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The pump-back test is widely adopted in the industry for characterizing and qualifying high-power converters. One popular pump-back test configuration is to tie the dc links of two converters together and circulate the current through the inductor connected between the ac terminals. In this configuration, one of the converters operates in the voltage mode to generate the virtual grid and the other converter regulates the circulating current, where hysteresis control could be applied. However, the switching characteristics of hysteresis control are unique due to the pulsewidth modulation type voltage being the virtual grid. This paper contributes to analyzing the switching frequency characteristics of the hysteresis control in this pump-back test configuration. The switching frequency tracking phenomenon is revealed and reported in this paper for the first time. Theoretical analysis, simulation validation, and experimental demonstration are provided to support the major conclusions. [ABSTRACT FROM AUTHOR]

Dual-comparison one-cycle control for the bidirectional power flow in single-phase grid-connected converters is proposed in this paper. Advantages of dual-comparison one-cycle control when compared to conventional one-cycle control is that it does not give any steady-state dc offset, no light-load instability, and implements unipolar pulsewidth modulation without having to sense the grid voltage. Addition of a fictitious current term, which is generated from the gating signal of one of the active devices, using a bandpass filter, enables the bidirectional power flow. The quality factor of the bandpass filter is shown to impact the total harmonic distortion in current, fundamental displacement angle, and steady-state dc offset. The optimal value of a quality factor, obtained with aid of simulations, gives a superior performance. The current drawn or injected into the grid is seen to lag the grid voltage. The reason for a nonunity displacement power factor is analyzed and a compensation to achieve a unity displacement power factor is also proposed in this paper. Detailed simulation and experimental studies are carried out to validate the proposed control and the high performance that can be obtained. [ABSTRACT FROM AUTHOR]

The neutral-point voltage-balancing control is a critical issue of a neutral-point-clamped converter. The conventional control strategy is to inject the specific zero-sequence voltage to regulate the redundant vector, but it is unacceptable to the three-phase four-wire system. This paper provides a neutral-point voltage-balancing control by the dipolar modulation, and the control freedom of the zero-sequence voltage is flexible. Therefore, the proposed method is suitable for both three-phase three-wire and three-phase four-wire systems. Besides, the proposed method improves the control dynamic in a reactive power system. The proposed neutral-point voltage-balancing control is verified by the mathematical analysis and experimental results. The control dynamic, power loss estimation, and the output current performance are analyzed in this paper. [ABSTRACT FROM PUBLISHER]

In this paper, a highly reliable back-to-back (BTB) power converter is proposed for doubly fed induction generator-based wind turbines (DFIG-WTs). When a power switch open-circuit fault is encountered in either the grid-side converter (GSC) or the rotor-side converter (RSC), a four-switch three-phase (FSTP) topology is formed to avoid using redundant bridge arms, which reduces the power circuit complexity and minimizes the conduction and switching losses. A simplified space vector pulsewidth modulation technique is used to eliminate sector identification and complex trigonometric calculations. In addition, the influence of dc-bus capacitor voltage unbalance on the electromagnetic torque is analyzed in detail. The offset current components are calculated, and they are deducted from the reference values in the modified control strategies to suppress the dc-bus voltage deviation. Moreover, the power loss model of a BTB converter is analyzed in detail, and the efficiency study is performed in various post-fault situations. Simulations in MATLAB/Simulink are carried out to verify the performance of a DFIG-WT based on a FSTP BTB converter. Furthermore, the control hardware-in-the-loop setup with RSC and GSC separately simulated in a digital real-time simulator is applied for experimental verification of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper extends the application of a frame-angle-based (FAB) direct torque controller (DTC) for permanent magnet synchronous motor (PMSM) drives to low and very low speeds. The FAB-DTC is intended for PMSM drives that are fed by $3\phi$ six-pulse wavelet-modulated dc–ac converters. The foundations of the FAB-DTC are based on regulating the $d\text{--}q$ -axis stator voltages, in response to variations in the load torque and/or drive speed. The adjustments in $d\text{--}q$ -axis stator voltages are created by changing the angle $\vartheta$ of the frame spanned by the $d\text{--}q$ -axis stator voltages. In order to extend the FAB-DTC to low and very low speeds, the changes in $\vartheta$ are accompanied by changes in the maximum scale. The values of maximum scale and $d\text{--}q$ -axis stator voltages are used to update or change the reference signals employed by the wavelet modulation to generate switching pulses to operate a $3\phi$ dc–ac converter. The complete PMSM drive system incorporating the modified FAB-DTC is implemented for a 10-hp PMSM drive system. The performance of the FAB-DTC is investigated for different changes in the command torque for various low and very low speeds. Performance results demonstrate stable, fast, dynamic, and accurate responses, which have minor sensitivity to variations in load torque and/or drive speed. [ABSTRACT FROM AUTHOR]

An adaptive control of DPWM implementable in clamped-three-level inverters with two strings of photovoltaic (PV) panels in cascaded connection is proposed in this paper. The proposed modulation is developed based on the so-called circuit-level decoupling concept. It is able to provide balance line voltage even under unbalanced dc links. The unequal dc voltages appeared due to asymmetric maximum point of power trackings (MPPTs) are controlled by proper injection of zero-sequence voltage to the common mode voltage, while the total dc voltage is regulated based on the voltage commands generated by the MPPT of each string. Thus, both PV strings are able to be operated based on their MPPTs while there is almost no low-order harmonic distortion at the inverter output current. Compared with the previous methods, the high capability of the proposed method is evaluated by simulation study and experimental tests. [ABSTRACT FROM AUTHOR]

This paper investigates ac–dc–ac multilevel topologies for three-phase four-wire applications obtained from an interconnection of three-leg voltage-source converters. The topologies can be applied in line voltage regulators, universal active power filters, and uninterrupted power supplies. Operating principles, a pulsewidth modulation (PWM) technique, and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the dc-link voltages and to reduce the harmonic distortion, switching stress, and power losses. Simulation results are used to compare the proposed configurations with a conventional solution in terms of harmonic distortion, semiconductor losses, and others characteristics. Experimental results are presented to validate the theoretical considerations and were obtained by using insulated-gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors. [ABSTRACT FROM AUTHOR]

In this paper, a fifth-order boost point-of-load converter is developed by cascading a modified fourth-order boost converter with a combination of L–C and diode. This topology has the following salient features: Single-switch topology, common ground between source and load, low-voltage stress across intermediate capacitors, and voltage gain same as other reported fifth-order boost converters with no common ground. Steady-state and dynamic analyses demonstrate the proposed converter's boosting feature and dynamic performance, respectively. A contoured robust Bode plot methodology is employed to design the robust voltage-mode controller to ensure load voltage regulation in the presence of uncertainties. The necessary and sufficient conditions under which the designed controller guarantees the load voltage regulation and robust stability are obtained. A step-by-step robust controller design procedure is outlined. The salient features of the proposed converter and its robust performance are studied analytically, using the MATLAB platform, and validated experimentally on a 60-W prototype module. [ABSTRACT FROM AUTHOR]

This paper investigates an ac–dc–ac multilevel power converter. The studied configuration is composed of two single-phase ac–dc–ac three-leg modules and series-connected H-bridges in the shared part of system. Because the proposed converter has shared legs between the input and output, it is employed in applications with same input and output frequency. Uninterrupted power supply and unified power quality conditioner are application examples for this converter. Such multilevel topology has lower dc-link voltage rating, which, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, a space-vector pulsewidth modulation (PWM) strategy to symmetrical and asymmetrical dc-link voltages, and an overall control strategy to adjust the system variables are presented. A power flux analysis shows the operation zone in which the individual dc-link voltage balancing is possible. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion, and switching stress. Two ac–dc–ac multilevel conventional structures are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

This paper investigates a multilevel inverter composed of series/parallel-connected H-bridges. The presented structure can be used for applications in which the use of semiconductor switches with low-voltage and low-current ratings is intended. A comprehensive system model, an overall control strategy to adjust the output voltage with constant magnitude and frequency, and a level-shifted PWM (LS-PWM) strategy based on a voltage vectors unidimensional analysis and a plane analysis are presented. The LS-PWM is capable of mitigating the low-frequency circulating current, thus generating multilevel voltage signals with low harmonic distortion, maximum number of levels, and low dv/dt. In addition, considering a wide range of values of voltages and currents and various power levels, the total converter losses are reduced compared with the conventional multilevel converters. Two multilevel conventional inverters with the same number of semiconductor switches are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

An optimal current control strategy for asymmetrical hybrid multilevel inverters (MLIs) is proposed in this paper enabling their use on motor drives, static synchronous compensators, and photovoltaic and wind generators, where a fast and precise current regulation is required. A key feature of these highly efficient converters is that an ac machine (motor or transformer) operates according to an open-end winding configuration, connected on one side to a main MLI and, on the other side, to an auxiliary two-level inverter (TLI). The first efficiently controls the main power stream operating at a low switching frequency, while the TLI acts as an active power filter, exploiting a conventional high-frequency two-level pulsewidth modulation (PWM) technique. The proposed control scheme optimally exploits the key features of the two inverters by suitably sharing the control task. In fact, a predictive current control is assigned to the MLI, which can be accomplished by low switching frequency operations, while the high switching frequency of the PWM-operated TLI is exploited to accomplish a fast and precise closed-loop current control, processing only a part of the power stream flowing through the system, thus producing low power losses. Simulations and experimental results confirm the consistency of the proposed approach. [ABSTRACT FROM AUTHOR]

In order to prevent the power switching devices (e.g., an insulated-gate bipolar transistor, IGBT) from shoot-through in voltage-source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in pulse width modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as “dead-time harmonics” hereafter) have to be compensated in order to achieve a satisfactory current quality, as required by standards. In this paper, the emission mechanism of dead-time harmonics in single-phase PWM inverters is, thus, presented considering the modulation schemes in detail. More importantly, a repetitive controller has been adopted to eliminate the dead-time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional-resonant-based fundamental-frequency current controller so as to mitigate the dead-time harmonics and also to maintain the control of the fundamental-frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead-time harmonics and other low-order distortions, and also, it is a simple method without hardware modifications. [ABSTRACT FROM AUTHOR]

This paper proposes a comprehensive and systematic approach in developing a new switching lookup table for direct power control (DPC) based on grid virtual flux estimation, implemented in a grid-connected three-phase ac-to-dc converter. The approach provides detailed information regarding the effects of a particular converter voltage space vector to the instantaneous input active and reactive power distributions in the converter system. Thus, the optimal converter switching states are able to be selected by the switching table, allowing the smooth control of the active and the reactive power for each sector. The usage of input ac voltage sensors for synchronization and input power calculation is avoided by applying a virtual flux concept in the control scheme. The grid virtual flux estimation technique is used to extract the grid voltage information from the converter switching states, line currents, and dc-link output voltage. Detailed explanation and analysis regarding the development of virtual flux DPC utilizing the proposed switching lookup table is given in this paper. Finally, the steady-state as well as dynamic performances of the proposed controller is tested both in simulations and laboratory experiments. There exist close agreements between the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Multilevel converters are a proven solution for medium-voltage and high-power applications, including renewable energy conversion. Developing 6.6-kV converters is a key goal for the wind turbines industry. Considering the voltage rating of commercially available semiconductors, five-level converters are necessary to reach 6.6 kV. The five-level active neutral-point-clamped converter (5L-ANPC) is one of the most advantageous topologies among five-level multilevel converters. This paper presents a new 5L-ANPC topology that overcomes the features of the previously employed 5L-ANPC topology. Along this paper, the properties and working principle of this new 5L-ANPC are explained. Finally, the validity of the new converter is validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

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

A multilevel boost power factor correction (PFC) rectifier is presented in this paper controlled by cascaded controller and multicarrier pulse width modulation technique. The presented topology has less active semiconductor switches compared to similar ones reducing the number of required gate drives that would shrink the manufactured box significantly. A simple controller has been implemented on the studied converter to generate a constant voltage at the output while generating a five-level voltage waveform at the input without connecting the load to the neutral point of the dc bus capacitors. Multicarrier pulse-width modulation technique has been used to produce switching pulses from control signal at a fixed switching frequency. Multilevel voltage waveform harmonics has been analyzed comprehensively which affects the harmonic contents of input current and the size of required filters directly. Full experimental results confirm the good dynamic performance of the proposed five-level PFC boost rectifier in delivering power from ac grid to the dc loads while correcting the power factor at the ac side as well as reducing the current harmonics remarkably. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel modulation technique and a new balancing control strategy for a single-phase five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter. The proposed modulator can control the FC voltage to follow the requested reference value and simultaneously generate the required ac output voltage regardless of the values of the dc capacitor voltages of the converter. By implementing this method, smaller values of the dc-link capacitor and FC can be used even in applications that could experience ripple or transient in the capacitor voltage. In a single-phase five-level ANPC converter applications, where the capacitors can experience pulsation power and dc-link balancing issues, such as grid-connected photovoltaic system, the selection of the reference voltage value for the FC can play an important role to balance the average values of the dc-link capacitor voltage. The proposed new control strategy uses a new reference voltage for the FC to be applied by the new modulator to have an average balanced dc-link voltages as well as an ac output voltage with good power quality. Simulation studies and experimental results demonstrate the effectiveness of the proposed modulation technique and control strategy even with relatively small dc capacitors to produce high-quality output voltage and current waveforms while maintaining an average balanced dc-link voltages. [ABSTRACT FROM PUBLISHER]

This paper presents a power factor correction (PFC)-based bridgeless Luo (BL-Luo) converter-fed brushless dc (BLDC) motor drive. A single voltage sensor is used for the speed control of the BLDC motor and PFC at ac mains. The voltage follower control is used for a BL-Luo converter operating in discontinuous inductor current mode. The speed of the BLDC motor is controlled by an approach of variable dc-link voltage, which allows a low-frequency switching of the voltage source inverter for the electronic commutation of the BLDC motor, thus offering reduced switching losses. The proposed BLDC motor drive is designed to operate over a wide range of speed control with an improved power quality at ac mains. The power quality indices thus obtained are under the recommended limits of IEC 61000-3-2. The performance of the proposed drive is validated with test results obtained on a developed prototype of the drive. [ABSTRACT FROM PUBLISHER]

This paper deals with the design, analysis, simulation, and development of a power-factor-correction (PFC) multiple-output switched-mode power supply (SMPS) using a bridgeless buck–boost converter at the front end. Single-phase ac supply is fed to a pair of back-to-back-connected buck–boost converters to eliminate the diode bridge rectifier, which results in reduction of conduction losses and power quality improvement at the front end. The operation of the bridgeless buck–boost converter in discontinuous conduction mode ensures inherent PFC operation and reduces complexity in control. The performance of the proposed multiple-output SMPS is evaluated under varying input voltages and loads by simulating this circuit in MATLAB/Simulink environment, and the results obtained through simulation are validated experimentally on a developed prototype. Both simulation and experimental results demonstrate the improved performance of the proposed SMPS. [ABSTRACT FROM AUTHOR]

Digital average current controllers for boost power factor correctors (PFCs) are usually designed for continuous conduction mode (CCM). However, discontinuous conduction mode (DCM) appears in the inductor current near the zero crossings of the input current at light loads, resulting in input current distortion. It is caused by inaccurate average current values obtained in DCM and by the linear CCM PFC controller that is unable to ensure input current shaping in DCM whereby the converter exhibits nonlinear characteristic. This paper proposes a simple digital DCM control scheme that is achieved with minimal changes to the CCM average current control structure. It is mathematically and computationally simple. The result of all arithmetic operations in the proposed current control loop to obtain the desired control output can be achieved in a single clock cycle, whereas other DCM control schemes require multiple clock cycles. Good input current shaping is achieved in both CCM and DCM with the proposed CCM–DCM digital controller. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of parasitic capacitances in the series connection of insulated-gate bipolar transistors (IGBTs) on their voltage sharing. These parasitics exist naturally due to gate driver interconnects and power circuit physical architecture. Two solutions, which can be combined, are proposed to minimize these effects in order to achieve a better voltage balancing. The first one is based on gate driver self-powering technique. The second one is based on a vertical structure assembly of IGBTs connected in series. The performance offered by these two complementary solutions is investigated and validated on a series connection of three IGBTs in a chopper converter. Both simulation and experimental results show the effectiveness of our approaches. [ABSTRACT FROM AUTHOR]