Power Electronic Inverters Research Articles

A Comprehensive Review on a Virtual-Synchronous Generator: Topologies, Control Orders and Techniques, Energy Storages, and Applications

In recent years, the penetration of renewable power generations into the electrical grid has substantially increased. Continuous deployment of power electronic-based distributed generations and the reduction of traditional synchronous machines with their essential dynamics in modern power networks are very critical in this change. The use of power electronic inverters leads to the dissociation of sources and loads and lowering the power system inertia. Under power imbalance, this drop causes an elevated rate of change in frequency and frequency divergences, which has a notable impact on the system’s frequency stability. As a result, enhanced control techniques for grid-tied electronic converters are required to secure the power system’s stability and support. The virtual-synchronous generator (VSG) control is used to mimic the dynamics of a rotating synchronous generator and improve the power system’s stability. In this article, the problems of such low-inertia power systems, as well as the VSG technologies, are explored. This research also looks at different control orders and strategies for virtual-synchronous generators (VSG). In addition, the utilization of energy storage and critical matters in VSG and further research recommendations are explained.

Intelligent Detection and Diagnosis of Power Failure Relying on BP Neural Network Algorithm.

The development of economy and the needs of urban planning have led to the rapid growth of power applications and the corresponding frequent occurrence of power failures, which many times lead to a series of economic losses due to failure to repair in time. To address these needs and shortcomings, this paper introduces a BP neural network algorithm to determine the neural network structure and parameters for fault diagnosis of power electronic inverter circuits with improved hazard. By optimizing the weights and thresholds of neural networks, the learning and generalization ability of neural network fault diagnosis systems can be improved. It can effectively extract fault features for training, sort out the business logic of power supply intelligent detection, analyze the potential hazards of power supply, and effectively perform circuit intelligent control to achieve effective fault detection of power supply circuits. It can provide timely feedback and hints to improve the fault identification ability and the corresponding diagnosis accuracy. Simulation results show that the method can eventually determine the threshold value for intelligent power fault detection and diagnosis by analyzing the convergence of long-term relevant indicators, avoiding the blindness of subjective experience and providing a theoretical basis for intelligent detection and diagnosis.

PI-based PLL and 24-sector control of a 3P-3L-NPC inverter for grid-tied PV system synchronization

This article addresses one of the most serious issues in electricity: frequency and voltage anomalies. Actually, because renewable energy production is intermittent, the frequency and voltage of electricity produced are unstable and dependent on weather conditions. This issue causes industrial processes to fail, affecting the quality of the electrical supply and having a massive economic impact. Power electronics inverters are designed to compensate for system fluctuations in solar power generation. However, measurement noise in the grid voltage desynchronizes the inverter and network signals. The authors propose using a phase-locked loop technique based on inverter period control and a network voltage observer to achieve such synchronization of grid-connected photovoltaic (PV) systems. In this work, the grid integration of the PV system is carried out through a three-phase three-level neutral point clamped inverter due to better current quality with fewer harmonics and lower stress voltage of the inverter's components when compared to two-level voltage source inverters. The method is successfully applied in a simulated case study and experimental results validate it.

A novel virtual synchronous machine implementation and verification of its effectiveness to mitigate renewable generation connection issues at weak transmission grid locations

AbstractLarge‐scale penetration of renewable resource based generation will displace conventional synchronous machine‐based power generation. This will lower the overall system inertia and will result in lower short circuit levels at point of connection (POC) of renewable resources. Renewable resources such as wind and solar photovoltaic (PV) are interfaced to the power system via power electronic inverters. Operation of inverter‐based equipment under low inertia and low short circuit conditions is challenging. Specific challenges include fault recovery response, unstable oscillatory interactions, and impact on torsional oscillations of thermal generating units. In this paper, the effectiveness of inverters, controlled as a virtual synchronous machine (VSM), to overcome some of these issues is investigated. A battery energy storage system (BESS) inverter is controlled as a VSM. The input signals provided to the BESS inverter are derived from solving the time domain equations of a synchronous machine. The response of exciter, governor, and power system stabilizer (PSS) are also included in the VSM strategy. The dynamic characteristics of the proposed VSM are verified using a single machine infinite bus (SMIB) test model. The effectiveness of the proposed VSM approach to mitigate specific technical challenges is verified by performing dynamic response studies on two test systems. The two test systems represent selected regions of practical power systems with high renewable penetration. The VSM response is compared with a conventional synchronous machine response in all test cases, to demonstrate the close correlation of dynamic response. The simulation results demonstrate that the VSM's response is as expected and is capable of mitigating stability‐related issues due to low system inertia and low short circuit strength.

Dual Voltage–Current Control to Provide Grid-Forming Inverters With Current Limiting Capability

The rapid uptake of renewable energy sources is causing synchronous generators (SGs) to be replaced by power electronic inverters, meaning that these inverters need to offer the characteristics traditionally associated with SG. As a result, it has been proposed that the inverters should be controlled in a grid-forming mode in order to support the voltage of the microgrids. Given that these inverters are controlled as a voltage source, temporary events, such as short circuits or overloads, could cause currents that are far higher than the rated current. As the semiconductors used in power electronics are highly sensitive to overcurrents, this article proposes a dual voltage–current control that provides the grid-forming inverters with the capability to quickly limit the current under any overload or short-circuit condition. The proposed method has been validated through experimental tests in standalone mode.

Parallel inverter control using different conventional control methods and an improved virtual oscillator control method in a standalone microgrid

Partly because of advances in power electronic converters, the share of renewable energy in power generation is steadily increasing. The main medium of interface for integrating renewable energy sources to the utility grid is the power electronic inverter. Virtual oscillator control (VOC) is a time-domain approach for controlling parallel inverters in a standalone microgrid (MG). The concept is to simulate nonlinear deadzone oscillator dynamics in a system of inverters to ensure a stable AC MG in the absence of communication. VOC is a time-domain and self-synchronizing controller that simply requires the measurement of filter current, whereas traditional droop control and the virtual synchronous machine (VSM) require low pass filters for active and reactive power calculations. In this work, a particle swarm optimization (PSO)-based VOC method (VOC-PSO) is proposed, in which the parameters of the VOC are designed using the PSO algorithm. The system performance using droop, VSM, VOC, and VOC-PSO controllers are investigated using MATLAB and Opal-RT real-time digital simulator platforms. The results show that the proposed VOC-PSO gives improved performance over other control strategies. The efficacy of the proposed VOC-PSO control method is also demonstrated by the experimental results.

CPT-Based Control Strategy for a Two-Phase Three-Wire Pv Inverter: a Multifunctional Perspective and a Comprehensive Review

Multifunctional inverters play an important role in electrical grids due to their capability to provide active power conversion from photovoltaic (PV) systems, as well as by concomitantly offering ancillary services that provide grid support and power quality improvement. Although control strategies for such inverters have been extensively explored for applications in single- and three-phase grids, their consideration for the two-phase three-wire topology has been superficially discussed in literature. Thus, first, this paper contributes to the literature by presenting a comprehensive review about the control of power electronic inverters in two-phase three-wire grids. As second contribution, this paper proposed a flexible control strategy based on the Conservative Power Theory capable of adequately synthesizing control references for a PV-based multifunctional inverter operating in a two-phase three-wire grid. Additionally, power quality services can be selectively offered by the inverter to achieve compensation of reactive, harmonic and unbalance current terms, as well as providing reduction in neutral currents. Hardware-in-the-loop experimental results comprising a multifunctional PV inverter under several scenarios of operation are shown to demonstrate and validate the flexibility of the method.

Impact of Solar Inverter Dynamics during Grid Restoration Period on Protection Schemes Based on Negative-Sequence Components

The growing penetration of renewable resources such as wind and solar into the electric power grid through power electronic inverters is challenging grid protection. Due to the advanced inverter control algorithms, the inverter-based resources present fault responses different from conventional generators, which can fundamentally affect the way that the power grid is protected. This paper studied solar inverter dynamics focused on negative-sequence quantities during the restoration period following a grid disturbance by using a real-time digital simulator. It was found that solar inverters can act as negative-sequence sources to inject negative-sequence currents into the grid during the restoration period. The negative-sequence current can be affected by different operating conditions such as the number of inverters in service, grid strength, and grid fault types. Such negative-sequence responses can adversely impact the performance of protection schemes based on negative-sequence components and potentially cause relay maloperations during the grid restoration period, thus making system protection less secure and reliable.

A Modified SOGI-PLL with Adjustable Refiltering for Improved Stability and Reduced Response Time

The controls of most power electronic inverters connected to an electrical power system (EPS) rely on the precise determination of the voltage magnitude, frequency, and phase angle at the point of common coupling. One of the most widely used approaches for measuring these quantities is the phase-locked loop (PLL); however, the precision of this measurement is affected during transients in the EPS and is a function of the type of event and the architecture of the PLL. PLLs based on the second-order generalized integrator (SOGI) are widely used in power converter synchronization, offering an adaptive or fixed-parameter prefilter with low-pass and band-pass characteristics. This article proposes a variant of the SOGI-PLL that offers improved stability and a faster response time. This is accomplished by decoupling the effect of the SOGI’s gains and adding feedback. The modification is carried out in the state space model of the SOGI. Manipulating the attenuation moves the poles of the SOGI to improve the stability. The performance of the proposed PLL is verified and validated under the processor-in-the-loop (PIL) approach.

Optimal Control of an Inverter-based Virtual Synchronous Generator with Inertial Response

Renewable energy sources are gradually replacing conventional synchronous generators, which are responsible for supplying the power grid inertia damping properties. This paper proposes a nonlinear optimal controller for a renewable energy generation system based on a power electronics inverter, in order to incorporate the system inertia behavior through imitating the rotor inertia of synchronous generators. The main contributions of this paper are: 1) the modeling and synthesis of a nonlinear optimal control scheme for a power inverter such that it dynamically behaves as a conventional synchronous generator, where the active and reactive power are regulated, and provides robustness against utility grid disturbances; 2) the dynamical modeling of the virtual inertia-based inverter generator and its corresponding response to power reference variations and utility grid voltage disturbances. Further, an analysis procedure is presented to compute a predefined value of the inverter inertia constant, proportional to the one that a synchronous generator could provide, but taking into account the rated power of the generator. Simulation results assess the proposed methodology effectiveness

Efficient metrics for the detection of partial discharges under steep-fronted voltage pulses

The increasing use of power electronic inverters in electrical drives is leading to the unexpected inception of partial discharges (PD) within the insulation system of electric machine stator windings. Unfortunately, the short rise and fall times of such voltages, below 100 nanoseconds in most cases, create high-magnitude conducted and radiated interferences that affect the measurements. Detecting partial discharges in these systems with inductive or electromagnetic sensors turns to be an important challenge, especially when interference and partial discharges share the same bandwidth. In this work, the authors propose a technique to detect the occurrence of PD in such systems, even when they are masked by disturbances. The proposed technique combines an analog high-pass filter stage and a digital band-pass to select a proper spectral interval. The resulting signal is converted to the base-band, where two metrics based on the peak-to-average power ratio are proposed. Experimental results obtained with the signals acquired with two antennas show that both proposed metrics exhibit a significant increase, about ten times greater, when the applied voltage exceeds the PD inception voltage. These contributions define new markers for the detection of PD events created by pulsed voltages with overlapped overshoots with promising results.

Performance Investigation of Power Inverter Components Submersed in Subcooled Liquid Nitrogen for Electric Aircraft

Investigating the performance of power electronics devices and thus power inverters at cryogenic temperatures for electric aircraft systems are of great interest. Accordingly, the purpose of this study is to examine the inverter circuit technologies used in cryogenically-cooled electric aircraft applications from three perspectives: inverter topologies, power capabilities, and electromagnetic interference (EMI) that may occur. At a cryogenic temperature, the characteristics of five power semiconductor switches with different technologies (Si MOS, SiC MOS, and GaN HEMT) used in cryogenically-cooled electric aircraft inverters were tested and the results were presented. Furthermore, the low-temperature performance of three types of capacitors commonly used in power electronics inverters was investigated. The research findings provide crucial considerations for the research and development of power inverters cooled by sub-cooled liquid nitrogen for modern electric aircraft.

Grid-Forming Inverters for Grid-Connected Microgrids: Developing “good citizens” to ensure the continued flow of stable, reliable power

The electric power grid is in transition. For nearly 150 years it has supplied power to homes and industrial loads from synchronous generators (SGs) situated in large, centrally located stations. Today, we have more and more renewable energy sources—photovoltaic (PV) solar and wind—connected to the grid by power electronic inverters. These inverter-based resources (IBRs) do not have the same characteristics as SGs, such as inertia and high fault current. This mismatch has not been a problem until now. Inverters have assumed that the grid is strong and will provide a stable and clean voltage and that they are able to inject real power into the grid without undue impact on its operation.

Pathways to the Next-Generation Power System With Inverter-Based Resources: Challenges and recommendations

Managing the stability of today’s electric power systems is based on decades of experience with the physical properties and control responses of large synchronous generators. Today’s electric power systems are rapidly transitioning toward having an increasing proportion of generation from nontraditional sources, such as wind and solar (among others), as well as energy storage devices, such as batteries. In addition to the variable nature of many renewable generation sources (because of the weather-driven nature of their fuel supply), these newer sources vary in size—from residential-scale rooftop systems to utility-scale power plants—and they are interconnected throughout the electric grid, both from within the distribution system and directly to the high-voltage transmission system. Most important for our purposes, many of these new resources are connected to the power system through power electronic inverters. Collectively, we refer to these sources as inverter-based resources.

A Fuzzy Logic-Based Emulated Inertia Control to a Supercapacitor System to Improve Inertia in a Low Inertia Grid with Renewables

The contribution of power generation from converter-dominated renewable energy sources (RES) has increased enormously. Consequently, the system inertia is decreasing, and it impacts the frequency of the system. With large-scale integration of power electronic inverter-based power generation from RES, inertia from energy storage devices would be unavoidable in future power grids. In this paper, the inertia emulator is formed with a supercapacitor (IE–SC) to improve inertia in a low inertia grid. To emulate the inertia in a low inertia grid, this paper proposes a fuzzy logic controller-based emulated inertia controller (FL-EIC) for an inverter attached to IE–SC. The proposed fuzzy logic controller estimates the inertial power required based on the frequency deviation and rate of change of frequency (ROCOF). The output of the fuzzy controller adds to the conventional emulated inertia control (EIC) technique to alter the load angle for the power electronic inverter of IE–SC. Specifically, the proposed FL-EIC achieves inertia emulation by proportionally linking the time derivative of the grid frequency and frequency deviation to active power references of IE–SC. A comparison of the conventional EIC and FL-EIC is carried out to prove the effectiveness of the proposed FL-EIC. Furthermore, real-time simulations with the help of the OPAL-RT real-time simulator (OP 5700) are presented to validate the advantage of the FL-EIC.

Improvement of system strength under high wind penetration: A techno-economic assessment using synchronous condenser and SVC

Variable speed wind turbine generators (WTGs) are replacing traditional fossil fuel based synchronous generators in the generation fleet as wind penetration increases. These variable speed WTGs are decoupled from the grid by power electronics inverters and usually generate less fault current compared to synchronous generators. As a result, system strength (indicates the fault recovery capability) at the point of common coupling (PCC) of wind power plants may reduce. A minimum value level of system strength is essential for wind power plants to properly identify and overcome a fault. To enhance system strength at wind PCC buses, supplementary devices such as synchronous condenser and Static VAR Compensator (SVC) can be deployed to have additional fault current. Since these devices are expensive, their optimal allocation considering economic feasibility is a major concern. In the existing literature, locations and ratings of the optimally allocated synchronous condenser are reported. However, this approach may cause oversizing of synchronous condensers. In addition, a SVC can be utilised instead of a synchronous condenser to enhance system strength. However, no detailed study is carried out yet to find the optimal size of SVCs. Evidently, both synchronous condenser and SVC can be installed to improve system strength. However, no comprehensive techno-economic assessment is performed for selecting an appropriate choice between them. To address these research gaps, this paper develops a framework to find the optimal sizes of synchronous condensers and SVCs by taking into account the long-term financial viability. Also, to ensure the maximum possible fault contribution, synchronous condensers/SVCs are connected directly to those wind PCC buses where system strength is below the acceptable limit. Afterwards, a detailed techno-economic assessment using synchronous condenser and SVC is performed in a wind dominated grid. In addition, post-fault voltage recovery characteristics with optimally sized synchronous condenser and SVC are explored. The developed methodology is applied to the IEEE 39 bus test system considering 45% wind power penetration scenario. Also, the performance of the proposed approach is compared to that of an existing technique. Finally, based on the technical and economic aspects, a better choice between synchronous condenser and SVC is recommended to improve system strength under high wind penetration.

A Magnetic-Sensing-Based Wide-Bandwidth Grid Impedance Measurement Technique With Small Perturbation Injection

Grid impedance is an important parameter in the impedance-based stability analysis method for analyzing the interaction between the power electronic inverters and the power grid. However, the existing measurement technique is deteriorated by narrow-bandwidth sensors, large perturbation injections, and inaccurate response components extraction based on the fast Fourier transform (FFT) algorithm. To overcome these problems, a magnetic-sensing-based wide-bandwidth grid impedance measurement technique with a small perturbation injection is proposed in this article. A novel impedance extraction algorithm based on the quadrature delay estimator (QDE) is developed to overcome the spectral leakages and frequency aliasing effect of the existing FFT-based impedance extraction algorithm. The proposed grid impedance measurement technique is implemented on a digitally controlled inverter system, and its effectiveness is verified through the experimental results.

Harmonic Minimization in Grid Coupled Photovoltaic Structures Using Selective Harmonic Elimination Pulse-Width Modulation in Multiple Level Series Linked Nano-Scale Double Gate Hetero-Structure MOSFET Based H Type Bridge Inverters

Semiconductor Chip makers and semiconductor device designers denote that, a reliable device should have a character with high speed and low power loss in its operation, which could be done in a nano-scale regime. A nano-scale double gate hetero-structure MOSFET based multilevel inverter is a power electronic arrangement system that generates multilevel output voltage with lower harmonic distortion and reduced power switching loss. In a grid-connected photovoltaic device, this power electronic inverter is a critical and essential component. Series coupled H-bridge multilayered inverter is a widely satisfactory arrangement for incorporation of renewable power among three multilevel inverter topologies, which might be directly fed by photovoltaic (PV) units, wind turbines, or fuel voltaic cells with enhanced power quality due to accessibility of an individual’s direct current sources. Furthermore, compared to traditional converters, this multilayered configuration will boost output voltage and current accuracy, resulting in lower total harmonic distortion. This concept proposes an innovative series of type H-bridge multilayered inverters arrangement for grid-connected photovoltaic structures. The optimization algorithm, particle swarm was incorporated to estimate the switching angles after the Selective Harmonic Elimination technique was developed to remove 5th, 7th, 11th and finally 13th lower number harmonics. For the first time, a cyclic choice method was used to keep up a constant balance of power among the different sources, in which the sources contribute equally to the output power over the course of operation. A simulation in the MATLAB/SIMULINK foundation was used to validate the integrated definition. The output taken from an experimental arrangement was used to verify the proposed principle of eradicating lower-level harmonics. The harmonic spectrum along with output waveforms for selective harmonic eliminated pulse-width modulation (SHE-PWM) technique was then obtained.

Minimum device usages of field programmable gate array (FPGA) verification of multilevel PWM inverter drive generation

Space Vector Pulse-Width Modulation (SVPWM) has now become an unavoidable PWM in the power electronics inverter development. If the SVPWM implementation can be made user-friendly, the operation can be easily soaked in by the future researchers and also the closed loop operation becomes sophisticated. This paper conveys a broad view about the state of art of different Field programmable gate array (FPGA) processors along with the inner views about the implementations of the 3-level SVPWM. The description of the different processors is discussed along with the implementation variance and also attempts to implement the SVPWM through Xilinx Spartan-III 3AN-XC3S400 using MATLAB-Xilinx System Generator (XSG) without deploying the direct Very High Speed Language (VHDL) code. It provides shortest translation designs into hardware implementations that are faithful, synthesizable and efficient, which permits the designer to minimise the time spent for the description and implementation of circuit. The synthesis result shows that the proposed implementation at 50 MHz frequency operation consumes a power of 13mW and occupies 1112 look up tables (LUTs) and 424 File File (FFs). Thereby, the Total Resource Utilization reduced drastically to 36%, which is far better than the other existing implementations. Also, the inference of less processing time can be seen from the synthesis.

Operational strategy of nine‐phase induction machine under the open‐switch fault condition

Multiphase induction machines are getting more attention in industry and academia because of their advantages and need for electric vehicles as well as ship propulsion. In this case, more number of power electronics devices are required due to higher number of phases. Moreover, in comparison with electromechanical systems, the probability of failure in power electronic inverter switches will be high. A fault in a semiconductor switch, without any proper alleviating methods, may result in the failure of the entire drive. To improve the reliability of induction motor drives (IMD), there is a necessity to enhance the postfault operation of the inverters. In this article, the proposed nine-phase IMD incorporates simple mathematical equations and less circuit reconfigurations to work under conditions of open-switch fault in either a single switch or the inverter's entire leg. This enables the drive to achieve balanced steady-state operation with minimal deration in output power/torque under the fault conditions. In addition, alternative operational technique, which modulates the healthy phases of fault phase group with 50% duty ratio and minimal circuit reconfiguration, is discussed in this article. Moreover, all possible fault conditions and associated reconfiguration details of the drive are described in detail. To validate the proposed concepts, finite element method analysis is performed using ANSYS Maxwell, and experimentation is performed in the laboratory for both normal and fault conditions on nine-phase IMD.