Power Electronics for Next-Generation Drives and Energy Systems. Volume 2: Clean generation and power grids
2: Department of Energy, Center for Research on Microgrids (CROM), Aalborg University, Denmark
3: Indian Institute of Technology Kharagpur, India
4: National Institute of Technology Durgapur, India
Power electronics converters are devices that change parameters of electric power, such as voltage and frequency, as well as between AC and DC. They are essential parts of both advanced drives, for machines and vehicles, and energy systems to meet required flexibility and efficiency criteria. In energy systems both stationary and mobile, control and converters help ensure reliability and quality of electric power supplies.
This reference in two volumes is useful reading for scientists and researchers working with power electronics, drives and energy systems; manufacturers developing power electronics for advanced applications; professionals working in the utilities sector; and for advanced students of subjects related to power electronics.
Volume 1 covers converters and control for drives, while Volume 2 addresses clean generation and power grids. The chapters enable the reader to directly apply the knowledge gained to their research and designs. Topics include reliability, WBG power semiconductor devices, converter topology and their fast response, matrix and multilevel converters, nonlinear dynamics, AI and machine learning. Robust modern control is covered as well. A coherent chapter structure and step-by-step explanation provide the reader with the understanding to pursue their research.
Inspec keywords: power grids; photovoltaic power systems; power generation control; power electronics; invertors
Other keywords: maximum power point trackers; high-frequency transformers; power electronics; power convertors; distributed power generation; power engineering computing; photovoltaic power systems; invertors; power generation control; power grids
Subjects: Power electronics, supply and supervisory circuits; Education and training; General electrical engineering topics; Power system control; Power convertors and power supplies to apparatus; Control of electric power systems; General and management topics; Solar power stations and photovoltaic power systems
- Book DOI: 10.1049/PBPO207G
- Chapter DOI: 10.1049/PBPO207G
- ISBN: 9781839534690
- e-ISBN: 9781839534713
- Page count: 254
- Format: PDF
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Front Matter
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1 Performance of modern industrial plants with renewable power generation: a comprehensive system analysis
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Nowadays, industrial plants are integrating more and more renewables-based power generation (RPG) in the existing grid-connected system for economic and environmental benefits. The RPG has the advantage of providing green and clean energy, thereby reducing the carbon footprints and annual energy production cost. For encouraging renewable penetration into the system, various subsidies are provided to the utilities and the consumers. The RPG, along with various industrial loads (linear and non-linear), constitutes the small-scale microgrid, which operates in grid-connected or islanded mode. Therefore, these grids can work in conjunction with the existing main grid as well as in a self-reliance mode to supply the connected loads. Usually, the integration of RPG is done using power electronics converters. On the other hand, the majority of the loads in the industrial units are the electric motors, which are also being controlled using power electronics converters. The converters (supply-side as well as load side), along with other non-linear loads, create issues in the operation and control of industrial units. Furthermore, the events such as switching, sudden load change, the occurrence of temporary faults, intermittency of RPG, and islanding are major concerns to the industrial unit (small-scale microgrid). Therefore, in this chapter, a thorough study and analysis of the aforementioned events in the small-scale microgrid are discussed under various cases such as the effect on the power-electronic controlled industrial motor drive during microgrid operating modes, namely grid-connected/islanded and the transition between these two modes, also the effect of non-linear loads such as power electronic controlled industrial motors on the photovoltaic (PV)-based generation, and vice versa is observed at different operating conditions such as steady-state mode, acceleration mode, deceleration mode, etc. In addition, the effect of transients such as capacitor switching, load switching, temporary fault, and islanding have also been discussed. In the prescribed study, the above key issues are presented with the help of analysis over a small-scale industrial microgrid system (IMS) with the renewable energy integration. An extensive simulation is performed under the MATLAB®/SIMULINK® environment.
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2 Maximum power extraction from partially shaded photovoltaic power conversion systems
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Partial shadowing conditions (PSCs) take place when certain PV cells/panels fall in partial or total shadowing by surrounding buildings, towers, trees, dust, deterioration, clouds, and other factors. The partially shaded photovoltaic (PSPV) decreases power output and causes hot spots. They also diminish the PV power conversion system's generated power output and efficiency. The energy losses of the photovoltaic (PV) system due to partial shadowing or an incorrect peak power tracker are significant and can exceed 70% of total power supplied. As a result, following the peak power is required, particularly in PSCs, to attain high energy efficiency. In case of PSCs, the power-voltage characteristic curve become more sophisticated where it has many power peaks; one global power peak (GPP) and some other local power peaks (LPPs). Numerous maximum power point tracker (MPPT) approaches were executed to discern the GPP instead of falling into one of the LPPs. This chapter will focus on the partial shading causes, effects in addition to the remediation methodologies of this problem. Moreover, it will focus on the nature inspired MPPT algorithms that can deal with this problem efficiently. They can track the GPP instead of trapping into one of the LPPs with a less convergence time and higher efficiency. Additionally, they have no fluctuations around the GPP. These nature-inspired MPPT algorithms are classified into evolutionary/artificial intelligence (E/AI) algorithms, physics/chemistry (P/C)-based algorithms, and bio-inspired (BI) algorithms. On the other hand, tracking the maximum power using three distinct MPPT algorithms (PSO, CSO, and P&O) from partially shaded PV (PSPV) energy conversion system were provided, discussed, and analyzed. The simulation findings revealed that CSO surpassed PSO in tracking the GPP without fluctuations and having shorter tracking time for both uniform irradiance and PSCs. Whereas P&O approach was trapped to the first peak irrespective of whether it is local peak or GPP and it fails to discern the GPP in case of PSCs.
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3 Transformerless grid-connected inverter for PV integration
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As of 2018, the cumulative installed capacity of the solar PV system has surpassed 505 GW which represents around 2% of the global energy output. Grid-connected system account for 60%, whereas the rest are being from distributed applications. By 2022, it is expected to increase to 580 GW. By 2030, it is expected that 80% of the electrical power would flow through power electronics. Depending on the rating of solar PV plant, several inverter architectures are available to integrate PV plants/panels to loads/utility. To effectively utilize the PV module, solution such as micro inverter, dc power optimizer has been investigated and commercialized but their market share is about 4%. Large PV forms (such as floating PV and roof top PV systems) are integrated to the grid via power converters and conventional line-frequency (LF)/high-frequency transformers or with inverter structure known as transformerless grid-connected inverter. The chapter intends to explore the need of transformerless inverter for grid integration of PV system. Different approaches of eliminating the leakage current such as clamping the common mode voltage (CMV), or decoupling from ac side or dc side, are available in the literature. An overview of the classification based on the above approaches and operation of various transformerless inverters are discussed. Detailed analysis of generation mechanism of leakage current in the various transformerless inverter topologies would be discussed. Discussion on simulation results of the developed model of various topologies in MATLAB®-Simulink® is provided to show their comparative performance in mitigating the leakage current issues in PV system.
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4 PMSG and DFIG-based wind energy conversion systems
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Wind energy generation systems are confronted with growing demands for power quality and active power control. Wind energy conversion systems (WECS) have become a key technology to harvest wind energy worldwide. With the advances in power electronics technology, the quick growth of variable speed WECS is now witnessed. This chapter explains the control of a grid tied WECS using permanent magnet synchronous generator (PMSG) and doubly-fed induction generator (DFIG). A comparative study on grid connected WECS (PMSG and DFIG) in terms of voltages, currents, and output powers and dynamic responses are presented. Both systems are connected to power grid through power converters. The PMSG is dominantly used in the present wind energy systems with full scale power converter. Due to the full-scale power converter, this type has smooth grid connection over the entire range of speed. The DFIG is modeled using the direct-quadrature rotating reference frame circuit along with the aligned stator flux, and the field-oriented control approach is applied for independent control of the active and reactive power and the DC-link voltage at the grid side. Improvement of the DFIG controllers from the rotor side and the grid side converters are done to enhance the dynamic performance. This chapter reviews the modeling of WECS, control strategies of controllers, and various maximum power point tracking (MPPT) technologies that are being proposed for efficient production of wind energy from the available resource. The MPPT of the wind turbines along with unity power factor operation of the system is also presented. The comparison also aims to present in a thorough and coherent way the aspects of power quality and stability during the fault period. Modeling of control strategies for both systems are explained clearly. In addition, control topologies applicable to power electronics converter/inverter used in wind electric generators are discussed. In this case, various control strategies prevalent to both the PMSG and DFIG have been analyzed. The dynamic performance comparison of both systems with the control strategies are presented using MATLAB®/SIMULINK®.
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5 Novel AI, machine, deep learning, and optimization-based computing for energy systems
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Dramatically increasing the integration of renewable distributed energy resources and new infrastructures of control in power systems, advanced communication devices, and novel monitoring system makes it essential to build an efficient and resilient power system. Also, due to the large volume of data, model complexity, and various uncertainties in modern power systems, traditional methods have some difficulties to reach the acceptable efficacy. However, these situations require reasonable solution/response time as well as acceptable accuracy to allow the controllers of system and operators of network to take actions that prevent and/or correct the disturbances. So, there is a basic need to choose optimal, fast, and accurate techniques for detection and identification in power systems. Recently, mathematical programming, artificial intelligence (AI), machine learning (ML), and deep learning (DL) techniques have been applied to achieve a reliable energy system.
In this chapter, first, a quick overview of the modern energy systems and their main components is performed. Next, a brief overview of AI, ML, and DL techniques and their application in modern power systems are provided. Moreover, advanced techniques in the field the energy systems have been reviewed. Furthermore, some real-world applications of intelligent systems on the modern power systems are investigated. This section provides an overview of various study horizons from short-term to long-term and different control modes. Also, dynamic security assessment and stability control issues have been addressed with a focus on computational intelligence applications. Finally, future perspectives of dynamic security assessment by ML methods are given.
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6 Converter topologies for grid-integration of renewable power sources
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Power electronics is playing a critical and decisive role in utilizing eco-friendly energy sources for feeding power to the utility grid or load. Generally, for interfacing a low voltage renewable energy source, like solar photovoltaic (PV) and small wind turbines, to an ac load or the utility grid, a line frequency transformer is used with a conventional voltage source inverter (VSI). Though it provides galvanic isolation, line frequency transformers are bulky, costly and have higher losses due to the switching harmonic currents which flow through them. The use of a high-frequency transformer mitigates the problem of reduced power density due to the decrease in the size of the magnetic core. However, the increase in the number of stages increases the losses and complexity of the inverter. Hence, transformer-less inverters with buck-boost capability serve as a smaller and more efficient grid interface for renewable sources. Additionally, non-isolated micro-inverters, for PV applications, must be equipped with some specific features like common mode leakage current (CMLC) minimization and power decoupling. Moreover, in uninterruptible power supplies (UPS), buck-boost inverters are required for interfacing the battery with the load during under-voltage or power loss conditions. In its most typical form, a buck-boost inverter involves a two-stage conversion comprising a dc-dc voltage boost stage followed by voltage inversion (DC to AC) in buck-mode. However, since this has been alleged to impair overall efficiency, single-stage topologies were reported, combining the boost and inversion stages, claiming higher efficiency.
Based on the number of sub-circuits involved in the production of bipolar output, single-stage inverters can be classified into three categories: quad-modal, bi-modal and uni-modal. There are four individual circuits in quad-modal, two for each half of the AC voltage, working synchronously to produce bipolar output. Similarly, bimodal inverters use two distinct topologies, while uni-modal configurations have a single circuit for generating bipolar output.
In this chapter, an extensive literature survey of the existing single-stage buck-boost inverters will be provided. Furthermore, the possibilities of achieving AC output by combining two different typical dc-dc buck-boost converters, which individually produce voltages of different polarity, will be delivered. The derivation strategy for a bimodal inverter will be explained in detail. Conventional second and fourth-order dc-dc converters will be examined for the creation of inverter topology. Out of the several combinations, only a few feasible bimodal circuits are found to be suitable for a buck-boost inverter system. Some of the essential issues related to micro-inverter topologies will be illustrated.
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7 PV powered DC microgrid with plug-in energy harvesting and EV incorporated functions
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This chapter presents the establishment of a photovoltaic (PV) powered DC microgrid with plug-in energy support and electric vehicle (EV) incorporated functions. The DC microgrid common DC-bus voltage is established by the PV panel through a 3-cell interleaved boost converter. The grid-connected isolated bidirectional load inverter consists of a single-phase three-wire (1P3W) 220 V/110 V inverter and a CLLC resonant converter. To enhance the microgrid powering quality, a hybrid energy storage system including a battery bank and a flywheel, is equipped. Moreover, a plug-in energy support mechanism is developed to let the possible harvested sources be inputted to the microgrid through the same PV interface interleaved boost converter. As the solar energy is insufficient to support demanded power, the converter cell in the interleaved converter is switched to accept the harvested sources. The single-phase switch-mode rectifier (SMR) is formed as the basic schematic, while the EV switched-reluctance motor (SRM) drive is interconnected with the PV-powered microgrid through the same schematic. Some measured results are presented to conduct the evaluation.
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8 Power electronics technology and applications in clean generation and power grids
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The deployment of renewable energy sources (RES) results in a degradation of power quality, necessitating the use of power conditioners such as active filters to alleviate these difficulties, while passive filters are inadequate of entirely mitigating power quality concerns in the presence of nonlinear loads. Numerous research have been undertaken to combine RES with active power filters in order to maximize the benefits of both RES and power conditioners in order to offer high-quality energy to customers. This chapter addresses the operation of RES in combination with active power filters. It also includes an interesting section on dual unified power quality conditioner (UPQC) operation and control, which helps clarify the active filter technologies that are viable for inclusion in the DG framework. The suggested UPQC is composed of an open-end winding transformers and series connected voltage source converters (VSCs). The proposed UPQC utilizes two photovoltaic arrays, with each array feeding a different dc-link of a two three-phase VSC. The feasibility of the suggested UPQC has been proven by simulated tests using Simulink®/MATLAB®.
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Back Matter
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