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Three-phase inverters in uninterrupted power supply, electric vehicles, and hybrid electric vehicles use an intermediate dc-link electrolytic capacitor, which has reliability issues and is one prominent cause of inverter failure and limited life. The large volume of an electrolytic capacitor increases the size and cost of the system. Recent research on electrolytic capacitorless inverters using six-pulse modulation technique along with high-frequency power conversion has attempted to address this issue. However, closed-loop operation and control has some issues due to capacitorless dc-link. In this paper, closed-loop operation, design, and implementation of an electrolytic capacitorless inverter is presented. A proof-of-concept 1-kW hardware prototype has been built and tested in a laboratory under different loading conditions. In total, 98% rated efficiency of the inverter is obtained with total harmonic distortion within 2%. Transient results during start-up and load change are smooth, demonstrating safe operation of the inverter. [ABSTRACT FROM AUTHOR]

A method for the seamless transition of three-phase inverters switched between grid-tied and stand-alone modes of operation is presented in this paper. In this method, only the inverter current and voltage sensors are utilized, and no control over the grid-side static transfer switch is needed. The presented method contains two strategies for grid-tied-to-stand-alone and stand-alone-to-grid-tied transitions. In the stand-alone-to-grid-tied transition strategy, a novel algorithm is presented for estimating the grid angle nearly instantaneously, which allows the three-phase inverter to respond very quickly if the grid and point-of-common-coupling voltages are out of phase. This fast response allows the inverter to effectively eliminate the transient overcurrent that would normally occur if it was connected to the grid without first being synchronized. The fast response also allows the inverter to return to normal operation very quickly after such an event. The strategy for the seamless transition from grid-tied to stand-alone mode is also presented. These strategies have been verified through experiments, and the results are presented in this paper. [ABSTRACT FROM PUBLISHER]

In this paper, the recently introduced model predictive pulse pattern control (\MP^3\C) strategy is adapted to the ACS 2000 medium-voltage (MV) drive of ABB. The drive system consists of a five-level active neutral-point-clamped (ANPC-5L) rectifier, an inverter, and an induction machine (IM). The inverter is fed with offline-computed optimized pulse patterns (OPPs) that produce minimum harmonic distortion in the stator windings of the ac machine. An optimal stator flux trajectory is calculated from these OPPs, and a trajectory controller tracks it in real time. In the proposed approach, trajectory tracking is based on model predictive control: a constrained optimal control problem is formulated and solved in real time in a computationally efficient manner. An event-based prediction horizon is employed in order to ensure fast tracking of the stator flux trajectory. The advantages of the proposed method are optimal steady-state behavior in terms of harmonic distortion and fast torque response. The method was tested on an MV ANPC-5L inverter coupled to a general-purpose 1.21-MW IM. Experimental results were obtained from this industrial setup, and they are presented in this paper to demonstrate the high performance of \MP^3\C. [ABSTRACT FROM PUBLISHER]

This paper presents a theoretical study with experimental validation of a circulating-current suppression method for parallel operation of three-phase voltage-source inverters (VSI), which may be suitable for modular parallel uninterruptible power supply systems or hybrid ac/dc microgrid applications. The basic concept of the proposed circulating-current suppression method is to modify the original current references by using the current difference among the parallel inverters. In the proposed approach, both cross circulating current and zero-sequence circulating current are considered, and are added into the conventional droop plus virtual impedance control. In the control architecture, the reference voltages of the inverters are generated by the primary control loop, which consists of a droop control and a virtual impedance. The secondary control is used to compensate the voltage drop on the virtual impedance. Furthermore, a circulating-current control loop is added to improve the average current-sharing performance among parallel VSIs. Experimental results are presented to show the effectiveness of the proposed control method to suppress both cross and zero-sequence circulating currents. [ABSTRACT FROM AUTHOR]

Computational burden is a major hurdle for practical implementation of finite-state predictive torque control (FS-PTC) of motor drive fed by a multilevel inverter. One of the reasons of computational complexity is that all voltage vectors are evaluated for prediction and actuation. This paper proposes a reduced number of voltage vectors for the prediction and actuation, which are called prediction vectors in FS-PTC. The performance is investigated for a three-level neutral-point clamped inverter fed motor drive in terms of torque and flux response, stator current total harmonic distortion, robustness, average switching frequency, and neutral-point voltage variation. The number of prediction vectors is reduced based on the position of stator flux and the deviation in stator flux from its reference. Experimental results confirm that the computational burden could be reduced by 38%, while the dynamic performance is comparable with the conventional all voltage vectors based FS-PTC. [ABSTRACT FROM AUTHOR]

The performance of a novel three-phase four-leg fault-tolerant T-type inverter topology is introduced in this paper. This inverter topology provides a fault-tolerant solution to any open-circuit and certain short-circuit switching faults in the power devices. During any of the fault-tolerant operation modes for these device faults, there is no derating required in the inverter output voltage or output power. In addition, overload capability is increased in this new T-type inverter compared to that in the conventional three-level T-type inverter. Such increase in inverter overload capability is due to the utilization of the redundant leg for overload current sharing with other main phase legs under healthy condition. Moreover, if the redundant phase leg is composed of silicon carbide metal-oxide-semiconductor field-effect transistors, quasi-zero-voltage switching, and zero-current switching of the silicon insulated-gate bipolar transistors (IGBTs) in the conventional main phase legs can be achieved at certain switching states, which can significantly relieve the thermal stress on the outer IGBTs and improve the whole inverter efficiency. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant T-type inverter topology. [ABSTRACT FROM PUBLISHER]

This paper identifies possible topological reconfigurability of a T-type inverter for direct torque controlled (DTC) induction motor drives when an open-switch fault occurs. In open-switch fault, inverter current path is different than normal path. This causes undesirable inverter switching states. Since DTC is based on a voltage vector selection criterion, open-switch fault causes ambiguous torque control. Analysis of DTC drive under two different inverter open-switch fault conditions viz. half-bridge and neutral-point switch fault are presented. The operation of the inverter in DTC mode against faults is achieved by simple topological reconfiguration. [ABSTRACT FROM PUBLISHER]

Short-circuit detection is a fundamental function of most inverters. In this paper, two new fast and easily implementable short-circuit detection approaches are presented. The first one offers a significantly accelerated desaturation detection. The second one allows a full inverter to be protected by only one short-circuit detection circuit. Both approaches are verified by simulations and hardware tests. [ABSTRACT FROM PUBLISHER]

This paper proposes and investigates a multilevel ac six-phase motor drive. The system is composed of five isolated three-leg voltage source inverters feeding the open-end windings of an asymmetrical six-phase induction motor (SPIM), which is adequate to generate multilevel voltages for high-power systems with voltage rating restrictions. A simple space vector pulse-width modulation (PWM) based on three similar individual planes and its implementation by means of equivalent level-shifted PWM are presented. A space vector pattern with a high number of voltage vectors redundancies is obtained. These redundancies and the application sequence of the voltage vectors are selected to minimize the amount of changes in the switching states and to decrease the harmonic distortion of the generated voltages. The vector pattern of this optimal modulation is obtained by analyzing only one plane and applied in the same way to the three planes as if they were independent. The developed PWM techniques have low computational complexity and are suitable for low-cost hardware implementations. Simulation results are used to compare the proposed topology with a conventional configuration in terms of harmonic distortion and semiconductor losses. Experimental results demonstrate the feasibility of the proposed drive system. [ABSTRACT FROM AUTHOR]

This paper presents a comparative evaluation of the loss and thermal performance of two advanced three-level inverter topologies, namely the partial silicon carbide (SiC) T-Type and the Hybrid-neutral-point-clamped (NPC), both of which are aimed at reducing the high switching losses associated with a conventional Si T-Type inverter. The first solution directly replaces the 1200 V primary Si IGBT switches with lower loss 1200 V SiC MOSFETs. The second solution strategically adds 600 V CoolMos FET devices to the conventional Si T-Type inverter to reduce the primary commutation losses. Semiconductor loss models, experimentally verified on calibrated heat sinks, are used to show that both variations can significantly reduce the semiconductor losses compared with the Si T-Type inverter. The results show that both alternatives are attractive if high efficiencies and reduced thermal stress are major requirements for the converter design. [ABSTRACT FROM PUBLISHER]

In this paper, a novel space-vector pulse-width modulation (PWM) scheme for reducing the common-mode voltage (CMV) in the three-phase five-level active neutral-point clamped (5L-ANPC) inverter is proposed, where only the 55 selected voltage vectors among the entire 125 that produce low values of the CMV are utilized. This PWM scheme can significantly reduce the CMV without the increase of switching losses and total harmonic distortion of the output voltages. With the 55 selected voltage vectors, the inverter can still operate up to the maximum modulation index. In addition, the capacitor voltages are controlled by redundant switches of the 5L-ANPC inverters. It has been shown that the peak value of the CMV is decreased to one-twelfth of the dc-link voltage from the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

One of the problems of the pulse-width-modulation (PWM)-controlled ac machines is the acoustic noise that could become unacceptable when used in sensitive environments. Random PWM (RPWM) in industrial and commercial adjustable-speed drives (ASD) results in the partial transfer of power from the discrete spectrum (narrowband noise) of the output voltage to the continuous spectrum (wideband noise), with advantageous effects on reducing the acoustic noise in the motor drive system. In this paper, the theoretical power spectrum analysis as the basis for RPWM is presented. Five state-of-the-art RPWM strategies, their voltage, current, and acoustic noise spectra characteristics are quantitatively evaluated. The PWM schemes and theoretical analysis are validated through a 2.2-kW 380-V 50-Hz ASD induction machine experimental setup. The results provide valuable data for practicing engineering community to choose the best option in real-world applications. [ABSTRACT FROM PUBLISHER]

Common-mode voltage (CMV) in voltage-source inverters (VSIs) has been well defined and is frequently referred to in the literature. While often referred to, there is no real consistency with respect to how the CMV properties of an individual modulation scheme are evaluated, lacking tools to assess the relative merits or disadvantages of a certain topology or modification of a control scheme. The way that it is analyzed is still mostly a matter of the different authors' foci. In this paper, we propose a metric for the analysis of the CMV, aiming to fill the aforementioned gap. Thereby, the CMV in VSIs is quantified by the number of possible levels and the step sizes between different levels, as well as the respective frequencies of occurrence. The first two are given by the number of levels and the number of phases of the inverter. Depending on the modulation (control) schemes, all possibly available levels or a few of these levels are present in the CMV. We illustrate the use of the tool by applying it to thoroughly study the CMV properties intrinsic to the topologies of multilevel multiphase single- as well as double-ended diode-clamped VSI drive systems. As part of this analysis, we uncover new relationships concerning the existence of zero CMV level. Furthermore, we exemplarily apply the developed tool to the assessment of the CMV properties of selected pulse width modulation (PWM) control schemes and translate the findings into an interpretation of the endangerment of a given drive to suffer damage from inverter-induced bearing currents. The theoretical findings are supported by measurements. This paper also reviews the literature on CMV in multilevel multiphase VSI systems. With the proposed metric in mind, the CMV being mostly discussed as an element of different foci becomes even clearer, confirming again the need for the development of such a tool. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of pulse width modulation (PWM) on the circulating current of parallel-connected four-pole inverters (FPIs). Detailed mathematical modeling shows that the common-mode voltage (CMV) outputs of PWMs are closely related to the circulating current, so this research presents the reduced CMV PWM techniques for FPIs to reduce the circulating current, and compares their performances with the conventional PWM schemes. This study also shows how the controller structure of FPI affects the use of PWM schemes and the resulting circulating current. Laboratory test results are provided to validate their effectiveness. [ABSTRACT FROM AUTHOR]

This paper identifies the characteristics of a current source inverter operating in discontinuous conduction mode, and proposes a new multiobjective pulse-width modulation (PWM) method to mitigate voltage boosting and harmonic distortion effects. The method takes into account load impedance effects. Controls are also developed to enable transition between the multiobjective PWM method and conventional PWM as the current source inverter operates in discontinuous and continuous modes of operation. The concept is verified experimentally on a 3 kW test bed. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of the independent drive characteristics of two three-phase induction motors (IMs) fed by a four-leg inverter (FLI). The FLI is a single inverter that can drive two three-phase ac motors independently. The inverter consists of four legs and two capacitors connected in a series. The U and V phases of both motors are connected in each leg, respectively, whereas the W phase of both motors is connected in the neutral point of two-sprit capacitors. The pulsewidth modulation technique in three-phase voltage source inverter is not directly applicable for the FLI because only two phases must be modulated. Then, this paper also analyzes about the neutral point potential of two-sprit capacitors and inverter output voltage. Next, the modulation technique in the FLI is also shown. The experimental results demonstrate the characteristics of two IM independent drives and the validity of those analytic results. [ABSTRACT FROM AUTHOR]

The conventional current-source inverter has two major problems: unidirectional power flow and voltage boost operation, which make it impossible to be used in many applications, such as hybrid electric vehicles and general-purpose variable-speed motor drives. Z-source inverters (ZSIs) can solve both problems. Quasi-ZSIs (qZSIs) were recently proposed as an important improvement to traditional ZSIs. Besides the advantages inherited from ZSIs, qZSIs also have several of their own merits. This paper presents a comprehensive study on the new features of current-fed qZSI, including the advantageous buck–boost function, improved reliability, reduced passive component ratings, and unique regeneration capability. The current-fed qZSIs are bidirectional with an additional diode, unlike the voltage-fed ZSI that needs a switch to achieve bidirectional power flow. A modified space vector pulse-width-modulation method is proposed, and the available operating regions for motoring and regeneration operation are analyzed in this paper. Since the current-fed qZSI has the same operation as the current-fed ZSI, many results of this paper are also applicable to the current-fed ZSI. A reverse-blocking insulated-gate bipolar-transistor-based current-fed qZSI prototype was developed in the laboratory. Simulation and experimental results are shown to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

A space-vector-based bang–bang controller, driving a rotating target system [space-vector bang–bang controller with flux aligned hysteresis shape (SVBF)] such as a machine or an ac power supply, is discussed in this paper. A two-level three-phase conventional inverter is used as a means of power conversion. The advantages, such as a low switching frequency as well as further opportunities of the SVBF, are specified. The results show the high degree of flexibility and potential for the SVBF in future applications. [ABSTRACT FROM PUBLISHER]

In this paper, a novel multilevel dc–ac inverter is proposed. The proposed multilevel inverter generates seven-level ac output voltage with the appropriate gate signals’ design. Also, the low-pass filter is used to reduce the total harmonic distortion of the sinusoidal output voltage. The switching losses and the voltage stress of power devices can be reduced in the proposed multilevel inverter. The operating principles of the proposed inverter and the voltage balancing method of input capacitors are discussed. Finally, a laboratory prototype multilevel inverter with 400-V input voltage and output 220\ \textV\text{rms}/2\,{\text{kW}} is implemented. The multilevel inverter is controlled with sinusoidal pulse-width modulation (SPWM) by TMS320LF2407 digital signal processor (DSP). Experimental results show that the maximum efficiency is 96.9% and the full load efficiency is 94.6%. [ABSTRACT FROM AUTHOR]

This paper proposes a simple, cost-effective, and efficient brushless dc (BLDC) motor drive for solar photovoltaic (SPV) array-fed water pumping system. A zeta converter is utilized to extract the maximum available power from the SPV array. The proposed control algorithm eliminates phase current sensors and adapts a fundamental frequency switching of the voltage source inverter (VSI), thus avoiding the power losses due to high frequency switching. No additional control or circuitry is used for speed control of the BLDC motor. The speed is controlled through a variable dc link voltage of VSI. An appropriate control of zeta converter through the incremental conductance maximum power point tracking (INC-MPPT) algorithm offers soft starting of the BLDC motor. The proposed water pumping system is designed and modeled such that the performance is not affected under dynamic conditions. The suitability of proposed system at practical operating conditions is demonstrated through simulation results using MATLAB/Simulink followed by an experimental validation. [ABSTRACT FROM AUTHOR]

In this paper, two modulation strategies called Mod-1 and Mod-2 are compared for a three-level diode neutral-point-clamped (NPC) inverter synchronous reluctance machine (SynRM) drive. These modulation strategies do not operate at a fixed switching frequency. A new modulation strategy which operates at a fixed switching frequency is proposed called Mod-3. The SynRM suffers from a poor power factor which makes it harder to archive capacitor voltage balancing for a three-level NPC inverter. These modulation strategies are of the nearest three vector (NTV) family. Mod-1 and Mod-3 choose certain vector states to achieve capacitor voltage balancing, whereas Mod-2 strategy makes use of the inverter vector state’s dwell time. The parameters of interest are the torque ripple, the neutral point (NP) voltage ripple, the inverter efficiency, and the $d$-axis current ripple. Though lower torque ripple and better power quality are registered on Mod-2 strategy. Mod-1 strategy has 14% improvement in inverter efficiency at lower modulation index ($m_i = 0.4$). Mod-2 strategy has 11% more NP voltage ripple at a modulation index of 0.4. One of the disadvantages of Mod-1 strategy is the varying switching frequency. Mod-3 scheme produced higher inverter efficiency, better balancing of the capacitor voltages, and guaranteed fixed inverter switching frequency. The disadvantage with Mod-3 strategy is that it generated higher torque ripple, $d$-axis current ripple, and current total harmonic distortion when compared to Mod-1 and Mod-2 at the same load conditions. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated field and armature current control strategy for a variable flux reluctance machine (VFRM) with an open-winding topology. By using an open-winding inverter, the field and armature currents can be injected into a single coil as a sinusoidal current biased by the dc offset rather than the separated field and armature windings. The integrated current control can reduce the copper loss to half and extend the operating speed range owing to the reduction in the winding resistance. In order to utilize the zero-sequence current as a field current, a zero-vector modification technique is proposed, in which the switching-on time of the zero vectors is modified to generate the constant zero-sequence voltage between two inverters. The proposed scheme is implemented in a synchronous $dq0$-axis frame with space vector modulation. For the validation of the proposed method, a machine model of the VFRM is developed and implemented in MATLAB/Simulink. The simulation and experimental results verify that the proposed strategy can effectively reduce the copper loss and extend the operating speed range. [ABSTRACT FROM AUTHOR]

A digital dead-beat current controller for voltage source converters is presented in this paper. The control structure is specified in a digital hardware description language, synthesized, and deployed on a field-programmable gate array chip. By updating, with negligible computation delay, the duty cycle twice in a switching period, the reference current error is nulled in half a modulation period, so that the controller's small-signal bandwidth is maximized. In addition, due to a simple transient detection circuit, the large-signal response delay is reduced to a small fraction of the modulation period, which is determined by the chosen current signal oversampling rate. The controller can effectively support different voltage-source inverter applications, such as active filters, uninterruptible power supplies, microgrid distributed energy resource controllers, and dc–dc converter applications, including interface converters for renewable energy sources, laboratory battery chargers, and electronic welding machines. [ABSTRACT FROM AUTHOR]

In the square-wave voltage signal injection sensorless drive of the interior permanent-magnet synchronous machine, the injection voltage can be distorted by the inverter nonlinearity effects especially when the injection voltage is low. If that happens, a high-frequency (HF) current signal which contains the rotor position information could be also distorted, which directly leads to an error in the position estimation. This paper analyzes the effects of the inverter nonlinearity on injection voltage, on induced current ripple, and on the position estimation performance in sequence and proposes a voltage injection method to minimize the impact of the inverter nonlinearity by the regulation of the HF current ripple. By simulations and experiments, the performance of the proposed method has been verified. The experimental results show 19.7% reduction of position estimation error under 15% of rated voltage signal injection without increasing the current ripple at a certain operating condition. Moreover, the performance of position estimation is kept uniform regardless of the loading condition. [ABSTRACT FROM AUTHOR]

The maximum power point should be continuously tracked in a photovoltaic (PV) inverter. However, the maximum power point could be found at very low dc-link voltages around sunrise or sunset. Then, the overmodulation (OVM) of the inverter has to be considered to keep the power generation even at low dc-link voltages. In this paper, a series of implementation schemes is proposed to keep the current regulation, even if the inverter is under the OVM. These schemes can be helpful to increase the operating time of the PV inverter, which correlates with the daily amount of power generation. After being examined in a small-scale prototype inverter, the proposed method has been tested with a 250-kW PV inverter installed at a proving ground. In a sunset, the operation time of the inverter has been extended by about 12 min, and the generated energy has been increased by 234 Wh, when compared to the normal operation without the proposed methods. [ABSTRACT FROM AUTHOR]

This paper proposes a novel 3 $\phi$ stand-alone solar photovoltaic (PV) system configuration that uses high-gain high-efficiency $(\approx\! 96\%)$ dc–dc converters both in the forward power stage and the bidirectional battery interface. The high-voltage-gain converters enable the use of low-voltage PV and battery sources. This results in minimization of partial shading and parasitic capacitance effects on the PV source. Series connection of a large number of battery modules is obviated, preventing the overcharging and deep discharging issues that reduce the battery life. In addition, the proposed configuration facilitates “required power tracking (RPT)” of the PV source as per the load requirements, eliminating the use of expensive and “difficult to manage” dump loads. High-performance inverter operation is achieved through $abc$ to $dq$ reference frame transformation, which helps in generating precise information about the load's active power component for RPT, regulation of ac output voltage, and minimization of control complexity. Inverter output voltage is regulated by controlling the modulation index of sinusoidal pulsewidth modulation, resulting in a stable and reliable system operation. The active power demand is controlled by regulating the dc link voltage. All the analytical, simulation, and experimental results of this work are presented. [ABSTRACT FROM PUBLISHER]

This paper presents the design process of a 312-kVA three-phase silicon carbide inverter using ten parallel-connected metal–oxide–semiconductor field-effect-transistor power modules in each phase leg. The design processes of the gate-drive circuits with short-circuit protection and power circuit layout are also presented. Measurements in order to evaluate the performance of the gate-drive circuits have been performed using a double-pulse setup. Moreover, electrical and thermal measurements in order to evaluate the transient performance and steady-state operation of the parallel-connected power modules are shown. Experimental results showing proper steady-state operation of the power converter are also presented. Taking into account measured data, an efficiency of approximately 99.3% at the rated power has been measured for the inverter. [ABSTRACT FROM PUBLISHER]

Three-level neutral point clamped (NPC) inverters exhibit a natural balancing property that can self-regulate the intermediate neutral point voltage to half the overall dc-link voltage. However, the underlying mechanisms of this process are not well understood, its performance under various load conditions has not been properly explored, and the requirements and benefits of ( $RLC$) balance booster filters to enhance the natural balancing response are not clear. This paper presents a generalized model of an NPC natural balancing process that allows these issues to be explored for various load structures and balance booster configurations (i.e., isolated wye, wye with a grounded star point, etc.). The model accurately predicts the dominant balancing time constant, identifies the harmonics that drive the balancing process, and can quantify the steady-state balance booster losses for a designed target natural balance response. Extensive simulation and experimental tests have been performed to validate the theoretical model. [ABSTRACT FROM PUBLISHER]

Multilevel converters (MLCs) emerged as standard solutions for medium voltage (MV) high-power industrial ac drives. MV drives require low device switching frequency operation due to the higher switching losses of semiconductor devices. However, low device switching frequency operation leads to an increase in the harmonic distortion of machine stator currents. Therefore, there is a need to implement low switching frequency modulation technique for MLCs, which does not compromise on the harmonic distortion of machine currents. The goal of this paper is to propose a new optimal pulsewidth modulation technique for a cascaded seven level (7L) inverter such that the maximum device switching frequency is limited to the rated fundamental frequency (50/60 Hz) and all power semiconductor devices operate at identical switching frequency. Optimal switching patterns were determined offline assuming steady-state conditions. Later, switching angles for each semiconductor device are determined and stored in an FPGA controller. A low-power prototype of the 7L cascade inverter has been developed to demonstrate the proposed modulation technique. The experimental results demonstrated that the proposed optimal modulation technique maintains the quality of machine stator currents while the device switching frequency is limited to the rated fundamental frequency. [ABSTRACT FROM PUBLISHER]

As required by international standards, the distributed energy generators, connected to the grid by an inverter, have to detect an islanding condition within a suitable time interval. In this paper, a phase-locked loop (PLL), based on a third-order prediction-correction filter, is proposed to implement an islanding detector with reduced detection time. Such a feature is obtained using the estimation of the grid angular frequency and acceleration provided by the PLL with a negligible time delay. The proposed approach is implemented on an industrial grade DSP and validated through the experimental comparison among different detection methods, such as rate of change of frequency (ROCOF) and Slip Mode frequency Shift (SMS). The combined use of ROCOF and SMS is also illustrated and discussed. [ABSTRACT FROM AUTHOR]

Resonant converters used as coil drivers in inductive links generally operate efficiently at optimum switching conditions for constant load values and ranges. Changes in load and range can shift the operation of the coil driver to a nonoptimum switching state which results in higher switching losses and reduced output power levels. This paper presents a method to adapt to variations in range for a Class E inverter used as a coil driver in a wireless power transfer (WPT) system based on inductive coupling. It is shown that by controlling the duty cycle of the inverter's switch and the value of its dc-feed inductance, the Class E inverter can be tuned to operate at optimum switching conditions as the distance between the coils of the WPT system changes. Mathematical analysis is presented based on a linear piecewise state-space representation of the inverter and the inductive link. Extensive experimental results are presented to verify the performed analysis and validity of the proposed tuning procedure. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid switch that parallels a power MOSFET and an insulated-gate bipolar transistor (IGBT) as the main switch of a zero-voltage switching (ZVS) inverter. The combination features the MOSFET conducting in the low-current region and the IGBT conducting in the high-current region, and the soft switching avoids the reverse recovery problem during the device turn-on. A custom hybrid switch module has been developed for a variable-timing-controlled coupled-magnetic-type ZVS inverter with a nominal input voltage of 325 V and the continuous output power of 30 kW for a traction motor drive. Experimental results of the hybrid-switch-based inverter with the total loss projected by temperature indicate that the inverter achieves 99% efficiency at the nominal condition and demonstrate ultrahigh-efficiency operation over a wide load range. At 375-V input, the maximum measured efficiency through temperature projection and loss separation analysis is 99.3%. [ABSTRACT FROM PUBLISHER]

There are several ways to model three-phase gridconnected voltage-source inverters (VSIs) with an $LCL$ filter. Such models often use simplifications like constant dc-link voltage or averaging over a switching period. These simplifications remove transistor switching and dc-link capacitor dynamics from the model. In this paper, a comprehensive modeling of a three-phase VSI, including an $LCL$ filter, is described and compared to models using one or more of the aforementioned simplifications. Advantages and disadvantages of different models are discussed. All simulations are verified by comparing with experimental results. [ABSTRACT FROM PUBLISHER]

The advancement in power electronics has made the use of any number of phases in ac machines possible since with the inverter, any number of phase voltages can be realized as long as the corresponding inverter exists. To supply multiphase drives requires multiphase voltage source inverters (VSIs) whose output voltages depend very much on the methods of generating the pulses to turn on and turn off the inverter devices appropriately. This paper presents an analytical technique for the determination of the expressions for the modulation signals used in the carrier-based sinusoidal and generalized discontinuous pulse width modulation schemes for two-level, five-phase voltage source converters. These expressions can be used for both balanced and unbalanced phase voltages generated by any two-level multiphase inverter, in generating the required reference signals appropriately. An example of a five-phase VSI is presented to illustrate the strategy. Simulation and experimental results are presented in which a close examination shows that both results are similar for the balanced and unbalanced load voltage cases. [ABSTRACT FROM AUTHOR]

This paper proposes a smooth transition control strategy for voltage-source inverters between standalone (SA) and grid-connected (GC) modes of operation. In the GC mode, the amount of power exchanged with the utility grid is controlled by regulating the phase currents. In the SA mode, the load voltage is regulated by the inverter with its phase dictated by the inverter control. The transition between SA and GC operations that will ensure continuous power delivery to the load requires continuation in the phase of the system voltage. The proportional–integral, trapezoidal, sinusoidal, and staircase frequency variation techniques have been analyzed to find the best approach for minimizing the total harmonic distortion (THD). A smooth frequency variation technique has been developed, which provides lower THD on the voltage waveforms compared with the other techniques. The new algorithm has been implemented on a 5-kW single-phase utility interactive inverter having the SA operation capability. The simulation and experimental results show that the proposed technique provides seamless transition between the inverter modes of operation with minimal distortion at the inverter output voltage. [ABSTRACT FROM PUBLISHER]

Operating a dual three-level inverter system from a single dc link circuit is an economic solution for generating five-level output voltage waveforms and to double the output power compared to a single three-level inverter. Such an inverter system is used for feeding a drive motor with open stator windings. A mechanism is then required to reduce the common-mode voltage components of the motor voltages. This paper describes an offline optimization method that minimizes both the harmonic distortion of the motor currents and the common-mode voltage components. The optimization permits reduction of the switching frequency to a very low value of 200 Hz without compromising the harmonic distortion. High performance operation of the drive system at low switching frequency is experimentally demonstrated. [ABSTRACT FROM PUBLISHER]

The five-level active neutral-point-clamped converter is a recently introduced topology that offers low harmonic distortion and a high output voltage. In addition to a neutral point potential in the dc link, this topology features, in each phase, a flying phase capacitor. Balancing these four internal converter voltages around their references while providing fast torque and/or current control for the machine is an intrinsically challenging control problem. Model predictive direct torque control (DTC) (MPDTC) is an ideal control methodology to address this problem. It is shown, in this paper, how MPDTC, originally developed for three-level inverters, can be adapted to this new five-level topology. Compared to DTC, the performance results of MPDTC are very promising—for the same switching frequency, the harmonic distortions of the stator currents and the torque can be more than halved. At the same time, the very fast torque response of DTC is maintained. [ABSTRACT FROM PUBLISHER]

This paper presents a 55-kW three-phase inverter based on soft-switching modules for hybrid electric vehicle drives at high-temperature conditions. The main switch of the module is composed of the hybrid switch, which is composed of parallel IGBT and MOSFET. Highly integrated soft-switching modules have been employed to achieve switching loss as well as conduction loss reduction. The operation principle of the proposed inverter is analyzed in detail. Experimental evaluations of the inverter have been conducted through both inductive load and motor-dynamometer load at coolant temperatures ranging from 25 ^\circ\C to 90 ^\circ\C. Efficiency measurement using power meter showed that the peak efficiency is around 99%, and it drops slightly at lower speed and higher temperature conditions. To ensure measurement fidelity, a double-chamber differential calorimeter system was designed and calibrated for the inverter testing. Through long-hour testing, the measured efficiencies consistently showed 99% and higher. The soft-switching inverter has been operated reliably and demonstrated high efficiency at different temperature and test conditions. [ABSTRACT FROM PUBLISHER]

This paper presents the development, implementation, and performance testing of a permanent-magnet generator (PMG)-based wind energy conversion system (WECS) for grid-connected applications. The grid-connected operation is constructed using the new three-phase resolution-level-controlled wavelet-modulated inverter. The output of the wind generator is fed to a switch-mode ac–dc converter, where the dc voltage is controlled to ensure extracting power from the wind under variable wind speed conditions in order to meet the grid active and reactive power demands. The resolution-level control of the grid-side inverter is designed as a current controller for adjusting active and reactive powers delivered to the grid. The proposed WECS is implemented both in software and hardware for performance testing on a direct-drive 6-kW laboratory PMG operated with variable speed. Test results demonstrate that an accurate control of the dc voltage on the generator side ensures adjusting the generator speed to extract power at each wind speed in order to meet the demand active and reactive power delivery to the grid. Also, test results show significant abilities of the resolution-level controller to initiate fast and accurate adjustments in the active and reactive powers delivered to the grid in order to follow any changes in their demand values under variable wind speed. [ABSTRACT FROM AUTHOR]

This paper demonstrates improved performance of a three-phase voltage source inverter (VSI) when digital multisampled space vector modulation is used. The modulator and the inverter controller are implemented entirely using a field-programmable gate array platform, thus achieving increased bandwidth with respect to a typical digital signal processor or microprocessor-based controller. Increased controller bandwidth results in lower output voltage harmonic distortion in the frequency range above the fundamental and below the switching frequency. Experimental validation is presented together with the analysis carried out using a state space model of a VSI with an output LC filter. [ABSTRACT FROM AUTHOR]

This paper proposes a novel complete electronic ballast for low-wattage metal halide (LWMH) lamps. The lamp driver is based on the integration of a flyback power factor correction (PFC) input stage and a buck–boost inverter stage. The resulting circuit supplies the lamps with a high-frequency (HF) square current waveform, operating from the mains facility. The main feature of the proposed ballast is that through an adequate integration of the stages, the circuit operates with only one controlled switch. This switch is shared by the active PFC input stage, by the output HF inverter stage, as well as by the igniter. The control of the ballast is carried out by adjusting the maximum current through the switch and by fixing the duty ratio. Thus, the resulting output characteristic is suitable for a proper operation of these discharge lamps, including ignition, warm-up stage, and steady-state operation. The obtained HF square waveforms in the lamp avoid the apparition of acoustic resonances. A complete prototype has been built and tested, and experimental results are shown. [ABSTRACT FROM AUTHOR]