instantaneous reclosing is not recommended for feeders with DG. Increasing the reclose interval from the usual 0.3 seconds to 1 second is recommended for these feeders. Dr. V S B Chaitanya Duvvury Case Study Single line diagram of a typical distribution network (DN) with distributed generation (DG) where sub-TL stands for sub-transmission line, CF and LF represent collector feeder and load feeder, respectively. Dr. V S B Chaitanya Duvvury Case Study 1) Fault Level Modification  A 3LG fault was applied to determine the fault current at different points with and without DG connection, as shown in Table. It is clear from the table that after introduction of DG, the fault current has increased by 28.5% at bus 2, by 51% at bus 4, and by 22.8% in the case of a fault at the end of LF1. Dr. V S B Chaitanya Duvvury Case Study 2) Blinding of Protection  Operation of a feeder OC relay may be disturbed in the presence of DG. Although DG increases the fault levels, the fault current seen by the feeder OC relay decreases due to the DG contribution in situations when DG is located between the fault point and the feeding station, as shown in Figure. This can result in delayed tripping of the feeder relay or, in a worst case scenario, no tripping at all. It is clear from Table, in the case of a 3LG fault at 90% of feeder length, the OC relay at LF1 operated in 0.23 s when no DG was connected and the same relay operated in 0.29 s when only DG2 was connected or when both DG units were connected. Dr. V S B Chaitanya Duvvury Case Study 2) Blinding of Protection Blinding of protection or delayed tripping scenario in the case of a 3LG fault at 90% of LF1 length with DG2 connection only. Operating times of protection devices in the case of a 3LG fault at 90% of the LF1 length (N/O stands for no operation and DR stands for distance relay) Dr. V S B Chaitanya Duvvury Case Study 3) Reduction in Reach of Distance Relay  Distance relays are set to operate in a specific time for any faults occurring within a predefined zone of a transmission line or a distribution feeder. Due to the presence of DG, a distance relay may not operate according to its defined zone settings. When a fault occurs downstream of the bus where DG is connected to the utility, impedance measured by an upstream relay will be higher than the real fault impedance (as seen from the relay). This can disturb the relay zone settings and can, thus, result either in delayed operation or, in some cases, no operation at all. Dr. V S B Chaitanya Duvvury Case Study 3) Reduction in Reach of Distance Relay  Table shows the zone settings for the distance relay installed at the Sub-TL 1 (shown in Figure). It is clear from the table that the range of zone 2 decreases to 67% when DG is connected from 79% when DG was not connected. Similarly, the reach of zone 3 is reduced to 91% with DG from its previous value of 100% when DG was not connected. Operating zones of distance relay with and without DG Dr. V S B Chaitanya Duvvury UNIT 5 Benefits of Microgrid Operation 1) Overview of Potential Microgrid Benefits. 2) Setup of Benefit Quantification Study. 3) Quantification of Microgrid Benefits under Standard Test Conditions. Reference Book: Microgrids, Architectures & Control, Wiley, Edited by Prof. Nikos Hatziargyriou, National Technical University of Athens, Greece. Dr. V S B Chaitanya Duvvury Overview of Potential Microgrid Benefits 1) Economic Benefits of a Microgrid 2) Technical Benefits of a Microgrid 3) Environmental and Social Benefits of a Microgrid Overview of microgrid benefits Dr. V S B Chaitanya Duvvury Overview of Potential Microgrid Benefits Technical Benefits of a Microgrid  Energy loss reduction due to decreased line power flows.  Improved voltage quality via coordinated reactive power control and constrained active power dispatch.  Relief of congested networks and devices, for example during peak loading through selective scheduling of Microsource outputs.  Enhancement of supply reliability via partial or complete islanding during loss of main grid. Environmental Benefits of a Microgrid  Shift toward renewable or low-emission (e.g. natural gas) fuels and adoption of more energy-efficient energy supply solutions (e.g. combined heat and power applications) including demand side integration. Dr. V S B Chaitanya Duvvury Overview of Potential Microgrid Benefits Social Benefits of a Microgrid  Raising public awareness and fostering incentives for energy saving and GHG emission reduction,  Creation of new research and job opportunities,  Electrification of remote or underdeveloped areas. Dr. V S B Chaitanya Duvvury Setup of Benefit Quantification Study Algorithm overview of microgrid benefit quantification study  An analysis of different microgrid benefits was carried out on a yearly basis using the sequential Monte Carlo simulation method. The general framework of this analysis is outlined as above. Dr. V S B Chaitanya Duvvury Setup of Benefit Quantification Study  Typical annual profiles of load, RES generation and market prices have been synthesized, based on measurements or historical data. As Microgrids are typically located at LV level, with mainly small residential or commercial customers, there are significant variations in load curves, which, in combination with the uncertainties from RES output as well as (wholesale) electricity price, turn the day-ahead microgrid scheduling task into a highly stochastic problem.  In order to deal with the modeling requirements of different Microsource types, RES units, storage and demand-side response resources are dispatched at priority, and then the DG unit schedules are created for active and reactive powers, respectively.  For the DG unit commitment, genetic algorithms or simply priority lists can be used to determine the optimal DG on/off states. Quadratic/linear programming models can be used for optimal power dispatch. Dr. V S B Chaitanya Duvvury Quantification of Microgrid Benefits under Standard Test Conditions  Quantifying the benefits of a microgrid under Standard Test Conditions (STC) involves evaluating its performance and potential advantages in a controlled environment that represents typical operating conditions. Technical Benefits:  Reduction of Losses and Voltage Variations Reduction of system loss (%)= 1 - (annual energy losses under microgrid) / (annual energy losses under passive grid operation) Reduction of voltage variation (%)=1 - (max absolute voltage variation in microgrid) / (max absolute voltage variation under passive grid operation) Peak Load Reduction Peak load reduction = 1 – (peak loading in microgrid) / (peak loading in passive grid operation) Dr. V S B Chaitanya Duvvury Quantification of Microgrid Benefits under Standard Test Conditions Economic Benefits Economic Benefits of Consumers Economic Benefits of Microsource Owners Environmental Benefits The total emission reduction (regulator perspective) index is the reduction of GHG emission level per kWh consumption in a microgrid when compared to the passive grid operation. Total emission reduction (p.u.) = 1 – (GHG emission level in microgrid)/(national GHG emission level, passive case). Reliability Improvement Optimum DG Penetration Level to achieve a minimum number of supply interruptions. Optimum Microsource Location from Reliability Perspective. Dr. V S B Chaitanya Duvvury Quantification of Microgrid Benefits under Standard Test Conditions Social Aspects of Microgrid Deployment Raise Public Awareness and Foster Incentives for Energy Saving and Emission Cutting. Creation of New Research and Job Opportunities. Electrification of Remote or Underdeveloped Areas. Dr. V S B Chaitanya Duvvury