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An introduction to the journal is presented in which the editor discusses an article on the real-time optimization of a step multilevel modulation, the use of zero state in the minimization of distortion, and the analysis of selective harmonic control based on the utilization of resonant filters.

This paper presents a simple but effective overmodulation scheme for direct torque controlled reluctance synchronous motor (RSM) incorporating field-weakening (FW) operation. To overcome the problems of high torque ripples and variable switching frequency experienced by conventional direct torque control (DTC), constant-switching-frequency-based torque regulator is employed. By combining the proposed overmodulation scheme with this torque regulator, the dynamic torque response and constant power speed range of RSM drives are improved. Simultaneously, low torque ripples are obtained. Furthermore, an adaptive activation algorithm is proposed to activate overmodulation only when high torque output is demanded. This algorithm also contributes to ensure the stability of drives with overmodulation through effective flux regulation, which is essential for FW operations. The validity of the proposed method is verified by experimental results supplemented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a new control system to regulate the reactive power supplied by a variable-speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter (MC), is presented. The control system discussed in this paper is based on an input current observer, implemented using an estimation of the modulation matrix, and a nonlinear control loop that regulates the displacement angle at the MC input. The reactive power capability of the proposed system is also investigated. The work presented in this paper demonstrates that, for the proposed WECS, the maximum reactive power supplied to the grid is about 40% of the nominal value. Experimental results obtained from an experimental prototype are presented in this paper. The performance of the system using a wind turbine emulator and typical wind profiles is discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper investigates and evaluates the performance of a single-phase split-source inverter (SSI), where an alternative unidirectional dc–ac configuration is used. Such configuration is utilized in order to use two common-cathode diodes in a single device instead of using two separate diodes, resulting in minimum parasitic inductance in the commutation paths. In this paper, the analysis and modulation of the single-phase SSI using this alternative configuration is discussed, and the analysis of the low-frequency component in the dc side is introduced. Moreover, the features behind employing the triangular, the trailing-edge sawtooth, and the leading-edge sawtooth carriers with the single-phase SSI are discussed, and the differences among these carriers are highlighted. In order to highlight the performance of the proposed SSI, a comparative study is conducted with the two-stage architecture and the single-phase quasi-Z-source inverter (qZSI). The introduced analysis is enhanced with simulation results using MATLAB/PLECS models, where a 1-kVA single-phase SSI is designed and simulated. Finally, the designed 1-kVA single-phase SSI is implemented experimentally and tested at different operating points, i.e., at different voltage gains, and a maximum efficiency of $95.5\%$ is obtained. [ABSTRACT FROM PUBLISHER]

A multilevel inverter topology for a four-pole induction-motor drive is presented in this paper, which is constructed using the induction-motor stator winding arrangement. A single dc source with a less magnitude when compared with conventional five-level inverter topologies is used in this topology. Therefore, power balancing issues (which are major challenges in conventional multilevel inverters) are minimized. As this configuration uses a single dc source, it provides a path for zero-sequence currents because of the zero-sequence voltages present in the output, which will flow through the motor phase winding and power electronic switches. To minimize these zero-sequence currents, sine–triangle pulsewidth modulation (SPWM) is used, which will shift the lower order harmonics near to switching frequency in the linear modulation region. However, in the case of overmodulation, harmonic voltages will be introduced close to the fundamental frequency. In this regard, a modified SPWM technique is proposed in this paper to operate the drive in the overmodulation region up to the modulation index of 2/\!\surd3. The proposed quad two-level inverter topology is experimentally verified with a laboratory prototype on a four-pole 5-hp induction motor. Experimental results show the effectiveness of the proposed topology in the complete linear modulation region and the overmodulation region. [ABSTRACT FROM PUBLISHER]

This paper proposes an analytical procedure for computation of all pairs of valid switching angles used in pattern generation in five-level H-bridge cascaded inverters. The proposed procedure eliminates harmonic components from inverter output voltage and, for each harmonic, returns the exact boundaries of all valid modulation index intervals. Due to its simple mathematical formulation, it can be easily implemented in real time using a digital signal processor or a field-programmable gate array. In this paper, after a detailed description of the method, simulation and experimental results demonstrate the high quality of achievable results. [ABSTRACT FROM PUBLISHER]

Zero-common-mode-voltage (CMV) operation of multilevel inverters results in reduced dc-bus utilization and reduced linear modulation range. In this paper, a method to increase the linear modulation range for zero-CMV operation without increasing the dc-bus voltage using a cascaded multilevel inverter with a single dc supply is presented. Using this method, the peak fundamental output voltage can be increased from 0.499 to 0.637  \textV\text{dc} with zero CMV inside the linear modulation range. Also, various pulse width modulation (PWM) switching sequences are analyzed in this paper, and the PWM sequence that gives minimum current ripple is used for the zero-CMV operation of the inverter. The inverter topology with single dc supply is realized by cascading a two-level inverter with two floating-capacitor-fed full-bridge modules. Simulation and experimental results for steady-state and dynamic operating conditions are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

For the case of unbalanced grid voltages, active power of pulse width modulation (PWM) rectifier is reduced due to the current limitation of power switches. Under unbalanced grid voltages, two existing control methods for the PWM rectifier are widely adopted, one for instantaneous active power control, and the other for balanced positive sequence current control. To maximize the PWM rectifier instantaneous active power capability and minimize active power oscillations during voltage dips, a control method combining balanced positive sequence and instantaneous active power control is proposed. The limitations of these two control methods are given, and the fluctuations on active and reactive power using the proposed control method are discussed in detail in this paper. The analysis in this paper is based on p.u. system, and some conclusions are drawn. Corroboration of the expected features of the proposed control method is carried out by means of experiments. [ABSTRACT FROM PUBLISHER]

Part I of this paper has proposed a duty-cycle-space-vector (DCSV)-based modulation strategy for three- and four-leg matrix converters (MCs). This paper develops a digital DCSV-based modulation strategy for the three- and four-leg MCs based on the results of Part I of this paper. The digital DCSV-based modulation strategy is implemented in a DSP–field programmable gate array (FPGA) platform. The objective is to reduce the calculation time of the modulation algorithm by performing the following: 1) reducing the total number of instructions needed to implement the modulation algorithm in the DSP and 2) implementing parts of the modulation algorithm in an FPGA to generate the switching pattern. Therefore, the calculation process of the modulation algorithm is split between the DSP and the FPGA. [ABSTRACT FROM PUBLISHER]

This paper presents a simple and generic model of a dual active bridge converter valid throughout its range of operation. It is suitable for all operating modes and modulation strategies such as phase-shift, extended phase-shift, dual phase-shift, or triple phase-shift modulation. It hypothesizes that any mode of its operation characterized by the duty ratios ($d_1$ , $d_2$) of the two full-bridge converter ac voltages and the phase shift ($\phi$) between them can be decomposed into four parallel dual active bridge circuits operating in simple phase-shift modulation. The hypothesis is proven mathematically; the average and small-signal models are derived and validated through simulations and experiments on a hardware prototype. [ABSTRACT FROM AUTHOR]

This paper proposes advanced speed control for a five-leg voltage source inverter (FLVSI) that drives the dual three-phase induction motor system used in industrial manufacturing processes. The advanced speed control method consists of two controllers: 1) The first is a slip controller that satisfies the application requirement, i.e., to control the mechanical speed of two motors equally regardless of the load condition. 2) The second is an angle controller that satisfies the FLVSI requirement, i.e., to control the phase angle difference between the two motors for minimizing the common leg current because the common leg current can be twice higher than other leg's current depending on the operation condition of the dual motor. Stability analysis of the two controllers under advanced speed control is implemented, and the whole performance of the advanced speed control for the FLVSI-fed dual-motor drive system is shown to identify its feasibility through the experimental results. [ABSTRACT FROM AUTHOR]

A hybrid pulsewidth modulation (PWM), combining the merits of both space-vector PWM (SVPWM) and selective harmonic elimination (SHE) PWM (SHEPWM), is proposed for three-level neutral-point-clamped (NPC) inverter-fed high-power adjustable-speed drives, which uses asynchronous SVPWM at low frequency and SHEPWM at high frequency. For SHEPWM, a novel formula is proposed to obtain the initial values of switching angles, leading to another valid solution that is different from the known ones in the literature. Furthermore, it is shown that, by eliminating the quarter-wave symmetry, unlimited groups of solutions to three-level SHEPWM can be obtained. The characteristics of the multiple solutions in terms of harmonic distribution, pulsewidth, and total harmonic distortion are investigated for the application of SHE in practical drives. Switching between SVPWM and SHEPWM is problematic if no appropriate measure is taken, particularly when the influence of the minimum pulsewidth (MPW) is considerable. A simple but effective method, taking into account the MPW, is proposed in this paper to address this problem. The multiple groups of solutions to SHE are simulated and experimentally verified on a low-voltage three-level NPC inverter prototype. Experimental results obtained from a low-voltage prototype and an industrial 6-kV/1250-kW three-level drive are presented to validate the smooth switching between SVPWM and SHEPWM. [ABSTRACT FROM PUBLISHER]

Different modulation methods have been proposed to control the multilevel inverters. This paper focuses on the staircase modulation that is very popular for multilevel inverters with low switching frequencies. Nonreal-time algorithms for the staircase modulation cannot be applied practically in multilevel inverters with varying voltage steps, since the sizes of lookup tables would be huge. We propose a real-time algorithm for multilevel inverters with unequal or varying voltage steps under the staircase modulation. The algorithm results in the minimal total harmonic distortion (THD) of the output voltage of the inverter, which is proved by rigorous mathematical derivations in this paper. A new expression of THD is presented to simplify the derivation significantly. Computational complexity of the algorithm is analyzed to estimate the time cost of the calculation. We implemented the algorithm on a digital signal processor and provide experimental results that verify the performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, phase-shifted schemes suffer from harmonic degradation when operated at the low carrier frequencies required in high-power high-level number applications. This paper develops a model predictive modulation (MPM) scheme that achieves superior harmonic performance, compared to phase-shifted modulation, while ensuring equal semiconductor loss distribution. With respect to complete-enumeration-based predictive techniques, the proposed modulation significantly reduces the number of times the system cost function is evaluated. Reducing the number of calculations by several orders of magnitude ensures computational feasibility. Simulation and experimental results are presented, which confirm correct operation of the modulation strategy. [ABSTRACT FROM PUBLISHER]

Induction heating (IH) is a key technology in modern household appliances and industries. Modern design trends require the design of high efficiency and multiple output power converters. This paper proposes a dual-output boost resonant full-bridge topology to provide a multiple-output converter with improved performance while keeping a cost-effective performance. The proposed converter is detailed and analyzed, and several modulation strategies are proposed to obtain proper output power control. Finally, an experimental prototype is built, verifying the proper operation and performance of the proposed topology. [ABSTRACT FROM PUBLISHER]

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, until now, its implementation has necessitated a capacitor voltage balancing scheme that degrades converter harmonic performance. This paper develops two phase-shifted carrier modulation schemes that avoid harmonic degradation by exploiting an extra degree of freedom in the available switching states. Simulation and experimental results are presented that confirm the correct operation of the modulation strategies. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel duty ratio modulated direct torque control (DDTC) to concurrently reduce torque ripple and stator flux ripple that are typically associated with conventional direct torque control (DTC). Three different methods of duty ratio determination are presented to achieve various control objectives, namely DDTC-final, DDTC-mean and DDTC-rms. Additionally, adjustable error weight coefficients are introduced to balance the torque ripple reduction and stator flux ripple reduction. Experimental results are presented to validate the effectiveness of proposed DDTC. Furthermore, the comparative evaluation of proposed DDTC, conventional DDTC and DTC is conducted on the basis of several criteria to verify the superiority of proposed DDTC. [ABSTRACT FROM PUBLISHER]

Common-mode voltage (CMV) is one of the most important issues for the power electronics inverters. An interesting space vector modulation of the three-leg current-source inverter has been reported for the CMV reduction recently. However, it has the disadvantages of the bipolar current pulses and modulation index range limitation. In order to solve these problems, a four-leg current-source inverter with a new space vector modulation is proposed in this paper. With the proposed method, the system CMV can be significantly reduced without bipolar current pulses and modulation index range limitation. Finally, the experimental tests are carried out on a four-leg current-source inverter, and the experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Three-phase impedance source inverters can be modulated using many modulation schemes, which are basically classified into two categories: three-phase-leg shoot-through-based (3P) and single-phase-leg shoot-through-based (1P) modulation schemes. These different modulation schemes have been comprehensively reviewed in Part I. Hence, in this paper, a comparative assessment among these different modulation schemes is introduced using the conventional Z-source inverter (ZSI). In this comparison, the ZSI voltage gain and stresses, current stresses, effective switching frequency of its different parts, spectrum of its output voltage, and switching losses are considered for each modulation scheme. Such comparative assessment introduces an effective benchmark for the researchers in order to determine the differences among these various modulation schemes, and easily select the appropriate one for their application. Finally, the state-of-the-art modulation schemes are experimentally assessed using a 3-kVA three-phase ZSI, where the shown results are consistent with the presented discussions and comparisons. [ABSTRACT FROM PUBLISHER]

A novel space vector pulse width modulation (SVPWM) strategy for three-phase four-wire neutral-point-clamped (NPC) inverter is proposed in this paper. The m-mode controllability of a three-phase four-wire NPC inverter, which is modeled as a switched linear system, is investigated. Then, on the basis of analysis of the m-mode controllability, taking the three-level property and the continuity of switching sequence into account, the controllable sets with the three-level property can be a new solution for the NPC inverter. With the sets of less operating modes, new modulation strategies named 18-mode SVPWM strategy, including 18-mode SVPWM(I), 18-mode SVPWM(II), and 18-mode SVPWM(III), are put forward. Compared with the conventional SVPWM strategy, the switching frequencies of the proposed 18-mode SVPWMs modulation strategy are significantly reduced by one-third. Therefore, the overall losses of the system can be reduced and the performance of the inverter can be improved. Finally, the simulation and the experiment results verify the correctness of the proposed approach. [ABSTRACT FROM PUBLISHER]

Vibration-based fault diagnosis of a planetary gearbox is challenging due to the revolving planet gears inducing modulation of vibration signals. For accurate fault diagnosis, researchers have suggested that vibration signals should be extracted by window function when the planet gears are positioned under the sensor. However, vibration modulation characteristics can be affected by operational and geometrical uncertainties. Thus, fault-related features can be inadvertently discarded when the window function is employed. Alternatively, periodicity analysis of anomalies can be employed with the entire vibration signal without the use of window function. However, it is challenging in a planetary gearbox because the fault-related features are also modulated. This paper proposes a health data map for toothwise fault identification in a planetary gearbox. In the proposed approach, samplewise health data are aligned in the domains of a pair of gear teeth of the planetary gearbox. The proposed approach represents the health state of every pair of gear teeth, while making it possible to isolate the location of any faulty teeth in the gears. For demonstration of the proposed method, two case studies are presented: an analytical model and a 2-kW testbed. The results suggest that the proposed method performs well even under unexpected vibration modulation characteristics. [ABSTRACT FROM PUBLISHER]

In this paper, the torque production of fractional-slot concentrated-winding (FSCW) permanent-magnet synchronous machines (PMSMs) is analyzed from the perspective of the air-gap field harmonics modulation accounting for slotting effect. It is found that the average torque of FSCW PMSM is produced by both the principle of conventional PMSM and the magnetic gearing effect. A finite-element analysis (FEA) based equivalent current sheet model and harmonic restoration method is first used in FSCW PM machines with different slot–pole number combinations to quantify the respective contribution of the conventional PMSM and the magnetic gearing effect to the average torque. The influence of slot opening on the magnetic gearing effect, cogging torque, and torque ripple is analyzed. The results show that the magnetic gearing effect makes a nonignorable contribution to the average torque when a large slot opening stator is used. The expression of the gear ratio in FSCW PMSMs is derived. The influence of gear ratio on the contribution of the magnetic gearing effect to the total torque is investigated by FEA. The FEA-predicted torques are validated by experiments on the prototypes. [ABSTRACT FROM PUBLISHER]

This paper presents hybrid automaton modeling, comparative model validation, and formal verification of stability through reachability analysis of pulse width modulation (PWM) dc–dc converters. Conformance degree provides a measure of closeness between the proposed hybrid automata models and experimental data. Nondeterminism due to variations in circuit parameters is modeled using interval matrices. In direct contrast to the unsound and computationally-intensive Monte Carlo simulation, reachability analysis is introduced to overapproximate the set of reachable states and ensure stable operation of PWM dc–dc converters. Using a 200 W experimental prototype of a buck converter, hybrid automata models of open-loop, and hysteresis-controlled converters are first validated against experimental data using their conformance degrees. Next, converter stability is formally verified through reachability analysis and informally validated using Monte Carlo simulations and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents the mathematical and harmonic analyses of output phase voltages of three-phase voltage source inverters which employ a hybrid two-dimensional–threedimensional (2-D–3-D) space vector modulation (SVM) voltage control algorithm. The explicit time-domain representation of the harmonic components in addition to the total harmonic distortion (THD) of the output phase voltages is given in terms of system and control parameters. This paper also investigates the harmonic characteristics and THD performance against the linearity of the modulation region which helps in the harmonic performance and design studies of such inverters employing the hybrid 2-D–3-D SVM. The fundamental component of the output voltages follows the reference with lower THD in the linear modulation region rather than the overmodulation region. Experimental results are used to validate these analyses as well as the effectiveness of the hybrid 2-D–3-D SVM algorithm for generating balanced and low THD phase voltages. [ABSTRACT FROM PUBLISHER]

A modular voltage-source inverter (MVSI) uses individual three-phase modules in a shunt connection to allow lower power rated inverters to be implemented in higher power applications. It is standard practice to implement each module with the same pulsewidth-modulation (PWM) pattern. This paper proposes a new PWM approach for MVSIs for which each module is made to operate with a different PWM pattern. It is shown in this paper how more output voltage harmonics can be eliminated with the new approach than with the standard approach and how the new approach can be expanded to significantly reduce zero-sequence current that circulates among the inverter modules. The mathematical formulations needed to generate appropriate PWM patterns for the new PWM approach and experimental results obtained from a prototype MVSI are presented in this paper as well. [ABSTRACT FROM PUBLISHER]

Modern development of semiconductor power-switching devices has promoted the use of power electronic converters as power transformers at the distribution level. This paper presents an ac–ac dual-active-bridge (DAB) converter for a solid-state transformer. The proposed converter topology consists of two active H-bridges and one high-frequency transformer. Four-quadrant switch cells are used to allow bidirectional power flow. Because power is controlled by the phase shift between two bridges, output voltage can be regulated when input voltage changes. This paper analyzes the steady-state operation and the range of zero-voltage switching. It develops a switch commutation scheme for the ac–ac DAB converters. Experimental results from a scaled-down prototype are provided to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a new high-frequency modulation method for multilevel converters. The proposed method provides a broad linear operating range and can be digitally implemented with minimal computational effort. This modulation method creates a phase voltage composed of a rectangular component superimposed on the top of a quasi-square-shaped reference function. The reference functions are defined such that the utilization of the dc-link voltage is maximized in any modulation index, while the dv/dt of the switches is always the minimum possible value. In order to implement the proposed method, an update time that is much shorter than the fundamental period is defined in the algorithm for updating the rectangular components of the reference voltage. The high-frequency rectangular component can then be imposed on the reference function to generate the final switching function by switching between two voltage levels during the time between two update instances. Several experimental results are provided to evaluate the performance of the proposed method and to compare its operation to conventional methods. [ABSTRACT FROM PUBLISHER]

Leakage current reduction of the single-phase transformerless cascaded H-bridge PV inverter is investigated in this paper. The high-frequency common-mode loop model of a typical single-phase cascaded H-bridge PV system is established. Based on the model, the main factors that affect the leakage current are discussed. The reason why the typical single-phase cascaded H-bridge inverter fails to reduce the leakage current is explained. In order to solve the problem, a cascaded topology based on the H5 inverter is presented, along with a new modulation strategy, which can ensure that the stray capacitor voltage is free of high-frequency components. In this way, the leakage current can be effectively reduced. Finally, a prototype with TMS320F28335DSP + XC3S400FPGA digital control is built. The performance tests of cascaded H-bridge and the proposed topologies are carried out. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

In this paper, a control method based on the derivative of power is introduced for single-stage single-phase grid-connected cascaded H-bridge (CHB) photovoltaic inverters. The proposed scheme uses solar arrays derivative of power with respect to current to track maximum power point of each array individually. Using this method along with hybrid modulation technique allows utilization of CHB cells up to their full potential. The control system has a simple structure, and is inherently able to stabilize the system under heavy mismatching conditions where the modulation index goes higher than unity. The effectiveness of the proposed technique is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In high-power traction drive systems, the switching frequency of the inverter is strictly limited owing to the restrictions on switching losses and cooling conditions. In this case, the multimode modulation strategy is usually adopted. Based on the analysis of a modified 24-sector space vector pulse width modulation (SVPWM) technique, several synchronous modulation strategies with different pulse numbers are proposed in this paper, which can be applied to the two-level six-phase voltage-inverter-fed asymmetrical dual-stator induction machines. By comparing the harmonic performance of the synchronized modulations, the authors present a set of multimode SVPWM strategy, which is suitable for the high-power traction drive systems under low switching frequency. At the same time, the switching strategy for transitions between different modulation modes is proposed as well. Simulation and experimental results verify the validity and effectiveness of the proposed synchronized modulation strategies and the switching strategy between different modulation modes. [ABSTRACT FROM AUTHOR]

Multilevel converters have received more attention recently. Multilevel converters can be used not only in high-voltage high-power applications, but also in energy storage systems, thanks to reduced harmonics and electromagnetic interferences. State-of-charge (SoC) balancing of the storage system cells within cascaded multilevel inverters, e.g., batteries, can be one of the challenges in practical applications. Different methods have been studied and reported in technical literature. However, the SoC balancing is still a challenging issue. In this paper, a new method is proposed to solve this problem by applying several clever but simple changes to the staircase modulation switching scheme without changing the output waveform properties. Validations for this simple method were performed through simulation and experimental prototype. Despite the simplicity of the method, the simulation and experimental results show that SoC balancing of the cells has significantly improved. [ABSTRACT FROM PUBLISHER]

Many different topologies based on the multilevel converter approach have been presented in the last decades. In order to obtain improved output waveforms, several modulation techniques have been developed for such converters. Some of those modulation schemes can be directly applied to almost any multilevel converter, while others require significant adaptation in order to be implemented in certain specific converters. This paper presents the implementation of a phase-disposition level-shifted pulsewidth modulation to the recently introduced hybrid multicell converter (HMC). The HMC uses a flying capacitor module on each cell to generate a positive variable dc-link voltage. The variable dc link is inverted at fundamental switching frequency by an H-bridge to generate the cell output voltage. It is desirable to use PD-PWM for its well-known high-performance waveforms. In this paper, a state-machine decoder is developed to balance the floating capacitor voltages and to equalize the supplied power for the series-connected cells of the HMC when using a PD-PWM pattern. Experimental results obtained from a 10-kW prototype are presented, confirming the good-quality waveforms of the HMC modulated with PD-PWM and the adequate balance of all floating capacitors. [ABSTRACT FROM PUBLISHER]

In this paper, an immune algorithm (IA) is developed for optimization of the harmonic performance of a three-phase inverter under the space-vector pulsewidth-modulation (SVPWM) control strategy. The presented algorithm employs the immune approach as the search method for finding the best optimal control vectors and action time of the three-phase inverter. As a result, the optimal control vectors and action time are calculated to minimize the objective function of the weighted total harmonic distortion of the output voltage waveforms. In addition, an experimental platform based on DSP and field-programmable gate array is built. This paper provides a detailed performance analysis of the method with comparison to the conventional SVPWM. The simulation and experimental results verify the superiority of the best control sequences generated by IA compared with the existing conventional control strategies. [ABSTRACT FROM PUBLISHER]

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a general comparison procedure for medium voltage - high power multilevel converter topologies and semiconductors, which is mainly based on analyzing the performance limits of the converters output characteristics such as the output voltage, current, active power, efficiency, etc. Afterwards, the general procedure is applied to compare some of the most relevant converter topologies oriented to a 6.6 kV drive application supplying quadratic torque loads and using 4.5 kV IGBT modules. The paper concludes evaluating the comparison factors of the different converter topologies and selected semiconductors obtained by the proposed procedure. The proposed procedure can potentially be extrapolated to any desired application framework. [ABSTRACT FROM PUBLISHER]

Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis. [ABSTRACT FROM PUBLISHER]

This paper proposes two sets of topologies for single-phase to three-phase four-wire ac–dc–ac power conversion. All proposed configurations are characterized by reduction in the number of switches. The first set includes five configurations using ten power switches, while the second one includes six configurations using eight power switches. Such configurations are conceived for supplying three-phase four-wire loads and to guarantee bidirectional power flow between grid and load. Besides collecting different configurations, this paper proposes a synchronization technique, which can be applied for configurations with shared leg. The overall control strategy for providing dc link voltage control, grid current control, and PWM generation are presented. Simulated and experimental results are presented as well. [ABSTRACT FROM AUTHOR]

This paper presents an integrated CMOS switching power converter that accommodates adaptive wireless powering scheme in biomedical implants. It employs the techniques of dual-loop error correction, observation-based oversampling, and \Delta–\Sigma modulation to enhance transient response, line/load regulation, and noise suppression performance. By adopting a digital filter for proportional-derivative compensation, fully on-chip frequency compensation is achieved. In addition, a double sampling technique is introduced to improve the signal processing speed. The converter was designed and fabricated with a 130-nm CMOS process. The measurement results demonstrate 23.2/20.4-\mu\s up-/down-tracking times to full-range reference voltage step changes. A 28.5-mV/V line regulation is achieved, when the supply voltage varies from 1.15 to 1.50 V. In addition, with a 1.20-V supply, the converter responds to a 10%-to-100% load current step change within 22.1 \mu\s. A maximum efficiency of 95.5% is measured at 0.90-V output voltage and 45-mW output power. Noise power spectrum demonstrates a 100-dB signal-to-noise ratio in the converter. [ABSTRACT FROM AUTHOR]

This paper proposes improvements to the control method based on the complete dynamical model published by Kömürcügil and Kükrer, which is very simple by operation in the stationary reference frame and lacks ac-line-current sensors. Nevertheless, the basic control method is very sensitive to variations of the line inductances, which provide difficulties in many industry applications. The modifications proposed in this paper overcome this disadvantage using a fuzzy logic controller to tune parameters and do more robust the basic control in view of line inductance parameters variations. Unfortunately, the new tuning method needs information about the reactive line current; therefore, ac-line-current reconstruction algorithm based on the dc-link current measurement has been included to keep the same number of sensors as the basic solution. Simulation and experimental results have proved the correct system operation at wide variations of the line inductance. [ABSTRACT FROM PUBLISHER]

This paper presents a current soft-commutation pulsewidth modulation (PWM) scheme for three-phase current source converter. With the presented PWM scheme, the incoming switch has a positive collector-to-emitter voltage while the outgoing switch has a negative collector-to-emitter voltage during current commutations. Therefore, natural soft commutations for switching transitions are achieved, while current-commutating durations are also lessened. Moreover, some particular advantages can also be obtained such as reduced switching frequency, high dc current utilization ratio, and in-phase transfer between line currents and their references. For more efficient control, this paper then designs logic equations for mapping out the assignments from references to gating signals, allowing a simple implementation using a digital signal processor or a programmable logic device. The theoretical analysis is verified by experimental results. [ABSTRACT FROM AUTHOR]

Flux harmonic distortion factors (HDFs) of two space vector pulse width modulation (SVPWM) schemes, aimed at sinusoidal output voltage generation with five-phase voltage source inverters, have been evaluated in Part 1 of this paper. Analytical considerations and numerical integration have been applied in order to determine the switching properties of the considered SVPWM methods. It has been shown that the SVPWM based on four large vectors leads to a considerably higher overall per-phase flux HDF than the method based on two large and two medium space vectors. The purpose of the second part of the paper is to relate flux HDFs to the current ripple and current total harmonic distortion and thus explore further switching characteristics of the two SVPWM techniques. The applied approach is based on simulation and experimentation, in conjunction with the subsequent fast Fourier transform of the waveforms, so that all the results for the ripple are obtained using a methodology completely different from the one in Part 1. Relationships that correlate the current ripple and the flux HDFs are established, and it is further shown that the current ripple can be easily calculated from the flux HDF values of Part 1 if the relevant leakage inductances of the two planes are known. Hence, the complete theory of Part 1 is fully verified by both simulation and experimentation. It is also shown that, in certain cases, the SVPWM based on four large vectors may lead to a smaller current ripple despite a considerably higher flux HDF. [ABSTRACT FROM AUTHOR]

Multiphase variable-speed drives supplied from two-level voltage source inverters (VSIs) are, at present, contenders for numerous industrial applications. Various pulsewidth modulation (PWM) methods for multiphase VSIs, aimed at sinusoidal output voltage generation, have been developed using both carrier-based and space-vector approaches. An increased number of voltage space vectors, available for the synthesis of the output voltage, offer greater flexibility for the PWM scheme development, compared to the three-phase case. This paper presents comprehensive analytical analysis and comparison of switching ripple characteristics of two continuous space vector PWM (SVPWM) methods for a five-phase two-level VSI. Considered SVPWM schemes select a different set of four active space vectors per switching period in order to generate sinusoidal output voltages. This paper also presents the evaluation of the flux harmonic distortion factors of the SVPWM techniques. Correlation with corresponding current ripple and total harmonic distortion is established in Part 2 of this paper, where theoretical considerations are verified by simulations and through experimental investigation on a five-phase VSI-fed induction motor drive. [ABSTRACT FROM AUTHOR]

This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed. [ABSTRACT FROM AUTHOR]

Most variable-speed ac generation systems use back-to-back converters to supply electrical energy, with fixed electrical frequency and voltage, to a stand-alone load or grid. Matrix converters (MCs) are a good alternative to back-to-back converters because they have several advantages in terms of size and weight. Therefore, MCs can be advantageously used in any variable-speed generation system where high efficiency, reliability, small size, and low weight are considered important factors. Nevertheless, to interface an MC-based generation system to an unbalanced 3\phi stand-alone load, a four-leg MC is required to provide a path for the zero-sequence load current. Space-vector-modulation (SVM) algorithms for the operation of four-leg MCs have been proposed in the literature. However, these modulation methods have high computational burdens, and they are difficult to implement, even in fast DSP-based control platforms. Therefore, only simulation results have been reported in these publications. In this paper, an SVM algorithm is optimized and experimentally tested. Moreover, the harmonics produced in the input current when a four-leg MC is feeding an unbalanced or nonlinear load are also mathematically analyzed in this paper, with experimental verification being provided. [ABSTRACT FROM AUTHOR]

Multilevel cascaded H-bridge converters have found industrial application in the medium-voltage high-power range. In this paper, a generalized modulation technique for this type of converter based on a multidimensional control region is presented. Using the multidimensional control region, it is shown that all previous modulation techniques are particularized versions of the proposed method. Several possible solutions to develop a specific implementation of the modulation method are addressed in order to show the potential possibilities and the flexibility of the proposed technique. In addition, a feedforward version of this technique is also introduced to determine the switching sequence and the switching times, avoiding low harmonic distortion with unbalanced dc voltages. Experimental results are shown in order to validate the proposed concepts. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to simplify the implementation of continuous and discontinuous 3-D space vector pulsewidth modulations (SVPWMs). This paper analyzes the relationships, whether in abc or \alpha\beta 0 coordinates, between three-phase voltages and the following elements: the tetrahedron in which the reference vector resides, three adjacent active switching vectors (or three switching states), and their duration times. Based on the analysis, the calculation of the turn-on time of each switch in the actual implementation is simplified, and discontinuous PWM (DPWM) methods in three-leg inverters can be extended to four-leg inverters without the phase angle. In addition, two more DPWM methods that are peculiar to 3-D SVPWM are presented. This simplified algorithm does not use irrational operations or look-up tables, and it alleviates the computation burden of the processor. The simulation and experimental results are provided to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, the application of a cascaded multilevel inverter as a dynamic voltage restorer (DVR) is investigated. Two discontinuous multilevel space vector modulation (SVM) techniques are implemented for DVR control and are shown to reduce inverter switching losses while maintaining virtually the same harmonic performance as the conventional multilevel SVM at a high number of levels. This paper also presents a mathematical relationship for computing the distortion at the point of common coupling (PCC) as a function of the distortion of the DVR. This enables the selection of the number of levels required for a certain application. An extended sag duration support compared to the two-level DVR is another advantage of the DVR with a cascaded multilevel inverter. The common-mode voltage (CMV) at the PCC has been evaluated for the three SVM techniques (the conventional multilevel SVM and the two discontinuous SVM), presenting a lower CMV for the second discontinuous SVM. A design example is presented for an 11-kV 5-MVA DVR multilevel cascaded inverter for up to 17 levels, employing the conventional multilevel SVM and the two discontinuous SVM techniques. [ABSTRACT FROM AUTHOR]

Neutral-point-clamped (NPC) inverters are the most widely used topology of multilevel inverters in high-power applications (several megawatts). This paper presents in a very simple way the basic operation and the most used modulation and control techniques developed to date. Special attention is paid to the loss distribution in semiconductors, and an active NPC inverter is presented to overcome this problem. This paper discusses the main fields of application and presents some technological problems such as capacitor balance and losses. [ABSTRACT FROM AUTHOR]

Space-vector modulation (SVM) is a well-suited technique to be applied to multilevel converters and is an important research focus in the last 25 years. Recently, a single-phase multilevel modulator has been introduced, showing its conceptual simplicity and its very low computational cost. In this paper, some of the most conventional multilevel SVM techniques have been chosen to compare their results with those obtained with single-phase multilevel modulators. The obtained results demonstrate that the single-phase multilevel modulators applied to each phase are equivalent with the chosen well-known multilevel SVM techniques. In this way, single-phase multilevel modulators can be applied to a converter with any number of levels and phases, avoiding the use of conceptually and mathematically complex SVM strategies. Analytical calculations and experimental results are shown, validating the proposed concepts. [ABSTRACT FROM AUTHOR]

This paper describes a sensorless position estimation method for a permanent-magnet (PM) motor fed from a threephase matrix converter using only its space-vector pulsewidth-modulation (S VPWM) sequence. The scheme employs measurements of di/dt of the motor line currents to construct orthogonal "resolverlike" position signals. In principle, the SVPWM waveforms provide sufficient excitation to extract the position signal from the motor current. However, in order to improve the signal-to-noise ratio of the di/dt signals, a small modification to the SVPWM is required. Sensorless control of the PM synchronous motor at zero and high speeds is demonstrated experimentally. The use of alternative input voltage vectors is also investigated to reduce the current ripple. [ABSTRACT FROM AUTHOR]