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In this paper five different flexibility options are analysed from a techno-economic perspective as alternatives to traditional grid expansion for a specific distribution grid in Germany. The options are: two reactive power control strategies with photovoltaic inverters (as a function of the power feed-in, or of the voltage at the connection point), one residential and two large scale battery storage applications (primary control reserve with autonomous reactive power control or self consumption maximisation strategy with autonomous reactive power control). For the pilot grid located in Southern Germany a photovoltaic expansion pathway is determined. The main goal of this work is to quantify the grid expansion actions that can be avoided by applying these five flexibility options for the assumed expansion pathway, focusing on large scale battery storages. It is shown that the five flexibility options increase the hosting capacity for PV systems, compared to a scenario without, by up to 45%. Furthermore, the results of the economic assessment indicate that the analysed flexibility options might be a viable alternative to traditional grid expansion as all of them show a cost reduction potential for the pilot region. These results could encourage DSOs to consider the integration of additional PV and battery storage systems not as a problem which triggers grid expansion, but as part of the solution reducing future grid expansion costs. [ABSTRACT FROM AUTHOR]

This paper deals with the design of the power train for a hybrid electric motorcycle (HEM). The HEM power train is composed of an internal combustion engine coupled to a synchronous electric machine (EM). The EM is fed by a standard three-phase inverter connected to a high-voltage battery pack. Low weight and volume are the main requirements for HEMs, and the energy storage system (ESS) is the most critical part. Different kinds of ESSs are compared to choose the best solution balancing cost, volume, and weight. A methodology of investigation is proposed in order to recognize all the data necessary to find out the ESS. Moreover, the design choices adopted for the electric drive are reported. In order to predict EM, power converter, and battery pack performances, efficiency maps have been computed. The whole power train has been prototyped. Experimental tests of the HEM prototype on test bench and on a real racetrack are presented. All the experimental measurements highlight a significant performance enhancement of the new HEM with respect to the original one. The HEM acceleration time and top velocity have been improved without affecting too much the original motorcycle weight. [ABSTRACT FROM AUTHOR]

The phasor-PWM-based current source inverter (CSI) is a boost inverter. The difference between conventional CSIs and the boost inverter is that the boost ratio (VLLrms/Vdc ) in the boost inverter can easily be above 3.0, whereas this ratio is around 1 in conventional CSIs. In order to realize the potential capabilities of the boost inverter and to assist its penetration into renewable energy systems, the boost inverter dynamic behaviors are studied in this paper. First, the large- and small-signal models as well as the dq-equivalent circuits of the boost inverter are presented. Then, the developed models are verified using circuit simulations and experiments on a laboratory-scale 2-kW 208/240- V_{\rm LLrms} V_{\rm dc}=65\ \hbox{V} $ boost inverter made of reverse-blocking IGBTs. Finally, the developed small-signal model is used to study the stability of the boost inverter through root locus of small signal poles (eigenvalues) as control inputs, and load parameters vary within the boost inverter's operating limits. [ABSTRACT FROM PUBLISHER]

Power generators contain control systems that are able to regulate system frequency, but the frequency setpoint values are rarely modified from nominal values. This paper describes design considerations for a communication system from generators to frequency-sensitive distributed energy resources (FS-DER) using changes to frequency setpoint values of generators. Signaling discrete system states by generating off-nominal system frequency values can be used as a novel narrowband unidirectional broadcast communications channel. This paper describes two protocols for utilizing off-nominal frequencies to carry information: First, a protocol for dispatching blocks of FS-DER that is suitable for systems restricted to relatively slow rates of change of frequency (ROCOF). Second, for systems that allow higher ROCOF values, the feasibility of using power generation resources as a power-line communication transmitter is shown. Data from an operating islanded power system with diesel generators are analyzed to demonstrate the feasibility of the proposed communication system in systems fed by rotating machines. The feasibility of the proposed communication system in systems fed by voltage-source inverters is shown with laboratory tests of a 20-kVA inverter. The inverter was found to have a maximum ROCOF of 2.2 Hz/s, sufficient to enable its use as a power-line communication transmitter. [ABSTRACT FROM AUTHOR]

Exploiting the rich switching redundancies of the dual inverter, new hybrid pulsewidth-modulation (PWM) switching methods are proposed in this paper using the degree of freedom of operating the individual inverters independently, in addition to exercising the degree of freedom of controlling the switching action of the individual legs independently. Two voltage entities, namely, common-mode voltage (CMV) and differential-mode voltage are identified in the dual inverter, and all hybrid PWMs are envisaged aimed at reducing and also eliminating the CMV in it. The effects of such attempts on motor shaft voltage and also the motor bearing currents are presented in detail. Furthermore, bearing current profiles of an open-end winding induction motor are also presented with both conventional and hybrid PWMs proposed in this paper. Electric discharge machining discharge currents are completely eliminated with the use of all hybrid PWM methods proposed in this paper. In addition, implications of completely eliminating the CMV are also presented in this paper. All hybrid PWMs proposed in this paper are first simulated using MATLAB and are experimentally verified on a dual two-level inverter feeding a 1.1-kW 415-V 3- $\phi$ open-end winding induction motor drive. [ABSTRACT FROM PUBLISHER]

Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector structure have advantages, such as complete elimination of fifth and seventh harmonics, reduction in electromagnetic interference, reduction in device voltage ratings, reduction of switching frequency, extension of linear modulation range, etc., making it a viable option for high-power medium-voltage drives. This paper proposes two power circuit topologies capable of generating multilevel dodecagonal voltage space vector structure with symmetric triangles (for the first time) with minimum number of dc-link power supplies and floating capacitor H-bridges. The first power topology is composed of two hybrid cascaded five-level inverters connected to either side of an open-end winding induction machine. Each inverter consists of a three-level neutral-point-clamped inverter, which is cascaded with an isolated H-bridge making it a five-level inverter. The second topology is for a normal induction motor. Both of these circuit topologies have inherent capacitor balancing for floating H-bridges for all modulation indexes, including transient operations. The proposed topologies do not require any precharging circuitry for startup. A simple pulsewidth modulation timing calculation method for space vector modulation is also presented in this paper. Due to the symmetric arrangement of congruent triangles within the voltage space vector structure, the timing computation requires only the sampled reference values and does not require any offline computation, lookup tables, or angle computation. Experimental results for steady-state operation and transient operation are also presented to validate the proposed concept. [ABSTRACT FROM PUBLISHER]

This paper presents a 100-kV high frequency transformer/rectifier package, which is capable of a dual output polarity operation. An H-Bridge inverter drives the primary of the high voltage (HV) transformer at a frequency of 20 kHz. The inverter is driven by a Microchip dsPIC33F digital signal controller using peak current mode control with adaptive slope compensation. The HV-tank has two HV-coax output cables with a grounded shield on each cable. If the center conductor of the coax cable designated as negative output is grounded, positive voltage is obtained from the coax cable designated as positive output and vice versa. This paper provides design details and experimental results from tests of the entire system. [ABSTRACT FROM PUBLISHER]

This paper presents a modified small-signal model of a voltage source inverter (VSI) and a voltage source converter (VSC) that captures model nonlinearities such as deadtime and modulation effects that were not presented in the literature. Previous research has concentrated on developing compensation methods for these types of phenomena in a switching model, but very little on predicting them. In this paper, the small-signal model of the VSI in literature is used, and the different phenomena are then incorporated into the model to get a complete one. In addition, the effect of voltage and current feedback control is also analyzed. The output impedance of the VSI is derived with the modified small-signal model, compared to the conventional one and validated with switching model and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, five projected tunnel FET (TFET) technologies are evaluated and compared with MOSFET and FinFET transistors for high-performance low-power objectives. The scope of this benchmarking exercise is broader than that of previous studies in that it seeks solutions to different identified limitations. The power and the energy of the technologies are evaluated and compared assuming given operating frequency targets. The results clearly show how the power/energy advantages of TFET devices are heavily dependent on required operating frequency, switching activity, and logic depth, suggesting that architectural aspects should be taken into account in benchmarking experiments. Two of the TFET technologies analyzed prove to be very promising for different operating frequency ranges and, therefore, for different application areas. [ABSTRACT FROM PUBLISHER]

This paper proposes a nonlinear decoupled current control scheme for a grid-connected inverter with LCL filter. Decoupling the active and reactive current control channels is one of the main demands in the control of inverters. For inverters with an L filter, the decoupling can be achieved by a proper feed-forward of grid voltages. However, the coupling of channels is a complex issue for converters with LCL filters. The resonance mode of the LCL filter may cause instability, which adds more complexity to the analysis. In this paper, state equations of the system are provided, which highlight the coupling between active and reactive currents injected into the grid. Accordingly, a non-linear control scheme is proposed which effectively decouples the channels and dampens the resonant modes of the LCL filter. The stability of the proposed control method is verified by the Lyapunov criterion. Independency of the system stability to the grid-impedance is another feature of the proposed approach. Moreover, only grid-side currents are needed for implementation of the proposed scheme, avoiding the need for additional current sensors for the output capacitor and grid-side inductor. For accurate modelling of the inverter, the computation and PWM sampling delays are included in the controller design. Finally, various case studies are provided that verify the performance of the proposed approach and the stability of the system. [ABSTRACT FROM AUTHOR]

Modularity, efficiency, power quality, and high reliability are the attractive advantages of multilevel inverters (MLIs). But it has limitations in terms of an increased number of semiconductor devices as compared to conventional 2-level inverters. In this paper, a fault-tolerant single-phase 5-level MLI configuration is proposed. The proposed fault-tolerant configuration of the MLI can significantly improve its reliability while maintaining the modularity of its software implementation. Examination, design, and implementing thought for both normal and abnormal operating situations of the proposed MLI are presented in this paper. The feasibility of the proposed fault-tolerant MLI is verified by simulation in MATLAB/Simulink environment and experimental results in a laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive power sharing control method of parallel‐connected hybrid inverters in microgrid. Normally the AC microgrid is composed of hybrid inverters, other power generation equipment and some loads in parallel. Droop control or virtual synchronous generator is usually adopted to control parallel inverters, so the output power ratio between each inverter is fixed by droop parameters. The input of hybrid inverter is PV panel and battery, so the power output ability of each hybrid inverter is different because of the different PV panel capacity, illumination condition, battery capacity and battery state of charge. Hence, the output power of some hybrid inverters is short or redundant sometimes, which makes microgrid unstable or causes power generation restraints. It is necessary to recognize the actual power capacity of each inverter and control the output power reasonably. This paper analyzes the characteristics of parallel‐connected hybrid inverters with droop control in microgrid. An adaptive power sharing method is developed to identify the unbalanced between the each inverter on DC bus. By adjusting the droop parameters, the output power of each inverter is regulated where the controlled parameters are defined in system transfer function with an optimal target. Experimental tests are executed following the numerical simulation. The results show that the output power of each inverter can be adjusted adaptively according to the practical needs. The excessive power from one inverter can be absorbed by the others. Therefore, the stability and the power capability in the system are both ensured by adopting the proposed methods. The outcomes of the study provide a reference to the development of the adaptive inverter in microgrid. [ABSTRACT FROM AUTHOR]

This paper presents a unified approach to the analysis of DC/AC converters based on an equivalent representation of their AC circuit as a series RLC circuit. The resonant DC/AC converter with reverse diodes was chosen as the basis of the examination, and the obtained ratios for this device were used to derive the main ratios describing the operation of the other types of DC/AC converters—voltage source inverters (VSI) and current source inverters (CSI). Based on the commonality of electromagnetic processes in power circuits, the expressions for the current through the inductance and the voltage of the capacitor are found in a compact form with their initial phases. The base ratios found through the analysis are normalized to the control frequency, thereby summarizing all possible operating modes. In this way, electromagnetic processes in a whole class of power electronic devices are described from general positions, which is convenient from a methodical point of view with a view to improving power electronics education. The proposed analysis approach is also applicable to three-phase DC/AC inverters, taking into account the specifics related to the presence of three phases and, accordingly, their mutual influence in the formation of the output currents and voltages. On the other hand, the basic ratios determined through the application of the unified analysis approach are also useful with a view to creating engineering design methodologies, in which the values of all circuit elements are determined with comparatively simplified calculation procedures. [ABSTRACT FROM AUTHOR]

Linear active disturbance rejection control (LADRC) has been extensively used in various areas due to its excellent disturbance suppression capability. When LADRC is applied to a single-phase inverter for tracking a sinusoidal reference signal, there is an inherent tracking inaccuracy problem. The steady-state error can be removed with the synchronous reference frame proportional-integral (SRFPI) control, which generates two orthogonal signals. In this paper, a modified control method based on compound SRFPI and LADRC for an off-grid single-phase inverter is put forward, where both output signals of SRFPI are employed as the reference signals of LADRC. Furthermore, a selective harmonic compensation method is performed by paralleling multiple SRFPI controllers to further reduce the selective harmonic components. Detailed theoretical analyses including system stability, robustness, performance of voltage tracking error and disturbance rejection are presented, which indicate that this organic combination fuses the merits of both SRFPI and LADRC without complicating the control design. Additionally, contrast experiments are conducted to demonstrate its effectiveness and superiority. These findings demonstrate that the system realizes a slight voltage tracking error and steady-state error, rapid dynamic response, and low total harmonic distortion (THD), especially under highly nonlinear load conditions. [ABSTRACT FROM AUTHOR]

Digital twins, a product of new-generation information technology development, allows the physical world to be transformed into a virtual digital space and provide technical support for creating a Metaverse. A key factor in the success of Industry 4.0, the fourth industrial revolution, is the integration of cyber–physical systems into machinery to enable connectivity. The digital twin is a promising solution for addressing the challenges of digitally implementing models and smart manufacturing, as it has been successfully applied for many different infrastructures. Using a digital twin for future electric drive applications can help analyze the interaction and effects between the fast-switching inverter and the electric machine, as well as the system's overall behavior. In this respect, this paper proposes using an Extended Kalman Filter (EKF) digital twin model to accurately estimate the states of a speed sensorless rotor field-oriented controlled induction motor (IM) drive. The accuracy of the state estimation using the EKF depends heavily on the input voltages, which are typically supplied by the inverter. In contrast to previous research that used a low-precision ideal inverter model, this study employs a high-performance EKF observer based on a practical model of the inverter that takes into account the dead-time effects and voltage drops of switching devices. To demonstrate the effectiveness of the EKF digital twinning on the IM drive system, simulations were run using the MATLAB/Simulink software (R2022a), and results are compared with a set of actual data coming from a 4 kW three-phase IM as a physical entity. [ABSTRACT FROM AUTHOR]

Temperature fluctuation is the primary reason for gradual failure of IGBT (Insulated Gate Bipolar Transistor) module in inverter system, and overall thermal management is an effective way to smooth temperature fluctuation and prolong the service life of IGBT module. Currently there are a series of problems with the module temperature management method of inverter system, including complicated control method, limited adjustment range, slow response, and poor control accuracy, etc. To cope with these matters, this paper aims to study a thermal management strategy for inverter system. At first, this paper built a model for temperature prediction and control of inverter system based on linear time-varying state space, the model measures system state based on estimation and can calculate the control variables with the mutual effect between different variables taken into consideration but without the necessity of system decoupling. Then, this paper proposed a thermal management strategy for inverter system based on predictive control and optimized it further. At last, the validity of the constructed model and the proposed strategy were verified by experimental results. [ABSTRACT FROM AUTHOR]

Microgrid (MG) bridges different inverter interfaced distributed energy resources (DERs) to operate and control efficiently within a grid. The multi‐master‐slave control strategy can provide robust control of inverter interfaced DERs in close proximity. The role of master DERs is significant in synchronising the slave DERs and reducing the effect of single unit failure. However, faulty master DERs and master side communication failure can also suddenly affect the synchronisation of the slave DERs. Unfortunately, previous studies on multi‐master‐slave MGs have not addressed this issue. So, in this paper, a synch invulnerable multi‐master‐slave control strategy is proposed by introducing a synch selector with the centralised secondary controller. The synch selector is designed to pick the synchronising references from the first available healthy master units while keeping other masters operational and sending the synchronising references to the slave DERs. It also significantly reduced the dependency on communication lines up to the possible extent. Real‐time simulation results are presented to demonstrate the effectiveness of the proposed control strategy. The presented results show that the unhealthy master units seamlessly can be side‐stepped, and the next possible healthy master unit can be assigned to send reference signals to the slave DERs, hence, resisting synch vulnerability. The observations also show accurate power‐sharing, full utilisation of DERs, and reliable and stable operation of the entire MG. [ABSTRACT FROM AUTHOR]

In photovoltaic (PV) systems, inverters have an essential role in providing an energy supply to meet the demand with power quality. Inverters inject energy into the grid considering that a renewable source is available; however, during intermittent periods or in the absence of power generation, the inverter remains inactive, which decreases the performance of the PV system. One way to increase the operation of inverters is to operate them as Volt-Amps Reactive (VAR) compensators to generate reactive power in the absence of renewable sources. The paper presents the development of a control scheme that allows the PV system's inverter to improve the power factor in the electrical system with or without PV power generation. The proposed control is based on using a sliding mode controller (SMC) current control loop and PI-based voltage control loop. The control scheme is developed in MATLAB/SIMULINK, and for real evaluation, a PV prototype is implemented. The control strategy efficiency is confirmed by the obtained results. The control scheme increases the practical utility of PV systems. Additionally, it improves the power factor in all cases during the injection of active power to the grid operating under intermittent conditions and/or in the absence of power generation. [ABSTRACT FROM AUTHOR]

The unexpected subharmonic oscillation with an evident asymmetric feature is one of the most salient dynamical behaviors in the grid-connected inverter, which will bring disaster to normal system operation. In view of time-varying equilibrium points and complex dynamical response of the system, this asymmetrical subharmonic oscillation is difficult to predict through traditional analysis methods. In this paper, a ripple-based current model is proposed to describe the special subharmonic oscillation of single-phase grid-connected DC–AC inverter with the One-Cycle Compensation (OCC) method. Based on the proposed model, the influence of dynamic response and the time-varying equilibrium points on the stability of the system are comprehensively analyzed, and the internal mechanism of asymmetric subharmonic oscillation is revealed. Furthermore, the critical points of the subharmonic oscillation at the beginning and the end of the whole circuit cycle are predicted. Particularly, a global stable operation boundary is identified from the ripple-based analysis to optimize circuit design. Finally, circuit experiments are performed to verify these numerical and theoretical results. [ABSTRACT FROM AUTHOR]

Today, transformerless inverters (TIs) are widely applicable in different solar photovoltaic (PV) grid-connected applications owing to their promising features, such as higher efficiency and power density. However, high-frequency common-mode voltage (CMV) in these topologies can result in high leakage current, electromagnetic interference, and lack of safety, reducing the whole system's reliability. To resolve the problems associated with TIs, this paper proposes a novel hybrid switched capacitor (SC)-based common-ground (CG) transformerless inverter (TI) topology, which can be applied in grid-connected photovoltaic (PV) applications. The boost inductor is integrated to achieve continuous input current and dynamic voltage gain. In addition, the proposed circuit comprises nine switches and two SCs with a single input DC source. It can generate five-level AC voltage with voltage boosting within a single-stage DC–AC power conversion. The working principles of the proposed topology, circuit description, and control technique are presented. Furthermore, the proposed inverter is comprehensively compared with other five-level TIs to show its superiority. Finally, a laboratory prototype is developed and tested to validate the practical viability of the proposed configuration. [ABSTRACT FROM AUTHOR]

Discussed in this study is a bidirectional power control technique for a three-phase grid connected inverter under different unbalanced grid conditions. Prior researchers have focused on either solving the unbalanced problem or controlling the power. However, this paper addresses both issues: solving the unbalanced problems of the point-of-common-coupling (PCC) voltages and grid currents, and reducing the large ripple in the real and reactive power while also applying a bidirectional power control under weak grid conditions. A phase-locked loop (PLL) is not required because a simpler PR controller was employed. A symmetrical components extraction method was used. Compared to previous symmetrical component techniques that used complicated transformations, this approach requires less computations. Since the unbalanced load issue has been resolved, other loads connected to the grid will not be impacted. MATLAB Simulink was used in simulation experiments, and a real-time interface platform dSPACE DS1202 was used to verify the proposed control method efficacy experimentally. [ABSTRACT FROM AUTHOR]

In distributed power generation systems, grid-connected inverters are becoming an attractive means of delivering the energy generated from renewable sources into the grid. However, the performance of the current controller drastically decreases in the presence of model uncertainty, grid harmonics, filter parametric, and grid impedance variations, which can jeopardize the entire system's stability. This paper presents a novel design of a super-twisting integral sliding mode control (ST-ISMC) strategy for the first time in the application of a three-phase voltage source grid-connected inverter. The designed controller has shown robustness and maintains a low total harmonic distortion (THD) in the presence of filter parameters drift, grid impedance variation, and grid harmonics distortion. The super-twisting action is added to remove the chattering problem associated with the conventional SMC strategy, and integral action is adopted to improve the grid's current steady-state error. The modeling and simulation of a complete system are carried out using MATLAB/SIMULINK. Finally, a real-world hardware prototype system is fabricated to demonstrate the performance and effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

To identify the parameters of variable flux reluctance machines (VFRMs), the input voltage value is usually obtained from the reference voltage indirectly. However, the reference and actual voltages may be different due to the nonlinearity of the open winding inverter when using zero-sequence current, leading to the inaccuracy of parameter identification. To solve this problem, this paper proposes an equivalent nonlinearity voltage error model of the open winding inverter to compensate for the input voltage of VFRM during the online parameter identification. Since in the proposed method the phase current direction is not required, the calculation time can be reduced. Moreover, in the developed parameter identification model of VFRM the derived equivalent nonlinear voltage error is used to correct the input of the identification model so as to improve the accuracy of parameters. Finally, the experimental results on the prototype VFRM are presented for verification. [ABSTRACT FROM AUTHOR]

The voltage rise problem due to the reverse power flow is one of the main obstacles to expanding the photovoltaic systems (PVSs) in distribution networks. In this paper, a decentralized control method for coordinated control of on-load tap changer (OLTC) transformers and PV inverters, is proposed for the voltage regulation of radial distribution networks. In this method, the allowable voltage range is divided into several zones, and appropriate corrective actions are adaptively taken according to each zone. To reduce the tension on the OLTC, first, the reactive power capability of the PV inverters is employed for the voltage regulation, and if it is insufficient, OLTC is used as the last solution. In this regard, the unused capacity of PV inverters is utilized for the reactive power compensation, considering the grid codes reactive power requirements. Furthermore, decentralized control based on a signaling method is used for coordination between OLTC and PVSs, which eliminates the need for communication links. Finally, the effectiveness of the proposed method is validated by the simulation results for the IEEE 33-bus distribution network, and the impact of different reactive power control methods on the number of OLTC operation is investigated. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive fuzzy sliding-mode control (AFSMC) system is investigated for an islanded inverter to achieve a high-performance power supply. A sliding mode control (SMC) law is designed initially to obtain both the voltage tracking error and the current tracking error of the inverter involved, to realize both the output-voltage regulation and the current protection with global stability. Moreover, to deal with uncertainties in the practical inverter system without the chattering phenomenon, an adaptive fuzzy system embedded with a self-adjustive translation width is developed to replace the switch term of the SMC. In addition, the adaptation laws, derived from the Lyapunov stability theorem, adjust the AFSMC parameters online to guarantee optimal and robust performance. Furthermore, the superior control performance of the proposed AFSMC is verified by a numerical simulation in MATLAB, producing experimental results on the prototype in comparison with the conventional SMC. [ABSTRACT FROM AUTHOR]

In high frequency AC (HFAC) distribution system, the resonant inverter is used to improve power quality and keep the stability of the output AC voltage. Aiming at the problems of poor output power quality and slow transient performance caused by unreasonable filter parameter design and load change during inverter operation, a single-phase H-bridge LCLC resonant inverter based on analog circuit controller implement is introduced in this paper for HFAC power distribution system (PDS). In this study, to design harmonic compensator and analyze the responsiveness of the inverter, it is necessary to analyze the output voltage total harmonic distortion (THD) of LCLC resonant inverter and the performance of the open loop system in detail. On the one hand, a proportional-integral-resonant (PIR) controller is designed to maintain the zero static error of the voltage output and suppress the output voltage THD of LCLC resonant inverter. On the other hand, an integral controller combines with phase-shift modulation (PSM) method is presented to effectively improve the transient performance of resonant inverter and provide the fixed frequency of the output voltage. On the basis of the above, the experimental prototype is implemented with the output AC voltage root mean square of 28 V, and the output voltage frequency for resonant inverter is equal to switching frequency. A rated output power of 130 W experimental platform is built to verify the effectiveness of the theoretical analysis, control strategy, and modulation method. [ABSTRACT FROM AUTHOR]

In modern power systems, the increasing penetration of renewables and power electronics, particularly inverter-based wind and solar power generation, is altering power system dynamics and bringing new stability concerns. One challenging issue that is attracting considerable attention is the wide range of power oscillations associated with multiple parallel grid-connected inverters. In such systems, the characteristics in terms of resonance and oscillation are significantly different from single-inverter systems. This paper investigates the mutual interaction and stability issues of multiple grid-interfacing inverters with LCL-filters in power-electronics-based power systems under various grid conditions. The investigation reveals that such interactions between power inverters and the grid may excite multiple resonances at various frequencies under certain grid conditions. The nodal admittance matrix concept, which was originally from power systems engineering, is adopted here. Moreover, this paper further develops an Interaction-Admittance model that can effectively describe these mutual interactions in terms of a physical network admittance. We apply our model to various scenarios such as stiff grid conditions and inductive grids with/without power factor correction capacitors. The results with the proposed framework demonstrate an intuitive interpretation of multi-inverter system resonance and instabilities. Finally, simulations and experiments on a lab-scale system are provided to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

For high-power electromagnetic (HPEM) applications at high-repetition rate, conventional microwave inverters based on pulse transformers are not practical. At high-repetition rates, the magnetic materials used in the inductive coupling saturate. In this paper, we present an alternate concept for an inverter based on the technology used for ultrawideband baluns which provides isolation through capacitive coupling. Design of the device is discussed through numerical modeling, and two implementations are built and demonstrated: a circuit element version and a transmission line version. The devices are demonstrated at charge voltages of 6 kV and repetition rates up to 100 Hz, with excellent performance between 20 MHz and 2.5 GHz. The circuit element device has a rise time of 445 ps with an insertion loss of less than 3 dB, while the transmission line device has a rise time of 240 ps with an insertion loss of less than 2 dB for most frequencies. The inverter is demonstrated as part of the feed network for a hyperband HPEM antenna with a differential input. [ABSTRACT FROM AUTHOR]

The instantaneous output power of the two-stage single-phase grid-connected photovoltaic (PV) inverter pulsates at twice the line frequency ($2f_{{\text{o}}}$), generating second harmonic current (SHC) in the front-end dc–dc converter and PV panel, which will affect the maximum power point tracking operation and deteriorate the overall conversion efficiency. The generating mechanism of the SHC is analyzed in this paper and it is pointed that in order to eliminate the SHC in the front-end dc–dc converter and PV panel, the voltage loop gain of the front-end dc–dc converter should be high enough at $2f_{{\text{o}}}$. Since there is a −180° phase abrupt at the resonant frequency of the input side filter capacitor and the inductor, the system may be unstable. To cope with this problem, the inductor current feedback active-damping scheme (ADS) is adopted. For further improving the loop gain at $2f_{{\text{o}}}$ , proportional–integral–resonant regulator with ADS (PIR + ADS) is proposed in this paper. Besides, a step-by-step closed-loop parameters design method is presented. Finally, a 3-kW two-stage single-phase grid-connected PV inverter has been fabricated and tested, and the experimental results verify the feasibility of the proposed control schemes. [ABSTRACT FROM AUTHOR]

This paper introduces a three-phase grid-connected inverter for commercial-scale photovoltaic systems. The circuit topology combines an ac-inductor-less active bridge with a parallel-connected pulsewidth modulation inverter acting as an instantaneous reactive power compensator. The active bridge, called a 120° conduction inverter, operates at a switching frequency equal to the grid frequency and outputs a 120° rectangular current, while the compensator eliminates the harmonic currents included in the rectangular current. The main advantage of this strategy is the reduction in size of the required ac inductor by a factor of 4, as well as the reduction of power losses in the switching devices. The theoretical analysis clearly shows that the compensator can synthesize a sinusoidal output current by controlling only instantaneous reactive power, thus eliminating the need for electrolytic capacitors. A 5-kW experimental setup validates the operating principle and the control method of the proposed inverter and exhibits an inverter efficiency as high as 99.2% with Si superjunction mosfets. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method to determine and control active and reactive power output of the virtual ocillator control-based inverter in grid-connected mode. An analytical expression is introduced to describe the quasi-steady-state relationship between the parameters of the inverter including its controllers, and the power injection and voltage at the inverter terminals. We introduce a new, complex valued parameter (K) to the conventional virtual oscillator control (VOC) scheme in order to control the inverter output power. We compare analytic and numeric solutions of the above analytical expression with time-domain simulation results, using different K values and line impedances to validate the analytical expression. In the second part of the paper, we design a controller: we use the above expression to derive K for given reference powers and use adaptive integrators to compensate for the remaining errors. We compare this control scheme to a method that uses PI controllers, and also to a simple decoupling method for independent control of active and reactive power. The controller based on the analytical method exhibits very good dynamic and decoupling performance. A single VOC-controlled inverter connected to a nonstiff grid is simulated in MATLAB/Simulink for demonstration, and is also validated using real-time simulations. [ABSTRACT FROM AUTHOR]

In this paper, a generalized droop control (GDC) is proposed for a grid-supporting inverter based on a comparison between traditional droop control and virtual synchronous generator (VSG) control. Both the traditional droop control and VSG control have their own advantages, but neither traditional droop control nor VSG control can meet the demand for different dynamic characteristics in grid-connected (GC) and stand-alone (SA) modes at the same time. Rather than using a proportional controller with a low-pass filter, as in a traditional droop control, or fully mimicking the conventional synchronous generator parameters in a VSG control, the active power control loop of the GDC can be designed flexibly to adapt to different requirements. With a well-designed controller, the GDC can achieve satisfactory control performance; unlike a traditional droop control, it can provide virtual inertia and damping properties in SA mode; unlike a VSG control, the output active power of an inverter with GDC can follow changing references quickly and accurately, without large overshoot or oscillation in the GC mode. Moreover, given specific controller parameters, the GDC can function as both a traditional droop control and a VSG control. The GDC's controller parameter design is more intuitive and flexible, and this paper provides a distinct design process. Finally, the effectiveness of the proposed control method is validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Motors and inverters are increasingly being used in vehicles. As more vehicle components are being adopted, requirement for safety and installation space are increasing. Growing attention is being paid to the use of six-phase permanent magnet synchronous motors (PMSMs) and their parallel control by two inverters, because of their reduced size and enhanced safety. This paper proposes a pulsewidth modulation (PWM) control algorithm for a six-phase PMSM. In low-voltage vehicle components such as electric power steering, the current is usually acquired with resistors placed under the low-side switching devices. In the proposed control algorithm, the neutral voltage of the two inverters is shifted to either a lower or higher voltage within a certain range to allow for the signal conditioning time delay after the switching device turns on or off, and the time taken for the phase current to rise or settle. The paper proposes a novel PWM control algorithm that ensures that the on-time of the low-side switching devices satisfies the restriction on current sensing with resistors and reduces the current in the capacitor at the same time. The work contributes to reducing the current in a practical configuration involving low-voltage vehicle components. [ABSTRACT FROM AUTHOR]

Voltage/VAR regulation (VVR) implemented by capacitor banks (CBs), on-load tap changers (OLTCs), and photovoltaic (PV)-associated inverters is effective to enhance voltage stability and reduce power loss. On the other hand, conservation voltage reduction (CVR) has been widely adopted in distribution networks to reduce load demand. Existing works mainly focus on each of them. This paper proposes a VVR method with CVR, forming a multi-objective optimisation problem which minimises (i) voltage collapse proximity indicator (VCPI), (ii) load demand, and (iii) power loss. Besides, PV power generation as uncertainty significantly impairs the VVR results. To deal with the uncertainty issue, this paper proposes a rollinghorizon framework to determine VVR and applies Taguchi's orthogonal array testing (TOAT) to model the uncertain PV power generation, achieving rolling-horizon-based multi-objective robust VVR. The proposed model is tested and demonstrated on the IEEE 33-bus and 69-bus systems, and simulation results verify that the proposed method can support robust solutions of the multi-objective VVR problem for decision-making. [ABSTRACT FROM AUTHOR]

A non-segmented PSpice model of silicon carbide metal-oxide semiconductor field effect transistor (SiC mosfet) with temperature-dependent parameters is proposed in this paper, which can improve the model's convergence and temperature characteristics. The non-segmented equations and the parameter-extraction method for the proposed SiC mosfet PSpice model are introduced first. Simulation and experiment results are given to verify the correctness of the model while considering the temperature-dependent parameters. The static characteristics of the model are verified by comparing the simulation curves with the static characteristic curves in the SiC mosfet's datasheet, and its dynamic characteristics are verified by comparing the simulation results with experimental results under different ambient temperatures (25, 75, and 125 °C) based on a double-pulse test platform. Moreover, the proposed non-segmented model, the conventional segmented model, and the model from the manufacturer are adopted and simulated in a full-bridge inverter. The simulation results show better convergence of the proposed non-segmented model. Therefore, an accurate and practical simulation model of SiC mosfet is provided for circuit design in this paper. [ABSTRACT FROM AUTHOR]

To reduce the common-mode voltage (CMV) and eliminate the CMV spikes for two-level voltage source inverters (2L-VSIs), an improved model predictive control (MPC) based CMV reduction method is proposed in this paper considering dead-time effects. First, an improved voltage vector (VV) preselection strategy is proposed to reduce the CMV spikes caused by the dead time. Second, a new hybrid VV preselection strategy based on a delay compensation strategy and a modified current sector division strategy is proposed to completely eliminate the CMV spikes. As the proposed hybrid VV preselection based MPC strategy makes full use of the six nonzero VVs of the 2L-VSI, the current total harmonic distortions and ripples are reduced. The simulation and experiments are carried out to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Multilevel inverters are now-a-days being applied in electric vehicles (EV). Considering the dynamic operating conditions of an EV propelled by an induction motor, this paper proposes a flexible discontinuous modulation strategy for three-level neutral-point-clamped (NPC) inverter that can shift modulation pattern seamlessly from sinusoidal pulsewidth modulation (SPWM) to discontinuous PWM (DPWM). The modulation scheme is generalized at each degree of discontinuity to ensure minimum switching losses for variable load power factors. Additionally, a hybrid voltage balancing strategy, which comprises two sets of compensating offset signals with complementary features, has been introduced to mitigate voltage deviation problem at neutral point of the inverter. The unique feature of the proposed hybrid balancing approach is that it generates uniform compensating neutral current regardless of the level of discontinuity. This results in identical and predictable voltage balancing dynamics for the entire modulation transition covering SPWM and DPWM. It has been shown that the proposed hybrid balancing strategy does not lose its unbalance compensation strength even during transition from one modulation pattern to another. The effectiveness of the proposed scheme for wide variations in operating conditions is studied through extensive simulation, and validated in experimentation using a prototype NPC inverter with induction motor loads. [ABSTRACT FROM AUTHOR]

A new controller for a grid-connected inverter with an LCL filter is proposed in this paper. The system is described by its complex representation, and the controller is designed using the complex root locus method. The complex representation allows a considerable reduction in the order of the system, simplifying the design task and making it possible to use advanced techniques, such as the complex root locus. The new complex controller adds an extra degree of freedom that makes it possible to move the poles of the systems and to improve the stability and speed of response compared with the conventional controls. This paper includes a detailed discussion of the effect of the gains of the controller on the root locus. The proposal is validated with simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the effect of negative-capacitance (NC) on germanium FinFET (GeFinFET) with the presence of fixed trap charges (${N}_{\text {ftc}}$) has been studied. The analysis of various parameters of NCGeFinFET has shown that the positive trap charges improve the device characteristics whereas the negative trap charges (NTC) degrade the performance of devices. Therefore, we have optimized properties of ferroelectric (FE) to suppress the degradation caused by NTC. Furthermore, the impact of ${N}_{\text {ftc}}$ has been studied on the output characteristics of NCGeFinFET inverter, and it has been shown that the degradation due to NTC reduces by optimizing the FE properties. It has also been demonstrated that NCGeFinFET exhibits excellently improved characteristics as compared to GeFinFET. [ABSTRACT FROM AUTHOR]

In grounded photovoltaic (PV) systems, dc leakage to earth is formed by the contribution of the PV modules, inverters, and dc circuitry. Ground faults in such systems occur when there is an unintentional connection between any dc-carrying conductor with a grounded surface or earth. On the occurrence of ground faults, dc leakage will be intensified and will flow through the earth or other conductive paths, before returning back to the source. Thus, it is highly probable that some portion of the dc leakage will attempt to return to the source through any low-resistance paths that exist in the nearby vicinity, for example, through nearby buried pipelines. Therefore, unattended dc leakage may induce stray current corrosion concerns on these pipelines. To this extent, this paper presents a detailed dc interference modeling for assessing the dc leakage activity in PV systems—particularly under undetected fault conditions. First, the modeling carried out embraces the topologically accurate consideration of all sources of dc leakage that are associated with the grounded PV systems. A second feature presented in the paper is the modeling of blind-spot dc faults and their impact on third-party infrastructure. [ABSTRACT FROM AUTHOR]

A power quality measurement system is introduced in this paper. While sampling with a high rate, it provides mains frequency synchronous voltage and current data in the form of 215 samples per cycle using a linear interpolation unit. The interpolation output sampling rate is provided by a mains frequency estimation unit, which conducts phase locking on the voltage measurements and additionally outputs the synchrophasor, frequency, and the rate of change of frequency. This algorithm is checked in simulations against the current standards, while discussing a phenomenon that is not yet taken into account by these standards: low-frequency interharmonic disturbances such as ripple control signals, which occur frequently in today’s power grids. To desensitize the system toward these, compromises must be taken when it comes to standard compliance under transient conditions. Thereafter, first measurements with an evaluation system are analyzed to get a first impression of the system response to real signals. [ABSTRACT FROM AUTHOR]

In this paper, speed control of solar powered single phase hybrid multilevel inverter fed induction motor using fuzzy proportional integral controller is proposed. The proposed control system has been developed using MATLAB/SIMULINK. Performance of the proposed controller is tested in reference speed conditions with step change. The parameter analyzed for the proposed controller is steady-state error and settling time. This is compared with the proportional integral controller. Proposed speed controller is tested with two speed region such as low speed region and high speed region. In low speed region, speed command is varied from 40, 60, and 80 rad/s with 0.6 s step time. In high speed region, speed command is varied from 100, 120, and 140 rad/s with 0.6 s step time. Corresponding, performance parameters are measured and analyzed for both regions with proposed controller and proportional integral controller. From the test results, fuzzy proportional integral speed controlled hybrid multilevel inverter fed induction motor outperforms than proportional integral controller. Finally, the results are verified experimentally. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of phase-locked loop (PLL) on the stability of LCL-type single-phase grid-connected asymmetrical cascaded H-bridge multilevel inverter (ACHMI) with synchronous reference frame proportional-integral (SRF-PI) grid current control under weak grid scenarios. The ACHMI system is composed of power stage circuit and control system, where the control system contains the dual-loop current control strategy established in the hybrid reference frame, the SRF-PLL, and the hybrid modulation method employed to synthesize the multilevel output voltage. The small-signal model of the whole ACHMI system is first established by using a simple step-by-step derivation method, and then, the small-signal analysis method is adopted to linearize the ACHMI, which is then utilized to derive the impedance model of the ACHMI system. Furthermore, an improved impedance stability criterion is derived, which is then employed to analyze the system stability. By using this criterion, the stability of the ACHMI can be evaluated with the variation of the bandwidth of PLL, the output power factor angle of the ACHMI, and the amplitude of the grid current reference signal under weak grid conditions. In this paper, a systematic design procedure for the optimal selection of the PI controller of the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system. With this design method, the dual-loop current control and PLL can be taken into account simultaneously when analyzing the stability margin of the ACHMI. Finally, the simulation and experimental results from a down-scaled grid-connected ACHMI prototype system are provided to confirm the validity of theoretical analysis. [ABSTRACT FROM AUTHOR]

Enhancement of dc bus voltage utilization for a five-level inverter with single dc source and capacitor-fed H-bridge (CHB) units is investigated in this paper. A carrier-based modulation technique is used for boosting the dc bus utilization, which is established by providing detailed mathematical analysis. The five-level inverter used here is realized by cascading a CHB unit to each phase of a three-level neutral point clamped inverter. The increase in dc bus voltage utilization owes to the pole voltage redundancies offered by CHB units. The floating capacitors of H-bridge units are balanced within a quarter fundamental cycle using the switching state redundancies of pole voltage levels. The aforementioned modulation technique allows the inverter to enhance the dc bus utilization from 0.577 $\text{V}_{\text{dc}}$ to 0.63 $\text{V}_{\text{dc}}$ under unity power factor. This enhancement is obtained in the linear modulation range without increasing the dc bus voltage, and thus, the inverter can operate without the presence of low-order harmonics in its phase voltages. The strength of this paper lies in its detailed mathematical analysis for finding out the limiting modulation index and power factor condition in the light of floating capacitor voltage balancing issue. Simulation as well as experimental verification of the modulation scheme is carried out on an induction motor drive under various operating conditions. It is shown that this carrier-based modulation technique is suitable for any single source inverter topology with one CHB unit per phase. [ABSTRACT FROM AUTHOR]

Finite control set-model predictive torque control (FCS-MPTC) has a fast dynamic response because this algorithm directly selects the optimal voltage vector by its cost function for induction machine drives fed by voltage source inverter (VSI). However, belonging to open-loop control paradigm, the FCS-MPTC has torque tracking error due to inevitable load disturbance and mismatched model parameters in reality. In traditional FCS-MPTC, the outer loop, i.e., speed loop, adopts a classic proportional integral (PI) controller, abbreviated as PI-MPTC. The lumped disturbance is only suppressed by a PI controller. However, pole placement of the PI controller is usually designed by cut-and-trial, which is difficult to simultaneously achieve optimal dynamic performance and optimal suppression of lumped disturbance. In this paper, the FCS-MPTC with mismatched parameters is first analyzed. Second, the deficiencies of the traditional PI controller are introduced. Third, disturbance feedforward compensation-based-model predictive torque control (DFCB-MPTC) of induction machine is proposed to compensate lumped disturbance and improve the performance of the system. Furthermore, a simplified stator flux observer is proposed, whose gain matrix is independent of rotor speed. Experimental results verify the feasibility of the proposed DFCB-MPTC. Compared with traditional PI-MPTC, the proposed DFCB-MPTC has better dynamic performance, steady performance, and stronger robustness. [ABSTRACT FROM AUTHOR]

This paper proposes an accurate and general method to calculate and characterize the couplings of patch antennas. It is found that the coupling effects of open-/short-circuited patches can be represented by J/K inverters. Unlike traditional ones, these J/K inverters should be with complex- and frequency-dependent values. Three different patch antennas are used to exemplify how to characterize couplings with J/K inverters. Once the values of J/K inverters are successfully extracted, the total equivalent circuits of these patch antennas can be easily given in a unified way. J/K inverters can also help us see how the couplings affect antenna bandwidth. To present advantages of the proposed method, comparison with traditional coupling calculation approach based on characteristic modes is conducted. Technical limitations and potential applications of the proposed method are also discussed. [ABSTRACT FROM AUTHOR]

An isolated single sourced multi-output dc/dc converter with a high-frequency link was proposed before to feed different cells of the Asymmetrical Cascaded H-bridge (ACHB) inverter. One of the fundamental advantages of the ACHB is that the main H-bridge is commutated with fundamental frequency, passing the majority of the inverter power. However, the isolated dc/dc converter needs to be connected to the main voltage source with high-voltage/high-frequency switches, which limits the power capability and the efficiency of the converter. In this paper, a switching pattern based on nearest level modulation method is proposed to command all the power to be transferred through the main H-bridge. Therefore, the power circulates between the auxiliary H-bridges with no need for high-voltage switches. As a result, a single-input single-output auxiliary converter is needed with only 5% of the power rating. This solution reduces cost and size while it improves the efficiency of the converter. Furthermore, the architecture makes the inverter more suitable for high power and high-voltage applications. The inverter switching strategy is based on programmable firing angles. The main dc-link of the grid connected inverter is controlled to achieve maximum power point tracking, while the dc/dc isolated converter is controlled to regulate the auxiliary dc-links. The proposed topology is verified by simulation and experimental results using a 1.5 kW hardware prototype. [ABSTRACT FROM AUTHOR]

Low-temperature plasma ion mobility spectrometry (LTP-IMS) is the method to identify some materials by measuring concentration of gas phase ions. IMS used in a wide range of laboratory-based biomedical research studies. A nanosecond pulse generator is necessary for LTP-IMS apparatus to enable direct analysis of various chemical compounds without having to evaporate the analyte or seek a solvent or any reagent. In this paper, a dual Marx pulsed generator for LTP-IMS Ionization power supply is proposed based on a new combination of some solid-state switches including insulated gate bipolar transistor (IGBT) and avalanche bipolar junction transistors (BJTs). The compact dual Marx generator is composed of a series of avalanche BJTs and an IGBT as the trigger switch, where its rise time is reduced from 100 to 5 ns by using an avalanche BJT in its command circuit. In this way, a controllable high-voltage pulse generator has designed, built, and tested. The proposed circuit can be used to generate the repetitive high-voltage pulses necessary for low temperature ionization in advanced IMS apparatus. The output voltage has an amplitude of up to 6 kV with pulse widths in the range of 40–1000 ns and pulse repetition rates up to 2 kHz, having rise time and fall time less than 10 ns independent of the load specifications. [ABSTRACT FROM AUTHOR]

We derive analytically expressions for the probability distribution of the propagation delay time of logic signals through a CMOS inverter when the inverter power supply voltage $V_{{\text{dd}}}$ (more precisely, gate voltage $V_{{\text{GS}}}$) is itself probabilistic for some reason (e.g., system noise or a random external electromagnetic disturbance). Since the propagation delay time is a function of the value of $V_{{\text{dd}}}$ , then some values of $V_{{\text{dd}}}$ may produce values of the inverter propagation delay time that cause the circuit in which the inverter resides to malfunction (e.g., by resulting in an inverter delay time value not conforming with the delay time margins for that circuit). Based upon the derived inverter propagation delay time probability distribution, we then derive a probability for the malfunction of a circuit containing a single inverter subject to such a stochastic $V_{{\text{dd}}}$. In this paper, we present no discussion of the application of our formalism to example probability density functions for $V_{{\text{dd}}}$ ; we rectify this situation by presenting three detailed such examples in a companion paper in this journal. [ABSTRACT FROM AUTHOR]

This paper addresses the resonance problem in a parallel-inverter-based grid-connected system. Harmonic interactions between inverters and the grid exhibit various number of complicated characteristics that threatens the system stability and power quality. In this paper, a method of harmonic resonance analysis is proposed to investigate the resonance problem in a multi-inverter grid-connected system based on resonance modal analysis (RMA) and participation factor (PF) calculations. Initially, an impedance-based analytical approach is employed and expanded to an electricity distribution network that is dominated by multiple inverters with LCL filters and proportional resonant controllers. Then, the RMA is introduced to investigate the resonant interactions among inverters and the grid. Specifically, harmonic resonance characteristics are addressed through transfer functions and the proposed method considering variation of inverter number, different inverter combinations, and critical system components. Finally, time domain simulations on the PSCAD/EMTDC platform are presented. The case study results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]