Technical solutions for low-voltage microgrid concept

fi=vertaisarvioitu|en=peerReviewed

Stability analysis of a PMSG based Virtual Synchronous Machine

This paper proposes a Virtual Synchronous Machine (VSM) strategy for Permanent Magnet Synchronous Generator based wind turbines which enables seamless operation in all operating modes. It guarantees Maximum Power Point Tracking in grid-connected operation, Load Following Power Generation in islanded operation and Low Voltage Ride Through capability during faults. To achieve optimal performance in all operating modes, the stability of the VSM is investigated in the event of small and large perturbations. The small-signal stability analysis of the VSM is conducted using a linearized state space model and the impact of the controllers on the dominant modes are derived using participation factor analysis. The transient stability and dynamic performance of the VSM are analyzed using a non-linear model. Based on this analysis, design guidelines and operational limits of the VSM are established. The results of this analysis are validated using time-domain simulations in MATLAB/SIMULINK

Design and Control of Virtual Synchronous Machine Based Energy Systems

Conventionally, the operation and stability of power systems have been governed by the dynamics of large synchronous generators (SGs) which provide the inertial support required to maintain the resilience and stability of the power system. How-ever, the commitment of the UK to drive a zero-carbon economy is accelerating the integration of renewable energy sources (RESs) into the power system. Since the dynamics and operation of RESs differs from SGs, the large-scale integration of RESs will significantly impact the control and stability of the power system.This thesis focuses on the design of grid-friendly control algorithms termed virtual synchronous machines (VSMs), which mimic the desirable characteristics of SGs. Although several VSM topologies have been proposed in literature, most of them require further modifications before they can be integrated into the grid. Hence, a novel VSM algorithm for permanent magnet synchronous generator based wind turbines has been proposed in this thesis.The proposed VSM performs seamlessly in all operating modes and enables maxi-mum power point tracking in grid-connected operation (assuming strong grid), load following power generation in islanded mode and fault ride-through during faults. To ensure optimal performance of the VSM in all operating modes, a comprehensive stability analysis of the VSM was performed in the event of small and large per-turbations. The result of the analysis was used to establish design guidelines and operational limits of the VSM.This thesis further evaluates the impact of VSMs on the power systems low-frequency oscillations (LFOs). A detailed two-machine test-bed was developed to analyze the LFOs which exists when VSMs replace SGs. The characteristics of the LFO modes and the dominant states was comprehensively analyzed. The LFO modes which exists in an all-VSM grid was also analyzed. Further, the role of the power system stabilizers in an all-VSM grid was comprehensively evaluated. An IEEE benchmark two-area four-machine system was employed to validate the results of the small-signal analysis.The analysis and time-domain simulations in this thesis were performed in the MAT-LAB/SIMULINK environment

Modeling & Small Signal Analysis of Grid Forming Inverter

There is a rising number of inverter-based resources (IBRs) being integrated with distribution systems are becoming a more common occurrence. With integration of IBRs inverters, power utilities are experiencing an increase of number of operations with regards to voltage and frequency support. To maintain grid stability and reliability, IBRs need to provide some of the services currently (or formerly) provided by synchronous generators. Interconnection standards, like the IEEE 1547. 2018 has include requirements for IBRs to have the capability to provide some of these services—such as frequency and voltage support—and the procurement and deployment of the services can be implemented either as mandatory interconnection requirements or as market products. All the IBRs deployed today are grid-following (GFL), and read the voltage and frequency of the grid and inject current to provide the appropriate amount of active and reactive power. The fundamental GFL IBR design assumption is that there are still enough synchronous generators on the grid to provide a relatively strong and stable voltage and frequency signal, which GFL IBRs can “follow.” But since levels of GFL are increasing, there will be a limit to how far GFL controls can be pushed, and, at some point, new advanced inverter controls (termed grid forming (GFM)) will be needed to maintain system stability. GFM IBRs will also be needed to establish voltage and frequency during operating conditions when there are zero synchronous machines (100 percent IBR penetration). Power systems around the world are at the point of now needing to make this technological leap; however, system operators and planners, equipment owners, and manufacturers today are facing a circular problem regarding the deployment of advanced IBR controls. Which comes first, the requirement for a capability or the capability itself? How do grid operators know what performance or capability is possible from new equipment (and therefore what they could require)? How can they evaluate costs and benefits of having such equipment on the grid? What drives manufacturers to invest in modern technology without its being mandated for interconnection to the grid or otherwise incentivized by the market? The objective of this thesis is to provide a better understanding of ride through fault capabilities of Grid Forming Inverter (GFM) tied into the generation side of the power grid when using control functions. Furthermore, to investigate the robustness of implementing time delay with a PLL system within the control settings for grid forming inverters. To this end, to identify the contributing factors that affects the stability of the time delay to better design and future models of GFMs. As discussed, the microgrid is a potential solution for future distributed generation systems. However, controlling a microgrid is still a complex issue and many proposed solutions, are only based on locally measured signals without any communications; thus, it is difficult to achieve global optimization. Future works on this topic will analyse the role of restoration practices, communication control techniques to better approximate the delay. The specific areas below will be discussed in this thesis

Modeling & Small Signal Analysis of Grid Forming Inverter

There is a rising number of inverter-based resources (IBRs) being integrated with distribution systems are becoming a more common occurrence. With integration of IBRs inverters, power utilities are experiencing an increase of number of operations with regards to voltage and frequency support. To maintain grid stability and reliability, IBRs need to provide some of the services currently (or formerly) provided by synchronous generators. Interconnection standards, like the IEEE 1547. 2018 has include requirements for IBRs to have the capability to provide some of these services—such as frequency and voltage support—and the procurement and deployment of the services can be implemented either as mandatory interconnection requirements or as market products. All the IBRs deployed today are grid-following (GFL), and read the voltage and frequency of the grid and inject current to provide the appropriate amount of active and reactive power. The fundamental GFL IBR design assumption is that there are still enough synchronous generators on the grid to provide a relatively strong and stable voltage and frequency signal, which GFL IBRs can “follow.” But since levels of GFL are increasing, there will be a limit to how far GFL controls can be pushed, and, at some point, new advanced inverter controls (termed grid forming (GFM)) will be needed to maintain system stability. GFM IBRs will also be needed to establish voltage and frequency during operating conditions when there are zero synchronous machines (100 percent IBR penetration). Power systems around the world are at the point of now needing to make this technological leap; however, system operators and planners, equipment owners, and manufacturers today are facing a circular problem regarding the deployment of advanced IBR controls. Which comes first, the requirement for a capability or the capability itself? How do grid operators know what performance or capability is possible from new equipment (and therefore what they could require)? How can they evaluate costs and benefits of having such equipment on the grid? What drives manufacturers to invest in modern technology without its being mandated for interconnection to the grid or otherwise incentivized by the market? The objective of this thesis is to provide a better understanding of ride through fault capabilities of Grid Forming Inverter (GFM) tied into the generation side of the power grid when using control functions. Furthermore, to investigate the robustness of implementing time delay with a PLL system within the control settings for grid forming inverters. To this end, to identify the contributing factors that affects the stability of the time delay to better design and future models of GFMs. As discussed, the microgrid is a potential solution for future distributed generation systems. However, controlling a microgrid is still a complex issue and many proposed solutions, are only based on locally measured signals without any communications; thus, it is difficult to achieve global optimization. Future works on this topic will analyse the role of restoration practices, communication control techniques to better approximate the delay. The specific areas below will be discussed in this thesis

Wind Power Integration Control Technology for Sustainable, Stable and Smart Trend: A Review

The key to achieve sustainable development of wind power is integration absorptive, involving the generation, transmission, distribution, operation, scheduling plurality of electric production processes. The paper based on the analyses of the situation of wind power development and grid integration requirements for wind power, summarized wind power integration technologies' development, characteristics, applicability and trends from five aspects, grid mode, control technology, transmission technology, scheduling, and forecasting techniques. And friendly integration, intelligent control, reliable transmission, and accurate prediction would be the major trends of wind power integration, these five aspects interactive and mutually reinforcing would realize common development both grid and wind power, both economic and ecological

A Review on Artificial Intelligence Applications for Grid-Connected Solar Photovoltaic Systems

The use of artificial intelligence (AI) is increasing in various sectors of photovoltaic (PV) systems, due to the increasing computational power, tools and data generation. The currently employed methods for various functions of the solar PV industry related to design, forecasting, control, and maintenance have been found to deliver relatively inaccurate results. Further, the use of AI to perform these tasks achieved a higher degree of accuracy and precision and is now a highly interesting topic. In this context, this paper aims to investigate how AI techniques impact the PV value chain. The investigation consists of mapping the currently available AI technologies, identifying possible future uses of AI, and also quantifying their advantages and disadvantages in regard to the conventional mechanisms