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This paper presents an extension of previous methods in order to find electrical series connections between multiphase machines, allowing the independent control of each one of them. These new electrical series connections explore the symmetrical disposition of the phases of even-multiphase machines, allowing the inversed connection of some of the phases, different from the direct connections as it was previously done. Therefore, electrical series connections of two symmetrical six-phase or of four symmetrical ten-phase machines are now possible. Besides that, this new solution ensures a natural independent control of permanent-magnet synchronous machines even if the back electromotive forces (back EMFs) generated by the rotor are not sinusoidal, without need of special machine conception or supplementary control strategy. This control independency is mathematically proved using the decomposition of multiphase machines in fictitious diphase and homopolar machines. Experimental results are presented to show the functioning and the advantages of this new coupling for two symmetrical six-phase permanent-magnet synchronous machines (PMSMs). [ABSTRACT FROM AUTHOR]

In this paper, a new reference current generation method is proposed for effective harmonics mitigation and reactive power compensation of three-level neutral-point diode clamped inverter-based shunt active power filter (SAPF) under nonideal grid voltage conditions. The proposed method is named as dual fundamental component extraction algorithm. In operation, the proposed algorithm extracts at the same time, the desired fundamental current and voltage components for generating reference current and synchronization phases, respectively. As a result, the proposed algorithm is able to generate reference current that ensures in phase operation of SAPF with the operating power system, without depending on any phase-locked loop elements. Besides, the proposed algorithm employs self-tuning filter (STF) for accurate computation of the fundamental components. Design concept and effectiveness of the proposed algorithm are thoroughly studied and evaluated in MATLAB–Simulink. Additionally, a laboratory prototype utilizing TMS320F28335 digital signal processor is built to validate its feasibility. Encouraging findings obtained from both simulation and experimental works demonstrate effectiveness of the proposed algorithm under both ideal and nonideal grid voltage conditions. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes a compact transformerless common mode active electromagnetic interference (EMI) filter (AEF) using a push–pull amplifier. Quantified design guidelines are then rigorously derived from the analysis with consideration for performance, stability, and high voltage transient immunity. The proposed AEF is manufactured based on the design guidelines, and its performance is validated by measurements using a vector network analyzer. The AEF is then implemented into a real 2.2 kW current resonant inverter, and the conducted emissions are reduced by 5–25 dB at a frequency range from 150 kHz to 6 MHz. In addition, the AEF's immunity against high voltage transients is demonstrated by lightning surge tests. [ABSTRACT FROM AUTHOR]

Three-phase three-leg inverter is one of the most popular topologies for inverters. When short-circuit fault occurs, the inverter is generally switched to the current-controlled mode from voltage-controlled mode to limit the fault currents. In this situation, the inverter becomes equivalent to a symmetric, three-phase, positive sequence current source. However, the voltage limiting may occur under asymmetrical fault. In this paper, a closed-loop model based on time-domain is originally developed as a means to investigate the fault current characteristics under asymmetrical fault. Based on the proposed model, a more intuitive insight into fault currents is presented as follows. 1) The positive sequence fundamental component of three-phase currents can still track the symmetric current references. 2) The magnitude of fault phase currents (ignoring the harmonics) will vary between 1 and $\sqrt 3 $ times of magnitude of current limiting references. Based on the conclusion, although the magnitudes of fault phase currents can be reduced by adopting smaller current limiting references, the actual magnitudes of fault phase currents will still vary in a range depending on the load impendence of healthy phase. Therefore, the reliable action of the protection devices is greatly affected and the selective protection cannot be realized. Furthermore, in order to achieve completely controllable fault currents under asymmetrical fault, two alternative current limiting strategies are presented with reverse current limiting references, and with current limiting references based on the introduced phase angle regulation. The theoretical results are validated by simulations and experimental results. [ABSTRACT FROM AUTHOR]

Arc welding inverter supply with switch and digital control is widely used, due to the advantages of high controllability, small size, and high efficiency. With the constant increasing of switching frequency and decreasing of arc welding machine size, the conducted electromagnetic interference (EMI) becomes serious, especially for common mode (CM)-conducted EMI. Meanwhile, as the development of digital processing technique, digital active EMI filter (DAEF) technology, which uses digital control and embedded mode, has become a hot research topic. However, the conventional DAEF fails to consider time delay effect. Its model cannot accurately describe DAEF filtering behavior. Moreover, decoupling circuit lacks scientific design method. To cope with these, this paper proposes a precise DAEF model which considers both the time delay of digital processing portion and the parasitic parameters of passive components. Moreover, based on impedance matching principle, a detailed and scientific design method of decoupling circuit is put forward. Meanwhile, the arc welding inverter system with embedded DAEF is designed, modeled, and compensated. Finally, experiment results show that the proposed precise model can predict the system filtering performance accurately. And the proposed design method of decoupling circuit is very effective to suppress the CM-conducted EMI. The embedded DAEF can improve system stability and dynamic performance. [ABSTRACT FROM AUTHOR]

This paper introduces a new analysis approach to modeling resonant converters that can be used to determine closed-form expressions for the exact resonant network waveforms. This approach, based on superposition of step responses to inverter and rectifier imposed steps, can easily be applied to resonant converters with high-order resonant networks, multiple inverters, and/or rectifiers. The usefulness of the proposed analysis approach is demonstrated first by applying it to a series-resonant converter, wherein it is used to determine accurate closed-form expressions for its tank current in different operating modes. These expressions are utilized to draw insights that help identify the converter's operating mode, and determine associated expressions for its output voltage and the switching frequency required to achieve a desired output power. The proposed approach is also applied to the multi-inverter multi-element impedance control network (ICN) resonant converter, wherein it is used to derive closed-form expressions for the converter's currents. These expressions are utilized to evaluate the behavior and optimize the design of an ICN resonant converter. A prototype 200-W 500-kHz ICN resonant converter optimized using the proposed approach is used to validate the modeling results. It is shown that there is an excellent agreement between the experimental and modeled waveforms during steady-state operation as well as during startup transients. [ABSTRACT FROM AUTHOR]

LCL-filter is among the best performing filters for grid-connected voltage source inverters. Designing of the filter parameters (grid-side and inverter-side inductors and capacitor), takes an iterative approach due to the coherence between the parameters and design requirements such as IEEE-519 Std for harmonic current limitations, reactive power compensation limit, and maximum allowable voltage drop across the filter to limit the switching losses. Most of the proposed LCL-filter optimization strategies emphasize on reducing the total inductance and losses of the filter while meeting the design requirements. There is less emphasis given on the capacitor selection and optimizing its value. Therefore, this paper proposes a method to compute the optimum capacitance requirement of the LCL-filter based on reactive power compensation of the filter rather than calculating it as a percentage of base capacitance of the filter as found in the literature. The proposed design methodology compared to the previously proposed designs is capable of reducing filter capacitance by 50% while meeting the harmonic limitation demanded by IEEE-519 Std and also considers the impact of the total inductance on reactive power compensation. Based on the proposed methodology an LCL-filter with minimum total inductance and capacitance is realized. Functionality of the proposed LCL-filter is verified and validated through simulations and experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with modeling and nonlinear modal analysis of two-stage boost inverter. An observer-pattern modeling method is proposed to eliminate the time-variance effect from both fundamental component in the load stage and “hidden” second-harmonic one in the source stage. Then, based on the observer-pattern model, the nonlinear modal analysis method is applied to obtain a closed-form analytical representation of the nonlinear system, which yields a great deal of physical insight into the system dynamics. First, fundamental modal analysis is calculated to indicate the correlation between fundamental modes, state variables, and circuit parameters. Such key parameters as C1 and T3 are found to be beneficial to the dynamical performance of the whole system. Second, the second-order nonlinear interaction indices are proposed to uncover the underlying mechanism of nonlinear interaction behaviors, and the relationship between modal interaction and system parameters is explored quantitatively. Finally, theoretical analysis is verified by circuit experiments. These results are beneficial to the improvement of transient performance as well as the understanding of the nonlinear interactions in transient behavior. [ABSTRACT FROM AUTHOR]

Pulse generator in an ultrasound system produces electrical pulsing signals to drive piezoelectric transducer, which causes mechanical vibration of the crystals and generates sound waves. Different from conventional imaging short pulses, high-power ultrasonic system for therapeutic applications requires MHz pulses bursts of up to tens of milliseconds. The capability of switching high voltage (±90 V) at multi-MHz, delivering effective power efficiently, is crucial for practical systems. The advantages of low device loss at high switching frequency, and high power density make gallium nitride (GaN) high electron mobility transistors better devices than traditional silicon (Si) MOSFETs in such system. The GaN-based high-frequency transformer push–pull inverter presented in this paper is capable to produce high energy pulsating output with burst pulse length up to 50 ms and bipolar pulse amplitude of 180 Vpp. The maximum pulse frequency can be up to 10 MHz. The peak output power is 90 W with power density of 50.85 W/in2. The peak power for all the 128 pulser channels reaches up to 11.5 KW with average power of 192 W. This is the highest output power for pulse drivers that have been reported. A novel power transistor based RF switch circuit is also proposed in this design as the interface between image signal, high power signal, and return signal. [ABSTRACT FROM AUTHOR]

This research proposes a novel low-voltage inverter-fed motor drive with variable parameters achieved through the independent armature winding for the automobile traction motor. The independent armature winding with low-voltage inverters can improve the total efficiency by reducing the converter losses. The inverters are able to change their connections to different coils groups of the armature winding in order to achieve the wide operating range. The voltage equation of each mode can be shown by using the transformation matrix when the winding connection is changed. Thus, the proposed motor is called the MATRIX motor. In this paper, the downsized model was designed to verify the principle. The principle model is able to achieve four motor parameters. It was confirmed that the principle model could extend the operating range and could achieve the high-efficiency driving in wide speed range. Furthermore, the novel winding reconfiguration method is proposed that not only avoids the surge voltage, but also compensates the torque reduction during the winding reconfigurations. [ABSTRACT FROM AUTHOR]

In this paper, a control strategy for the parallel operation of three-phase inverters forming an online uninterruptible power system (UPS) is presented. The UPS system consists of a cluster of paralleled inverters with LC filters directly connected to an ac critical bus and an ac/dc forming a dc bus. The proposed control scheme comprises two layers: 1) a local layer that contains a “reactive power-to-phase droop” in order to synchronize the phase angle of each inverter and a virtual resistance loop that guarantees equal power sharing among inverters; and 2) a central controller that guarantees synchronization with an external real/fictitious utility, and critical bus voltage amplitude restoration. Improved transient and steady-state frequency, active, reactive, and harmonic power sharing, and global phase-locked loop resynchronization capability are achieved. Detailed system topology and control architecture are presented in this paper. Furthermore, a mathematical model was derived in order to analyze critical parameters effects on system stability. The proposed control approach has been validated by means of experimental results obtained for several case-study scenarios. [ABSTRACT FROM AUTHOR]

This paper introduces a high-gain single-stage boosting inverter (SSBI) for alternative energy generation. As compared to the traditional two-stage approach, the SSBI has a simpler topology and a lower component count. One cycle control was employed to generate ac voltage output. This paper presents theoretical analysis, simulation and experimental results obtained from a 200 W prototype. The experimental results reveal that the proposed SSBI can achieve high dc input voltage boosting, good dc–ac power decoupling, good quality of ac output waveform, and good conversion efficiency. [ABSTRACT FROM AUTHOR]

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

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

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation. [ABSTRACT FROM PUBLISHER]

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

Paralleling is the development tendency of the auxiliary inverter. This paper analyzes the problems of the parallel process in detail. First, for inherent contraction between voltage regulation performance and current sharing performance, the paper adopts the resistive droop method. Second, the paper improves dynamic performance and reliability of the droop method by improving power calculation and introducing the whole cycle adaptive droop method. Third, in order to solve the unshared current problem caused by inconsistent parameters, the paper increases active power proportion droop coefficient, and introduces voltage compensation strategy to compensate voltage drop caused by increased proportion droop coefficient. Fourth, the auxiliary parallel system has complicated load characteristics; the paper proposes voltage compensation strategy to compensate voltage drop caused by the pump load. This paper utilizes three-phase total reactive power to droop frequency and active power of each phase to droop amplitude, unbalanced current can be shared. This paper introduces special virtual impedance technology to solve the harmonic current sharing problem caused by the nonlinear load. Finally, the effectiveness of above theory is fully verified by simulation and experiment. [ABSTRACT FROM PUBLISHER]

With increasingly prominent role of rail transit in the entire urban transport system, an auxiliary inverter is used increasingly. The complicated and fluctuating load condition of the auxiliary inverter implies special designs about structure and control strategy are necessary. For this purpose, a comprehensive control strategy is proposed. First of all, this paper proposes a structure that is capable of suppressing unbalanced voltage. Second, the control strategy based on the resonant controller is proposed, which can balance split capacitors voltage, is capable of suppressing the effect of unbalanced load and nonlinear load. This paper introduces the design method of the control system in detail. Then, this paper simulates the proposed comprehensive control strategy in MATLAB. Finally, experimental results are presented, which fully demonstrate the excellent performance of the comprehensive control strategy. [ABSTRACT FROM PUBLISHER]

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

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

Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application. [ABSTRACT FROM AUTHOR]

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

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

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

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

The four-switch three-phase (FSTP) inverter has been proposed as an innovative inverter design to reduce the cost, complexity, size, and switching losses of the dc–ac conversion system. Traditional FSTP inverter usually operates at half the dc input voltage; hence, the output line voltage cannot exceed this value. This paper proposes a novel design for the FSTP inverter based on the topology of the single-ended primary-inductance converter (SEPIC). The proposed topology provides pure sinusoidal output voltages with no need for output filter. Compared to traditional FSTP inverter, the proposed FSTP SEPIC inverter improves the voltage utilization factor of the input dc supply, where the proposed topology provides higher output line voltage which can be extended up to the full value of the dc input voltage. The integral sliding-mode control is used with the proposed topology to optimize its dynamics and to ensure robustness of the system during different operating conditions. Derivation of the equations describing the parameters design, components ratings, and the operation of the proposed SEPIC inverter is presented in this paper. Simulation model and experimental setup are used to validate the proposed concept. Simulations and experimental results show the effectiveness of the proposed inverter. [ABSTRACT FROM AUTHOR]

In this paper, we propose model predictive control methods to reduce the common-mode voltage of three-phase voltage source inverters (VSIs). In the reduced common-mode voltage-model predictive control (RCMV-MPC) methods proposed in this paper, only nonzero voltage vectors are utilized to reduce the common-mode voltage as well as to control the load currents. In addition, two nonzero voltage vectors are selected from the cost function at every sampling period, instead of using only one optimal vector during one sampling period. The two selected nonzero vectors are distributed in one sampling period in such a way as to minimize the error between the measured load current and the reference. Without utilizing the zero vectors, the common-mode voltage controlled by the proposed RCMV-MPC algorithms can be restricted within ±Vdc/6. Furthermore, application of the two nonzero vectors with optimal time sharing between them can yield satisfactory load current ripple performance without using the zero vectors. Thus, the proposed RCMV-MPC methods can reduce the common-mode voltage as well as control the load currents with fast transient response and satisfactory load current ripple performance compared with the conventional model predictive control method. Simulation and experimental results are included to verify the effectiveness of the proposed RCMV-MPC methods. [ABSTRACT FROM AUTHOR]

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

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

Direct ac/ac topologies for ac-to-ac power conversion benefit from the absence of dc-link capacitors, and therefore, are highly reliable and have low cost as compared to the traditional voltage-source inverter (VSI)-based topologies. This paper deals with one of the more important tradeoffs considered in designing highly efficient converters: Losses. It is shown in this paper that the direct ac/ac converters have an inherently higher efficiency than their VSI-based back-to-back counterparts due to a dramatic reduction in switching losses (nearly 60%). Further, this paper compares the performance of three different device types (SiC MOSFETs, hybrid Si IGBT/SiC diode, and Si IGBTs) using wide-range device characterization that help to create detailed loss models. It is conjectured that traditional datasheets lack the level of detail needed for computing losses in direct ac/ac converters, and the availability of a multivalue voltage, current, and temperature-based loss profile is advocated. Using the obtained loss models, a comparison is drawn between the considered devices through simulations when operated in a 13-kV/1-MW direct ac/ac power flow controller, the controllable network transformer (CNT). The same loss-models are also used to compute losses in an experimental prototype of a 720-V, 10-kVA CNT and the results are compared with direct efficiency measurements. A similar computation is carried out for another experimental prototype at a 6.7-kV, 400-kVA, three-level, paralleled CNT. These experimental tests are used to confirm the validity of the analytical results presented in this paper. [ABSTRACT FROM AUTHOR]

A multilevel topology with medium-frequency ac link for medium-voltage grid integration of utility photovoltaic (PV) plants is discussed in this paper. A megawatt-scale PV plant is divided into many zones, each comprising of two series-connected arrays. Each zone employs a medium-frequency transformer with three secondaries, which interface with the three phases of the medium voltage grid. An insulated-gate bipolar transistor full-bridge inverter feeds the MF transformer. The voltages at the transformer secondaries are then converted to three-phase line frequency ac by three full-bridge ac-ac converters. Second line frequency harmonic power does not appear in the dc bus, thereby reducing the dc capacitor size. Cascading several such cells, a high-quality multilevel medium-voltage output is generated. A new control method is proposed for the cascaded multilevel converter during partial shading while minimizing the switch ratings. The proposed topology eliminates the need for line frequency transformer isolation and reduces the dc bus capacitor size, while improving the power factor and energy yield. This paper presents the analysis, design example, and operation of a 10-MW utility PV system with experimental results on a scaled-down laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper describes motor drive system fed by a single-phase diode rectifier without power factor correction (PFC) circuit or the input filter. The system considered in this paper consists of a single-phase diode rectifier, a three-phase inverter, and a small dc-link capacitor. Since dc-link capacitance of the proposed system is few microfarads, the shape of the grid input current is directly affected by electrical output power of the inverter. Using this aspect, two goals of the drive system, controlling torque of the motor and suppressing the grid input current harmonics, can be simultaneously achieved by controlling the output power of the inverter. The proposed method includes the motor current reference generation and the direct output power regulation by modifying the output voltage reference. With the proposed method, the harmonic components of the grid input current can be reduced under the limits of the regulation IEC61000-3-2, lower than those in the conventional method. Also, the cost and size of the inverter system can be significantly reduced by removing electrolytic dc-link capacitor and input filter from the system. The performance of the proposed shaping method was validated by the experimental results using the motor drive system with a 5μF film capacitor at dc link. [ABSTRACT FROM AUTHOR]

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

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

Based on the Z-source inverter, this paper proposed a novel approach to zero-crossing point (ZCP) detections during the shoot-through vectors for sensorless brushless dc motor (BLDCM). The proposed approach separates the ZCP detections from speed adjustment, and makes the shoot-through vector not influence the motor speed-adjustment directly, while the zero-vectors and active-vectors are used exclusively to adjust the speed of BLDCM. With the proposed approach, the sensorless BLDCM can operate in a wide speed range without switching the detection points and the reference levels, and it is unnecessary to change the reference levels according to the PWM technique. The terminal voltages limited by diode can be directly compared with the reference zero level during the shoot-through vectors, so as to reduce the detection error caused by attenuation. Moreover, Z-source inverter not only provides boost voltage for sensorless BLDCM drive system, but also improves the utilization rate of dc source voltage and the safety of the drive system. In addition, this paper analyzed the terminal voltages of the floating phase during each vector. The experimental results verified the correctness of above theories and proved the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

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

Impedance networks cover the entire of electric power conversion from dc (converter, rectifier), ac (inverter), to phase and frequency conversion (ac-ac) in a wide range of applications. Various converter topologies have been reported in the literature to overcome the limitations and problems of the traditional voltage source, current source as well as various classical buck-boost, unidirectional, and bidirectional converter topologies. Proper implementation of the impedance-source network with appropriate switching configurations and topologies reduces the number of power conversion stages in the system power chain, which may improve the reliability and performance of the power system. The first part of this paper provides a comprehensive review of the various impedance-source-networks-based power converters and discusses the main topologies from an application point of view. This review paper is the first of its kind with the aim of providing a “one-stop” information source and a selection guide on impedance-source networks for power conversion for researchers, designers, and application engineers. A comprehensive review of various modeling, control, and modulation techniques for the impedance-source converters/inverters will be presented in Part II. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

This paper presents a fast and generalized space vector pulse width modulation (SVPWM) scheme for any multilevel inverter. The SVPWM scheme generates all the available switching states and switching sequences based on two simple and general mappings, and calculates the duty cycles simply as if for a two-level SVPWM, thus independent of the level number of the inverter. Because the switching states, duty cycles, and switching sequences are all obtained by simple calculation in the proposed SVPWM scheme, no lookup table is needed and the scheme is computationally fast. The generalized method of generating the switching states (first mapping), calculating the duty cycles, and determining the switching sequence (second mapping) is described in this paper. The scheme is suitable for any reference vector with any modulation index, and can be conveniently extended to meet specific requirements, such as symmetric switching sequences. Compared with prior methods, the SVPWM scheme proposed in this paper provides two more degrees of freedom, i.e., the adjustable switching sequences and duty cycles, thus offering significant flexibility for optimizing the performance of multilevel inverters. The influence of redundant switching sequences in the output phase voltage of inverters is demonstrated for a nine-level inverter. This paper also thoroughly compares the proposed SVPWM scheme with prior methods. Both simulation and experimental results are given. [ABSTRACT FROM AUTHOR]

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

This paper presents and compares control strategies for three-phase open-end winding drives operating in the flux-weakening region. A six-leg inverter with a single dc link is associated with the machine in order to use a single energy source. With this topology, the zero-sequence circuit has to be considered since the zero-sequence current can circulate in the windings. Therefore, conventional overmodulation strategies are not appropriate when the machine enters in the flux-weakening region. A few solutions dealing with the zero-sequence circuit have been proposed in the literature. They use a modified space vector modulation or a conventional modulation with additional voltage limitations. This paper describes the aforementioned strategies, and then, a new strategy is proposed. This new strategy takes into account the magnitudes and phase angles of the voltage harmonic components. This yields better voltage utilization in the dq frame. Furthermore, inverter saturation is avoided in the zero-sequence frame, and therefore, zero-sequence current control is maintained. Three methods are implemented on a test bed composed of a three-phase permanent-magnet synchronous machine, a six-leg inverter, and a hybrid digital signal processor /field-programmable gate array controller. Experimental results are presented and compared for all strategies. A performance analysis is conducted as regards the region of operation and the machine parameters. [ABSTRACT FROM AUTHOR]

Due to their remarkable merits, the soft-switching ac-link universal power converters have received noticeable attention during the last few years. These converters, which can be configured as dc-dc, dc-ac, ac-dc, or ac-ac, are compact, reliable, and offer longer life time compared to the other types of converters. However, they require more switches, which make the control process more complicated. This paper proposes a modified configuration for the dc-ac power conversion, which reduces the number of switches without changing the principles of operation. This converter, which is named sparse ac-link buck-boost inverter, reduces the number of switches from 20 to 18. Despite reducing the number of switches, the partial resonant time, during which no power is transferred, is as short as the original configuration. An important feature of this inverter is that it can be fabricated by IGBT modules, which are more compact and more cost-effective compared to the discrete devices. This paper presents the principles of the operation of this configuration, and compares the efficiency, the failure rate, and the current rating of the switches in the proposed and original inverters. It is shown that the failure rates of the sparse configuration are lower than the original configuration. Therefore, they have longer lifetime. The efficiency of the sparse configuration is slightly lower than that of the original configuration. However, by using reverse blocking IGBTs in the sparse configuration, the efficiency of the proposed inverter will be improved significantly. This paper evaluates the performance of the proposed inverter through simulation and experiment. [ABSTRACT FROM AUTHOR]

Model-predictive power control (MPPC) takes the switching nonlinearity of power converters and system constraints into consideration. It is a promising control technique for three-phase four-switch rectifiers (TPFSRs) because capacitor-voltage-balancing control and instantaneous power control can be simultaneously designed for this type of power converters. However, since only one switching vector is allowed in each control interval, conventional MPPC (C-MPPC) may lead to significant output power ripples that can severely degrade system power quality. This is particularly true for TPFSRs due to the limited number of switching states as well as the constraint imposed by the capacitor-voltage-balancing control. To improve the performance of TPFSRs, this paper proposes a multiple-vector MPPC scheme, which can minimize active power and reactive power ripples and achieve capacitor voltage balancing with a constant switching frequency. An equivalent zero-voltage vector model and a capacitor-voltage-balancing model are derived to implement the proposed control scheme. Comparative experimental results are presented to demonstrate the superiority of the proposed control scheme over the C-MPPC. [ABSTRACT FROM PUBLISHER]

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

The instantaneous output power of the two-stage single-phase inverter pulsates at twice the output frequency $(2f_{{\rm{o}}})$, generating notorious second-harmonic current (SHC) in the front-end dc–dc converter and the input dc voltage source. This paper focuses on the SHC reduction for a two-stage single-phase inverter with boost-derived front-end converter. To reduce the SHC, a virtual series impedance, which has high impedance at $2f_{{\rm{o}}}$ while low impedance at other frequencies, is introduced in series with the boost diode or the boost inductor to increase the impedance of the boost-diode branch or boost-inductor branch at $2f_{{\rm{o}}}$. Meanwhile, for achieving good dynamic performance, a virtual parallel impedance, which exhibits infinite impedance at $2f_{{\rm{o}}}$ while low impedance at other frequencies, is introduced in parallel with the dc-bus capacitor to reduce the output impedance of the boost-derived converter at the frequencies except for $2f_{{\rm{o}}}$. The virtual series impedance is realized by the feedback of the boost-diode current or the boost-inductor current, while the virtual parallel impedance is implemented by the feedback of the dc-bus voltage. Based on the virtual-impedance approach, a variety of SHC reduction control schemes are derived. A step-by-step closed-loop parameters design approach with considerations of reducing the SHC and improving the dynamic performance is also proposed for the derived SHC reduction control schemes. Finally, a 1-kW prototype is built and tested, and experimental results are presented to verify the effectiveness of the proposed SHC reduction control schemes. [ABSTRACT FROM AUTHOR]

This paper proposes a switched-capacitor multilevel inverter for high-frequency ac power distribution systems. The proposed topology produces a staircase waveform with higher number of output levels employing fewer components compared to several existing switched-capacitor multilevel inverters in the literature. This topology is beneficial where asymmetric dc voltage sources are available, e.g., in case of renewable energy farms based ac microgrids and modern electric vehicles. Utilizing the available dc sources as inputs for a single inverter solves the major problem of connecting several inverters in parallel. Additionally, the need to stack voltage sources, like batteries or supercapacitors, in series which demand charge equalization algorithms, are eliminated as the voltage sources employed share a common ground. The inverter inherently solves the problem of capacitor voltage balancing as each capacitor is charged to the value equal to one of the input voltage every cycle. State analysis, losses, and the selection of capacitance are examined. Simulation and experimental results at different distribution frequencies, power levels, and output harmonic content are provided to demonstrate the feasibility of the proposed multilevel inverter topology. [ABSTRACT FROM PUBLISHER]