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The conventional three-level inverter only has voltage buck capability. The quasi-Z-source three-level T-type inverter (QZS 3LT $^2$ I) has been proposed to realize voltage buck–boost operation. In this paper, we further propose a novel modulation scheme for the QZS 3LT $^2$ I to realize voltage boosting, reduce the common-mode voltage (CMV), and control the neutral-point voltage balance simultaneously. The proposed scheme adopts a large vector, a medium vector, a small vector with low CMV magnitude, a zero vector, and a shoot-through vector to generate the output voltage. According to sector number and neutral-point voltage difference, a p-type or n-type small vector with low CMV magnitude is properly selected to balance the neutral-point voltage. Shoot-through states are inserted within zero vector to boost the dc input voltage without affecting the ac output voltage. Dwell times of basic vectors are calculated through the revised volt–second balance equation. Furthermore, a coordinate control strategy between neutral-point voltage balance and voltage boosting is proposed. Doing so, the CMV magnitude can be restricted within one-sixth of dc-link voltage and neutral-point voltage imbalance can be effectively mitigated. The effectiveness of the proposed scheme is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a novel fault-tolerant method for active–neutral-point-clamped (ANPC) inverter using a modified carrier-based pulsewidth modulation. At a fault event, the ANPC inverter is divided into subinverters, and the modulating signal is modified to two modulating signals. The modified modulating signals are used to control the subinverters and allow continuous operation of the three-level ANPC inverter during faulty conditions even up to four open-switch faults per phase. This technique provides the fault-tolerant capability of the ANPC inverter without the need to add any additional phase legs or complex control strategies. Furthermore, the proposed technique ensures the voltage balancing of the dc-link capacitors. The performance of the proposed fault-tolerant technique is verified through simulation studies in MATLAB/Simulink under different faulty conditions. The feasibility of the proposed technique is also verified experimentally. [ABSTRACT FROM AUTHOR]

In $LCL$ -type grid-tied inverters, the lumped disturbance, including parameter uncertainties, unmodeled dynamics, and grid harmonics, will deteriorate the current tracking performance and lead to high total harmonic distortion (THD). The uncertainty and disturbance estimator (UDE) scheme provides an effective way to attenuate the lumped disturbance. However, UDE for the current control in $LCL$ -type grid-tied inverters is far from perfect. In this paper, a discrete-time modified UDE (MUDE) scheme is proposed to improve the current tracking performance and robustness. In MUDE, a reduced-order model of the $LCL$ filter, combined with an active damping scheme, is proposed. The stability performance is discussed in detail, and a rigorous stability condition is proposed for the first time. Moreover, the analysis of the controller sampling frequency and grid impedance, and their influences on the system stability is presented. A design case based on the stability condition is also given. Comparative experiments are conducted to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In recent years, a number of bidirectional inductive power transfer systems (BD-IPT) suitable for wireless grid integration of electric vehicles have been developed. These developments have been fueled by the enhanced efficiency and spatial tolerance offered by BD-IPT systems. A typical BD-IPT system utilizes two synchronized full-bridge converters operating at fixed duty cycles to drive the primary and secondary magnetic couplers. However, in order to cater for a wide range of loading conditions, additional circuitry is employed at the expense of cost and power density. As an alternative solution, this paper proposes a novel power converter, named a boost active bridge (BAB), to replace the full-bridge converters. The BAB topology caters to a wide range of loading conditions without the need for any extra switching devices. A comprehensive mathematical model that predicts steady-state currents, voltages, and power transfer is presented to highlight the operating principles of the BAB technology. Experimental results obtained from a 3.5-kW prototype show a nearly constant efficiency under all loading conditions, validating the viability of the proposed BAB topology. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on finite control set model predictive current control, validated experimentally with a rear axle electrical drive unit used in automotive applications. An improved problem formulation is suggested which lowers the computational turnaround time of the solver with approximately $\text{40}\%$ for an horizon length of $N=4$. Apart from the computational requirement aspects, the assessment focuses on inverter efficiency, phase current total demand distortion, and acoustic performance. The proposed solution is evaluated against a standard double proportional and integrator (PI) field-oriented current controller with pulsewidth modulation. It is shown that the proposed solution is feasible, the associated optimization problem at hand can be solved in real time, while exploiting the attractiveness of the proposed improvements. In summary, it is concluded that the inverter efficiency can be improved without deteriorating neither the phase current harmonics nor the acoustic performance. [ABSTRACT FROM AUTHOR]

A multilevel dodecagonal voltage space vector generation scheme for variable-speed drive applications with single-dc-link operation requires a large value of capacitance for cascaded H-bridge (CHB) filters, when operated at lower speeds. In existing schemes, the multilevel dodecagonal structure is obtained by cascading a flying capacitor inverter with a CHB. In this paper, a new scheme has been proposed to minimize the capacitance requirement for full speed operation by creating vector redundancies using modular and equal voltage CHBs. Also, an algorithm has been developed to optimize the selection of vector redundancies among the CHBs in order to minimize the voltage ripple of the floating capacitors. The proposed algorithm considers instantaneous capacitor voltages and phase currents for optimal selection of vector redundancies. A mathematical model for capacitor voltage deviation is presented, and the effectiveness of the proposed algorithm is verified in both the simulation and the experiment. [ABSTRACT FROM AUTHOR]

Input-series-output-parallel (ISOP) inverter system is very suitable for high dc input voltage and large ac output current power conversion applications. If this topology is applied to the grid-connected occasion, a bulky-capacity grid-connected inverter can be built with multiple small-capacity standardized inverter modules, which can significantly improve the reliability of the system operation and facilitate system design. In this paper, we investigate an ISOP LCL-type grid-connected inverter system, and put forward an optimized way for the topology of combined LCL filters first. Then, the inverter-side inductor current is carefully chosen as the controlled variable and thus a concise distributed control method is proposed to achieve multiple control objectives. On the basis of the presented distributed control, the redundant control technique is also provided to heighten the reliability of the grid-tied ISOP inverter indeed. Finally, a three-module prototype is built and the experimental results validate the effectiveness of the raised strategy. [ABSTRACT FROM AUTHOR]

Failure of the commutation process is a serious malfunction in line-commutated high-voltage direct current (HVdc) converters, which mainly occurs due to inverter ac faults and may lead to outage of the HVdc system. In this paper, an improved strategy is developed that functions based on the SIEMENS HVdc control system under normal conditions and switches to a designed commutation failure inhibition module (CFIM) during an inverter ac fault. From the response speed point of view, since the designed CFIM does not require any proportional-integral controller, the inverter control system has a quick performance in prevention of the commutation failure. This is achieved by direct measurement of the overlap area using the waveforms of the valves anode–cathode and commuting voltages. In addition, from the accuracy aspect, the proposed method has a superior performance in comparison with the existing strategies. It is because of the fact that by direct measurement of the overlap area, variations of both direct current and the commutation inductance are considered, and hence, the unnecessary increase of the inverter reactive power consumption during the fault and the repetitive commutation failures are prevented. The practical performance and feasibility of the proposed strategy is validated through the laboratory testing, using the real-time Opal-RT hardware prototyping platform. The experimental results demonstrate that the proposed strategy can effectively inhibit the commutation failure or repetitive commutation failures under different fault types by considering the lowest possible reactive power consumption. [ABSTRACT FROM AUTHOR]

The introduction of virtual-synchronous machine and generator as well as synchronous inverter (synchronverter), in recent years, has facilitated the integration of inverter-interfaced distributed energy resources (IIDERs) into the synchronous generator (SG) dominant microgrids and power grid. In this concept, the voltage source inverter (VSI) is controlled in such a way that it mimics the behavior of SG. To provide a reliable utilization of the IIDERs, a seamless transition of the VSIs between islanded and grid-connected operation modes is required. This paper integrates a novel virtual torque and virtual flux linkage-based synchronizing technique into the synchronverter controller to provide a plug ‘n’ play capability of the VSIs and their smooth transition between these two operating modes. Comprehensive mathematical modeling, design, and dynamic stability analysis as well as dSPACE-based real-time simulation are provided to validate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

A multilevel drive can be realized by using an open-ended machine, fed from dual two-level inverters. The topology supplied from isolated dc sources is suitable for transportation electrification. In vehicular systems, it is essential that the isolated dc sources, comprising of battery packs, should discharge uniformly and maintain balanced dc voltage at the dc-link terminal. A simple carrier-based pulsewidth modulation (PWM) technique is presented in this paper, which can effectively regulate the power drawn between the two two-level inverters while maintaining the multilevel operation of the drive. The modulation technique can balance the instantaneous state of charge of independent battery packs and dynamically equalize the power flow from the two inverters, based on drive requirement. This will enhance the reliability of the propulsion system in electric vehicles. The operation of the proposed PWM technique has been validated through detailed simulation and experimental tests. [ABSTRACT FROM AUTHOR]

In this paper, a two-degrees-of-freedom control algorithm based on uncertainty and disturbance estimator (UDE), aimed to minimize the total harmonic distortion of inverter output voltage is proposed, possessing enhanced robustness to fundamental frequency variations. A multiple-time-delay action is combined with a commonly utilized low-pass UDE filter to increase the range of output impedance magnitude minimization around odd multiples of fundamental frequency for enhanced rejection of typical single-phase nonlinear loads harmonics. Marginal robustness improvement achieved by increasing the number of time delays is quantified analytically and revealed to be independent of delay order. The performance of the proposed control approach and its superiority over two recently proposed methods is validated successfully by experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes an extended Kalman filter (EKF) based control strategy for fault ride-through operation in two-stage grid-connected photovoltaic (GPV) system. Unlike the conventional controllers for ride-through operation, the proposed strategy does not compromise with power quality improvement features in the system while enabling ride-through operation. The controller accounts for nonlinear loads in the system, grid harmonic-currents elimination, and grid-currents balancing even during the harmonic/distorted grid voltages. The IEEE Standard-1547.4 compels the distributed resource to ride-through during voltage disturbances caused by faults. For the ride-through operation, a limit is imposed on PV active power injection to prevent inverter overcurrents and dc-link energy aggregation, which reduces the lifetime of dc-link capacitor. The reactive power is fed to the grid, as per the depth in voltage-sag. The derated PV array power is supplied in cases where the inverter cannot handle the utmost PV-power. The power quality improvement is ensured using EKF state estimator, which precisely estimates the fundamental load currents. In distribution network with modern nonlinear loads, especially at far radial ends, the grid voltages are prone to huge diversions and the proposed controller provides a possible solution to maintain active/reactive power support and maintain power quality in the network. The effectiveness of the strategy is demonstrated through simulations and experiments. Under all disturbances, the harmonic content in grid currents is observed within limits, in accordance with the IEEE Standard-519. [ABSTRACT FROM AUTHOR]

This paper deals with the analysis of the input dc-link voltage ripple in multilevel inverter based on H-bridge and level doubling network (LDN). The LDN is basically a half-bridge fed by a floating capacitor, with voltage self-balancing capability, recalling the concept of a flying capacitor configuration. The amplitude of the LDN voltage ripple is analytically determined considering both the low-order and the switching harmonic components. In particular, peak-to-peak distributions of voltage ripples over the fundamental period are analytically determined, making possible the design of dc-link capacitor relying only on the dc-voltage ripple requirements. The case study makes reference to negligible switching ripple in the output current. It well represents either grid connection or passive load having almost sinusoidal currents. Numerical simulations carried out by MATLAB/Simulink and a complete set of experimental verifications are given to confirm the theoretical developments. [ABSTRACT FROM AUTHOR]

In this paper, a novel structure of switched capacitor converter (SCC) is proposed. First, the basic unit of the proposed SCC is presented. After that, a generalized structure of the proposed SCC is discussed. The presented SCC uses one dc source, several switches, diodes, and capacitors to produce multistep dc boosted output voltage. The capacitors in the SCC can be charged in trinary asymmetrical pattern. A detailed comparative study between the proposed and other recently developed SCC structures is presented. It is shown that the proposed SCC can produce an output voltage level with lower total standing voltage and lower maximum switch stress voltage as compared to most of the suggested SCC structures. Further, a switched capacitor multilevel inverter (SCMLI) based on cross-switched multilevel inverter has been developed and analyzed for symmetric and asymmetric dc source configurations. For fair comparison with the existing SCMLI structures, the overall cost of the structures is compared based on a cost function (CF). The proposed SCMLI provides lower cost function/output voltage level (CF/NL) in comparison with most of the other SCMLI structures for both symmetric and asymmetric dc source configurations. Extensive experimental studies validate the operation and performance of the proposed SCMLI structure. [ABSTRACT FROM AUTHOR]

This paper presents a new resonant generator topology for dual-frequency induction heating. The design offers functionalities that are not present in other solutions, which allow the ratio of equivalent resistance to be controlled at high (HF) and medium (MF) resonant frequencies. A simulation is performed of its interactive work during dual-frequency induction heating, using a specially developed software algorithm. The simulation combines coupled numerical calculations of the electromagnetic and thermal fields during dual-frequency heating of the workpiece with the analysis and modification of the resonance frequencies and power at HF and MF, in accordance with a user-imposed duty cycle. The results are used as the basis for a 100-kW physical model of the generator. The proposed LCLC topology for a dual-frequency resonant inverter with adjusted series inductance allows better use of the ac–dc power supply system, easier implementation of sequential dual-frequency heating, and easier control of MF and HF power waveforms. [ABSTRACT FROM AUTHOR]

Beat phenomenon is an important concern in the reduced dc-link capacitance motor drive system. In previous research works, the topic is mainly concentrated on the beat phenomenon caused by the interaction of the fluctuated dc-link voltage and the motor phase voltage. In this paper, another form of the beat phenomenon generated by the fluctuated dc-link voltage and the severely fluctuated load torque is investigated. The effect of the beat phenomenon on the grid current and the motor speed is analyzed, which fluctuate with the low-frequency oscillation. In order to improve the drive system performance, a power balancing controller is proposed to suppress the grid current fluctuation, and a resonant controller is utilized to regulate the periodic power signals. Meanwhile, the applied fluctuated torque suppression method could improve the performance of the motor speed, which is only sensitive to the frequency of the fluctuated load torque. Experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

For parallel-connected LCL-type inverters in islanded operation, it is difficult to reshape the large harmonic impedance by the conventional capacitor voltage control due to the presence of grid-side inductor, which seriously deteriorates the voltage quality at the point of common coupling (PCC) under nonlinear loads. To address this issue, a harmonic voltage distortion damping method is proposed in this paper, which mainly includes a direct output voltage control and the parallel virtual-admittance control. First, the direct output voltage control converts the grid-side inductor into the equivalent output impedance of the inverter itself by changing the voltage feedback variable from capacitor voltage to output voltage, and then the harmonic impedance is reshaped from a large value to a small value with the P + Repetitive controller. However, it is found that the direct output voltage control fails to damp PCC voltage distortion with droop-frequency offset. That is because its voltage controller cannot guarantee the resonance bandwidth of main harmonic frequency, and then a slight droop-frequency offset can cause a large increase in the harmonic impedance. For this, the parallel virtual-admittance control is further proposed to limit the size of the output impedance to no more than that of the impedance in parallel, which effectively reduces the adverse effect of droop-frequency offset on the quality of the PCC voltage. Further, the parallel virtual-admittance control is simplified with the same harmonic voltage distortion damping consequent. The system stability conditions are analyzed in detail, and its proper control parameters are selected without complicated trial. Finally, the experimental results validate the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents the design and experimental validation of disturbance observer (DO)-based control for grid-tied photovoltaic (PV) inverters fed by a dc–dc boost converter considering unbalanced grid voltages. The control scheme uses multiples controllers that are developed based on employing DO technique along with a feedback-linearizing (FBL) control. The main controller is designed to regulate the active and reactive powers injected into the grid via controlling the grid-tied inverter. Under unbalanced grid voltages, the active and reactive power is composed of a dc component as well as an ac component that oscillates at twice the grid frequency. Therefore, the unknown perturbation, representing the mismatch between the nominal and actual system, can be treated as a sum of a constant offset and a sinusoidal disturbance. To ensure accurate control of the active/reactive power, a DO is designed to estimate the unknown perturbation, which is then canceled by a FBL control. By considering the control input limitation in the observer synthesis, an antiwindup compensator arises naturally in the control law, which attenuates the effect of the windup phenomenon during control saturation. Moreover, a simplified representation of the DO is proposed to facilitate real-time implementation. The proposed approach for the power control can be used in both balanced and unbalanced systems since it can reject constant and sinusoidal disturbances. Experimental tests were performed to investigate the ability of the proposed control scheme to achieve good transient and steady-state performances. [ABSTRACT FROM AUTHOR]

The nine-arm modular multilevel converter (9A-MMC) has been recently proposed as a reduced MMC topology variation for six-phase drive applications, with 25% reduction in the number of employed arms and associated components, compared to a standard dual three-phase MMC, however with a limited output voltage amplitude. This paper proposes a hybrid 9A-MMC comprised of half-bridge submodules (SMs) in both the upper and lower arms, and full-bridge SMs in the middle arms. By employing the negative-voltage state of the full-bridge SMs, the hybrid 9A-MMC avoids the limitations imposed on the dc-link voltage utilization, while achieving further reduction in the component count, compared to a standard 9A-MMC with identical half-bridge SMs. The operating principles of the proposed hybrid 9A-MMC are illustrated with mathematical analysis, whereas its characteristics are verified through both simulation and experimentation. An assessment of the proposed topology quantifying its employed components is also provided, in comparison to other MMC-based six-phase machine drives. [ABSTRACT FROM AUTHOR]

Aluminum electrolytic capacitors (AECs) are connected in a bank to meet the requirement of capacitance, voltage, and current rating for dc-link of power electronic converters. The performance of capacitor bank deteriorates with time due to the degradation of AECs in the bank. Further, each AEC in the bank degrades differently based on its core temperature, which in turn depends on the current and its equivalent series resistance (ESR). Therefore, health monitoring of a bank would require monitoring of individual AECs in the bank. However, extending the available literature on health monitoring of an AEC to the capacitor bank would require voltage/current sensors for individual AECs. To address the aforementioned issue, this paper suggests a method to assess the health of individual AECs online in the bank without using sensors for each AECs. The proposed method involves estimation of current through each capacitor, which is used to determine the core temperature by using a thermal model of AEC. The core temperature is used for estimation of ESR and capacitance of each capacitor using physics-of-failure based degradation model. For the consistent matching of the degradation model to the actual degradation of the capacitor, the coefficients of the model are sequentially updated. For updating, an algorithm based on extended Kalman filter is used. The proposed scheme is experimentally validated on laboratory prototype of single-phase, grid-connected solar PV inverter under variable load conditions. [ABSTRACT FROM AUTHOR]

Two-stage single-phase inverter system has found many applications in distributed generators and grid-connected systems. However, the existence of double-line frequency ripple on the dc-bus voltage due to single-phase inverter's operation has given rise to some design and reliability issues. Some of these are the degradation in the quality of inverter's output voltage and shortening of dc-bus capacitor's lifetime. The problem is rooted in the controller design of the front-end dc–dc converter, which is often designed based on a simplified mathematical model of the dc–dc converter that fails to account for some complex phenomena, such as system's nonlinearities and circuit parameter variations due to temperature and aging effects. In this paper, a disturbance-observer-based control is proposed where these unmodeled effects are treated in the form of lumped disturbance and compensated for in a feed-forward manner. The major advantage of this control solution is that only minimal plant information is needed for controller design and that a decoupled composite controller can be realized, where the feedback compensator is designed to meet certain stability criteria while the disturbance-observer-based feed-forward compensator is designed to handle fast transient events. A prototype of a dual-active-bridge (DAB) dc–dc converter implemented with disturbance-observer-based control is constructed to verify its effectiveness. Experimental results show that the dynamic response of the DAB converter is significantly improved and the double-line frequency ripple on the dc-bus voltage is effectively suppressed by the proposed control solution. [ABSTRACT FROM AUTHOR]

In the paper by Chen et al. (IEEE Trans. Ind. Electron., vol. 66, no. 4, pp. 2837–2846, Apr. 2019), the authors proposed two fault-tolerant control strategies for T-type three-level inverters considering neutral-point (NP) voltage oscillations. However, some basic problems are worth being discussed about the proposed fault-tolerant control methods. This letter presents some comments and results concerning the paper by Chen et al. [ABSTRACT FROM AUTHOR]

The second harmonic pulsating power flows through the dc side of a single-phase quasi-Z-source inverter (qZSI), which requires bulky capacitor banks and inductors to suppress low-frequency ripple of dc-link voltage and inductor currents in the passive ripple reduction way. However, the resultant huge qZS network seriously deteriorates the system reliability, efficiency, volume, weight, and cost. This paper proposes an active-filter-integrated single-phase qZSI to transfer low-frequency power ripple directly from ac load to active filter's ac capacitor, so that low-frequency power ripple does not present in dc side anymore and constant inductor currents and constant capacitor voltages are ensured. Thus, much small qZS impedance is employed to only smooth high-frequency ripple and active filter's capacitor supports ac voltage (large ripple allowed) with small capacitance. The operation principle, parameter design method, and modeling and control strategy of the proposed topology are investigated. Comparative evaluation, simulation, and experimental results verify the proposed new topology system. [ABSTRACT FROM PUBLISHER]

For cascaded multilevel inverter topologies with a single dc supply, closed-loop capacitor voltage control is necessary for proper operation. This paper presents zero and reduced common-mode voltage (CMV) operation of a hybrid cascaded multilevel inverter with predictive capacitor voltage control. Each phase of the inverter is realized by cascading two- three-level flying capacitor inverters with a half-bridge module in between. For the presented inverter topology, there are redundant switching states for each inverter voltage levels. By using these switching state redundancies, for every sampling instant, a cost function is evaluated based on the predicted capacitor voltages for each phase. The switching state that minimizes cost function is treated as the best and is switched for that sampling instant. The inverter operates with zero CMV for a modulation index upto 86%. For modulation indices from 86% to 96%, the inverter can operate with reduced CMV magnitude (Vdc/18) and reduced CMV switching frequency using the new space-vector pulsewidth modulation (SVPWM) presented herein. As a result, the linear modulation range is increased to 96% as compared to 86% for zero CMV operation. Simulation and experimental results are presented for the inverter topology for various steady state and transient operating conditions by running an induction motor drive with open loop $V/f$ control scheme. [ABSTRACT FROM PUBLISHER]

The concept of the virtual synchronous generator (VSG) is emerging as an attractive solution for controlling the grid-connected inverter when the renewable energy has a high penetration level into the grid. This paper focuses on the small-signal modeling and parameters design of the power loop of the VSG, and points out that the bandwidth of the power loop should be far less than twice the line frequency for the purpose of avoiding the VSG output voltage to be severely distorted. Consequently, the line-frequency-averaged small-signal model of the VSG is derived for system analysis and parameters design. Based on the model, the decoupling conditions between the active power loops (APLs) and the reactive power loops (RPLs) of the VSG are given. Finally, a step-by-step parameters design method is proposed to facilitate the design of the control parameters of the VSG. A 10-kVA prototype is built and tested in the laboratory, and the experimental results are given to verify the effectiveness of the theoretical analysis and the proposed parameters design method. [ABSTRACT FROM PUBLISHER]

This paper presents a model predictive control (MPC) scheme for quasi-Z-source (qZS) three-phase four-leg inverter. In order to cope with the drawbacks of traditional voltage source inverters (VSIs), a qZS three-phase four-leg inverter topology is proposed. This topology features a wide range of voltage gain which is suitable for applications in renewable energy-based power systems, where the output of the renewable energy sources varies widely with operating conditions such as wind speed, temperature, and solar irradiation. To improve the capability of the controller, an MPC scheme is used which implements a discrete-time model of the system. The controller handles each phase current independently, which adds flexibility to the system. Simulation and experimental studies verify the performances of the proposed control strategy under balanced and unbalanced load conditions as well as single-phase open-circuit fault condition. [ABSTRACT FROM PUBLISHER]

Open-ended winding induction machines fed from standard two-level voltage source inverters (VSIs) provide an attractive arrangement for ac drives. An alternative approach is to use a dual-output indirect matrix converter (IMC). It is well known that the IMC provides fully bidirectional power flow operation, with small input size filter requirements. While a standard IMC consists of an ac–dc matrix converter (MC) input stage followed by a single VSI output stage, it is possible to replicate the VSI to produce multiple outputs. In this paper, an open-end winding induction machine fed by an IMC with two output stages is presented. The IMC modulation strategy aims to reduce the common-mode voltage (CMV), while compensating any zero-sequence voltage fed to the machine. The system is modeled using a PSIM and MATLAB/Simulink platform. Experimental results demonstrating the viability of the method are presented using a 7.5-kW prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a robust continuous nonlinear model predictive control (CNMPC) for a grid-connected photovoltaic (PV) inverter system. The objective of the proposed approach is to control the power exchange between the grid and a PV system, while achieving unity power factor operation. As the continuous nonlinear MPC cannot completely remove the steady-state error in the presence of disturbances, the nonlinear disturbance observer-based control is adopted to estimate the offset caused by parametric uncertainties and external perturbation. The stability of the closed-loop system under both nonlinear predictive control and disturbance observer is ensured by convergence of the output-tracking error to the origin. The proposed control strategy is verified using a complete laboratory-scale PV test-bed system consisting of a PV emulator, a boost converter, and a grid-tied inverter. High performance with respect to dc-link voltage tracking, grid current control, disturbance rejection, and unity power factor operation has been demonstrated. [ABSTRACT FROM PUBLISHER]

In this paper, a new predictive control for grid-connected inverters is presented, which provides the best performance in terms of transient response and stability margins when analog filters in current sensing circuits are used. These filters are necessary to avoid aliasing in the A/D conversion process, which causes an important ripple on injected current into the grid and increases the total harmonic distortion. However, predictive controls are very sensitive to delays on the acquisitions, so when such anti-aliasing filters are used a reduction of stability margins is produced and the transient response is affected. The proposed predictive control allows to compensate the effect of the filter, for any order and cutoff frequency, providing the best transient response in the reference tracking and the highest stability margins. Furthermore, a modification on the adaptive strategy of current error is proposed, which allows to work with single-phase grid-connected inverters. The proposed predictive control has been tested on a 3.3-kVA single-phase grid-connected inverter with LCL filter, using different anti-aliasing filters, obtaining in all cases, better results than those offered by other predictive controls recently published. [ABSTRACT FROM PUBLISHER]

High-performance permanent-magnet synchronous machines show nonlinear behavior due to saturation effects. Nonlinear differential equations describe these phenomena which makes feedback control challenging. This paper presents a unified approach based on the current, flux linkage and voltage plane to visualize the physics of machine dynamics. A predictive control method to precisely control arbitrary dynamic trajectories in all planes can then be developed. Four real-time strategies for dynamic trajectory identification are deduced: two straight trajectories, a strategy that yields a fast torque response, and a strategy that reaches the reference currents in minimal time. The performance of the four approaches is analyzed using simulations and test bench measurements. Advantages and disadvantages of specific trajectories are identified. It is thus shown how the dynamics of permanent-magnet synchronous machines with nonlinear magnetics can be controlled both precisely and optimally. [ABSTRACT FROM PUBLISHER]

In this paper, a new topology for half-bridge switched boost inverter (HB-SBI) is proposed. The proposed half-bridge inverter uses more active elements rather than capacitors and inductors in comparison with the conventional half-bridge Z-source inverter with two Z-networks, which results in reduction of weight, size, and cost. Moreover, the proposed inverter has the capability of eliminating inverter leg short-circuit issues and is able to further increase the output voltage level in comparison with its conventional types. Generating zero-level output voltage is also another advantage of this topology. Based on theoretical calculations, the steady-state and small-signal analysis of the proposed topology in different operating modes are performed and the ripple of inductors’ current and capacitors’ voltage are also calculated. A comprehensive comparison is also made between the proposed inverter and the conventional types. Finally, the experimental results are provided to reconfirm the performance of the proposed inverter. [ABSTRACT FROM PUBLISHER]

This paper presents a novel predictive model reference adaptive system (MRAS) speed estimator for sensorless induction motor (IM) drives applications. The proposed estimator is based on the finite control set-model predictive control (FCS-MPC) principle. The rotor position is calculated using a search-based optimization algorithm which ensures a minimum speed tuning error signal at each sampling period. This eliminates the need for a proportional–integral (PI) controller which is conventionally employed in the adaption mechanism of MRAS estimators. Extensive experimental tests have been carried out to evaluate the performance of the proposed estimator using a 2.2-kW IM with a field-oriented control (FOC) scheme employed as the motor control strategy. Experimental results show improved performance of the MRAS scheme in both open- and closed-loop sensorless modes of operation at low speeds and with different loading conditions including regeneration. The proposed scheme also improves the system robustness against motor parameter variations and increases the maximum bandwidth of the speed loop controller. [ABSTRACT FROM PUBLISHER]

Modular multilevel converter (MMC) is a promising new topology for high-voltage applications. The MMC is made of several identical submodules. For proper operation, each submodule can be considered as a controlled voltage source where capacitor’s voltage should be maintained at a certain level. Besides, the minimization of the circulating current, which does not flow to the load, is crucial for achieving stable and efficient operation of the MMC. The interrelations among the load current, circulating current, and capacitor voltages complicate the MMC control. This paper aims to achieve stable and balanced voltage and current control with reduced circulating current in various operating conditions. The proposed control uses weighted model predictive control based on a normalized cost function to select the inverter switching patterns, which control the load current, while minimizing voltage fluctuation and circulating current. The weighting factors were selected based on minimizing the load-current total harmonic distortion (THD) and circulating current. The analysis is conducted on a low-power case study of single-phase four-cells MMC with possible extension to higher number of cells. The low-power three-level prototype is designed and built to validate this proposed method. Theoretical analysis, simulation, and experimental results are presented and compared. Parameter sensitivity analysis was also conducted. They all confirm the effectiveness of the proposed control method. [ABSTRACT FROM PUBLISHER]

Finite-state predictive torque control (FS-PTC) is computationally expensive, since it uses all voltage vectors (VVs) available from a power converter for prediction and actuation. The computational burden is rapidly increased with the number of VVs and objectives to be controlled. Moreover, designing a cost function with more than two control objectives is a complex task. This paper proposes a simplified algorithm based on a new direct torque control (DTC) switching table to reduce the number of VVs to be predicted and objectives to be controlled. The new switching table also assists to reduce average switching frequency and its variation range. As a result, the cost function is simplified by not requiring to include the frequency term. Experimental results show that the average execution time and the average switching frequency for the proposed algorithm are greatly reduced without affecting the torque and flux performances achieved in the conventional FS-PTC. [ABSTRACT FROM PUBLISHER]

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future. [ABSTRACT FROM PUBLISHER]

The flying capacitor multilevel inverter (FCMLI) is one of the well-known structures of multilevel inverters having attracted considerable attention because of its merits. In spite of its many advantages, it has some limitations such as high volume and complicated control method because of its bulky capacitors and their voltage balancing requirement. Moreover, the high number of power semiconductors required makes this structure susceptible to failure. To increase the ratio of the number of levels to the number of components, an uneven distribution of capacitor voltages has been suggested in previous reports; however, this approach complicates the control method. Up to now, almost all presented methods suffer from high computational load and/or structure-dependent algorithm. In this paper, a simple state-based and structure-independent method is proposed for capacitor voltage regulation. The proposed method is straightforward and can perform online computation of switching sequences in a computationally efficient manner without any need for stored information or look-up tables. The method is conveniently extendible to any number of cells and levels in an FCMLI structure with arbitrary dc link voltage distribution schemes. Simulation and experimental results show the effectiveness and simplicity of this method. [ABSTRACT FROM PUBLISHER]

In this paper, a common grounded Z-source dc–dc converter with high voltage gain is proposed for photovoltaic (PV) applications, which require a relatively high output–input voltage conversion ratio. Compared with the traditional Z-source dc–dc converter, the proposed converter, which employs a conventional Z-source network, can obtain higher voltage gain and provide the common ground for the input and output without any additional components, which results in low cost and small size. Moreover, the proposed converter features low voltage stresses of the switch and diodes. Therefore, the efficiency and reliability of the proposed converter can be improved. The operating principle, parameters design, and comparison with other converters are analyzed. Simulation and experimental results are given to verify the aforementioned characteristics and theoretical analysis of the proposed converter. [ABSTRACT FROM PUBLISHER]

This paper presents an innovative and effective linear current regulator for grid-connected converters interfaced by an LCL filter. The proposed scheme entails the use of voltages measured at the terminals of the output filter capacitors as feedforward signals to be included in a classical structure of proportional–resonant (PR) controller. Processing these signals by an opportune filter K(s), the resonance effects characterizing the LCL filter are neutralized and the impact of the grid impedance’s variations on the converter’s performances is greatly reduced. The proposed solution simplifies the controller’s design, whose gains are obtained by a straightforward mathematical formula which prevents complex root locus analyses. Moreover, for a given phase margin, the proposed technique ensures the achievement of maximum possible bandwidth of closed-loop system, sidestepping the guesswork typical of the conventional methods used for selecting the crossover frequency. Conclusions are supported by a detailed mathematical analysis and validated by laboratory results obtained with a 7.5-kW three-phase inverter prototype connected to a power grid with time-variant impedance characteristics. [ABSTRACT FROM PUBLISHER]

It is well known that predictive control methods can be affected by the presence of modeling errors. The extent to which finite-control-set model predictive control (FCS-MPC) is influenced by parametric uncertainties is a recurrent concern at the moment of evaluating the viability of this method for power electronics applications. This paper proposes an analytic approach to examine the influence of model parametric uncertainties on the prediction error of FCS-MPC for current control in a three-phase two-level inverter. The analysis shows that the prediction error is not only determined by parametric mismatch but also by the instantaneous values of load current and inverter output voltage. This implies that within each sampling period of the predictive algorithm several conditions of prediction error are generated, as multiple voltage vectors are evaluated. Simulation and experimental results are provided and discussed showing the effects of inaccuracies in the modeling of load resistance and inductance parameters on the performance of FCS-MPC. Even though steady-state performance is noticeably affected with parameter changes, especially when the load inductance is overestimated by the model, its fast transient step response is less affected by parameter changes. [ABSTRACT FROM PUBLISHER]

This paper presents a new control strategy based on Lyapunov-function and proportional-resonant (PR) controller for single-phase grid-connected LCL-filtered voltage-source inverters (VSIs). While Lyapunov-function-based control guarantees the global stability of the system, the PR controller is employed to process the grid current error and determine the inverter current reference. However, it is shown that the conventional Lyapunov-function-based control (CLFBC) together with the PR control cannot damp the inherent resonance of the LCL filter. Therefore, this control approach is modified by adding a capacitor voltage loop so as to achieve the desired resonance damping. In addition, a transfer function from the reference grid current to actual grid current is formulated in terms of the LCL-filter parameters and their possible variations in the proposed control strategy. An important consequence of using the PR controller is that the need for performing first and second derivative operations in the generation of inverter current reference is eliminated. Also, a zero steady-state error in the grid current is guaranteed in the case of variations in the LCL-filter parameters. The computer simulations and experimental results obtained from a 3.3-kW system show that the proposed control strategy exhibits a good performance in achieving the required control objectives such as fast dynamic response, zero steady-state error, global stability, and sinusoidal grid current with low total harmonic distortion (THD). [ABSTRACT FROM PUBLISHER]

This paper presents a boost-multilevel inverter design with integrated battery energy storage system for standalone application. The inverter consists of modular switched-battery cells and a full-bridge. It is multifunctional and has two modes of operation: 1) the charging mode, which charges the battery bank and 2) the inverter mode, which supplies ac power to the load. This inverter topology requires significantly less power switches compared to conventional topology such as cascaded H-bridge multilevel inverter, leading to reduced size/cost and improved reliability. To selectively eliminate low-order harmonics and control the desired fundamental component, nonlinear system equations are represented in fitness function through the manipulation of modulation index and the genetic algorithm (GA) is employed to find the optimum switching angles. A seven-level inverter prototype is implemented and experimental results are provided to verify the feasibility of the proposed inverter design. [ABSTRACT FROM AUTHOR]

This paper presents proportional integral direct torque control (PIDTC) and fuzzy-2 DTC (F2DTC) of the induction motor (IM) drive using space vector pulse width modulation (SVPWM) for three-level diode-clamped inverter (TDCI). The above control schemes have been implemented in the laboratory using 2 HP IM through a DSPACE DS-1104 controller. The control schemes are capable to balance the dc-link capacitor voltages of TDCI by selecting an optimum voltage vector without using an extra controller. However, the three-level PIDTC of an IM gives poor transient performance during starting, loading, and speed reversal with considerable current and voltage total harmonic distortion (THD). In addition, it takes more time to reach the steady state with large spikes on capacitor voltages during the load or speed variation. This is due to poor performance of the PI controllers (speed and torque). In F2DTC, the conventional PI controllers are replaced by Mamdani-type fuzzy-2 controllers using a centroid method with simple logical rules. The simulated and experimental performance show that F2DTC for the three-level inverter-fed IM drive provides a fast dynamic response, less current and voltage THDs, considerable less distortion in flux and torque, and fewer spikes on capacitor voltages as compared to PIDTC. [ABSTRACT FROM PUBLISHER]

In an electric drive vehicle (EDV), the available voltage on a dc-link is limited, and so the inverter output voltage and, consequently, the line motor maximum speed are limited. The fundamental voltage of the inverter output is increased approximately 27% using a square wave (SW) switching pattern instead of a sine wave switching pattern. However, this pattern can only be used at high speeds, and at lower speeds a pulsewidth modulation (PWM) pattern should be used. In order to achieve proper control, the switching pattern should be changed seamlessly. In the present paper, a new PWM scheme for single-mode seamless control of Vernier motors is proposed. In the proposed scheme, the reference voltage is modified to change the switching pattern continuously so that the voltage changes smoothly from a high-frequency pattern to an SW and voltage discontinuity does not occur. Experimental results reveal that the inverter-switching pattern changes smoothly from a sinusoidal PWM pattern to an SW pattern, and so seamless control from the constant-torque region to the constant-power region, and vice versa, is achieved. Since the proposed scheme is a single-mode control, it is much simpler than current technologies, which are based on multimode controllers. Also the proposed method has a lower total harmonic disturbance (THD) as well as a lower harmonic distortion factor (HDF) compared to some existing methods. [ABSTRACT FROM PUBLISHER]

In this paper, a single-stage solution for solar photovoltaic (PV) pumping system using a dual-inverter fed open-end winding induction motor drive is presented. The three-level dual-inverter requires a low PV bus voltage compared with its conventional three-level counterpart. This could avoid large string of PV modules and helps in reducing the voltage rating of the capacitors and semiconductor devices used in the system. This may further help in reduction of cost of the system. The proposed single-stage system is operated using an integrated control algorithm, which includes the maximum power point tracking (MPPT), the $V/f$ control, and the sample-averaged zero-sequence elimination (SAZE) pulsewidth modulation (PWM) technique. While the MPPT algorithm ensures the extraction of maximum power from the PV source, the $V/f$ control improves the motor pump performance. Furthermore, the zero-sequence current is avoided by the SAZE PWM algorithm. Thus, the integrated control algorithm improves the overall performance of the system. Furthermore, this paper also presents the details of system design and analysis of its dynamic behavior during transient environmental conditions. The performance of the system is verified using MATLAB simulation and hardware prototype. [ABSTRACT FROM PUBLISHER]

Commutations existing in a brushless dc motor (BLDCM) drive system not only aggravate the torque ripple and reduce the power factor but also cause the catastrophic failure of a sensorless drive based on the zero-crossing detection of back electromotive force when the commutation duration approaches or exceeds 30 electrical degrees. For a sensorless BLDCM drive system with a long commutation time, it is necessary to shorten the commutation time. In this paper, a technique making the commutation time significantly reduced by means of a novel inverter topology is presented. The proposed topology is based on the idea of supplying higher dc-link voltage for the freewheeling phase. First, the dc link of the backward freewheeling path is decoupled from that of the forward energy flow path. The superiority of dc-link decoupling for commutation control is analyzed. Then, in order to provide adjustable voltage higher than the dc source voltage for the dc link of the freewheeling path, a double-layer C-dump converter is proposed. Compared with the traditional unipolar C-dump converter, it not only upraises the potential of the positive rail but also lowers the potential of the negative rail. Finally, the proposed inverter topology is verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a novel grid-connected high step-up inverter is proposed. The topology is composed of two stages. The first stage is a single-switch high step-up dc–dc converter with bipolar outputs, and the second stage is a conventional half-bridge dc–ac grid-connected inverter. Negative grounding of the photovoltaic (PV) module has resulted in elimination of unwanted ground leakage currents in the PV system. Simple structure, employing few semiconductor switches, simple control, and high efficiency are the features of the proposed topology. Theoretical analysis and principal operation of the circuit are discussed. An experimental prototype is implemented to verify the performance of the proposed inverter. The experimental results confirm the aforementioned features and the theoretical analysis of the converter operation. [ABSTRACT FROM PUBLISHER]

A high-order ( $LCL$ or $LLCL$) power filter with a small grid-side inductor is becoming more preferred for a grid-tied inverter due to less total inductance and reduced costs. In a microgrid, the background harmonic voltage (BHV) may distort the injected currents of the grid-tied inverters. In order to resist the effect of the BHV, a feedforward voltage compensator and a proportional resonant regulator with harmonic compensation are often adopted. However, they still have their own limitations, particularly when there are higher order BHVs at the point of common coupling and when the equivalent grid impedance widely varies due to the different numbers of grid-tied inverters in parallel. Thus, an extra damper should be inserted to keep the system stable. In this paper, the control bandwidth limitation of a multiloop control active damping (AD) method is analyzed and illustrated by the capacitor-current-feedback AD. Based on this, a single-loop current control with a hybrid damper is proposed for a single-phase $LCL$- or $LLCL$-filter-based grid-tied inverter. A step-by-step design of the controller method is also introduced in detail. Experiments on a 2-kW prototype fully demonstrate the strong robustness of the stability and the high harmonic rejection ability of the inverter using the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper proposes a new topology for an enhanced-boost Z-source inverter (ZSI) with combined two Z-impedance networks. By two Z-impedance networks and low shoot-through duty cycle, the proposed inverter produces high output voltage gain. In traditional ZSIs for high boosting voltage, a low modulation index is required; hence, under these conditions, the output voltage will have low quality with high total harmonic distortion. Compared with the conventional high-boost ZSI topologies, the proposed inverter uses shorter shoot-through duration and a larger modulation index to improve the output waveform quality. Comparison between the proposed topology and previously proposed schemes, in terms of inductor numbers, voltage and current stresses on elements, sizes of inductors and capacitors, efficiency, and switching device product (SDP) factors of diodes, is made, and the results verify the priority of the proposed topology. The operating principle of the proposed topology is analyzed in detail. Both simulation and experimental results verify the high performance of the proposed inverter. [ABSTRACT FROM PUBLISHER]

This paper presents a sliding-mode control (SMC) strategy for single-phase grid-connected \mboxLCL-filtered voltage source inverters (VSIs) with double-band hysteresis scheme. The proposed SMC is simpler than the existing SMC methods devised for grid-connected VSIs since its sliding-surface function requires the sensing of capacitor voltage and grid current only. In addition, a double-band hysteresis scheme which ensures the switching of a transistor in the VSI during a half cycle while it remains either on or off in the other half cycle of the fundamental period is used to mitigate the switching frequency. Furthermore, the analytical expressions for the instantaneous and average switching frequencies are derived. The theoretical considerations and analytical results are verified through computer simulations and experimental results obtained from a 3.3-kW system. Simulation and experimental results show that the proposed SMC strategy exhibits an excellent performance in achieving the required control objectives such as fast dynamic response, robustness, sinusoidal grid current with low total harmonic distortion, and simplicity in a practical implementation. [ABSTRACT FROM PUBLISHER]

Model-based predictive control is a powerful control strategy to drive electrical machines. Conventional cascade proportional–integral (derivative) [PI(D)] controllers are often used to control speed, torque, and current. However, for low-inertia machines, achieving a high-performance and wide speed range is far beyond the application conditions for which these controllers are designed for. Using two cascaded PI(D) controllers for the speed/current control of a low-inertia machine, changes in the speed set point should be slowly applied in order to avoid stability problems. In this paper, a model predictive control algorithm that is able to control the speed of a low-inertia brushless direct-current machine with a high bandwidth and good disturbance rejection properties is proposed. The algorithm is implemented on a SPARTAN 3E 1600 field-programmable gate-array board, and experimental results verify the performance of the proposed algorithm. [ABSTRACT FROM PUBLISHER]