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Grid-forming (GFM) inverters are promising solutions for future power systems with high penetration of renewables. The successful design of GFM inverters is crucial for achieving current limiting, enabling them to withstand disturbances such as voltage sags and phase jumps in grid voltages. However, when the parameters are not properly tuned, a cascaded voltage and current controller can compromise grid stabilization performance due to issues like controller windup, post-fault recovery failure, and harmonic instability. To address this challenge, this paper proposes a dual control scheme consisting of GFM and current control that work in parallel. The dual control scheme incorporates emulation signal generators integrated with the dual controllers. This integration allows for adjusting their internal states during standby mode to track to references, enabling a seamless transition between the running and standby modes. Numerical simulations and experiments demonstrate that the proposed controller exhibits promising performance under both normal and faulted conditions. • The proposed controller eliminates the issues caused by the cascaded controller. • The proposed controller avoids transient instability during the current limitation. • The proposed emulation signal generator enables smooth switching between GFM and current control. [ABSTRACT FROM AUTHOR]

• Proposing an improved current controller structure to address low-order harmonics issue,. • Adopting an adaptive embedded-factor thought to improve dynamic performance,. • Considering different constraint conditions to design controller parameters accurately,. • Evaluation of the proposed controller by simulation and experimental results. This paper presents an improved current controller based on a series proportional integral resonant structure in synchronous reference frame in order to address low-order harmonics issue of the injected-grid current for three-phase grid-connected inverter. Additionally, to improve dynamic performance, an adapted factor is embedded into the proposed controller structure. Moreover, to design the parameters of the proposed controller, different constraint conditions are investigated. Based on the proposed controller structure and parameters design method, satisfactory steady-state and faster dynamic performances are both obtained in comparison to those of the conventional parallel proportional integral resonant controller. What's more, the proposed controller is easy to implement in practice. Simulation and experimental results are finally given to verify the effectiveness and superiority of the proposed controller. [ABSTRACT FROM AUTHOR]

• A new model of dust impact on grid-connected PV was proposed. • The dust characterization and effects in Sohar, Oman was investigated. • Experimental validation of the proposed model with the techno-economical evaluation presented. A grid-connected photovoltaic system was tested and investigated for the entire year under desertic weather exhibited. The system contains 1.4 kW PV and 1.7 kW inverter —the data was measured every second and used to model and evaluate the system performance. However, dust is one of the essential parameters that affect grid-connected photovoltaic performance, yield, and profitability. In this paper, a proposed model has been takes into consideration the dust impact on grid-connected photovoltaic performance in a novel way. The outcomes demonstrate that the proposed model precisely anticipated the system performance and validated through experimental results. However, it is found that the photovoltaic, inverter, and performance efficiencies are 10.80%, 94.00%, and 73.00%, respectively. Besides, the average yield factor is 141.39 kWh/kWp, and capacity factor is 19.64%. It concluded that the system productivity in Oman is within the prospected rate. The information in this paper is valuable for investors, researchers, and engineers interested in grid-connected photovoltaic and dust impact in Oman and neighboring countries. [ABSTRACT FROM AUTHOR]

The three-level inverter is extensively preferred in medium-voltage industrial applications over the conventional inverter due to its benefits. The performance of inverter is better when the space vector modulation (SVM) approach is preferred. However, the implementation of conventional SVM approach is more complex. In this paper, a decomposition-based new SVM algorithm for three-level inverter is proposed to reduce computational complexity and implementation time using a low-cost digital controller. Initially, the performance of the proposed SVM algorithm is studied through MATLAB simulation using the conventional switching sequence 0127. Further enhancing the performance, the proposed algorithm is implemented with various advanced discontinuous SVPWM strategies using the advanced switching sequences of 1012–2721 and 0121–7212. The no-load motor current THD and switching loss analysis for ADSVPWM and conventional SVPWM strategies at different modulation indices are presented is this paper for a comparison point of view. The no load motor current THD results obtained through simulation are validated experimentally by implementing the proposed algorithm on real-time interface tool through dSPACE, which is used to control constant V/F-controlled three-level inverter-fed induction motor. Further to show the effectiveness of the proposed technique, the experimental investigation is done on induction motor at loaded condition and the results are presented. [ABSTRACT FROM AUTHOR]

A novel single-phase transformerless dual-mode interleaved multilevel inverter (DMIMI) is proposed in this paper, which can inject a highly sinusoidal ac current to the grid even with the input dc voltage less than the peak grid voltage. Furthermore, dead-beat controllers are developed to directly calculate the optimal duty cycles in a digital control platform. As compared to the traditional dual-mode multilevel approaches, the DMIMI offers high efficiency, less number of components conducting simultaneously in each operation mode, and the capability of reactive power exchange. This paper presents the theoretical analysis and the experimental results obtained from a 1-kW prototype. The experimental results reveal that the proposed DMIMI can achieve high conversion efficiency and low leakage current as well as high quality grid current. [ABSTRACT FROM AUTHOR]

Reduction in the overall power devices such as power semi-conductor switches, gate drivers with the associated circuits and DC voltage sources reduces the size, cost, complexity in addition with enhancing the overall performance of the inverter. This paper presents a new and generalized multilevel inverter topology with reduced number of power components. To identify the significance of proposed inverter, the generalized formulae for all the parameters are calculated and a comprehensive comparison of different performance parameters are presented in tabular as well as in graphical form. Multicarrier pulse width modulation strategy is adopted for generating the switching pulses. Simulation of the proposed MLI topology for the 9-level and 17-level inverter have been performed in MATLAB/Simulink and the corresponding experimental results are incorporated for one unit and two units, respectively, experiments are carried out at RL load. Nevertheless, level per switch Ratio (L/S) is introduced and compared with some of the new discussed MLI topologies. Moreover, the switching and the conduction losses of the inverter are also calculated and incorporated in this paper. [ABSTRACT FROM AUTHOR]

• To present a single-phase T-type cascaded nine-level (TCHB) grid connected inverter. • Comparatively analyse TCHB against other fundamental MLI topologies. • State a novel PWM switching technique with one triangular carrier and eight references. • Provide mathematical modelling of the inverter operation and PWM method. This paper presents the control and application of a single-phase T-type nine-level cascaded H-Bridge (TCHB) multilevel inverter (MLI) topology. This paper focuses on the effectiveness of the TCHB and its control by presenting the inverter operation based on a PI current controller along with a Maximum Power Point Tracking (MPPT) scheme to realize a grid-tied photovoltaic (PV) system and a novel PWM method offering self-balancing at the DC-link capacitors. In order to attain gating signals for power transistors (IGBTs), the TCHB employs a PWM with one triangular carrier signal and eight reference signals. In addition, a mathematical modelling of the PWM method, along with a theoretical explanation of the self-balancing process has also been provided. To prove the effectiveness of the proposed TCHB topological design, it has been comparatively analysed against other fundamental MLI and symmetric CHB topologies. In addition, to corroborate the working of the control and the PV system application, employing TCHB inverter offering nine output voltage levels (±2Vdc, ±2¾Vdc, ±Vdc, ±½Vdc, 0), simulation and hardware results have been presented. [ABSTRACT FROM AUTHOR]

This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a 3rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup. [ABSTRACT FROM AUTHOR]

The paper deals with the construction design, thermal simulation analysis and cooler control proposal of double three-phase inverter suitable for electric vehicles. It gives a discussion on basic mechanical design and electric topology, both having strong influence on electrothermal operability. The paper also presents the thermal analyses of the converter operated at specified loading profile and gives control possibilities. Finally, the paper presents the cooler control design and demonstrates its functionality. The paper also discusses its impact on the converter lifetime and implementation. [ABSTRACT FROM AUTHOR]

To realize a soft-switching inverter with the advantages of a simple structure, high efficiency, low-voltage stress, and easy to control, a novel parallel resonant dc-link inverter with the function of pulse current regeneration is proposed in this paper. All switches in the inverter main circuit can achieve zero-voltage switching (ZVS) turn-on and ZVS turn-off. In addition, all switches in the auxiliary commutation circuit (ACC) can achieve soft switching. The power in the ACC is small. Freewheeling diodes in the inverter turn off under zero current condition, which can reduce the reverse recovery loss of freewheeling diodes. In addition, the bulk capacitors are avoided in the circuit and there is no neutral point potential variation problem. At the same time, the zero-voltage duration is independent of the load current, and the time of transition can be selected freely. According to the equivalent circuits in different operation modes under the proposed modulation strategy, the operation principle, soft-switching implementation condition, and parameter design procedure of the proposed inverter are analyzed successively in this paper. Finally, a 10 kW, 10 kHz soft-switching inverter prototype with insulated gate bipolar transistor based switches is built. Experimental results are given to demonstrate the validity and features of the soft-switching inverter. [ABSTRACT FROM AUTHOR]

This paper presents an enhanced current controller for improving the performance of a class of single-phase grid-connected inverters operating in weak and distorted grid conditions. An inverter designed to operate at normal (strong or stiff and clean) grid conditions may not perform satisfactorily during weak and distorted grid conditions. One major reason is the interfering dynamics of the synchronization or phase-locked loop (PLL). This paper proposes an enhanced control structure for a popular class of single-phase inverters to address this problem. The proposed idea is to include the PLL state variables into the main inverter controller thereby minimizing the undesirable interactions of the PLL with the other components. A method for optimally designing the controller gains is also proposed. Compared to the conventional one, the proposed controller is shown to have a more robust performance over a substantially wider range of weak and distorted grid conditions. Extensive simulation and experimental results are presented to validate the proposed controls. [ABSTRACT FROM AUTHOR]

Capacitor-current-feedback active damping has been widely used in LCL-type grid-connected inverters. However, the damping performance is deteriorated due to the negative equivalent resistance resulted by the digital control delays, and thus the grid-connected inverter is apt to be unstable under the grid impedance variation. To address this issue, this paper proposes the capacitor-current proportional-integral (PI) positive feedback active damping method that can ensure a positive equivalent resistance almost within the Nyquist frequency, i.e., the full controllable frequency range. In theory, the proposed damping method can be implemented by feeding back the capacitor current through a PI function. However, the integral term will continuously accumulate the noise and dc bias arising from the feedback signal. To overcome this drawback, a more practical implementation solution is drawn in this paper. Furthermore, a straightforward design procedure is presented for the convenience of selecting the proper controller parameters. With the proposed damping method and its practical implementation, high inverter robustness against the grid impedance variation can be achieved. Experiments are performed on a 6-kW prototype and the experimental results are in well agreement with the theoretical expectations. [ABSTRACT FROM AUTHOR]

• The dynamic model of different kinds of air-to-water heat pumps is presented. • Single-stage (SSHP), multi-stage (MSHP) and inverter-driven (IDHP) units are considered. • The detailed energy loss modelling linked to on-off cycling is shown. • Heat pump control algorithms can be optimized by means of the developed models. • Cycling losses have a significant influence on SSHPs seasonal energy performance. In this paper, the impact of on-off cycling losses on the seasonal energy performances of three reversible air-to-water heat pumps having equivalent thermal performance at full load but different power modulation capacity is discussed by means of a series of dynamic simulation models. The analysis of the heat pump performance at partial load, the development and comparison of different control algorithms for heat pumps and, finally, the modeling and evaluation of the degradation effect due to the heat pump on-off cycles at partial load conditions are numerically investigated by means of a series of innovative TRNSYS models not available in the software standard library. The models are able to take into account the variation of the heat pump performance at partial load conditions for multi-stage, inverter-driven and single-stage devices. The findings of this paper point out that the energy losses introduced during the start-up transient of the heat pump has a significant impact on the overall energy performance of the system only for single-stage units, which perform on-off cycles during the whole season, with a decrease of the seasonal performance factor (SPF) up to 12%. On the other hand, modulating heat pumps (i.e. multi-stage and inverter-driven units) avoid carrying out on-off cycles and, of course, cycling losses for a significant part of the season according to their enhanced modulation capacity. It is shown how the accurate dynamic simulation of heat pump-based systems is a useful tool for HVAC designers in order to optimize their control system parameters, with the aim to reduce the compressor maximum hourly number of cycles. [ABSTRACT FROM AUTHOR]

The staircase modulation strategy is the best choice for asymmetric cascaded H-bridge multilevel inverter (ACMI) because it makes the output voltage to present a high number of levels and makes one of the ACMI modules to operate at low frequency. However, the staircase modulation is usually employed without giving its deserved attention. This paper presents a clear understanding of the staircase modulation strategy and its applications in both isolated and grid-connected ACMI.  The main novelty of this paper is the obtaining of the switching function for each module. The principle of operation is carefully described, also indicating how to command the ACMI transistors. The output voltage of the two superior modules is evaluated for different values of iterations. Special attention is given to the power distribution among the ACMI modules when the staircase modulation is applied. It is demonstrated on how the power is processed in each module considering an ACMI with three modules. The analysis is presented showing the staircase modulation within a closed-loop control strategy for isolated and grid-connected modes of operation, showing that the content of this paper is valid for both modes. Experimental results clarify and show the efficacy of the content presented in this paper. [ABSTRACT FROM AUTHOR]

Emulation of an electric machine allows the testing of a drive inverter and controller of an electric drive system, prior to the manufacture of a machine prototype. This paper presents the emulation of a variable flux machine (VFM). The VFM emulator system proposed in this paper uses a detailed look-up table-based machine model for the purpose of emulation. This allows the emulator to mimic all machine magnetic and geometric behaviors such as saturation and torque ripple. In addition, the machine emulator proposed in this paper uses high-performance high-bandwidth linear amplifiers as power amplifiers. This enables a high bandwidth; leading to a high accuracy machine emulation. A detailed control description for the proposed machine emulator system and a machine model look-up table data verification against a prototype machine is initially presented. Experimental results are then presented to validate the utility of the proposed VFM emulator system to emulate various machine transient behaviors at different magnetization levels. Experimental results obtained from the emulator are subsequently compared against the experimental results obtained from a prototype VFM drive to verify the emulation accuracy. [ABSTRACT FROM AUTHOR]

One promising solution for future large wind turbine power conversion is to use medium-voltage power conversion systems for high efficiency and high power-density, e.g., by using a cascaded structure presented in this paper. However, a medium-frequency (MF) oscillation issue was observed while testing the experimental prototype of the above system. Given the complex multivariable coupling models of the multiwinding transformer and multiple inverters, conventional single-variable theories are not suitable. Therefore, this paper presents a new decoupling analysis method. Using a proposed linear transformation matrix, the output currents of multiple inverters can be transformed to a summation (grid) current and difference currents, where the former is the summation of inverter currents and the latter are the differences between currents of any two inverters. This transformation has enabled the use of single-variable theories, e.g., Bode diagram to analyze the summation current and difference current separately. It was found that the MF oscillation issue is caused by the equivalent impedance of the summation current being much larger than that of the difference current. Specifically, using small controller parameters cannot ensure the grid current quality and using large parameters may cause oscillation in the difference current. The proposed method can provide guidelines to design the parameters of current regulators and filters in multiple-inverter systems. Experimental results of a downscaled wind energy conversion system are presented to verify the proposed method. [ABSTRACT FROM AUTHOR]

In islanded microgrids, voltage source inverters working in parallel are expected to provide regulation of the local frequency while granting active power sharing. This paper presents a local control approach at each inverter based on an event-driven operation of a parameter-varying filter. It ensures perfect active power sharing and controllable accuracy for frequency restoration without requiring the exchange of control data between inverters over the communication network. This paper includes stability analysis and design guidelines for the control parameters using a modeling approach that considers the interaction between inverters. Selected experimental results on a three-inverter laboratory microgrid corroborate the effectiveness of the proposed control scheme, and outlines its advantages with respect to previous similar schemes and the performance cost that implies not using communications. [ABSTRACT FROM AUTHOR]

Three-phase grid-connected inverter modeling depends on the equivalent resistance and inductance between the inverter and the grid. However, these parameters are not fixed during the operation of the inverter and vary with the operating conditions. In this paper, a new globally stable adaptive controller is proposed to estimate these values online and update the controller during its operation. A model reference adaptive system (MRAS) based on two fictitious quantities with no physical significance is utilized, namely $M = v \cdot i^*$ and $N = v^* \times i$ , where $v$ and $i$ are the steady-state values of voltage and current in synchronously rotating frame of reference. Detailed stability analysis of the proposed estimation technique has been presented using a Lyapunov energy function-based approach proving the global stability of the technique. Small-signal modeling and analysis of the proposed scheme has also been presented so as to understand the local dynamics of the system. The guidelines to select the parameter of the proposed MRAS system along with updating the controller are elaborated in this paper. Detailed simulation based on MATLAB/Simulink and PLECS, along with experimental studies through a Texas Instruments TMS320F28377S microcontroller, validates the feasibility of the proposed control architecture. [ABSTRACT FROM AUTHOR]

The supply-side current of an inverter-fed induction motor (IM) is easily accessible and less affected by noises than the motor stator current. This paper proposes a novel sensorless speed estimation method for an IM using the spectrum of the supply-side current. However, due to the influence of fundamental supply frequency, it is difficult to carry out the speed detection straight from the supply-side current signal. In this paper, an analytic model for characterizing the supply-side current of an inverter-fed IM using the modulation theory and the switching function concept is developed. Then, the Hilbert transform is applied to extract the speed harmonic component from the supply-side current. Finally, an interpolated Goertzel algorithm is put forward to enhance the estimation precision of IM speed. The performance of the proposed sensorless speed estimation method is proved by the speed estimation results obtained from hardware experiments of an IM fed by an inverter under different load conditions. [ABSTRACT FROM AUTHOR]

In order to improve the conversion efficiency and mitigate the EMI problem of conventional hard-switching inverters, a new soft-switching DC-AC inverter with a compact structure and a low modulation complexity is proposed in this paper. In the proposed structure, resonant inductors are connected in series for the arm branches, and resonant capacitors are connected in parallel for the neutral point branches. With the help of resonant components, the proposed structure achieves zero-current switching on the arm branches and zero-voltage switching on the neutral point branches. When compared with state-of-art soft-switching topologies, the proposed topology does not need auxiliary switches. Moreover, the commutation algorithm to realize soft-switching can be easily implemented. In this paper, the principle of the resonant operation of the proposed soft-switching converter is presented and its performance is verified through simulation studies. The feasibility of the proposed inverter is evaluated experimentally with a 2.4-kW prototype. [ABSTRACT FROM AUTHOR]

Due to their run-time reconfigurability, short time-to-market, and lower prototype costs, FPGAs have become increasingly popular since their introduction. They found use in a wide variety of applications, including high-performance computing. However, when compared to ASICs, FPGAs offer lower performance, and they are power-hungry devices with low energy-efficiency. The emergence of Approximate Computing (AxC) represents a significant advancement in terms of enabling technology when applied to FPGA-based computing platforms. It has been effectively exploited in several application fields, achieving significant savings in energy and latency through a selective degradation of the output quality. Nevertheless, a generalized and systematic methodology for FPGA-based circuit design is still lacking. Indeed, most of the methods target ASIC-based systems, and, consequently, they offer minimal advantages or even an increase in resources when synthesized for FPGAs due to the architectural differences between the technologies. In this paper, we attempt to address this shortcoming by introducing our method for designing combinational logic circuits. It is based on and-inverter graph rewriting and multi-objective optimization, aiming for optimal trade-offs between quality of results and hardware overhead. Extensive experimental campaigns empirically prove that both generic logic and arithmetic circuits benefit from this approach. [ABSTRACT FROM AUTHOR]

The increasing penetration of renewable energy systems into the global energy matrix is a necessity for sustainable development. The benefits impact the well-being of humanity and the environment directly. However, these power generation systems demand reliable controllers to regulate the current injection into the electrical grid. Therefore, this paper presents a smart parametrisation for a robust adaptive proportional integral controller applied to grid-injected current control of a voltage inverter source with an LCL filter. Controller parameter optimisation and the initialisation of their gains are performed using the particle swarm optimisation algorithm. Three cost functions are assessed on controller parametrisation, considering the current tracking error minimisation and control action limitations: integral of absolute error (IAE) + integral of absolute control action (IAU), integral of square error (ISE) + IAU, and integral of the time-weighted absolute error (ITAE) + IAU. A framework for performance analysis and an in-depth discussion are presented, providing a systematic decision-support methodology for controller configuration. The function determined as the best one is implemented experimentally and compared with a designer's experience-based robust adaptive proportional integral controller using a hardware-in-the-loop test bench, where the improvements in controller performance are corroborated, contributing to the enhancement of energy quality in renewable energy systems. In addition, the controller's robustness is evaluated on a weak grid and an uttermost weak grid, where it presents high robustness and global stability. [ABSTRACT FROM AUTHOR]

The high-level goal of this research work is to enhance solar integration into power distribution grids with a lower cost and less complexity. High penetration levels of solar can lead to power quality issues at the point of interconnection such as flicker and voltage violation. This paper presents a novel Delta-Q approach that determines the most appropriate amount of reactive power support independent of the time step. The proposed scheme is embodied in the solar smart inverters' Volt-VAR control. It concurrently mitigates voltage violation and smoothens the voltage profile in areas where the solar irradiance is highly intermittent. The performance of the proposed control scheme is evaluated on the Typhoon HIL digital twining testbed along with the dSPACE MicroLabBox rapid control prototype unit. The real-time analysis shows the effectiveness of the proposed technique in lowering voltage violations and also mitigating voltage fluctuations. • A novel Volt/VAR control is proposed for smart solar inverter. • The proposed control strategy contributes to power quality enhancement in smart grids. • A digital twining testbed is utilized for validation/verification. • The proposed control scheme brings the cost and complexity down. [ABSTRACT FROM AUTHOR]

Thermal stress is one of the most important factors leading to power module failure. Under the load condition of high current with low fundamental frequency or largely changed load current, it would cause high junction temperature swing amplitude (JTSA) of chips, which could accelerate the failure of power module. To address this issue, this paper proposes a dual fuzzy logic controller‐based active thermal control (ATC) strategy to reduce the JTSA of chips in cases of variable power profiles. Two fuzzy logic controllers are designed to reduce the JTSA of chips by adjusting the switching frequency and pulse width modulation (PWM) strategy, respectively. One fuzzy logic controller is designed to reduce the transient JTSA of chips, which is done by changing the switching frequency according to the fundamental frequency and transient JTSA. The other one is to reduce the mean JTSA of chips, which is implemented by regulating the switching frequency and PWM modes according to the mean junction temperature and its variation. The minimum one is selected as the switching frequency of power inverter. Finally, the effectiveness of the proposed ATC strategy is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a model predictive control strategy for 15 level Packed-U-Cell inverter that satisfies multiple-objectives of low current total harmonic distortion (THD), capacitor voltage balances, supply of desired active and reactive power, as well as lower switching and lower voltage stresses on the switching devices. The proposed device performs well under dynamic conditions and can successfully track the current command during step changes in the power demand. A detailed modeling is presented and discussed. MATLAB/Simulink is used for obtaining the simulation results, and the results are validated in the real time by using a hardware-in-the-loop (HIL) Typhoon 402 real-time emulator. [ABSTRACT FROM AUTHOR]

The presented topology in this paper represents a boosting topology known as extended boost active switch‐controlled switched inductor Z‐source inverter (EBASCSI‐ZSI). The presented topology has the ability to provide high boost output voltage with lower shoot‐through duty cycle. Three existing topologies in the field of Z‐source inverter, namely, qZSI, DA‐qZSI, and CA‐qZSI, have been compared with the presented topology. It has been found that the boosting factor of the presented topology is higher compared to the three topologies. The presented topology has used the same number of inductors and a less capacitor compared to CA‐qZSI topology, the same number of inductors and capacitors as compared to DA‐qZSI topology, a more capacitor, and an inductor compared to qZSI topology. The voltage stress across the capacitors of the presented topology is approximately the same compared to CA‐qZSI topology at higher shoot‐through state, and the voltage stress is more compared to DA‐qZSI and qZSI topologies at the same shoot‐through state. The current stress across the inductors of the presented topology is similar across some inductors of the DA‐qZSI and CA‐qZSI topologies while in some other inductors, it is lower than that of CA‐qZSI topology. The presented topology has been designed with a common ground between the source and inverter bridge while drawing continuous current from the source. The simulation model and its hardware prototype have been developed in the laboratory. The theoretical formulae obtained from the proposed model are matching with outcome of the simulation and hardware model. [ABSTRACT FROM AUTHOR]

The demand for very efficient and top-performing power converters and drives is rising, which requires a new controlling strategy for the drive system. The induction motor (IM) and quasi-ZSI (q-ZSI) have elicited increasing interest in electric vehicle (EV) applications due to their unique features and benefits. However, it requires a perfect controlling scheme to reduce torque ripple and achieve a fast and dynamic IM response. The study in this paper has been carried out on a q-ZSI (impedance source inverter)-supplied IM drive. The PI controller, together with a fuzzy logic controller (FLC), is used as a speed regulator. The FLC with speed regulation reduces the torque ripple and SMC chattering of the IM. The sliding mode controller (SMC) replaces the two current PI controllers of indirect field-oriented control (IFOC). The proposed hybrid control strategy FLC-SMC-IFOC is implemented for the IM drive. The control system is implemented on the MATLAB/Simulink software and the results are compared with the conventional IFOC control. The proposed system results in improved dynamic response, minimized torque ripple, and fast convergence. [ABSTRACT FROM AUTHOR]

This paper presents a dual-motor drive system with a three-phase two-level inverter for independent speed control of a three-phase motor and a single-phase motor. The single-phase motor is connected in series between the neutral point of the three-phase motor and the midpoint of two split DC-link capacitors. As the single-phase motor current is a zero-sequence component flowing in the three-phase motor, it does not affect the operation of the three-phase motor. The proposed drive system can reduce the number of power switches compared with the conventional drive system that uses a single-phase and a three-phase inverter. Thus, the proposed system can reduce the cost of the drive system. Simulations and experiments are presented to verify the proposed drive system. [ABSTRACT FROM AUTHOR]

• A mathematical model for inverters' connection transients in weak and strong grids. • An improvement of transients using a phase limiter algorithm. • A set of experiments which validates the proposal. • Analysis of virtual impedance and measurement filter dynamics. This paper derives a mathematical model suitable for analysis of connection behavior of the inverter-based grids and, using that model, it presents guidelines to control grid-forming inverters' rate of change in frequency as function of output power (virtual inertia), or in other words "measured power filters". Furthermore, in order to improve the transient response, an angle difference limiter control is proposed. An angle difference limiter is a control algorithm which is constantly checking the angle difference between the inverter and the grid in the connection point limiting power peaks during the transients. The performance of the angle difference limiter is analyzed in detail and validated with an experimental microgrid consisting of two three-phase inverters and a variable load. The paper analyzes the connection of inverters in weak and strong grids validating the performance of the proposed angle difference limiter. [ABSTRACT FROM AUTHOR]

Power converters often suffer the disturbance from input source or load during operation. The disturbance could cause large overshoot and harmful oscillation and even make the power converter break down. In order to ensure the reliability of the converter, it is necessary to accurate design the dynamic characteristics of a power converter, namely, the settling time and the overshoot. However, there is no quantitative dynamic characteristics design method of power converters so far. In this paper, an eigendecomposition-based (ED) dynamic characteristics design method is firstly proposed for the quantitative dynamic characteristics design of power converters and is employed into a three-phase grid-connected inverter. Then, the control-parameter regions of the three-phase inverter that satisfy the indexes of the settling time and the overshoot are obtained by using the proposed ED dynamic characteristic design method. Finally, the effectiveness and correctness of the proposed ED dynamic characteristics design method is verified by circuit simulation. Therefore, this paper provides an accurate and quantitative dynamic characteristic design method for power converters, which is helpful to improve the reliability of power converters. [ABSTRACT FROM AUTHOR]

This paper presents a novel DSO support tool with visualisation capability for forecasting network congestion in distribution systems with a high level of renewables. To incorporate the uncertainties in the distribution systems, the probabilistic power flow framework has been utilised. An advanced photovoltaic production forecast based on sky images and a load forecast using an artificial neural network is used as the input to the tool. In addition, advanced load models and operating modes of photovoltaic inverters have been incorporated into the tool. The tool has been applied in case studies to perform congestion forecasts for two real distribution systems to validate its usability and scalability. The results from case studies demonstrated that the tool performs satisfactorily for both small and large networks and is able to visualise the cumulative probabilities of nodes voltage deviation and network components (branches and transformers) congestion for a variety of forecast horizons as desired by the DSO. The results have also shown that explicit inclusion of load‐voltage dependency models would improve the accuracy of the congestion forecast. For demonstrating the applicability of the tool, it has been integrated into an existing distribution management system via the IoT platform of a DMS vendor, Atos Worldgrid. [ABSTRACT FROM AUTHOR]

Inverter transformers are one of the key components in a PV plant and their operating patterns are considerably different from that of transformers in a substation. Moreover, these transformers experience higher level of harmonics generated by the inverters. Therefore, investigating the ageing profile of the inverter transformer is a timely requirement. In this paper, the ageing of inverter transformers in a medium-scale solar PV plant is studied by utilizing various real-time measurements including load current, top-oil temperature (TOT), ambient temperature, moisture in top oil, solar irradiance and individual current harmonics. An updated moisture-dependent thermal model (MDTMH), with consideration of current harmonics is developed to estimate the hot-spot temperature (HST). The influence of weather conditions, which directly determine the load current of inverter transformers on the loss of life (LOL) of an inverter transformer is also investigated. Furthermore, the effect of current harmonics levels on the inverter transformer's HST and LOL is explored. Finally, comparisons of HST and LOL of inverter transformers connected to PV arrays with three different tracking technologies, i.e., fixed-tilt, single-axis and Dual-axis PV arrays are performed. [ABSTRACT FROM AUTHOR]

The power quality of virtual synchronous generator (VSG) inevitably deteriorates in the presence of local nonlinear loads and distorted grid. In this paper, the conflict involved in the simultaneous elimination of distortion for both the inverter local load voltage and the grid exchanged current is first described. A unified control structure is presented that enables a tunable tradeoff between the two constrained harmonic sources. Then, a hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop. The local voltage harmonic control loop aims to scale down the inverter output impedance via a negative feedback loop, while the grid current-controlled compensator is intended to counteract the adverse effects from a weak grid via an additional voltage, which leads to substantially lower total harmonic distortion for both the local load voltage and the grid current at the same time. Small-signal modelling is performed to investigate the system stability and its robustness to parameter perturbations. The effectiveness of the proposed methodology is verified using hardware-in-the-loop simulations. [ABSTRACT FROM AUTHOR]

This paper focuses on the current control of single-phase LCL-filtered grid-connected inverters in the presence of parametric uncertainties and weak grid condition. Therefore, a novel neural network dynamic surface control (NNDSC) method is proposed by overcoming the problem of 'explosion of complexity'. In addition, radial basis function neural networks (RBFNNs) are employed to approximate the system parametric uncertainties. Furthermore, by considering practical considerations, a novel state observer (SO) is designed to estimate the inverter-side current and capacitor voltage. As a result, additional current and voltage sensors are not required, which makes the implementation of the proposed approach straightforward and reliable. The origin neighbourhood convergence of estimated and tracking errors is assured through Lyapunov stability theorem and Young's inequality. The effectiveness and performance of the proposed NNDSC+SO approach is demonstrated through MATLAB/Simpower simulations in view of the reference current changes, LCL filter parametric uncertainties and weak grid condition. [ABSTRACT FROM AUTHOR]

The conventional selective harmonic elimination method of random pulse width modulation (RPWM) is only suitable for the two‐level inverter. Furthermore, when the harmonics below 6 kHz are selectively eliminated, it is easy to cause a low average switching frequency of the inverter, which leads to the increase of load current distortion rate. This paper proposes an RPWM selective voltage harmonic elimination method for a single‐phase five‐level MPUC (modified packed U‐cells) inverter based on cell division. The MPUC inverter is supposed to be divided into three series cells, and the carrier stacking strategy is used to realize the coordinated control between each cell. In the process of RPWM, the average switching frequency can be controlled within a certain range by selecting the random number. This method is divided into normal mode and master–slave mode. In the normal mode, the selective harmonic elimination is realized by the method of cancelling the front and back terms of Fourier series in each cell. In the master–slave mode, the master cell is mainly used for fundamental power output, and the slave cell is mainly used for RPWM selective harmonic elimination. The effectiveness of the proposed method is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a detailed implementation of a current source inverter using unipolar sinusoidal pulse width modulation. This method is uncommon in these types of inverters and the semiconductor devices, integrated circuits, sensors, and filters used in conjunction with the TMS320F28379D microcontroller will be discussed. The inverter was tested in both an open and closed loop with a proportional resonant controller. Satisfactory results in terms of the harmonic distortion factor at the voltage output and the regulation indices for lineal loads were obtained. The response circuit demonstrated its viability for the subsequent connection to an electrical distribution network. [ABSTRACT FROM AUTHOR]

The paper presents a novel approach for low-order harmonic power mitigation in a single-phase, three-level DC/AC inverter. Traditionally, a bulk electrolytic capacitor is used at the DC bus to eliminate the low-frequency ripple. However, owing to the low-frequency components and large capacitor, this technique is not a practical solution. A new active filtering technique using a ripple port without an external circuit or additional switching power devices is proposed. The new technique harnesses the superior features of switched-capacitor circuits to create a topology with a multiport structure. As a result, a small DC-link capacitor can be applied by controlling the modulating reference waveforms between the different ports of the inverter. Additionally, the use of fast wide bandgap devices will allow for smaller passive components, and with high operating temperatures, the heat sink size can be greatly reduced. The theoretical analysis of the ripple reduction technique is explained in detail. The prototype was built in a laboratory, and experimental results are provided. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a three‐phase single‐stage grid‐connected photovoltaic (PV) system with active power filtering capability by means of a three‐level T‐type inverter is presented. The system is intended to fulfill many functions: harmonic mitigation, unity power factor operation, maximum power extraction from PV source, and so on. For the proposed system to achieve these tasks with a good dynamic performance, a new control strategy based on the fuzzy logic controller is developed. Fuzzy control has three main stages and each one requires many settings or selection of parameters. A new approach of setting the scaling factors which considerably affect the system's response is proposed. Furthermore, a methodology to properly set the fuzzy rules is suggested. The electrical power chain of the system comprises a farm of a PV source, three‐level T‐type inverter space vector pulse width modulation controlled, inductor filter, non‐linear load, and the utility grid. To evaluate the performance of the proposed control, a processor‐in‐the‐loop is performed as a hardware verification of the inverter control algorithm using a low‐cost STM32F4 discovery board, while the power circuit plant is modeled in the host computer using Matlab/Simulink. The obtained results are very satisfactory and confirm the role of each component, especially in terms of maximum power tracking, power quality, unity power factor operation, and control robustness. [ABSTRACT FROM AUTHOR]

Summary: The switched capacitor differential boost inverter (SCDBI) is a single‐stage single‐phase step‐up bidirectional inverter, in which the voltage gain lifts as the number of switched‐capacitor cells increases. When this inverter is applied to grid‐connection as herein proposed, its capacitive output‐voltage feature enables a grid current with low ripple, even when a simple L filter is employed. In addition, the SCDBI is free of high frequency common mode voltage, which mitigate the common mode current circulation between the input and output sources. These attributes favor the employment of this inverter in grid‐connected systems. Although these are positive aspects, the SCBDI also presents some challenges related to its nonlinear voltage gain and high‐order dynamic models. In this paper, a reduced order dynamic model is derived to simplify the SCDBI modeling and a static gain linearization technique is proposed in order to simplify the control strategy, therefore enabling the use of classical control methods. Experimental results achieved from a 250 W prototype, dc input voltage of 60 V, and electrical grid of 220 V rms, corroborated the inverter operation, in which a peak efficiency of 90% and a grid‐current total harmonic distortion less than 5% were reached. [ABSTRACT FROM AUTHOR]

Summary: An effective peak current‐limiting control strategy is presented in this paper, for improved dynamic performance of a grid‐connected photovoltaic (GCPV) inverter under unbalanced grid voltages. A simple analysis is developed for calculating the rated inverter power under unbalanced grid voltages without tripping the PV inverter for reliable operation. The active power oscillations induced due to the unbalance in the grid voltages are minimized by equating the active power oscillating terms to zero in the reference current generation. The prime focus of this work is on estimating the reference currents and limiting the inverter currents to rated value and providing low‐voltage ride‐through capability by judiciously balancing positive and negative sequence currents. A prototype hardware is developed in the laboratory and the proposed control scheme is implemented using dSPACE 1103 real‐time controller board. A solar simulator has been used to replicate the PV array. The simulation (MATLAB/Simulink) and the experimental results establish that the proposed controller scheme effectively minimizes the oscillation in active power and limits the inverter currents. [ABSTRACT FROM AUTHOR]

Filters are inevitable for grid‐connected inverters to attenuate the current harmonics caused by the pulse width modulation which is usually used in power conversion systems. High‐order filters have attracted much attention because they attenuate the current harmonics effectively. Nevertheless, the high‐order filters have some resonances which cause instability of the system. In addition, the resonance frequencies shift to high as the inductors and capacitors are smaller. It implies that the resonance frequencies may be beyond the Nyquist frequency in downsizing the filter. This complicates the stability and performance analyses of the system. This paper investigates rigorous input–output stability and analyses a robust performance based on the sampled‐data control theory regardless of whether the resonance frequencies are beyond the Nyquist frequency or not. Our analysis contributes to downsizing the filter synthesis while the stability and the robustness are guaranteed even if the resonance frequencies are beyond the Nyquist frequency. The effectiveness of the proposed method is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

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]

Summary: This paper presents the design and control of single‐phase five‐level cascaded H‐bridge multilevel inverter (CHB‐MLI) as a shunt active power filter (SAPF) unit to mitigate the various power quality (PQ) problems such as reactive power burden, injection of harmonics in the supply, poor power factor, and so on. The control of CHB‐MLI has been done using the normalized least mean absolute third (NLMAT) algorithm, which overcomes the shortcoming of conventional least mean square (LMS), normalized LMS (NLMS), and least mean absolute third (LMAT) algorithm. The control algorithm is designed in MATLAB Simulink, and its scaled down prototype model is developed in the laboratory to find the fundamental active component of load current and to mitigate the aforementioned PQ problems. The proposed system is tested for single‐phase grid‐connection, and it works satisfactorily under steady state and dynamic load conditions. A dSpace1104 microcontroller is used to test the proposed algorithm and to generate firing pulses. Besides, the detailed comparison in the context of mean square error (MSE), weights convergence and intermediate error with conventional LMS, NLMS, and LMAT algorithm have also been discussed. Moreover, the harmonic distortion observed in the source current is within stipulated IEEE‐519 limits. [ABSTRACT FROM AUTHOR]

Reports on the Rockwell Automation's publishing of a white paper detailing the causes and solutions to motor-bearing current concerns for induction motors driven by inverters.

The advancement of multilevel inverters has led to an increase in efficiency and reliability. This paper demonstrates the design and implementation of a reduced switch extendable-level inverter-fed open-end winding permanent magnet synchronous motor (PMSM) drive. Unlike traditional multilevel inverter topologies, output voltage levels in the proposed inverter depend on the operating frequency of the switches. As the frequency of operation is very high, the levels in the output voltage reach infinity and hence the term extendable-level inverter. It achieves infinite voltage output levels, with a reduced component count. The configuration of the open-end winding enables the application of the AC voltage directly to the independent motor phases and hence achieves the merits of operation at a reduced input DC voltage. The proposed drive achieves a very high DC-link voltage utilization, reduced inverter switching losses, enhanced power quality, and excellent dynamic response using a single DC source and a minimum number of components. A comparative analysis of the proposed drive with different MLI-fed OEWPMSM drives in terms of the component count and total harmonic distortion is provided. FPGA-based improved sinusoidal PWM control of the proposed drive reduces execution time and enhances the control performance of the inverter. Dynamic characteristics of the proposed drive are provided for analyzing the dynamic response of the drive to a step change in load torque. The proposed drive is simulated using MATLAB/Simulink platform for theoretical analysis and evaluation. The experimental prototype is designed and implemented for validating the proposed drive operation. [ABSTRACT FROM AUTHOR]

Summary: In this paper a novel topology of switched capacitor based multilevel inverters is proposed. In this topology, to increase the output voltage levels and to add the voltage boosting capability, several switched capacitor units are cascaded in series. Having voltage boosting capability and generating maximum number of output voltage levels using minimum number of circuit components, is a merit for this topology. To highlight the attributes of the proposed topology, it is compared with other recently proposed multilevel inverters on number of circuit components such as power electronic switches, diodes and capacitors, voltage boosting capability, total standing voltage, cost and efficiency. The comparison results verify the superiority of the proposed topology over other proposed topologies on number of circuit components, and number of output voltage levels. It is also clear that, this topology has lower voltage stress on power electronic switches, which makes it an appropriate solution for industrial applications. Finally, to show the capabilities of the proposed topology, and to verify the accurate operation of the topology, circuit analysis as well as the experimental results are provided. [ABSTRACT FROM AUTHOR]

This paper presents a novel hierarchical framework for real-time, network-admissible coordination of responsive grid resources aggregated into virtual batteries (VBs). In this context, a VB represents a local aggregation of directly controlled loads, such as smart inverters, electric water heaters, and air-conditioners. The coordination is achieved by solving an optimization problem to disaggregate a feeder's desired reference trajectory into constraint-aware set-points for the VBs. Specifically, a novel, provably-tight, convex relaxation of the AC optimal power flow (OPF) problem is presented to optimally dispatch the VBs to track the feeder's desired power trajectory. In additionto the optimal VB dispatch scheme, a real-time, corrective control scheme is designed, whichis based on optimal proportional-integral (PI) control with anti-windup, to reject intra-feeder and inter-feeder disturbances that arise during operation of the power system. Simulation results conducted on a modified IEEE test system demonstrate the effectiveness of the proposed multi-layer VB coordination framework. [ABSTRACT FROM AUTHOR]

Unintentional islanding detection is one the mandatory criterion that must be met by PV inverters before connecting them into the grid. Acceptable time for inverter for islanding detection is less than 2 seconds. In this paper voltage parameters after islanding occurrence and before turning off the inverter are analyzed. In order to simulate islanding state and perform measurements the testing system was build. Three different commercial PV inverters were tested. Measured signals were used to calculate voltage envelope, phasor, frequency and ROCOF. Collected data proved to be helpful to compere different inverters. [ABSTRACT FROM AUTHOR]

In this paper, a five-level diode clamped inverter fed DTFC-SVM of Permanent Magnet Synchronous Motor (PMSM) drive is proposed for high power industrial applications. In Direct Torque and Flux Control with Space Vector Modulation (DTFC-SVM) technique, the speed of PMSM drive is regulated by controlling stator flux and electromagnetic torque directly and independently such that it abandons the use of direct torque control for PMSM Drive. The proposed multilevel inverter fed DTFC-SVM based PMSM drive gives very less ripples in stator flux and electromagnetic torque and also gives very less total harmonic distortion (THD) in the stator winding voltages and currents which consequences excellent dynamic and steady-state performance of drive. The five-level inverter switching pulses are designed using five-level space vector modulation (SVM) based on two-level SVM, so that it reduces the complexity of the SVM and also gives very good performance under all environmental conditions. The proposed model is simulated in MATLAB/SIMULINK software under various conditions, such as, No-load, load, reversal speed, and change in speed. In order to show the feasibility and effectiveness of the proposed model, it is also implemented in the experimental setup under various conditions. [ABSTRACT FROM AUTHOR]

Summary: This paper aims to develop a new cascaded asymmetrical multilevel inverter with less number of switches for photovoltaic power generation. The structure contains three sources and 11 switches. A design of proposed structure is suggested for PV application. A few more algorithms for cascade extension are also proposed to obtained maximum voltage levels using least numbers of switching devices. PD LS‐PWM modulation is used to control gate pulses of the switches. The structure produce 15 levels using one inverter, whereas 85 levels using a cascaded inverter. The magnitude of sources in cascade inverter is governed by algorithms. A comparative assessment for optimal algorithm is developed considering, sources, switches, and other performance parameters. The simulation and hardware is performed for 15‐level and 85‐level asymmetrical inverter for variation in modulation index and frequency. The efficiency of multilevel inverter is evaluated using PSIM tool. The performance indices, power loss analysis, switching stresses, and blocking voltages across the switches are simulated and validated. The cascade structure, 85 levels produce high quality waveform, for which THD is less than 5%. Thus, this structure suits series combination of various PV panels and achieve power utilising renewable energy sources. [ABSTRACT FROM AUTHOR]