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This paper presents dynamic control and performance of a unified power flow controller (UPFC) intended for installation on a transmission system consisting of two sets of three-phase transmission lines in parallel. When no UPFC is installed, interruption of either three-phase line due to a fault reduces an active power flow to half, because the line impedance becomes double before the interruption. Installing the UPFC makes it possible to control an amount of active power flowing through the transmission system. The validity of the theoretical analysis developed in this paper is verified by experiments using a 10-kVA laboratory setup, as well as a computer simulation. [ABSTRACT FROM AUTHOR]

Z-Source inverters have recently been proposed as an alternative power conversion concept as they have both voltage buck and boost capabilities. These inverters use a unique impedance network, coupled between the power source and converter circuit, to provide both voltage buck and boost properties, which cannot be achieved with conventional voltage-source and current-source inverters. To facilitate understanding of Z-source inverter modulation, this paper presents a detailed analysis, showing how various conventional pulse-width modulation strategies can be modified to switch a voltage-type Z-source inverter either continuously or discontinuously, while retaining all the unique harmonic performance features of these conventional modulation strategies. This paper starts by analyzing the modulation requirements of a single-phase H-bridge Z-source inverter, and subsequently extends the analysis to cover the more complex three-phase-leg and four-phase-leg Z-source inverters, with carrier-based implementation reference equations derived for all the inverters. The theoretical and modulation concepts presented have been verified both in simulation and experimentally. [ABSTRACT FROM AUTHOR]

The switching characteristics of an inverter feeding an induction motor controlled with the direct torque control (DTC) technique are assessed in steady state. At first, the application share of the inverter voltage vectors for the stator flux covering half a sextant is defined and predicted. The prediction indicates that, under operation at fixed inverter dc link voltage and stator flux magnitude, the application share depends only on the supply frequency of the motor and, to a small extent, on the load. Afterwards, the inverter transitions and the corresponding phase commutations within a stator flux sextant are analyzed. The outcome of the analysis permits to compute the commutations of the inverter phases in one turn of the stator flux and, from them, the inverter switching frequency is obtained. Its value is influenced by the sampling interval and the control delay arising from the microprocessor implementation of DTC. For given sampling interval and control delay, it is shown that the inverter switching frequency depends on the same quantities as the application share of the inverter voltage vectors. A comparison with the switching characteristics of an inverter controlled with the space vector modulation technique is carried out. At last, the paper discusses the sensitivity of the switching frequency of an inverter for DTC to the following quantities: inverter dc link voltage, sampling interval and control delay. Throughout the paper simulation and experimental results are given to confirm the theoretical findings. [ABSTRACT FROM AUTHOR]

A novel single-stage high-power-factor electronic ballast obtained from the integration of a buck dc-to-dc converter and a half-bridge resonant inverter is analyzed in this paper. The buck converter is operated in discontinuous conduction mode and at constant frequency providing an input power factor high enough to satisfy present standard requirements. The operation of the proposed ballast is also investigated in detail in the paper, obtaining the important equations and characteristics in order to allow interested readers to perform an easy design. A ballast prototype supplying two 36 W fluorescent lamps has been both simulated and implemented at the laboratory. The results predict good market possibilities for the proposed topology in terms of reliability, cost, efficiency, and lamp life. [ABSTRACT FROM AUTHOR]

In this paper, angular modulation index (AMI) implemented through a modified space vector modulation for the dual voltage source inverters (VSI) is proposed with the primarily aiming to reduce switching losses. The desired voltage across the load is synthesized by applying appropriate phase-angle displacement between space vector references. The proposed approach avoids the use of a dc/dc boost converter (which imposes loss and weight/price penalty to duplicate the dc-link voltage) and results to be particularly suitable for electrical/hybrid vehicle applications. Namely, the application of saving energy to keep driving has been identified as major concern. Hence, this work focuses on the strategy to enhance efficiency. The principles of the proposed controlling method and switching loss, which is reduced at least by 50%, are theoretically evaluated. This paper proposes a pioneering mathematical approach to correctly determine total harmonic distortion (THD) value of the voltage/current for the dual-VSI structure. Furthermore, simulation and experimental results prove that the proposed method insures benefits in terms of common-mode voltage, THD of the voltage, and switching loss reduction. The dual-VSI prototype supplying 1.5-kW induction motor is assembled in the laboratory to experimentally evaluate performance of the proposed method. Also, the simulation results carried out through MATLAB/Simulink environment are given to confirm performance of this easy-to-implement and high-efficient method. [ABSTRACT FROM PUBLISHER]

This paper presents a new application of power and voltage balance control schemes for the cascaded H-bridge multilevel inverter (CHMI)-based solid-state transformer (SST) topology. To reduce load on the controller and simplify modulation algorithm, a master–slave control (MSC) strategy is designed for the dual active bridge (DAB) stage. The master controller executes all control and modulation calculations, and the slave controllers manage only device switching and protection. Due to the inherent power and dc-link voltage unbalance in cascaded H-bridge-based SST, this paper presents a compensation strategy based on three-phase dq decoupled current controller. An optimum zero-sequence component is injected in the modulation scheme so that the three-phase grid currents are balanced. Furthermore, to tightly regulate the output voltage of all the DAB modules to target value, a dynamic reference voltage method is also implemented. With this proposed control method, the three-phase grid currents and dc-link voltage in each module can be simultaneously balanced. Finally, simulation and experimental results are presented to validate the performance of the controller and its application to microgrid SST. [ABSTRACT FROM PUBLISHER]

This paper proposes an inductors coupling technique to cancel input current ripples of a quasi-Z-source inverter (ZSI) without adding any additional components. The source input filter thus might be suppressed. This remains valid whatever the boost factor value. This cancellation property is made possible by a suitable coupling of the two existing quasi-Z-source inductors according to mathematical condition. The considered system in this paper is an electric drive system composed of a motor fed by the proposed coupled quasi-ZSI. An experimental prototype to validate both the theoretical and simulation analyses has been developed. The results have validated the proposed coupling strategy and show that it does not degrade the global efficiency of the system. [ABSTRACT FROM PUBLISHER]

This paper proposes a new class of on-board chargers for electric vehicles (EVs). Instead of being placed on-board as a separate unit, the three-phase (fast) chargers reutilize the existing components in EVs, which are already used for the propulsion. These are primarily the inverter and the machine, which however have to be multiphase (with more than three phases). The concept is valid for all multiphase propulsion drives with a prime number of phases higher than three and a single neutral point in motoring and is illustrated in detail for the five-phase inverter/five-phase machine configuration. During the charging mode, electromagnetic torque is not produced in the machine so that the rotor does not require mechanical locking. Hardware reconfiguration between propulsion and fast charging is required, but it is achieved with only two switches, which are the only two nonintegrated elements. The integrated topology is explained in this paper, together with the control scheme, and extension from five phases to higher phase numbers is illustrated using the seven-phase system as an example. Finally, the propulsion-mode operation with complete suppression of low-order harmonics, which map into the second plane, is achieved for the five-phase machine. Experimental verification of theoretical results and proposed control is provided for both charging and vehicle-to-grid mode of operation, as well as for propulsion. [ABSTRACT FROM PUBLISHER]

In this paper, a modulation and control method for the new transformerless unified power flow controller (UPFC) is presented. As is well known, the conventional UPFC that consists of two back-to-back inverters requires bulky and often complicated zigzag transformers for isolation and reaching high power rating with desired voltage waveforms. To overcome this problem, a completely transformerless UPFC based on an innovative configuration of two cascade multilevel inverters has been proposed. The new UPFC offers several advantages over the traditional technology, such as transformerless, light weight, high efficiency, low cost and fast dynamic response. This paper focuses on the modulation and control for this new transformerless UPFC, including optimized fundamental frequency modulation for low total harmonic distortion and high efficiency, independent active and reactive power control over the transmission line, dc-link voltage balance control, etc. The new UPFC with proposed control method is verified by experiments based on 4160-V test setup. Both the steady-state and dynamic-response results will be shown in this paper. [ABSTRACT FROM PUBLISHER]

This paper describes a hybrid modulation scheme for a high-frequency ac-link (HFACL) multistage inverter comprising a front-end dc/ac converter, followed by isolation transformers, an ac/pulsating-dc converter, and a pulsating-dc/ac converter. The hybrid modulation scheme enables 1) removal of the dc-link filter evident in conventional fixed dc-link (FDCL) inverters placed after the ac/pulsating-dc converter stage and before an end stage voltage source inverter and 2) significant reduction in switching loss of the inverter by reducing the high-frequency switching requirement of the pulsating-dc/ac converter by two-third yielding higher efficiency, improved voltage utilization, and reduced current stress. Unlike the FDCL approach, in the HFACL approach, hybrid modulation enables the retention of the sine-wave-modulated switching information at the output of the ac/pulsating-dc converter rather than filtering it to yield a fixed dc thereby reducing the high-frequency switching requirement for the pulsating-dc/ac converter. Overall, the following is outlined: 1) hybrid modulation scheme and its uniqueness, 2) operation of the HFACL inverter using the hybrid modulation scheme, 3) comparison of the efficiency and losses, current stress, and harmonic distortion between the hybrid-modulation-based HFACL inverter and the FDCL inverter, and 4) scaled experimental validation. It is noted that the term hybrid modulation has no similarity with the modulation scheme for a hybrid converter (which are conjugation of two types of converters based on a slow and fast device) reported in the literature. The term hybrid modulation scheme is simply chosen because at any given time only one leg of the inverter output stage (i.e., pulsating-dc/ac converter) switch under high frequency, while the other two legs do not switch. The outlined hybrid modulation scheme is unlike all reported discontinuous modulation schemes where the input is a dc and not a pulsating modulated dc, and at most only one leg stays on or off permanently in a 60° or 120° cycle. [ABSTRACT FROM AUTHOR]

This paper demonstrates the functionality of a power-electronics-based energy management system (EMS). The EMS includes batteries and a digitally controlled single-phase voltage source inverter (VSI), which can be controlled as a current source or a voltage source depending on the status of the ac grid and the user's preference. The EMS guarantees that the critical loads are powered when the ac grid fails; in which case, the VSI is controlled as a voltage source. It also accomplishes peak power control by supplying battery power to the local loads while they are powered by the ac grid if the loads get large. The electricity cost savings accomplished by peak shaving are estimated. The EMS functionality is demonstrated by experimental measurements on a laboratory prototype. The control architecture and logic embedded in the EMS are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper first analyzes the current paths on a planar busbar based on insulated-gate bipolar transistor bridge switching states and dc-link capacitor configurations. The busbar's circuit models which include both self- and mutual inductances are developed based on the identified current paths. The inductance circuit models are analyzed and reduced for different switching states, transition states, and dc-link capacitor configurations. Inductance and current sharing is analyzed based on circuit theory. Both simulations and measurements are conducted to verify the developed technique. [ABSTRACT FROM AUTHOR]

In order to solve the neutral-point voltage unbalancing problem for three-level inverters, this paper proposes a method to balance the neutral-point voltage for three-level inverters with variable modulation wave offset sinusoidal pulse-width modulation (SPWM) control. Based on the mathematical expressions of neutral-point voltage unbalancing, the factors are studied, which affect the fluctuation of neutral-point voltage. Theoretically the mathematical expressions of the neutral-point voltage with the proposed method are derived, and the mathematical relationship between the fluctuation of neutral-point voltage and the adjusting offset of modulation wave is studied. This proposed method realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the modulation wave based on SPWM (DCOSPWM). This DCOSPWM method is very simple, which has good steady-state performance and is easy for digital implementation. The simulation results verify the correctness of the theoretical analysis in this paper, and the feasibility and effectiveness of this method is verified by the experiments in the experimental platform of neutral point clamped three-level inverters based on digital signal processor (DSP)-complex programmable logic device (CPLD). [ABSTRACT FROM AUTHOR]

According to the number of segments, the space vector modulation (SVM) can divide into conventional SVM sequence (CSVMS) and special SVM sequence (SSVMS). It is well known that SVM can be equivalently realized by carrier-based pulse width modulation (CBPWM) with a zero component injection in both two-level and three-level inverters. For eight segment CSVMS in three-level inverters, many papers have ever got the injected zero component equation. But similar approach does not work for SSVMS, which has more than eight segments, e.g., 10, 12, or 14. What more, the accurate injected zero component has never been achieved so far. To solve above problems, therefore, a generated decomposition method of modulation wave has been proposed in this paper. By strict theoretical derivation, the same correlation can be extended to SSVMS and the corresponding zero component expression can be acquired. Based on this method, this paper puts a lot attention on the essential feature explanation, mathematical proof, and gives a detailed process to get the zero component equation, using it can realize SSVMS by CBPWM. The simulation and experimental results illustrate that the generated decomposition method of modulation wave is correct, and the unified theory of CBPWM and SVM is verified. [ABSTRACT FROM AUTHOR]

This paper presents an integrated solution for a photovoltaic (PV)-fed water-pump drive system, which uses an open-end winding induction motor (OEWIM). The dual-inverter-fed OEWIM drive achieves the functionality of a three-level inverter and requires low value dc-bus voltage. This helps in an optimal arrangement of PV modules, which could avoid large strings and helps in improving the PV performance with wide bandwidth of operating voltage. It also reduces the voltage rating of the dc-link capacitors and switching devices used in the system. The proposed control strategy achieves an integration of both maximum power point tracking and V/f control for the efficient utilization of the PV panels and the motor. The proposed control scheme requires the sensing of PV voltage and current only. Thus, the system requires less number of sensors. All the analytical, simulation, and experimental results of this work under different environmental conditions are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper has presented a stability analysis of a LCL-type grid-connected inverter in the discrete-time domain. It has been found that even though the system is stable when the resonance frequency fr is higher than one-sixth of the sampling frequency ( fs/6), an effective damping scheme is still required due to the potential influence of the grid impedance. With a conventional proportional capacitor-current-feedback active damping (AD), the valid damping region is only up to fs/6. This however is not sufficient in the design process for obtaining a high quality output current and the system can easily become unstable due to the resonance frequency shifting. Considering the resonance frequency design rules of the LCL filter, this paper proposes an improved capacitor-current-feedback AD method. With a detailed analysis and proper parameter design, the upper limit of the damping region is extended to fs/4, which can cover all the possible resonance frequencies. Then, the damping performance of the proposed AD method is studied. It shows that the optimal damping is obtained when the actual resonance frequency is (fr + fs/4)/2. Moreover, an approximate calculation for the optimal damping coefficient R is given. Finally, the experimental results have validated the effectiveness of the proposed AD method. [ABSTRACT FROM AUTHOR]

Pulse width modulation schemes are aimed at adjusting the fundamental component while reducing the harmonic content of an inverter output voltage or current. This paper addresses the topic of optimal inverter operation in reference to a given objective function. The objective function could embody either a single performance criterion, such as voltage or current total harmonic distortion (THD), or a weighted sum of multiple criteria. The proposed method ensures primacy of the chosen solution while imposing no restriction over its modulation index. In particular, operating the inverter by the chosen solution would result in performances superior to any other modulation scheme commutating in an equal number of switching angles per fundamental cycle. The proposed method allows for the consideration of practical inverter constraints and prevents the possibility of impractical switching sequence. A detailed investigation of the method is given, accompanied by two practical cases minimizing, respectively, phase-voltage THD and line-current THD of a three-level inverter. Selected simulation and experimental results are presented to validate the theoretical part. [ABSTRACT FROM AUTHOR]

This paper proposes multilevel topologies based on the concept of nested arrangement. Such topologies are called nested multilevel converters, since the central point of the legs are connected at the same point, with the external legs involving the internal ones. Nested configurations present advantages as compared to the equivalent NPC topologies in terms of reduced number of diodes and consequently higher efficiency. In addition to proposing a new family of power electronics converters, this paper presents an optimized pulse widthmodulation strategy that allows synthesizing voltage waveforms with higher quality, a losses comparison with the NPC topology, and a general comparison with other topologies proposed in the technical literature. Simulated and experimental results are presented to validate the theoretical expectations. [ABSTRACT FROM AUTHOR]

In this paper, an immune algorithm (IA)-based dead-time elimination PWM control strategy is proposed. For existing dead-time elimination applications, one of the major problems is the dead-time control around the zero-current-crossing points. To deal with this problem, this paper proposes a different PWM control method which first restricts the control sequence to a specified level around the zero-crossing zone. Also, the proposed method can improve the current waveform quality by using the IA approach and three-level control strategy. Compared with conventional dead-time elimination methods, this technique has the features of simple hardware requirement and adaptive control. Moreover, this control strategy effectively eliminates the effect of dead-time, while at the same time significantly reducing the total harmonic distortion of output current and improving the amplitude of output RMS value in different modulation indexes and loads conditions. To verify the analysis, an experimental platform based on DSP and field-programmable gate array is built. The simulation and experimental results are given to demonstrate the effectiveness and feasibility of this new method. [ABSTRACT FROM AUTHOR]

This paper presents a simple controller integrating a new reactive current reference algorithm for enhancing the transient performance of static synchronous compensator (STATCOM). A multilevel cascaded inverter with separated dc capacitors which is driven by carrier-based pulse width modulation is used to implement the STATCOM. The voltage across each dc-link capacitor is regulated by the rotated switching swapping scheme. In this paper, the STATCOM is controlled to provide both reactive power (VAR) compensation and grid power factor correction at the point of common coupling with a dynamically varying reactive load system. The proposed algorithm enhances the transient performance of the closed-loop system with only proportional controller and minimizes the STATCOM reactive current ripples. STATCOM based on a five-level cascaded inverter is presented in this paper and the performance of the proposed controller is investigated through various simulation studies using MATLAB/Simulink software for both steady state and transient conditions. A laboratory prototype is also developed to verify the simulation results where a good match between simulation and experimental results is achieved. [ABSTRACT FROM AUTHOR]

This paper presents a small film capacitor inverterbased induction motor control approach to enhancewith reliability and power density of three-phase variable speed drive applications. A robust hybrid motor controller is developed to prevent performance degradation caused by the electrolytic capacitor-less inverter fed by front-end diode rectifiers. The structure of the controller combines a model-based controller (MBC) and a hexagon voltage manipulating controller (HVC). The MBC determines the command output voltage with the intersection of the torque and rotor flux linkage command. In the HVC mode, the command voltage vector is determined simply by the torque command and the hexagon-shaped inverter voltage boundary. Successful application of the control approach is corroborated by a graphical and analytical means that naturally lead to a single voltage selection rule. This paper also examines the operation sensitivity under motor parameter drifts to determine how to decouple its effect using a voltage disturbance state-filter design. [ABSTRACT FROM AUTHOR]

Multifunctional grid-tied inverters (MFGTIs) have been paid much attention to handle the commonly concerned power quality issues of the microgrids. An MFGTI can not only interface the renewable energy resource into the utility grid, but also can compensate the harmonic and reactive current in the microgrid as an auxiliary service. However, the apparent capacity of an MFGTI for power quality compensation is limited. Therefore, how to enhance the power quality of the microgrid by optimal utilization of the limited and valuable capacity becomes a technical challenge. In this paper, two optimal control objectives of MFGTIs are presented based on a comprehensive power quality evaluation algorithm by means of analytic hierarchy process theory. One objective aims to obtain the expected power quality using minimal apparent capacity of the MFGTI. Another objective focuses on enhancing the power quality as well as possible in the given available apparent capacity condition. The two proposed strategies are compared in performance, and the paper also discusses how to use them in practice for the best performance. Experimental results performed on a microgrid in the laboratory confirm the validation and feasibility of the proposed optimal control strategies. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase to three-phase power conversion system with parallel rectifier and series inverter to cope with single-phase to three-phase asymmetry. Such converter guarantees both reduction in the input current processed by rectifier circuit and reduction of the output voltage processed by the inverter circuit. It is worth mentioning that, in spite of proposing a topology with features not yet observed on the technical literature, this paper presents a comprehensive model of the proposed converter, modulation strategy, and a general comparison with the conventional configuration. Simulated and experimental results are also presented. [ABSTRACT FROM AUTHOR]

Two-stage single-phase inverters have been widely used as they can achieve voltage matching and galvanic isolation between the input and output. Due to the pulsating output power of the downstream inverter, an ac current at twice the output frequency, which is called second harmonic current (SHC), arises in the input side of the downstream inverter. This SHC will penetrate to the front-end dc-dc converter, leading to reduced conversion efficiency. This paper first analyzes the propagation mechanism of the SHC and load transient response of two-stage single-phase inverters from the viewpoint of output impedance. Then, based on the current mode control and load current feed forward, two control methods to achieve low SHC in the front-end dc-dc converter and fast dynamic performance during load transient are proposed in this paper. Finally, a 2-kW two-stage single-phase inverter prototype has been constructed and tested, and the experimental results are provided to verify the effectiveness of the proposed control methods. [ABSTRACT FROM AUTHOR]

This paper presents a new multilevel selective harmonic elimination pulse-width modulation (MSHE-PWM) technique for transformerless static synchronous compensator (STATCOM) system employing cascaded H-bridge inverter (CHI) configuration. The proposed MSHE-PWM method optimizes both the dc-voltage levels and the switching angles, enabling more harmonics to be eliminated without affecting the structure of the inverter circuit. The method provides constant switching angles and linear pattern of dc-voltage levels over the modulation index range. This in turns eliminates the tedious steps required for manipulating the offline calculated switching angles and therefore, easing the implementation of the MSHE-PWM for dynamic systems. Although the method relies on the availability of the variable dc-voltage levels which can be obtained by various topologies, however, the rapid growth and development in the field of power semiconductor devices led to produce high-efficiency dc-dc converters with a relatively high-voltage capacity and for simplicity, a buck dc-dc converter is considered in this paper. Current and voltage closed loop controllers are implemented for both the STATCOM and the buck converter to meet the reactive power demand at different loading conditions. The technique is further compared with an equivalent conventional carrier-based pulse-width modulation to illustrate its enhanced characteristics. The effectiveness and the theoretical analysis of the proposed approach are verified through both simulation and experimental studies. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase boost-inverter topology is used to condition a typical low output voltage fuel cell (FC) as a stand-alone power supply. The key benefits of the proposed power supply include ability to deliver both the boosting and inversion functions in a single stage, compactness, and low cost. Additionally, the power supply incorporates a battery storage unit through a bidirectional converter to support the slow dynamics of the FC and simultaneously protect the FC as it acts as a filter for the low-frequency harmonics. The three-phase output voltage of the boost-inverter is voltage-mode controlled and the battery unit is current-mode controlled. Analysis, simulation, and experimental results taken from a 1-kW laboratory prototype three-phase boost-inverter operating at 20 kHz and bidirectional converter with two 12 V-24 Ah lead acid batteries are presented to confirm the operational performance of the proposed power supply. [ABSTRACT FROM AUTHOR]

Recent papers have shown advantages of robust controllers compared to the controllers based on classical control theory. Further improvements in performance and stable operating range may be realized through the use of multiple robust controllers, but these are typically complicated to synthesize and implement. The complexity is somewhat relaxed for bumpless-transfer controllers, which have appeared in the literature as an ad hoc gain-scheduling control scheme. The approach is less conservative, easier to synthesize, and easier to implement than a gain-scheduled polytopic controller or other interpolation scheme, and has a larger operating range than a nominal controller. In this paper, an inverter connected to a microgrid is modeled as a linear parameter varying system and bumpless controllers are scheduled using polytopic coordinates and applied to inverters in a microgrid. [ABSTRACT FROM AUTHOR]

Leakage current minimization is one of the most important considerations in transformerless photovoltaic (PV) inverters. In the past, various transformerless PV inverter topologies have been introduced, with leakage current minimized by the means of galvanic isolation and common-mode voltage (CMV) clamping. The galvanic isolation can be achieved via dc-decoupling or ac-decoupling, for isolation on the dc- or ac-side of the inverter, respectively. It has been shown that the latter provides lower losses due to the reduced switch count in conduction path. Nevertheless, leakage current cannot be simply eliminated by galvanic isolation and modulation techniques, due to the presence of switches' junction capacitances and resonant circuit effects. Hence, CMV clamping is used in some topologies to completely eliminate the leakage current. In this paper, several recently proposed transformerless PV inverters with different galvanic isolation methods and CMV clamping technique are analyzed and compared. A simple modified H-bridge zero-voltage state rectifier is also proposed, to combine the benefits of the low-loss ac-decoupling method and the complete leakage current elimination of the CMV clamping method. The performances of different topologies, in terms of CMV, leakage current, total harmonic distortion, losses and efficiencies are compared. The analyses are done theoretically and via simulation studies, and further validated with experimental results. This paper is helpful for the researchers to choose the appropriate topology for transformerless PV applications and to provide the design principles in terms of common-mode behavior and efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a novel energy conversion system for variable speed drives. It consists of a wound rotor machine and an inverter without any rectifier and input filter. In the proposed system, the stator of the machine is directly connected to a single-phase grid and the rotor is connected to three-phase inverter isolated with any external power source. The inverter can not only be connected through slip rings but also integrated on the rotor due to the structure. In this paper, based on the positive and negative sequence model, the rotor, stator powers, and the torque capability in the rotor energy balance and unity grid power factor are analyzed. From these analyses, the vector control methods of the torque, speed, the dc-link voltage of the isolated inverter, and the grid power factor are proposed. Since the power supplied from the single-phase grid is pulsating and the machine is directly connected to the grid, the controlled torque and power inevitably pulsates at twice the grid frequency. Nevertheless, the machine can start, accelerate, and decelerate in the wide range. The experimental results present the performance and the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid electronic and magnetic structure named a variable-inverter-rectifier-transformer (VIRT) that enables a transformer with fractional and reconfigurable effective turns ratios (e.g., 12:0.5, 12:2/3, 12:1, and 12:2). This functionality is valuable in converters with wide operating voltage ranges and high step-up/down, as it offers a means to reduce the turns count and copper loss within the transformer while also facilitating voltage doubling and quadrupling. These properties are especially beneficial for miniaturizing the transformer stage in many power electronics applications, such as universal serial bus wall chargers. We introduce the principle of operation of the structure and present models for its magnetic and electrical behavior. The instance of VIRT described in this paper comprises four half-bridge switching cells distributed around a planar magnetic core and connected to two “half-turns” wound through that core. By controlling the operating modes of the half-bridge cells, we gain control over the flux paths and current paths used in the transformer, and this hybridization enables fractional and reconfigurable effective turns ratios. An experimental prototype integrates the VIRT with a stacked-bridge LLC converter to accommodate a widely varying input (120–380 \textV\text{dc}) and output (5–20 \textV\text{dc}), and VIRT is shown to be highly beneficial in keeping efficiency high over this wide output voltage range. [ABSTRACT FROM AUTHOR]

This paper proposes a new single-phase single-stage switched-boost inverter with four switches. Like the quasi-Z-source inverter and quasi-switched boost inverter (qSBI), the proposed inverter has the main features as continuous input current, buck/boost voltage with single-stage conversion, and shoot-through immunity. Compared to the qSBI, the proposed inverter uses one more capacitor and one less switch. This paper presents the operating principles, pulse-width modulation control strategy, parameter design guidelines, and simulation results for the proposed inverter. To verify the performance of the proposed inverter, an 800-W prototype was built with an 110 V/50 Hz output voltage in stand-alone and grid-connected modes. The simulation and experimental results matched those of the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a new type dc/ac inverter named: hybrid-coupling grid-connected inverter (HGCI) for photovoltaic active power generation with power quality conditioning, which consists of a full-bridge three-phase dc/ac inverter coupling to the power grid in series with a thyristor-controlled LC filter. Compared with the conventional inductive-coupling grid-connected inverter (IGCI) and capacitive-coupling grid-connected inverter (CGCI), the proposed HGCI has distinct characteristics of wide operational range and low dc-link operating voltage. Based on these prominent characteristics, the system cost and operational cost can be reduced. Moreover, it can transfer the active power and compensate reactive power, unbalanced power, and harmonic power simultaneously. In this paper, the analysis of the structure, parameter design, and control method of the HGCI is proposed and presented. Finally, simulation and experimental results are provided to verify the effectiveness and performance of the proposed HGCI in comparison with the IGCI and CGCI. [ABSTRACT FROM AUTHOR]

Wear-out condition monitoring of IGBT modules with failure mode separation gives some benefits. First, it allows proactive maintenance plans. Further, depending on the failure mode, different proactive control strategies can be applied to inverters in order to improve the reliability and availability of power electronic systems. This paper proposes a new method for the separation of two representative wear-out failure modes of wire-bonded IGBT modules in a grid-connected inverter in real time. The proposed method requires just two preliminary I– V characterizations of IGBT modules. Further, only one monitoring parameter is used, and thus, it is cost-effective compared with using one more monitoring parameter in order to separate failure modes. Experimental results verify the validity and feasibility of the proposed method. [ABSTRACT FROM PUBLISHER]

Fast-switching power converters are a key enabling technology for the more electric aircraft (MEA), but the generated electromagnetic interference (EMI) poses significant challenges to the electrification effort. To meet the stringent aerospace EMI standards, passive filters are commonly employed, despite the weight and size constraints imposed by the MEA. Alternatively, the EMI source, i.e., the high dv\text/ dt and di\text/ dt slew rates, can be addressed through waveform-shaping techniques. For example, while most soft-switching converters can reduce switching loss, they do so by switching the semiconductor devices in a slower and smoother manner, resulting in the attenuation of high-frequency harmonics. This paper examines the auxiliary commutated pole inverter (ACPI) topology, and its first contribution is the attenuation of the high-frequency content of its EMI source, that is, the output voltage, in a predictable manner, through the active control of the resonant circuit. This is achieved by first, discussing the time-domain characteristics of trapezoidal and S-shaped pulse-trains that lead to attenuated high-frequency harmonic content, and second, by analyzing the equivalent LC circuit of the ACPI. The design of the inverter is then focused on the active control of the resonant parameters, for a predetermined and enhanced output voltage high-frequency response. The second contribution of this paper is the comparison of the EMI performance of hard switching and of three soft-switching modes, fixed-timing control, variable-timing control, and capacitive turn-offs, and how this informs important metrics such as power efficiency, current stress, and implementation complexity. Finally, the third contribution is on the trade-offs that arise when the primary design goal is enhanced EMI performance as opposed to switching loss reduction. A 5-kW, 3-phase ACPI prototype is used for validating the high-frequency content attenuation at source. It is shown that the ACPI can achieve a 37 dB harmonic attenuation of its output voltage at 4 MHz, compared to a hard-switched inverter. [ABSTRACT FROM AUTHOR]

LCL filters feature low inductance; thus, the injected grid current from an LCL -filtered voltage-source inverter can be easily distorted by grid-voltage harmonics. This problem is especially tough for the control system with inverter-side current feedback (ICF), since the grid-current harmonics can freely flow into the filter capacitor. In this case, because of the loss of harmonic information, traditional harmonic controllers fail to mitigate the grid-current distortion. Although this problem may be avoided using the grid-voltage feedforward scheme, the required differentiators may cause the noise amplification. In light of the above issue, this paper develops a simple method for the ICF control system to mitigate the grid-current harmonics without extra sensors. In the proposed method, resonant harmonic controllers and an additional compensation loop are adopted at the same time. The potential instability introduced by the compensation loop can be avoided through a special design of the compensation position. Finally, the effectiveness of the proposed method for harmonic rejection is verified by detailed experimental results. [ABSTRACT FROM PUBLISHER]

In the traditional three-resistor-based current sampling scheme, the sampled currents will become inaccurate when the duration of zero-voltage vectors of an inverter is too short, which leads to a limited modulation index (MI). To overcome this problem, an improved three-resistor sampling method is proposed by establishing a predictive current model of an inverter load, which is that of an induction motor on the synchronous rotating frame for the demonstration purpose in this paper. The principle of this method is detailed in the paper. Then a simulation model of a vector-controlled induction motor drive that utilizes the proposed current sampling scheme is built in the Simulink environment. Finally, the experiment on the new sampling scheme is performed in both steady-state and dynamic conditions. The results verify that the existing current sampling problems can be solved effectively and the motor can perform well with higher MI under the new scheme. As a result, the loading capacity of the system can be enhanced notably. [ABSTRACT FROM PUBLISHER]

Grid faults are one of the most severe perturbations in power systems. During these extreme disturbances, the reliability of the grid is compromised and the risk of a power outage is increased. To prevent this issue, distributed generation inverters can help the grid by supporting the grid voltages. Voltage support mainly depends on two constraints: the amount of injected current and the grid impedance. This paper proposes a voltage support control scheme that joins these two features. Hence, the control strategy injects the maximum rated current of the inverter. Thus, the inverter takes advantage of the distributed capacities and operates safely during voltage sags. Also, the controller selects the appropriate power references depending on the resistive–inductive grid impedance. Therefore, the grid can be better supported since the voltage at the point of common coupling is improved. Several voltage objectives, which cannot be achieved together, are developed and discussed in detail. These objectives are threefold: to maximize the positive sequence voltage; to minimize the negative sequence voltage; and to maximize the difference between positive and negative sequence voltages. A mathematical optimal solution is obtained for each objective function. This solution is characterized by a safe peak current injection, and by the optimization of the voltage profile in any type of grid connection. Therefore, the proposed control scheme includes advanced features for voltage support during voltage sags, which are applicable to different power facilities in different types of networks. Due to system limitations, a suboptimal solution is also considered, analyzed, and discussed for each of the optimization problems. Experimental results are presented to validate the theoretical solutions. [ABSTRACT FROM AUTHOR]

In this paper, a type of low-frequency integrated ac inductor without inductance coupling is proposed for differential rectifiers/inverters. The objective is to increase the power density of these converters by replacing their two bulky and low-frequency ac inductors with the proposed integrated ac inductor, which is much more compact. The principles of the proposed magnetic integration approach and the optimization procedures are explained in detail. An integrated inductor with 34.9% reduction in volume as compared to its discrete-inductor counterpart is designed and tested via simulations using the software Maxwell. Three integrated inductor prototypes with a core volume reduction of up to 30.9% are constructed in the laboratory and are applied to a buck differential rectifier for experimental verification. Their performance in terms of coupling effect, thermal temperature, power efficiency, and system switching frequency is examined. [ABSTRACT FROM AUTHOR]

This paper presents the tradeoff study of heat sink and output filter volume of a GaN HEMT based single-phase inverter. The selected topology is three-level active neutral point clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under the wide range of operating conditions. The paper starts by introducing the inverter topology, selected pulse width modulation scheme and followed by the device features, static, and dynamic characterization and continues with presenting and discussing the results of extensive experimental and analytical characterization. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of the single phase prototype. The findings from static, dynamic characterization, and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter leads to reduction of the combined total volume, including output filter and heat sink volume. [ABSTRACT FROM AUTHOR]

Microinverters for grid-connected photovoltaic (PV) power conversion systems often require voltage boost due to the low dc voltage of the PV panels. A high-frequency (HF) transformer-isolated differential-mode Ćuk inverter (DMCI) is an attractive topology due to its inherent voltage boost capability and high power density. One of the significant operational issue of the DMCI addressed in this paper is the presence of lower order harmonic distortion in the injected grid current. It is shown that lower order odd and even harmonic voltages are generated with this topology. This problem is accentuated due to the low damping offered by the grid to harmonic voltages. A systematic low-complexity control design is proposed to address this issue. It is shown experimentally that the DMCI operates stably with effective attenuation of the lower order harmonics using the proposed design. Practical operational issues of the DMCI with fast switching GaN field-effect transistor (FET) devices are analyzed and solutions are proposed. It is shown that there can be significant HF noise generation in the DMCI with a frequency range higher than the switching frequency. Practical solutions for resolving HF issues using a combination of circuit layout design and additional passive components are proposed and validated. All of the experimental results are demonstrated on a 500-W GaN-FET-based microinverter prototype. [ABSTRACT FROM PUBLISHER]

Inductive power transfer (IPT) converters are resonant converters that attain optimal energy efficiencies for a certain load range. To achieve maximum efficiency, it is common to cascade the IPT converter with front-side and load-side dc/dc converters. The two dc/dc converters are normally controlled cooperatively for the requirements of output regulation and maximum efficiency tracking using a control technique based on perturbation and observation, which is inevitably slow in response. In this paper, a decoupled control technique is developed. The load-side dc/dc converter is solely responsible for output regulation, while the front-side converter is responsible for impedance-matching of the IPT converter by controlling its input-to-output voltage ratio. The controls are linear and therefore fast. DC and small-signal transfer functions are derived for designing the control parameters. The performances of fast regulation and high efficiency of the IPT converter system are verified using a prototype system. [ABSTRACT FROM AUTHOR]

This paper presents model predictive control of dual-mode Z-source inverters (ZSIs) with capability to operate in islanded and grid-connected mode. The transition from islanded to grid-connected mode and vice versa can cause significant deviation in voltage and current due to mismatch in phase, frequency, and amplitude of voltages. The proposed controller offers seamless transition between the two modes of operations. The main predictive controller objectives are direct decoupled power control in grid-connected mode and load voltage regulation in islanded mode. The proposed direct decoupled active and reactive power control in grid-connected mode enables the dual-mode ZSI to behave as a power conditioning unit for ancillary services such as reactive power compensation. The proposed controller features simplicity, seamless transition between modes of operations, fast dynamic response, and small tracking error under steady-state condition of controller objectives. The operation of the proposed system is verified experimentally. [ABSTRACT FROM PUBLISHER]

Several single-stage topologies have been introduced since kicking off the three-phase Z-source inverter (ZSI), and among these topologies, the quasi-ZSI (qZSI) is the most common one due to its simple structure and continuous input current. Furthermore, different modulation strategies, utilizing multiple reference signals, have been developed as well. However, prior art modulation methods have some demerits, such as the complexity of generating the gate signals, the increased number of switch commutations with continuous commutation at high current level during the entire fundamental cycle, and the multiple commutations at a time. Hence, this paper proposes two modified space vector modulation strategies, aimed at the reduction of the qZSI number of switch commutations at high current level for shorter periods during the fundamental cycle, i.e., reducing the switching loss, simplifying the generation of the gate signals by utilizing only three reference signals, and achieving a single-switch commutation at a time. These modulation strategies are analyzed and compared to the conventional ones, where a reduced-scale 1-kVA three-phase qZSI is designed and simulated using these different modulation strategies. Finally, the 1-kVA three-phase qZSI is implemented experimentally to validate the performance of the proposed modulation strategies and verify the reported analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a novel six-pulse low-frequency (LF) fluctuating high-voltage dc-bus-based power system architecture for fuel cell vehicles (FCVs) application. A novel hybrid modulation scheme consisting of six-pulse modulation at LF scale and modified secondary modulation and 33% pulse width modulation at high-frequency (HF) scale is proposed. Three-phase ac waveforms for the propulsion system of FCVs are generated from LF fluctuating high-voltage dc bus. The proposed modulation technique significantly reduces the switching losses of the bidirectional dual-stage inverter: 1) soft-switching of both sides of the front-end current-fed full-bridge converter is realized; and 2) at any moment, only one leg of back-end three-phase inverter is switched at HF, while the other two legs are kept in on or off states. This tremendously reduces the bidirectional inverter's switching losses and improves the system efficiency. The LF fluctuating high-voltage dc bus allows the elimination of large electrolytic dc-link capacitor, which contributes to a more reliable and compact design. This paper presents the operation, analysis, and design of a bidirectional inverter implementing the proposed hybrid modulation technique. Simulation results obtained from power electronics simulation software PSIM and experimental results from the lab prototype clearly validate the effectiveness of the proposed modulation technique. [ABSTRACT FROM PUBLISHER]

Voltage-sensorless control has been investigated for voltage source inverters (VSIs) for many years due to the reduced system cost and potentially improved system reliability. The VSI-based resistive-active power filters (R-APFs) are now widely used to prevent the harmonic resonance in power distribution network, for which the voltage sensors are needed in order to obtain the current reference. In this paper, a grid-voltage-sensorless control strategy is proposed for the R-APF with series LC-filter. Unlike the traditional resistance emulation method, this proposed control method reshapes the output impedance of the R-APF at the harmonic frequencies, which is independent of the current reference. A fundamental grid-voltage estimation method is also proposed to control the dc-link voltage. The performance of the proposed control method is verified in both simulations and experiments. The results show good accuracy of the emulated resistance and functionality of the dc-link voltage control. With the proposed method, the cost of the R-APF can also be reduced with potentially improved system reliability. [ABSTRACT FROM PUBLISHER]

Stability analysis of power converters in ac networks is complex due to the nonlinear nature of the conversion systems. Whereas interactions of converters in dc networks can be studied by linearizing about the operating point, the extension of the same approach to ac systems poses serious challenges, especially for single-phase or unbalanced three-phase systems. A general method for stability analysis of power converters suitable for single-phase or unbalanced ac networks is presented in this paper, based on linear time periodic theory. A single-phase grid-connected inverter with phase-locked loop (PLL) is considered as case study. It is demonstrated that the stability boundaries can be precisely evaluated by the proposed method, despite the nonlinearity introduced by the PLL. Simulation and experimental results from a 10-kW laboratory prototype are provided to confirm the effectiveness of the proposed analysis. [ABSTRACT FROM PUBLISHER]

Grid impedance and the output impedance of grid-connected inverter are important parameters for the operation of grid-connected systems, such as solar, wind, and other distributed-generation resource systems. The impedance mismatch between the grid and the interfacing circuit often generates harmonic resonances that lead to reduced power quality and even instability. Since the impedances usually vary over time as a function of many parameters, online measurements are required for stability assessment and adaptive control of the inverters. Several methods have been proposed for quick, accurate measurements of impedances, but the use of multiple-input multiple-output (MIMO) identification techniques have not been considered. Applying the MIMO techniques, different components of the inverter output impedance or grid impedance can be simultaneously measured during a single measurement cycle. Therefore, the operating conditions of the system can be kept constant during the measurements, and the overall measurement time is significantly reduced. This paper shows the use of orthogonal binary sequences to simultaneously measure the “d” and “q” components of grid-connected inverter output impedance and/or grid impedance. Experimental results based on a three-phase grid-connected inverter are presented and used to demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

This paper introduces series work of common-mode (CM) voltage reduction for the paralleled inverters. The paralleled inverters’ phase-legs are connected through coupling inductors and the combined three-phase currents are provided to the load. Interleaving is an approach to reduce the CM voltage for the paralleled inverters but it cannot eliminate CM voltage. A novel pulse-width-modulation (PWM) method for paralleled inverters which can theoretically achieve zero CM voltage is developed. Considering the basic voltage vectors in each inverter, novel paralleled voltage vectors which have zero CM voltage are proposed to combine the reference voltage vector. The action time's distribution and voltage vectors’ sending sequence for each inverter are also introduced. The proposed PWM method can make sure the voltage of the two inverters are balanced in each switching cycle and limits the circulating current through small coupling inductors. Similar to interleaving space vector PWM, the proposed zero CM PWM also has the ability to reduce the output current ripple and electromagnetic interference (EMI). Simulation and experimental results are provided to show the advantage of paralleled inverters in CM voltage reduction and validate the proposed method has good performance to reduce CM current and CM EMI noise. [ABSTRACT FROM PUBLISHER]

Open-circuit (OC) fault diagnosis of voltage source inverters on trains still has two problems to be improved. First, it is usually forbidden to change the system structures of trains or to add any extra sensor. Therefore, diagnostic methods which need pulse width modulation control signals or extra output voltage sensors are no longer suitable for trains. Second, loads on the train vary in a wide range and have significant influence on output currents. In order to solve these problems and increase the maintenance efficiency, an online diagnostic method for single switch OC (SSOC) faults and double switches OC (DSOC) faults is proposed. Supposing that three phases are balanced, it is proved that the trajectory of two output currents is an ellipse in the Cartesian coordination, and each OC fault has a unique trajectory. SSOC faults and DSOC faults can be isolated by detecting abnormal slopes and directions of several consecutive points on the trajectory. The fastest diagnostic process takes less than half a period. Load variation has impact on the size and shape of the trajectory but does not affect the diagnostic method. Experimental tests are carried out on dSPACE platform. Results show the accuracy of the mathematical model and the effectiveness of the online diagnostic method proposed in this paper. [ABSTRACT FROM PUBLISHER]

This paper proposes a current sensorless control strategy for the dual active bridge (DAB) converter with nonlinear disturbance observer (NDO)-based load current feedforward. The proposed method can regulate both the dc-bus voltage and the current of the DAB converter without current sensors. Several performance indexes are established for the parameter design and a detailed design method is presented in this paper. When a single-phase H-bridge inverter is connected, the double-frequency oscillation from the feedback path is suppressed by proper parameter design, while the transient response of dc-bus voltage can be further improved by the NDO-based load current feedforward with a notch filter in the feedforward path. The performance of the proposed control method and the effectiveness of the parameter design are verified in a prototype by experimental results. [ABSTRACT FROM PUBLISHER]