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In distributed generation systems, the inverter is the main power interface and its stability directly determines the reliable operation of the grid-connected system. As a typical topology for a three-phase four-wire inverter, the LCL-type three-phase four-wire split capacitor inverter (LCL-TFSCI) is taken as the research subject of this paper. Compared with the three-phase three-wire inverter, there is an additional zero-sequence path in the LCL-TFSCI. Therefore, it is not only necessary to consider the stability of the positive and negative sequence system, but there is also the need to consider the stability of the zero-sequence system when performing stability analysis for the LCL-TFSCI. In this paper, a small-signal impedance model considering the zero-sequence loop of LCL-TFSCI is firstly established. Subsequently, the instability risk is revealed when LCL-TFSCI is connected to the grid with parallel compensation capacitors. Through instability analysis, an impedance-reshaping method based on the complex filter and combined differential elements is proposed, which can reshape the impedance characteristic of LCL-TFSCI within the wide frequency range and expand the stability domain of the grid-connected system. Finally, the proposed method is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

Microgrid (MG) is not only undergoing rapid upsurge and an effective combination of distributed generations (DGs)-based renewable energy sources, but it also fulfills a significant function in upgrading grid infrastructure. It is necessary for DGs, during and after any disturbances in the voltage, to stay connected in order to enhance the voltage, most importantly guaranteeing the stability of the power system. In this present context, the behavior of the distributed generations control systems has a significant impact on the MG performance. This paper investigates the effect of different control schemes of the inverter-based DG unit on the stable operation of MG after the occurrence of faults that lead to islanding events. In this paper, an appropriate control strategy is proposed to enhance the fault ride-through of MG. Within the scope of the study, the MG consists of a conventional diesel generator and an inverter-based DG unit. The MG also contains several load types; RLC load as a static load and induction motor as a dynamic load. The MATLAB Simulink is used to model the MG and its inverter control schemes. In order to assure MG stability, the variations of the voltage and frequency are possessed as key references. Results indicate that the control strategies of the inverter have a strong influence on the stability of MG. Moreover, the MG configuration with the proposed FRT resists fault effects for longer durations and this enhances the stability. [ABSTRACT FROM AUTHOR]

This paper aims at resolving problems of harmonic, reactive power and current imbalance. In the process of photovoltaic grid connection, a multi-objective control strategy is proposed, in which the three-phase network controller simultaneously controls the harmonic and realizes the reactive power and current balance. The I P , I q current detection method, which is based on the current reactive power characteristic theory, can detect the compensation current. In order to reduce the measurement error of PLL, a software PLL based on decoupled double synchronous reference coordinate transformation is introduced, and the principle of multi-objective rule of three-stage network inverter is also given. The simulation and test results show that the harmonic distortion rate decreases from 2.57% to 1.10% with the proposed strategy, and the unbalance between reactive power and current is compensated, which verifies the correctness and feasibility of the strategy. [ABSTRACT FROM AUTHOR]

The discontinuous conduction mode (DCM) of the inductor current is an effective way to achieve high efficiency and high power density of inverters because it has the advantages of zero-current switching and small inductance of the filter inductor. Although the DCM can operate at a fixed switching frequency, there has been no linear model for realizing high-performance digital control. This paper provides a solution for this problem. Firstly, a linear first-order charge quantity model (CQM) for a DCM inverter with a fixed switching frequency is established, which uses charge quantities output by the inverter bridge as a control variable. Secondly, a direct charge control (DCC) method is proposed, and the design process is significantly simplified. Finally, the performance of the proposed control method is verified by the experiments using a 1 kW prototype, and a high-quality output voltage waveform with a peak efficiency of above 98% was achieved. The proposed method outperforms existing works because the CQM is a first-order linear model that realizes the high-performance digital control and significantly simplifies the design of controller. [ABSTRACT FROM AUTHOR]

The grid-connected inverter is a key device in the renewable energy power generation system and large-scale energy storage system, which the operational stability and reliability are the basis for the efficient and safe application of electrical energy. A real-time fault diagnosis method of a three-phase for grid-connected application combining a mixed logic dynamic (MLD) model and finitecontrol set model predictive control (FCS-MPC) is proposed. This paper not only realizes the open circuit fault diagnosis and location of the switching devices in the main power circuit, but also discusses the threshold issues and post-fault operations. The advantage of the proposed method is that it directly uses the control data and measurement signals of the controller without extra sensors and calculation, which will shorter the fault diagnosis time and occupy less calculation resource of the main processor. Simulation results illustrate the quickness of the fault identification and accurate position with robustness to the interference of the diagnosis method. Finally, the effectiveness of the diagnosis method was verified by a 1500 W experimental prototype in a laboratory. [ABSTRACT FROM AUTHOR]

Although the voltage feedforward control based on the point of common coupling (PCC) has been widely studied in the grid‐connected inverters to suppress the harmonics in the grid current, harmonic instability still occurs when the PCC voltage contains a series of background harmonics under weak grid condition. To this end, this paper applies the grid voltage sensed by phasor measurement units instead of the PCC voltage for feedforward. Meanwhile, considering that coupling between the phase‐locked loop (PLL) and the grid impedance would cause instability under weak grid condition, a novel compensation term is introduced to eliminate the negative influence of PLL. In addition, a method to improve the transient response of the system is also proposed so that the cut‐off frequency does not change with the impedance of the grid. By analysing the output impedance of the system, it can be proved that the strategy proposed can effectively improve the stability of the system. The experimental results indicate that the harmonics in the grid current are obviously reduced and the dynamic performance of the system is improved, which verifies the analysis. [ABSTRACT FROM AUTHOR]

The space vector modulation (SVM) method was recently proposed and captured the interest of scientific research in the following years. In this paper, besides a brief review of the SVM methods proposed in the literature, a new SVM strategy based on the calculation of the minimum (Min) and maximum (Max) of three-phase voltages is proposed. The proposed SVM technique does not have to calculate the sector and angle, as is done in the traditional SVM technique. Therefore, it is the easiest technique to accomplish compared to the traditional SVM method and other existing methods. Compared with the traditional pulse width modulation (PWM), the advantage of using this new SVM strategy is that the scheme is simple and the total harmonic distortion (THD) value in the output of the two-level inverter is minimized. The technology has been simulated by MATLAB/Simulink, and then implemented on a real traditional two-level inverter using the dSPACE card. It is worth reporting the reduction obtained for THD using the proposed SVM technique (where THD is about 70%) compared to the traditional PWM technique (where THD is about 79.5%). [ABSTRACT FROM AUTHOR]

Considering the presence of different model parameters and controlling variables, as well as the nonlinear nature of DC to AC inverters; stabilizing the closed-loop system for grid current balancing is a challenging task. To cope with these issues, a novel sliding mode controller is proposed for the current balancing of local loads using gridconnected inverters in this paper. The closed-loop system includes two different controlling loops: a current controller which regulates the output current of grid-connected inverter and a voltage controller which is responsible for DC link voltage regulation. The main features of the proposed nonlinear controller are reactive power compensation, harmonic filtering and three-phase balancing of local nonlinear loads. The developed controller is designed based on the state-space averaged modelling its stability and robustness are proved analytically using the Lyapunov stability theorem. The accuracy and effectiveness of proposed controlled approach are investigated through the PC-based simulations in MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

A large class of three-phase electrical power systems possess symmetry conditions that make it possible to describe their behavior using single-input single-output transfer functions with complex coefficients. In such cases, an extended root locus method can be used to design control laws, even though the actual systems are multi-input multi-output. In this paper, the symmetric conditions for a large class of power systems are analyzed. Then, the root locus method is revisited for systems with complex coeffcients and used for the analysis and control design of power systems. To demonstrate the benefits of the approach, this paper includes two examples: 1) a doubly fed induction machine and 2) a three-phase LCL inverter. [ABSTRACT FROM PUBLISHER]

Although the concept of a multiphase drive system dates back to the middle of the 20th century, the initial pace of development was rather slow, as witnessed by the first two surveys of the area published in the beginning of this century. However, considerably new developments have resulted in the last decade of the 20th century and the beginning of this century, leading to an authoritative survey of the asymmetrical six-phase drive control and subsequently of the review of the complete area. This also initiated the organization and subsequent publication of the first IEEE Transactions on Industrial Electronics "Special Section on Multiphase Machines and Drives" in May 2008, which commenced with another survey paper, and that contained 12 original research papers. Since the publication of this Special Section in May 2008, the level of interest and pace of developments in the area have further accelerated and substantial new knowledge has been generatedwith an ever-increasing number of published research papers and reported new industrial applications. Such a trend has been emphasized in a recent paper. It therefore seemed appropriate to revisit the area and organize this Special Section as a sequel to the first one. The call for the Special Section papers resulted in 51 submissions, almost twice as many as the total back in 2008, thus confirming a substantial growth of the area. Indeed, the amount of new knowledge acquired since the publication of the first Special Section in 2008 has meant that it was not possible to provide a complete and thorough survey of the field in a single review paper. [ABSTRACT FROM AUTHOR]

This paper is concerned with the use of a three-level inverter for a synchronous reluctance machine (SynRM). The SynRM suffers from a poor power factor due to poor machine saliency. This makes it harder to operate the three-level neutral-point-clamped inverter due to a strict requirement to have the two dc-link capacitor voltages balanced. This paper proposes a new nearest three vector modulation algorithm which can balance the two dc-link capacitors even at poor machine saliency ratio (poor power factor). In this paper, a method of sizing the two dc-link capacitors based on the machine power is also proposed. A comparison between two- and three-level inverters was conducted. The SynRM registered lower $d$-axis current ripple with a three-level inverter, indicating lower core losses in the machine. [ABSTRACT FROM PUBLISHER]

The large-scale integration of renewable energy sources and power electronic devices has led to increasingly dispersed and networked characteristics of power quality disturbances in distribution systems. Traditional control devices, limited by their fixed-point control, no longer meet the development needs of modern distribution systems. Considering the distribution and structural characteristics of the current new-type sources and loads, a multifunctional inverter power quality coordinated control strategy based on comprehensive evaluation is proposed. This strategy aims to achieve power quality coordinated control by utilizing optimal compensation capacity while the grid-connected inverter provides active power output. Firstly, the traditional ipiq power quality detection method is analyzed and improved to enable detection of harmonics, reactive power, and three-phase imbalance currents in single-phase systems or threephase four-wire systems. Secondly, in the power quality assessment, a balanced algorithm is employed to obtain the comprehensive evaluation index of power quality, thereby improving the deficiencies of single-weight evaluation. Next, to ensure the grid-connected inverter achieves optimal power quality coordinated control with minimal compensation capacity, an optimization compensation function is established between compensation capacity and comprehensive power quality index. This function is optimized using non-dominated sorting genetic algorithm to enhance equipment utilization and system economy. Finally, the feasibility and effectiveness of the proposed method are validated through simulations, demonstrating the achievement of optimal capacity configuration for power quality coordinated control while ensuring active power output by the grid-connected inverter. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge inverters, which belong to strongly nonlinear time-varying system with complex dynamics, have been widely used in high-voltage and high-power engineering fields. In this paper, a carrier phase-shifted sinusoidal pulse-width modulation cascaded H-bridge inverter is taken as an example with piecewise analysis to establish the discrete iterative mathematical model. Furthermore, the nonlinear dynamic behavior of this inverter system is investigated using folding diagrams, spectrum diagrams, bifurcation diagrams, Lyapunov exponents, etc. We find that this inverter can exhibit multiperiod bifurcation, tangential bifurcation and paroxysmal chaos within certain ranges of control coefficients and other circuit parameters, which will influence the system's stability seriously. On the basis of this discovery, the sinusoidal time-delay feedback control method is proposed. The difference between the load current of the controlled object and its own delay is used to form a feedback term, which is then fed into the sine function and proportional link to obtain the control term. Moreover, the Jacobian matrix of this feedback inverter system is derived, and the constraints on the feedback control coefficient are obtained based on the Jury criterion. Simulation results have verified the effectiveness of such a sinusoidal time-delay feedback control method, which can improve the stability and anti-interference of the system. The research can be used to provide some reference and guidance for the circuit design, debugging and control of cascaded H-bridge inverters. [ABSTRACT FROM AUTHOR]

This article presents a novel 3-Φ inverter that operates from a single direct current source and is based on the idea of switched-capacitor (SC) techniques. Each phase leg of the proposed topology (PT) consists of eight switches, two capacitors, and a diode. This configuration enables the generation of seven levels (line-to-line) voltage waveforms. The proposed design has several advantages, such as the capacitors' natural balancing, the ability to boost, minimum voltage stresses on the power switches, and fewer switching components. When compared to the conventional two-stage design, single-stage dc–ac power converters with boost capabilities present an intriguing option. This paper introduces a novel boost-type inverter for use in a wide variety of applications, including rolling mills, fans, pumps, maritime appliances, mining, tractions, and more. The study explains the proposed design, principle, control mechanism, and loss analysis in great depth. The advantages of the PT have been demonstrated through comparison with recently published SC topologies. Finally, a 1550-W downscale prototype is used to experimentally verify its viability and performance, with an estimated efficiency of around 96.6%. [ABSTRACT FROM AUTHOR]

The modern photovoltaic inverter has an active power-reactive power (Watt-VAr) control curve that is part of its management modes. The Watt-VAr curve, whose settings can be remotely modified, regulates the inverter reactive power output in function of its active power. This paper proposes the optimization of inverter segregated linear decision rules (LDRs), starting from the legacy Volt-VAr optimization in distribution networks. As opposed to classical LDRs that are interfaced with Volt-VAr optimization, the segregated LDRs are piecewise linear continuous curves that directly satisfy the reactive power capability of inverters, and their multiple segments can capture the correlation in solar power variability. The paper presents linear programming formulations for optimizing the segregated linear decision rules using stochastic optimization, robust optimization, and distributionally robust optimization. The optimization schemes are demonstrated on both meshed and radial networks, and their performance is validated via Monte-Carlo simulation. [ABSTRACT FROM AUTHOR]

Bidirectional synchronized transfer (BST) in variable frequency drive (VFD) systems implies automatic synchronization with seamless transfer of the motor to the grid or take‐over of the motor from the grid. This feature is realized if the magnitude, frequency, and phase angle of the VFD voltage and the grid voltage are synchronized. So, an accurate synchronization algorithm is necessary. This paper proposes a new BST method based on the discrete Fourier transformation (DFT) that obtains the magnitude, frequency and phase angle of VFD and grid voltages precisely through determining the fundamental components. This new BST coordinates the output voltage of the VFD with the grid using two error amplifiers. Also, additional decoupling reactors or transformers are no longer required by using this method due to exact estimation and synchronization. Furthermore, the algorithm can be integrated into any motor control strategy. This paper presents the principle of the proposed BST comprehensively and evaluates it by experimental results. The algorithm is tested on an induction motor via a 13‐level cascaded H‐bridge (CHB) inverter and the V/Hz constant control. The effect of BST on the motor voltage and current, the inverter current and dc‐link voltage is also examined. Results confirm the proposed strategy. [ABSTRACT FROM AUTHOR]

Regarding the problems of resonance and direct current (DC) components when the Z-source inverter (ZSI) without an isolation transformer is connected to the grid through an LCL filter, this paper proposes a novel DC component suppression strategy for a grid-connected ZSI based on the split capacitor method of disturbance observer (DOB). The split capacitor method is utilized to convert a third-order LCL filter into a first-order one to eliminate the resonance problem. The DC component of the inverter output voltage is regarded as an external disturbance, and the employed DOB is used to observe it, which is fed forward to suppress the DC disturbance component. Various comparison results of the simulation and experiment show that the proposed control strategy can effectively reduce grid-connected DC components injected into the grid at less than 0.5%, which decreases the DC component from 1.8% to 0.1%. [ABSTRACT FROM AUTHOR]

According to the traditional voltage and current double closed-loop control mode, the inverter management strategy for photovoltaic grid connection has insufficient anti-interference ability and slow response. This paper proposes a control strategy that applies adaptive-linear active disturbance rejection control (A–LADRC) to the outer loop control to achieve the purpose of anti-interference. The control strategy uses the linear extended state observer (LESO) to evaluate external interference caused by the change of external conditions and the internal disturbance caused by parameter uncertainty. PD controller compensates the disturbances and adds adaptive control to simplify parameter adjustment. Finally, this paper takes advantage of Lyapunov theory to conduct stability analysis. Compared with the traditional linear active disturbance rejection control (LADRC), the superiority of this control strategy is verified. The experimental results show that the system has better control performance and anti-interference ability in the face of various disturbances. [ABSTRACT FROM AUTHOR]

Nature's remarkable and merciful gift to the planet Earth is sunlight which may be highly lucrative if harvested and harnessed properly. Photovoltaic (PV) panels are used to convert the solar energy to electrical energy which are currently used to feed AC loads/grid. In this paper, modelling, performance and power flow studies of grid connected single phase inverter fed from PV array under steady state as well as transient conditions are considered. This paper focuses on the study and development of analytical model of micro-grid integrated single phase five level cascaded H-bridge inverter (MGISPFLCHBPVI) powered by a PV panel. A simple power control strategy for MGISPFLCHBPVI is also considered. The simulations are completely carried out using MATLAB software for power-flow studies. The performance characteristics of the inverter are studied from the analytical model developed. The validation of the analytical model is carried out by comparing the results of simulation in Simulink/Matlab. In order to reduce the time to reach steady state taken by the system, a simple PQ control strategy for insolation is introduced in this paper. The proposed method is evaluated based on performance parameters such as settling time and rising time of the system compared with the results available in the literature. [ABSTRACT FROM AUTHOR]

In order to improve the communication efficiency of the CAN bus application layer communication protocol of the inverter network monitoring system, this paper proposes a TTCAN scheduling optimization algorithm for the robot inverter remote monitoring system based on PLC and cloud platform. According to the analysis of the communication requirements of the frequency converter monitoring system, this paper designs the application layer protocol of the nodes in the system and establishes the system scheduling matrix. The time triggered can bus protocol (TTCAN) combines the event triggered mechanism with the time triggered mechanism. The hybrid scheduling strategy is used to optimize the system matrix of TTCAN; that is, the hybrid particle swarm optimization algorithm is used for periodic messages. For nonperiodic messages, uniform scheduling strategy and dynamic scheduling algorithm are adopted. The simulation is carried out by MATLAB tools. The simulation results show that the sum of partial minimum transmission time is 1928 and there are multiple optimal individuals through the hybrid particle swarm optimization algorithm. Compared with the traditional genetic algorithm and single particle swarm optimization algorithm, the hybrid algorithm is better than the traditional genetic algorithm and particle swarm optimization algorithm in terms of iteration times and average fitness value. In conclusion, the optimized TTCAN protocol improves the real-time performance, reliability, and bandwidth utilization of the communication network. [ABSTRACT FROM AUTHOR]

The conventional DC-link type quasi-Z-source inverter has been known as a buck–boost inverter with a low component voltage rating. This paper proposes an active DC-link type quasi-Z-source inverter by adding one active switch and one diode to the impedance-source network to enhance the voltage gain of the inverter. As a result, the component voltage rating of the inverter is significantly reduced, which is demonstrated through some comparisons between the proposed topology and others. A discontinuous pulse width modulation (DPWM) scheme is proposed to control the inverter, which reduces the number of commutations compared to the traditional strategy. Under this approach, the insertion of a shoot-through state does not cause any extra commutations compared to the conventional voltage-source inverter. Details about control implementation, steady-state analysis, and design guidelines are also presented in this paper. Simulation and a laboratory prototype have been built to test the proposed inverter. Both buck and boost operations of the proposed inverter are implemented to validate the performance of the inverter. [ABSTRACT FROM AUTHOR]

Different types of distributed generation (DG) units based on renewable and non-renewable energy sources can create a local energy system in microgrids. The widespread penetration of distributed energy resources (DERs) has affected many power system issues, such as the control and operation of these networks. For the optimal operation of microgrids, optimal energy planning and management in the new space governing the distribution system requires extensive research and analysis. Getting acquainted with the latest research about the evaluation of the problems and challenges in the design of control systems plays an important role in providing a guidance map for researchers to find the recent challenges and propose new solutions. This paper tried to list the challenges of distributed generation sources for MG applications, opportunities, and solutions. These challenges are reported in hierarchical control strategies and power-sharing categories. Therefore, Model Predictive Control (MPC)-based approaches are reviewed for different recent control levels and power sharing strategies in a comprehensive and simple point of view. The performance comparison of MPC methods together and different allocated fitness functions and implementation algorithms are dedicated. Another hand, the potential of MPC methods to control inverters for increasing the reliability of the grid, which this feature could not be achieved by using conventional strategies, while has not been investigated by researchers widely, is introduced in a short review. Therefore, this paper shows an intersection guidance map for readers to facilitate future research works in these exciting and undiscovered fields. [ABSTRACT FROM AUTHOR]

Motor current signature analysis (MCSA) has been widely used for fault diagnosis of induction motors (IMs) because of its non-invasiveness and comparatively low cost. However, the spectral leakage of the fundamental supply frequency can obscure the fault characteristic component when IMs operating at no-load or low-load conditions. In this paper, a broken rotor bar (BRB) fault diagnosis approach based on the third-order energy operator (TOEO) demodulated current signals is presented. The TOEO approach performs effectively in reducing the negative impact of the fundamental supply frequency spectral leakage and enhancing the BRB fault features. Theoretical and experimental results show that the TOEO approach can excellently reveal the fault characteristic frequency, instead of the sideband frequencies. Besides, the results are compared with the Teager-Kaiser energy operator (TKEO). The capability of the presented approach has several advantages over the TKEO, especially when the IMs are fed by an inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a grid-connected single-phase micro-inverter (MI) with a rated power of 300 W and an appropriate control strategy for photovoltaic (PV) systems. The proposed MI is designed based on a two-stage topology. The first stage consists of a SEPIC DC-DC converter with high voltage gain to step up the voltage of the PV panel and harness the maximum power, while the second stage includes a full-bridge DC-AC converter. The advantages of the proposed MI are the use of fewer components to provide suitable output voltage level for connection to a single-phase grid, continuous input current, limited voltage stress on the switch, high efficiency, long operational lifetime, and high reliability. Lower input current ripple and the presence of film capacitors in the power decoupling circuit increase the lifetime and reliability of the proposed MI. In the proposed MI, the active power decoupling circuit, which is normally used in a typical single-stage SEPIC-based MI, is eliminated to achieve both a long lifetime and high efficiency. The operating principles of the proposed MI are analyzed under different conditions. The results of design and simulation confirm the advantages and proper performance of the proposed MI. [ABSTRACT FROM AUTHOR]

Multilevel Inverters (MLIs) are widely sought after in medium-voltage applications like electric ships, electric aircraft, and renewable energy integration due to excellent advantages like lower device stress, better power quality, and modularity. However, non-sinusoidal excitations from MLIs pose a serious problem to motor-insulation and lead to their premature breakdown. This paper investigates stress in medium-voltage motor insulation when the stator winding is excited by 3-, 5-, and 7-level multilevel inverter output waveforms. The effect of firing angle on insulation stress is also studied for each of the multilevel inverters. Results show that in addition to the number of output voltage levels, PWM wave shape is a critical factor which affects the insulation stress. Both these factors work together to impact the insulation health. A strong correlation is shown between the increase in the voltage root mean square (RMS) value and increase in dielectric stress when ignoring the dv/dt impact for a fixed DC input voltage and operating frequency of the inverter. Similarly, the dielectric stress in the stator insulation increased with an increase in firing angle for each of the MLIs. This paper shows a potential that both the RMSs can be optimized to reduce the insulation stress and improve the power quality of MLIs in medium voltage drives. [ABSTRACT FROM AUTHOR]

In modern power systems, the integration of renewable energy sources relies on dedicated inverters whose power electronic circuitry switches at high frequencies and causes conducted emissions in the supraharmonic range, i.e., from 9 to 150 kHz. In this regard, the normative framework is still lacking a reference measurement method as well as a set of emission limits and performance requirements. From a metrological point of view, it is important to evaluate whether some of the power quality indices adopted for radiated emissions could be transposed also in this context. In particular, the paper considers a recent algorithm for the identification of supraharmonic components and discusses how its estimates affect the estimation of quasi-peak values. To this end, the paper describes the implementation of a fully digital approach and validates the results by means of an experimental comparison against a traditional quasi-peak detector. The proposed analysis confirms the potential of the considered approach and provides some interesting insights about the reliability of quasi-peak estimation in supraharmonic range. [ABSTRACT FROM AUTHOR]

This paper discusses systematic efficiency considering the efficiency of both a motor and airflow in an inverter-driven single-phase brushless direct-current (BLDC) motor with two different lamination designs for a cordless vacuum cleaner. In other words, multi-physical lamination design has to be conducted, and hence, the shape and placement of a whole electromagnetic structure are investigated in terms of a tradeoff between the electrical and mechanical efficiencies. In this paper, a single-phase BLDC motor for cordless vacuum cleaners is designed to satisfy starting and continuous torques by means of asymmetric air gap, and fluid analysis is performed to determine which shape of a single-phase BLDC motor has better system efficiency. The prototype of a single-phase BLDC motor has been tested, and the speed of the operation is ranged from 84468 r/min up to the rated speed of 100020 r/min. The motor efficiency of 94.7% has been measured to verify a good match with the estimated efficiency of 94.5%. [ABSTRACT FROM AUTHOR]

The nine papers in this special section focus on photovoltaic module and sub-module level power electronics. Grid connected photovoltaic energy systems have experienced an explosive growth over the last decade, with a cumulative installed capacity surpassing the 400 GW milestone as of 2017. Among PV system configurations, distributed module-level converter architectures can lead to a higher energy yield by mitigating partial shading, persistent shading (soiling, snow, bird droppings, and fallen leaves), mismatch, and aging, through a higher maximum power point tracking (MPPT) efficiency. Also, distributed electronics might be the key for implementing diagnostic and prognostic actions at a module level. Among these configurations, microinverters (also known as ac-module inverter), which connect a single PV module to the grid, and PV power optimizers, which are dc–dc converters performing the MPPT function at a module level, have attracted the academic and industrial interest in the last decade. So much so, that both microinverters and dc–dc power optimizers are commercialized by tens of companies around the world, with a great variety of circuit topologies, which comprise combinations of one or more power stages, interleaved converters, resonant converters, topologies with and without isolation, etc. [ABSTRACT FROM AUTHOR]

This paper examines metal–ferroelectric–insulator–semiconductor negative-capacitance FinFET (NC-FinFET) based VLSI subsystem-level logic circuits. For the first time, with the aid of a short-channel NC-FinFET compact model, we confirm the functionality and evaluate the standby-power/switching-energy/delay performance of large logic circuits (e.g., dynamic 4-bit Manchester carry-chain adder and the formal hierarchical 32-bit carry-look-ahead adder) employing 14-nm ultra-low-power NC-FinFETs. Our study indicates that the inverse Vds-dependence of threshold voltage (VT), also known as the negative drain-induced barrier lowering, of negative-capacitance field-effect transistor is not only acceptable but also beneficial for the speed performance of both the static and pass-transistor logic (PTL) circuits, especially for the PTL at low VDD. [ABSTRACT FROM AUTHOR]

The increasing penetration of renewable generation and large implementation of the DC loads are challenges that stress the current distribution systems by causing uncertain voltage variations. The AC−DC hybrid distribution network is seen as an innovative solution to address the problem of accommodating highly dispersed sustainable energy. Specifically, the solid-state transformer (SST), which is capable of enhancing power-quality performance and controllability of the power distribution, has attracted increasing focus in this decade as a promising advanced converter. It is of great interest to investigate how to operate the multiple SSTs with different modes in a coordinated manner to optimise the distribution network performance. This paper formulates the coordinated operation model for multiple SSTs to enable fast voltage regulation for the hybrid active distribution network equipped with large-scale penetration of invertor-based solar power and DC load. A hybrid optimal power flow describing the controlling modes of SSTs and operating interaction between AC−DC subsystems is proposed in this paper. The case studies on a modified IEEE 33-AC−DC hybrid power distribution system show that the voltage profile can be optimised by using the flexible controlling resource of SSTs, facilitating the timely performance adjustment in the presence of fast fluctuating distributed generator's output. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency single-phase T-type boundary conduction mode (BCM) microinverter. The conventional full-bridge BCM microinverter has achieved zero voltage switching (ZVS) and thereby improved the efficiency, but it suffers from high switching losses under light load conditions. The proposed T-type BCM microinverter reserves ZVS and uses a multilevel technique to further decrease the switching losses. The BCM operation with multilevel technique will have too low switching frequency when the grid voltage approaches half of the dc link voltage. To solve this problem, this paper adopts a third operation mode for the T-type switching leg to maintain the switching frequency above a minimum value. The corresponding mode transitions are also detailed to ensure a smooth operation. Because of the turn-offdelay of the freewheeling transistor, the actual lower current boundary deviates from the programmed one, which will distort output current. To address this issue, this paper also proposes a boundary compensation method. A prototype has been built for performance verification, which can test both full-bridge and T-type topology. Compared with the full-bridge BCM microinverter, the proposed T-type BCM microinverter has a higher efficiency over the whole load range. [ABSTRACT FROM AUTHOR]

This paper proposes a vector control strategy for independent control of two permanent-magnet synchronous motors (PMSMs) using a single four-leg inverter (4LI). An expanded two-arm modulation to obtain a balanced three-phase output voltage is described. This paper also proposes a method to compensate for the fluctuations in the neutral point voltage of two split capacitors in the dc link. The experimental results show that independent speed and position control of two PMSMs can be achieved using a single 4LI with the proposed vector control method. [ABSTRACT FROM AUTHOR]

This paper presents a novel configuration for a high-Q tunable waveguide (WG) filter with a constant absolute bandwidth (BW). The key feature of this filter is that it is tuned by a single tuning element. This paper investigates the theory of coupling behavior of single septum and double septa to achieve constant absolute BW. The theory is presented for both the coupling matrix-based and inverter-based filter topologies. The filter design methodology is lucidly presented covering the design strategy adopted for interresonator coupling, input–output coupling and tuning element. The tuning mechanism of the proposed filter is explained with measurement results presented for a $Ku$ -band tunable WG filter designed at 15 GHz with a 2% BW to achieve 15% tuning range. The filter promises to be useful in emerging 5G millimeter-wave applications, where the filter size is very small to accommodate many mechanical tuning elements. Furthermore, the proposed design methodology is scalable, i.e., the tuning mechanism is independent of the filter order. [ABSTRACT FROM AUTHOR]

This paper presents a novel platform for accurate mathematical modeling of the propulsion system of electric cars. It provides, for the first time, a hardware-in-the-loop (HIL) real-time experimental verification case study of a General Motor Chevrolet Volt for power, control systems, and the mechanical systems. The contribution of this paper can be categorized into three approaches: First, each component of the powertrain is accurately modeled taking transient dynamics of all components of the electric vehicle into consideration. Further, a PSIM simulation platform is consequently developed to demonstrate the validity of this mathematical modeling. Finally, the Typhoon HIL is used to provide the experimental verification of the proposed model in real time, which precisely validates the viability of the model. HIL technology is used to prototype and test the proposed control system while simulating the power circuit on the HIL module platform. The permanent magnet synchronous motor and the power electronics hardware components are simulated in real time at which the parameters can be changed during the simulation. However, the control algorithm is generated as a C code and downloaded to the TI controller that exists on a digital signal processing board. The results from the simulation based on PSIM environment and hardware validations using HIL are in agreement, which validates the developed model. The performance has been investigated under different load operating conditions in real time to verify its robustness. The case study can be extended for any electric car as it provides a generic platform for modeling any propulsion system. [ABSTRACT FROM AUTHOR]

In this paper, we develop and examine permanent magnet synchronous motors (PMSMs) by use of both stator and rotor cores made of nanocrystalline magnetic materials (NMMs). We report core loss properties of the PMSM with the NMM under inverter excitation. In addition, we compare core losses of the PMSM with conventional non-oriented (NO) steel sheets under inverter excitation to discuss the core loss characteristics of the NMM motor. In average, under inverter excitation, the reduction ratio in core loss of the PMSM made of NMM is about 60% as compared with the core loss of the PMSM with NO sheets. In particular, the average decrease obtained by using NMM rotor core instead of NO rotor core is about 30%. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [ABSTRACT FROM AUTHOR]

The pump-back test is widely adopted in the industry for characterizing and qualifying high-power converters. One popular pump-back test configuration is to tie the dc links of two converters together and circulate the current through the inductor connected between the ac terminals. In this configuration, one of the converters operates in the voltage mode to generate the virtual grid and the other converter regulates the circulating current, where hysteresis control could be applied. However, the switching characteristics of hysteresis control are unique due to the pulsewidth modulation type voltage being the virtual grid. This paper contributes to analyzing the switching frequency characteristics of the hysteresis control in this pump-back test configuration. The switching frequency tracking phenomenon is revealed and reported in this paper for the first time. Theoretical analysis, simulation validation, and experimental demonstration are provided to support the major conclusions. [ABSTRACT FROM AUTHOR]

In this paper, the conventional I- and T-type three-level neutral-point-clamped (3L-NPC) inverter for low-voltage renewable energy systems is first investigated. Literature research shows that the T-type inverter improves I-type's insulated-gate bipolar transistor (IGBT) $+$ IGBT current paths. However, the IGBT $+$ diode paths are the same. The calculation in this paper further reveals that the IGBT $+$ diode current paths dominate the conduction losses and even the whole semiconductor losses. Based on the aforementioned recognitions, a novel T-type inverter is presented as an alternative to be applied in the low-voltage renewable energy systems. In the proposed 3L-NPC, four CoolMosfets replace the IGBT $+$ diode middle bidirectional switch. In the proposed topology, there is no diode involved in the current path supposing the unity power factor. In this way, the conduction loss is expected to be reduced compared with that from the conventional T-type 3L-NPC, particularly in the low and medium power ranges. [ABSTRACT FROM PUBLISHER]

This Paper presents a framework to carry out a simulation for closed loop speed control of BLDC motor with PID and Modified PID controller. The novelty of this paper lies in the design of modified PID controller to track the reference trajectory with and without load in addition to minimizing the initial overshoot. The simulation includes all realistic values and components of the motor. The three phase inverter and its control algorithm is modeled and simulated using MATLAB Simulink. The PID and Modified PID controller track the reference speed with and without load disturbances in closed loop control but the demerit of conventional PID can be observed in its steep overshoot in the closed loop transient response. The speed, torque, dc-link current and back-emf waveforms are analyzed for various load torque conditions through MATLAB Simulink. [ABSTRACT FROM AUTHOR]

Cascaded inverters can improve efficiency and reduce cost, so it is widely used in photovoltaic (PV) grid connected power generation system. However, aging or partial shielding of PV panels will lead to their different maximum power points (MPP). This paper proposes a decentralized control strategy for grid‐connected cascaded PV inverters without any communication, which is capable of integrating PV inverters of different capacities connected in series into the grid, and enable them to achieve maximum power point tracking (MPPT) independently. Compared with the traditional centralized control method relying on real‐time communication, the proposed scheme has advantages of improved reliability and decreased costs. The overall system stability is analysed, and the stability condition is derived as well. The Hardware‐In‐the‐Loop test results show that all the inverters in the cascaded system have their output frequency and voltage phase synchronized autonomously, and achieve MPPT independently even in the presence of variation of light condition. Thus, the feasibility of the proposed method is verified. [ABSTRACT FROM AUTHOR]

Multilevel inverters, known for their low switching loss and suitability for medium- to high-power applications, often create a heavy computational overhead for the controller. This paper addresses the aforementioned limitation by presenting a novel approach to Direct Model Predictive Control (DMPC) for a grid-tied 289-level ladder multilevel inverter (LMLI). The primary objective is to achieve perfect inverter current control without enumeration. The proposed control method provides a single best solution without complete exploration of the search space. This generalized method can be applied to any multilevel inverter (MLI), enabling them to be used in the grid-tied mode without the computational burden due to a large number of switching states. The DMPC of LMLI with 289-level output and corresponding 289 control inputs, utilizes a discrete model to predict the future state of the state variable. In order to alleviate the enumeration burden, virtual sectors on a linear scale are introduced, and a general formula is provided to identify the single best state among the 289 states, reducing the time required to find the best optimal state per sampling period. Moreover, the proposed control scheme is independent of objective evaluation. [ABSTRACT FROM AUTHOR]

In response to the model predictive control (MPC) driving system, this paper proposes a multi-adjustment strategy for phase current reconstruction based on a coupled current sampling method. The proposed coupled current sampling method eliminates the need to modify the inverter's internal wiring. The current signals utilized in the proposed method are all external current signals from the inverter and do not involve any current signals from the internal circuitry of the inverter. By analyzing the current sampling mechanism of duty-cycle model predictive control (DC-MPC) as a modulation method, the underlying principles of the non-reconstructible current regions in the coupled current sampling method are revealed. The non-reconstructible regions are accurately delineated into low and high-modulation regions using coupled current sampling. A multi-adjustment strategy for phase current reconstruction is proposed to address the non-reconstructible regions. In the low-modulation regions, phase current reconstruction is achieved through compensated voltage vector pulse injection. In the high-modulation regions, phase current reconstruction is accomplished using the zero-voltage vector insertion approximation method, which maintains the symmetry of the PWM waveform and avoids current distortion. Experimental results on a permanent magnet synchronous motor validate the effectiveness and feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive review of reduced device count multilevel inverter (RDC MLI) topologies for PV systems. Multilevel inverters are widely used in medium-voltage and high-power applications such as wireless power transform applications, flexible AC transmission (FACT), active filters, AC motor drives, high-voltage DC transmission (HVDC), and renewable energy sources due to their high modularity and high-power quality output. Multilevel inverters have the ability to diminish the harmonics content in the output voltage by applying various modulation techniques. The literature in this field showed that the high-power quality and high modularity of the output demand an undeniable need for multilevel inverter topology. Research in this field has identified various multilevel inverter topologies, each possessing their own merits and demerits. The ubiquitous availability of multilevel inverter topologies illustrates the complexity of their accurate selection. To avoid such complexity, this review shows the state of the art of various reduced device count (RDC) multilevel inverter (MLI) topologies. Details of the various RDC MLIs, along with their comparisons, are provided in this paper. This review will be an important reference tool for future work on RDC MLI for photovoltaic (PV) systems. [ABSTRACT FROM AUTHOR]

Using a low pulse ratio, the electromagnetic interference and switching loss of an inverter can be effectively reduced, particularly in high-power applications. However, due to variations in grid impedance, it is a challenging task to achieve stable operation of an LCL-type grid-connected inverter (GCI) using the active damping method with low pulse ratio. Thus, a novel three-phase dual-frequency GCI is presented to ensure the symmetry of the output power and the stable operation of the system address stability issues. The proposed inverter topology in this article is composed of two inverters in parallel, which are, respectively, a power inverter unit (PIU) and an auxiliary harmonic elimination unit (AHEU). To reduce the switching loss and improve the inverter efficiency, the switching frequency of the PIU is relatively low, injecting current into the grid. Moreover, the feedforward compensation method is used in AHEU. AHEU operates at high switching frequency to generate a current component that is symmetrical with the ripple com-ponent, improving the power quality, without extracting the current harmonic as the current reference. The operating principle of feedforward compensation is explained, and a proper parameter design procedure is presented in this paper. Since L filters are used for the proposed inverter, the system can operate stably where the ratio of switching frequency to fundamental frequency is low. A 10 kW laboratory prototype was built. The experimental results showed that the grid current ripple could be effectively eliminated and the THD of the grid current was 3.01%. The proposed inverter has good stability in a weak grid, and the efficiency of the proposed inverter is 95.98% at rated current, which is 0.81% higher than the traditional GCI, effectively increasing the efficiency of the system. [ABSTRACT FROM AUTHOR]

Introduction. The advantages of a high-power quality waveform and a high voltage capability of multilevel inverters have made them increasingly popular in recent years. These inverters reduce harmonic distortion and improve the voltage output. Realistically speaking, as the number of voltage levels increases, so does the quality of the multilevel output-voltage waveform. When it comes to industrial power converters, these inverters are by far the most critical. Novelty. Multilevel cascade inverters can be used to convert multiple direct current sources into one direct current. These inverters have been getting a lot of attention recently for high-power applications. A cascade H-bridge multilevel inverter controller is proposed in this paper. A change in the pulse width of selective pulse width modulation modulates the output of the multilevel cascade inverter. Purpose. The total harmonic distortion can be reduced by using filters on controllers like PI and fuzzy logic controllers. Methods. The proposed topology is implemented with MATLAB/Simulink, using gating pulses and pulse width modulation methodology and fuzzy logic controllers. Moreover, the proposed model also has been validated and compared to the hardware system. Results. Total harmonic distortion, number of power switches, output voltage and number of DC sources are analyzed with conventional topologies. Practical value. The proposed topology has been very supportive for implementing photovoltaic based multilevel inverter, which is connected to large demand in grid and industry. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model of 255 kW grid-connected solar photovoltaic (SPV) system. To study the performance characteristics of the grid-connected SPV system, a new hybrid adaptive grasshopper optimization algorithm with the recurrent neural network (AGO-RNN) control technique was implemented. Furthermore, the power quality at the point of common coupling (PCC) has been studied using the conventional (PSO) and proposed AGO-RNN controllers. The characteristics of the PV system were analyzed under varying environmental (variable irradiance and temperature) conditions considering 3 different cases such as (i) standard test conditions (STC), (ii) variable radiation with constant temperature, and (iii) variable radiation with variable temperature. For each case, the total harmonic distortion (THD) has been calculated using the proposed AGO-RNN control technique, and the results were compared with particle swarm optimization (PSO) technique. The 255 kW PV model is initially developed and connected to a three-level NPC inverter, an MPPT-based perturbation and observation algorithm. Later, the PV model is controlled by an AGO-RNN pulse width modulation (PWM) controller and is then integrated to the main grid at PCC. The main advantage of this technique is exploiting the separate DC-DC converter between the SPV module and the inverter. Finally, the proposed grid-connected SPV system was simulated on MATLAB for analyzing the performance of the system based on its I-V and P-V characteristics, inverter voltage, grid power, gird voltage, grid current, power factor, and THD under different environmental conditions. The simulation results demonstrate that the current magnitude and THD of the SPVGC system are improved with the cutting-edge AGO-RNN controller compared to PSO in all three different scenarios, and this value is less than 1.6%, which is within the permitted limits of IEC 61727 standards. [ABSTRACT FROM AUTHOR]

In this paper, the explicit state-space model for a multi-inverter system including grid-following inverter-based generators (IBGs) and grid-forming IBGs is developed by the two-level component connection method (CCM), which modularized inverter control blocks at the primary level and IBGs at the secondary level. Based on the comprehensive state-space model representing full order of system dynamics, eigenvalues of the overall system are thoroughly analyzed, identifying potential adverse impacts of not only grid-following inverters, but also grid forming inverters on the system smallsignal stability, with the underlying principle of oscillations also understood. Numerical and simulation results validate effectiveness of the proposed methodology on IEEE benchmarking 39-bus system. [ABSTRACT FROM AUTHOR]

Quasi‐Z source inverters (qZSI) can overcome the disadvantages of conventional wind power systems, because of achieving the balanced DC‐link voltage by using its boost ability. The majority of currently used control methods for conventional inverters are susceptible to parameter changes, and the qZSI are controlled by finite switching sequence model predictive control (FSS‐MPC). In this paper, a Variable weight coefficient Model Predictive Control (V‐MPC) strategy is proposed. First, based on the optimal scheduling algorithm, according to the priority of the controlled object. The proportioning weights of the global feasible solution and the local optimal solution in the algorithm are coordinated. Then, using the equality‐constraints quadratic programming method, according to the relationship between the system frequency and the reference value, increase the weight of the qZSI algorithm or increase the proportion of VSG control to improve the ability to suppress frequency fluctuations. It can give full play to the short‐term power support role of the virtual synchronous wind turbine. The modeling and testing findings validate the suggested control strategy. When compared to the conventional finite control set model predictive control (FCS‐MPC), the V‐MPC can minimize the big store inductance current ripple and have lower THD in the load currents waveform. [ABSTRACT FROM AUTHOR]

In the field of signal processing, it is interesting to explore signal irregularities. Indeed, entropy approaches are efficient to quantify the complexity of a time series; their ability to analyze and provide information related to signal complexity justifies their growing interest. Unfortunately, many entropies exist, each requiring setting parameter values, such as the data length N, the embedding dimension m, the time lag τ , the tolerance r and the scale s for the entropy calculation. Our aim is to determine a methodology to choose the suitable entropy and the suitable parameter values. Therefore, this paper focuses on the effects of their variation. For illustration purposes, a brushless motor with a three-phase inverter is investigated to discover unique faults, and then multiple permanent open-circuit faults. Starting from the brushless inverter under healthy and faulty conditions, the various possible switching faults are discussed. The occurrence of faults in an inverter leads to atypical characteristics of phase currents, which can increase the complexity in the brushless response. Thus, the performance of many entropies and multiscale entropies is discussed to evaluate the complexity of the phase currents. Herein, we introduce a mathematical model to help select the appropriate entropy functions with proper parameter values, for detecting open-circuit faults. Moreover, this mathematical model enables to pick up many usual entropies and multiscale entropies (bubble, phase, slope and conditional entropy) that can best detect faults, for up to four switches. Simulations are then carried out to select the best entropy functions able to differentiate healthy from open-circuit faulty conditions of the inverter. [ABSTRACT FROM AUTHOR]

Recently, the establishment of technical standards for grid connection has gained interest in academia and industry. These standards have focused on the reactive power control function of the grid-connected inverter and maintenance of grid operation, and include detailed information about the grid support function. However, remote control communication and control devices for grid support functions, and other distributed sources, such as wind power and energy storage systems, other than inverters have not been addressed. In this paper, the control of the interlinking converter (ILC) in a hybrid microgrid considering low voltage ride-through (LVRT) among grid support functions is investigated. The proposed method consists of an energy management system considering LVRT and a cooperative control scheme. In the energy management system, an algorithm capable of mode selection was constructed by applying the LVRT curve. Then, considering the LVRT situation, the allowable reactive power range of the ILC was mathematically analyzed through the cooperative control of the energy storage device and the ILC. The proposed method enables us to perform active and reactive power control of the ILC in a hybrid distribution network, considering the power factor under various conditions. This functionality, such as supplying reactive power, significantly contributes to the enhanced grid resilience with distributed power sources, including renewable energy. The proposed strategies were verified through experiments after configuring an experimental set of distributed power sources. [ABSTRACT FROM AUTHOR]