Search

This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n-level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme. [ABSTRACT FROM AUTHOR]

Wide bandgap semiconductors with fast switching speed capability are becoming an enabler to achieve the higher power density design. However, the further increase of switching frequency cannot continuously improve the power quality of ac-side waveforms in dc–ac/ac–dc application. The main reason is the distortion of pulsewidth modulation (PWM) voltage at switching point under high switching frequency. In general, there are two contributors causing PWM voltage distortions in bridge-based topologies. One is the deadtime, which occupies higher ratio in the small duty cycle case under high switching frequency and induces the voltage errors. The other one is the turn-off transient in the small load current or around the zero-crossing point of the ac-side current, because the relatively slow rising slope of the drain–source voltage will affect the right duty cycle. To solve this issue, this paper proposes a closed-loop modulation scheme to compensate the duty cycle distortion of PWM voltage based on one-cycle control or charge control. Compared to the traditional feedforward type of compensation, the proposed scheme does not need online calculation and instantaneous inductor current sampling, and it shows potential to be a general scheme for variety of topologies and modulations. Simulations and experiments are carried out on a 400-kHz single-phase full-bridge inverter with 400-Hz fundamental frequency to demonstrate the performance of the proposed approach. [ABSTRACT FROM AUTHOR]

In voltage-source converter (VSC) systems, utilization of filter inductors with deep saturation characteristics is often advantageous due to the improved size, cost, and efficiency. However, with the use of conventional current regulation (CCR) methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes the inverse dynamic model (IDM)-based compensation method to overcome these performance issues. The method converts the nonlinear inductor of the plant to a fictitious linear inductor such that linear current regulators can perform satisfactorily. In conjunction, identification of L–R parameters is performed to obtain IDM of the system within an acceptable range of sensitivity yielding satisfactory performance. The performance issues of CCR methods with saturable inductor are demonstrated by simulations and experiments. Then, the proposed method is experimentally verified on a single-phase 1.5-kW grid-connected VSC. The performance improvement over the CCR methods is verified by a detailed comparison of experimental waveforms. [ABSTRACT FROM AUTHOR]

Power factor correction (PFC) converter suffers from serious double-line-frequency output voltage ripple due to the difference between instantaneous ac input power and dc output power. To suppress such double-line-frequency output voltage ripple, a ripple cancellation circuit (RCC) is utilized to generate the same magnitude but 180° phase shifted double-line- frequency voltage ripple. This paper provides an insight into the relationship between control scheme and double-line-frequency ripple suppression from the perspective of audio susceptibility model. For the purpose of reducing the double line frequency ripple, the closed-loop audio susceptibility of series RCC should be designed relatively low at double line frequency. According to such requirement, a ripple controller with improved voltage feed-forward (FF) scheme and quasi-proportional-resonant (QPR) compensator is designed. As QPR compensator can increase the denominator of the closed-loop audio susceptibility, while voltage FF scheme can reduce its numerator, its magnitude at double line frequency is thus greatly reduced and double-line-frequency ripple is also significantly suppressed. Moreover, due to the flexibility of QPR compensator, the proposed ripple controller presents good ripple suppression in a different line frequency application. Finally, experimental results of a flyback PFC with buck-type RCC quasi-single-stage ac–dc converter are provided to verify the validity of the proposed ripple controller. [ABSTRACT FROM AUTHOR]

This paper proposes an explicit predictive current control scheme implemented with a low carrier frequency pulsewidth modulation (PWM) on an induction machine fed by a three-level neutral point clamped inverter. The PWM carrier and the main current sampling frequency are both set to 1 kHz, resulting in a 500 Hz average switching frequency per device, which is very suitable for large drive applications. The explicit predictive control is introduced to optimize the available bandwidth provided by such a low sampling frequency, maximizing the dynamic performance. The strategy has been tested in a 2.2-kW induction motor experimental prototype. [ABSTRACT FROM AUTHOR]

Three-phase pulsewidth modulation inverter fed induction motor drive system is widely applied in high power drive applications. Sensor faults are very common in the drive system, which, once occur, might result in degraded system performance or even system shutdown. In order to rapidly and accurately diagnose the sensor faults, this paper proposes an intelligent time-adaptive data-driven method to identify the fault location and fault type of sensors in the drive system. An emerging machine learning technology named extreme learning machine (ELM) is applied to learn the sensor fault dataset; an ensemble ELM classifier is then designed to improve diagnostic accuracy, based on which a time-adaptive fault diagnosis process is proposed to achieve a high and balanced diagnostic accuracy and speed. As a data-driven method, the proposed method only employs the phase current, dc-link voltage, and speed signals as the inputs to the ensemble ELM classifiers and requires no additional sensors and other hardware. Simulated and experimental tests show that the proposed method can rapidly and accurately detect the fault sensor location and identify offset fault, stuck fault, and noise faults with an average diagnostic accuracy of 98% and the average decision time of 10 ms after the fault occurs. Moreover, such diagnosis method is robust to the fluctuation of catenary voltage and dc-link voltage, fault severity, and variation of model parameters, speed, and load. [ABSTRACT FROM AUTHOR]

Passivity-based analysis and controller design offer a promising approach to guarantee the stability of power systems. If all grid-connected components act strictly passive, critical oscillations cannot arise. Recent research establishes design guidelines for current-controlled voltage-source converters that allow obtaining a nonnegative real part of the converter input admittance for a wide frequency range. In this paper, the findings are extended and generalized from a control engineering point of view. Utilizing passivity indices to quantify the degree of the input admittance's passivity, the current controller design is reviewed and assessed. Further, generic and necessary passivation design criteria are proposed and carried out exemplarily for passive as well as for active damping using voltage feed-forward filters. Finally, the theoretical findings are validated by experiments. [ABSTRACT FROM AUTHOR]

Power line communication (PLC) technology has proved itself in the last decade as an interesting solution for data transmission and communication in domestic application. Lately, this technology has been considered as a potential solution for monitoring and diagnosis of a motor-fed inverter setup. Information issued from sensors would be sent via power cables back to the controller despite the harsh environment and the switching of the inverter. This paper discusses the use of PLC technology over a pulsewidth modulation network by underlining the effect of the power cable length and the inverter switching on communication. A new approach based on the measurement of scattering parameters is used for this purpose, and the effect of the cable length is analyzed. It is shown that, for long distances, the PLC technology may not be effective, and hence, it is not possible to use power cables for communication. [ABSTRACT FROM PUBLISHER]

A two-motor drive, supplied by a five-leg inverter, is considered in this paper. The independent control of machines with full dc-bus voltage utilization is typically achieved using an existing pulsewidth modulation (PWM) technique in conjunction with field-oriented control, based on PI current control. However, model predictive control (MPC), based on a finite number of control inputs [finite-control-set MPC (FCS-MPC)], does not utilize a pulsewidth modulator. This paper introduces three FCS-MPC schemes for synchronous current control in this drive system. The first scheme uses all of the available switching states. The second and third schemes are aimed at reducing the computational burden and utilize a reduced set of voltage vectors and a duty ratio partitioning principle, respectively. Steady-state and transient performances are analyzed and compared both against each other and with respect to the field-oriented control based on PI controllers and PWM. All analyses are experimental and use the same experimental rig and test conditions. Comparison of the predictive schemes leads to the conclusion that the first two schemes have the fastest transient response. The third scheme has a much smaller current ripple while achieving perfect control decoupling between the machines and is of low computational complexity. Nevertheless, at approximately the same switching loss, the PI-PWM control yields the lowest current ripple but with slower electrical transient response. [ABSTRACT FROM PUBLISHER]

This paper proposes a solution for reducing the ground leakage current in transformerless single-phase grid-connected photovoltaic converters. This is obtained with the introduction of an active common-mode filter able to compensate for variations of the output common-mode voltage of the power converter. The active common-mode filter is applied to a widespread and efficient full-bridge driven by a three-level pulse width modulation, allowing the power converter to operate with low ground leakage current and with an arbitrary power factor. After showing the desired voltage waveform for common-mode voltage compensation, this paper presents the design guidelines for the needed additional magnetic component together with the power loss considerations for all the devices added for the proposed solution. Experimental results show the performance of the proposed solution in terms of ground leakage current reduction, effectiveness of dead-time compensation, total harmonic distortion of the injected grid current, and power losses. [ABSTRACT FROM PUBLISHER]

The Z-source inverter (ZSI) employs an LC impedance network between the main inverter bridge and the power source. The unique feature of the ZSI is that it can operate either in buck or boost mode with a wide range of obtainable output voltages from a given input voltage. This topology also exhibits better electromagnetic-interference noise immunity when compared to a traditional voltage-source inverter (VSI). However, the LC impedance network of ZSI significantly increases the size and cost of the power converter and can make it unsuitable for low-power applications. This paper proposes a novel topology called switched boost inverter (SBI) which exhibits similar advantages of ZSI with lower number of passive components and more active components compared to ZSI. The steady-state and small-signal analyses of SBI, along with its pulsewidth modulation (PWM) control strategies, have been discussed in this paper. This paper also presents a comparison of SBI and ZSI with the same input and output parameters. The theoretical analysis given in this paper has been validated using a laboratory prototype of SBI, and the experimental results are presented for verification. The experimental harmonic spectrum of the inverter's output voltage with the proposed PWM technique is also plotted and compared with that of a traditional VSI. All the experimental results show good correlation between theory and experiments. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation strategy for the modular multilevel converter (MMC) which provides the voltage balancing of the capacitors of different submodules comprising the converter. Not only is this modulation applicable to MMCs constructed with classic two level (2L) submodules, but it is also effective for arrangements with different submodule concepts, for instance, topologies like neutral point clamped (NPC), flying capacitors (FCs), neutral point piloted (NPP), etc. Therefore, firstly, the general modulation philosophy is explained applied to the two level (2L) submodule concept, and secondly, the extension to 3L-NPC and 3L-FC submodule topologies is analyzed. After that, the validation of the studied modulation strategy is carried out by means of successful simulation results, at different switching frequencies and number of submodules. The corresponding experimental results are shown in Part II of this paper after having implemented the aforementioned modulation strategy in a real test bench. In addition to this, a comparison based on thermal analysis and sizing of elements among the four studied submodule topologies is also included. [ABSTRACT FROM PUBLISHER]

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method. [ABSTRACT FROM PUBLISHER]

In this paper, a new soft switching flyback dc–dc converter with a simple zero-voltage and zero-current switching (ZVZCS) cell is proposed. The auxiliary resonant cell consists of one switch, one diode, one inductor, and two capacitors. It provides ZVZCS not only for the main switch but also for the auxiliary switch at both turn-on and turn-off times. In addition, all the auxiliary diodes and body diodes of the switches operate under full ZVZCS except the output diode which turns off only with zero current switching. This soft switching technique makes the proposed converter have less switching losses which leads the converter to operate in higher frequencies and efficiency. Another outstanding feature of the proposed converter is using the auxiliary resonant cell out of the main power path to have lower voltage stress on the switches. In this paper, pulse width modulation (PWM) is employed to control the main switch. A detailed mode analysis of the proposed converter operation is presented along with design procedure. Finally, the accuracy performance of the converter is verified through a 60 W experimental prototype results. [ABSTRACT FROM AUTHOR]

This paper aims to improve the full speed sensorless drive for permanent-magnet (PM) synchronous machines on the region of initial zero speed and the region of medium speed. At zero and low speed, the saliency-based drive using the square-wave voltage injection has demonstrated the comparable performance to the sensor-based drive using the encoder with hundreds of pulses per revolution. For PM machines at initial state, the magnet polarity is typically identified based on the injection of voltage pulses before the saliency-based drive. Instead of pulses injection, this paper directly adds the polarity detection capability in the saliency-based drive by superimposing the same square-wave voltage. A fast detection period and negligible current spikes are benefits for the drive using the same square-wave injection voltage for both the polarity detection and position estimation. At medium speed, electromotive force voltage can be estimated to replace the saliency for the sensorless drive. To achieve a smooth operation between two estimation methods, a transition algorithm is also proposed based on a single-phase-lock loop by blending two feedback position signals. According to the experimental evaluation, the reduced power consumption as well as the smooth switch between two different drives is achieved. All the sensorless methods are verified by an interior PM machine with a saliency ratio of 1.37 (Lq/ Ld\,= \,1.37 ). [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]

A wheeled human-conveyance vehicle (WHCV) with a low-level microprocessor is realized in this paper. WHCVs are environmentally friendly short-range transportation vehicles. This paper proposes a simple Mamdani-like fuzzy controller for self-balancing WHCV control. System stability is guaranteed by establishing sufficient conditions based on the Lyapunov stability analysis. Finally, experimental results show that the proposed Mamdani-like fuzzy control strategy can control the WHCV. [ABSTRACT FROM PUBLISHER]

Modern grids are facing a massive integration of power electronics devices, usually associated to instability issues. In order to assess the likelihood and severity of harmonic instability in the high-frequency region, this paper develops a multivariable input-admittance model that accurately reflects the following aspects: 1) the discrete controller frequencies are defined inside a spectrum region limited by the Nyquist frequency and 2) the physical system aliases are transformed into lower frequency component inside the discrete controller. The proposed model shows that dynamic interactions are not theoretically band-limited; however, the control action tends to be strongly limited in a low-frequency range, due to the natural low-pass filter behavior of acquisition and modulation blocks. This is reflected in a reduced resistive part (either positive or negative) of the input-admittance in the high-frequency range. More specifically, considering the input-admittance passivity criterion, the excursions into the nonpassive area are very smooth at high frequencies, where the input-admittance is well-described by simply its inductive filter. Comprehensive experiments are conducted on a lab scale prototype, which includes measurements beyond the Nyquist frequency and alias identification. The experimental results well-match the theoretical model. [ABSTRACT FROM AUTHOR]

Among multilevel converter topologies, the cascaded H-bridge (CHB) converter is one suitable solution for multiple applications, such as flexible ac transmission systems and motor drives. CHB presents a natural high modularity because it is formed by the serial connection of H-bridges. This paper deals with a CHB where the cells do not have the same aging because the maintenance during the years of operation forces to replace some damaged cells of the converter with new or repaired ones. A method based on clamping one power cell can be used to reduce the power losses of that cell reducing its temperature and increasing its lifetime. However, clamping one cell of the CHB introduces high harmonic distortion around twice the carrier frequency due to the CHB unbalanced operation when a conventional phase-shifted pulsewidth modulation (PWM) is applied. A deep harmonic distortion analysis of the CHB output voltage with thermal control based on clamping one cell is presented. Using this analysis, the harmonic distortion at twice the carrier frequency is eliminated applying a nonconventional phase-shifted PWM where the angles between the carriers of consecutive power cells are modified. Experimental results show how the thermal control applying the clamping of a power cell is achieved while the harmonic distortion around twice the carrier frequency is eliminated. [ABSTRACT FROM AUTHOR]

Multiphase machines are famous for their fault-tolerant capability. Conventional fault-tolerant model predictive current control (FT-CMPC) of multiphase machines suffers from high computational burden, low switching frequency, and relatively high current harmonics. This paper proposes a fault-tolerant PWM predictive control (FT-PWMPC) to enhance the performance of fault-tolerant predictive control strategy without using complex enumeration method. The reference phase voltages are generated by a postfault mathematical model in stationary reference frame and transformed to duty cycles with a properly set common-mode voltage. Then, a comparative study of fault-tolerant predictive control strategies is presented, including FT-CMPC, FT-two-vector-based-predictive control, and the proposed FT-PWMPC. The control strategies are implemented with the same sampling frequency or switching frequency on a six-phase permanent magnet synchronous machine test bench. Experimental results of dynamic response, steady-state currents, vibration, and parameter sensitivities are given to identify the advantages and limitations of each control strategy. [ABSTRACT FROM AUTHOR]

This paper deals with torque ripple estimation and reduction in a vector controlled double-inverter-fed wound rotor induction machine (DI-WRIM) drive by employing different pulsewidth modulation (PWM) techniques applied to stator and rotor side voltage source inverters (VSIs). The influence of PWM switching sequences on torque ripple is studied in terms of stator and rotor flux ripples. A novel rotor speed independent transformation has been proposed to visualize the nature of stator and rotor flux ripples from a common frame of reference. The expression for instantaneous torque ripple is formulated and a PWM combination is proposed resulting in lower root mean square (rms) and peak–peak torque ripple. The estimated instantaneous, rms, and peak–peak torque ripple is verified through simulation and experimental results from a 3-kW vector controlled DI-WRIM drive. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

A trinary multilevel converter uses a few heterogeneous H-bridge submodules (SMs) to synthesize an output voltage with multiple levels. Two major limitations of this converter are that it needs multiple dc sources and it cannot operate under pulsewidth modulation (PWM). This paper addresses these limitations by adding a low-voltage H-bridge SM to this converter and proposing a new switching algorithm. The resulting PWM-based asymmetric cascaded H-bridge converter uses only one dc source and synthesizes a high-quality output voltage. This improved converter can be a potential choice for real and reactive power support in power system applications. This paper also proposes methods for stability analysis and design of this converter. Experimental case studies evaluate the performance of the proposed converter for both standalone and grid-connected modes of operation. [ABSTRACT FROM AUTHOR]

Two parallel interleaved two-level (2L) three-phase voltage source inverters (VSIs) can be analyzed as a single three-level (3L) VSI. A generalized carrier-based method is proposed in this paper for implementing different 3L pulsewidth modulation (PWM) techniques using two parallel interleaved 2L VSIs. The proposed method modifies the given three-phase reference signals of 3L VSI for implementation of the PWM technique using two parallel interleaved 2L VSIs. The influence of nonidealities on the equivalent 3L PWM switching sequences is also discussed. To overcome the effect of nonidealities, a new modified discontinuous PWM technique (MDPWM1) is proposed. The analysis of different performance indices is carried out for different 3L PWM techniques, and the key advantages of different PWM techniques are identified. Simulation and experimental results are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a five-phase dual random space vector pulsewidth modulation (FPDR-SVPWM) strategy with an optimized probability density function (PDF) for a five-phase voltage-source inverter, and its performance and evaluation are also analyzed. Based on the nearest four vectors modulation method, the FPDR-SVPWM strategy, combined with random switching frequency and random zero vector, is investigated to significantly reduce the amplitude of high-order harmonics near the switching frequency and its integer multiples. For the nonsinusoidal power supply, third harmonic injection is introduced in this modulation strategy as well. Considering the effect of random numbers on the performance, an optimized Beta distribution is studied in detail. In order to analyze harmonic dispersion degree qualitatively and quantitatively, the power spectral density and the harmonic spread factor are both employed to assess the performance of the FPDR-SVPWM strategy. A series of results of simulation in MATLAB and experiments based on field programmable gate array demonstrate that the proposed modulation strategy is correct and valid, and it distributes high-order harmonics into a wide range without affecting the fundamental wave and third harmonic. [ABSTRACT FROM AUTHOR]

This paper develops a modulation based fault-tolerant (FT) strategy for restoring the operation of three-phase modular multilevel converters (MMCs) with faulty switches. This FT strategy is based on a proposed modified space vector modulation (SVM) technique that generates balanced line-to-line (line) voltages even in the case of a fault occurrence. In the postfault operation, the proposed strategy is able to restore the fundamental amplitude of the line to the neutral (load) voltages to that of the normal operation condition with a slightly increased voltage stress over the switches in the faulty phase. In this paper, first a brief background about MMCs and SVM technique is provided. Then, the proposed FT strategy and the modified SVM technique are presented. Finally, several simulation and experimental results are provided to validate operation of the proposed strategy. [ABSTRACT FROM AUTHOR]

Standard pulsewidth modulation (PWM) schemes for modular multilevel converters (MMC) have neglected deviations of the module voltages from the mean module voltage of an MMC arm as well as the dynamic change in the module voltages since their last measurement and during the switching period. This induces an output voltage error. Large output voltage errors disturb the higher level closed-loop control of the MMC, such that control targets cannot be met anymore. The output voltage error can be reduced using advanced PWM methods that predict and include the dynamic change of the individual module voltages during a switching period in the calculations for the duty cycle. This paper shows measurement results obtained from an experimental medium-voltage prototype, proving that advanced methods lead to much lower output voltage errors than the standard methods, but cannot fulfill the expectations raised by the simulations documented in the literature. In order to overcome the limitations of the old method, a new method that includes the semiconductor voltage drop and parasitic resistances is introduced and evaluated with measurements in this paper. Furthermore, simulation results showing the influence of the considered modulation methods on the closed-loop current control performance are presented. [ABSTRACT FROM AUTHOR]

A fully digital driving circuit for thin-film transistor liquid crystal display can offer benefits, including less power consumption and a shortened design schedule. Using the pulsewidth signal to control the moment to stop the ramp voltage, the pixel voltage can be set accurately. In this paper, the possible issues of power consumption, device nonuniformity, and parasitic capacitance are well-studied to prove the feasibility and advantages of the digital driving method. It is prospectively expected to substitute for the conventional analog driving method in the future. [ABSTRACT FROM AUTHOR]

A nonisolated dc–dc converter with chain links of submodules (SMs) is proposed in this paper. The converter can perform as a dc transformer with a low step-up ratio. To demonstrate the step-up dc–dc conversion, the converter is operated in a resonant conversion mode, achieving soft switching and inherent balancing of the SM capacitor voltages. The circuit configuration is presented and the operation principle is analyzed in this paper. Experimental results based on a downscaled prototype validate the performance of the proposed converter as a low step-up ratio dc transformer. The converter also exhibits a good linearity covering a broad range. [ABSTRACT FROM AUTHOR]

The circulating current of modular multilevel converter (MMC) has a great impact on the power losses, the submodule (SM) capacitor voltage ripples, and the rating of power devices. Existing analysis of circulating current has considered the capacitor voltage and the modulation signal. In this paper, the effect of semiconductor devices on the circulating current is further presented. In order to realize the different circulating current injection targets under different conditions, a unified online calculation scheme by using the instantaneous information of MMC is proposed in this paper to generate the circulating current injection references. It avoids detecting the amplitude and phase of the output current or using an extensive lookup table. Besides, a mathematical analysis model is built and it reveals the impact on the capacitor voltage ripple and the rms value of arm current with different injection references, thus guide the determination of the injection ratio. Experimental results based on a three-phase MMC prototype with six SMs per arm are presented to demonstrate the analysis of circulating current and the proposed circulating current injection references generating method is verified by different circulating current control targets with different loads. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is very attractive in a high-voltage dc (HVdc) transmission system due to its high modularity and scalability. It is also a promising candidate for medium-voltage applications. An MMC has many power devices that lead to a relatively low reliability based only on a direct failure rate calculation. The reliability of an MMC can be improved by redundant designs. Lots of redundant designs and strategies have been proposed in recent years, while their reliability improvements are hardly quantified in existing literature. In practice, reliability improvement with constraint costs is a challenge. In view of these, this paper proposes a reliability and cost assessment scheme for MMC redundant designs and strategies. Reliability and cost are quantified for comparison purposes. A medium-voltage application is used to demonstrate the reliability and cost assessment scheme. The reliability analysis is based on a combinatorial model and the Poisson process model. The cost analysis focuses on capital cost and power loss cost. The proposed reliability and cost analysis scheme provides a guideline for MMC redundant design and redundant strategy selection. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have been widely used in voltage source converter HVdc, and the capacity of MMCs has reached 1000 MW. The accurate calculation and theoretical analysis of the loss has attracted more and more attention, especially in high-power applications. This paper presents a simplified analytical calculation model of average power loss for MMC based on the root mean square (RMS) and absolute values of the arm current. In this model, the analytical expressions of the conduction loss and the switching loss are derived in terms of the whole arm of MMC rather than a single submodule. It avoids the effect of the complexity of its switching pattern on the calculation accuracy of the model. The explicit expressions of the presented model show the relationship between the loss, the voltage balancing methods, and the main variables of MMC directly in comparison with the conventional loss evaluation methods. PSCAD/EMTDC simulation and experimental results of the ±350 kV/1000 MW MMC in the Luxi Back-to-Back DC Asynchronous Networking Project verify the correctness and the accuracy of the proposed simplified calculation model. [ABSTRACT FROM AUTHOR]

Interleaved three-phase voltage source converters (VSCs) are widely applied in industry. The circulating current issue has been the focus so far in literature. However, the common-mode voltage (CMV) generated from interleaved VSCs, which is also a key factor that influences the system's performance, has not yet been studied in detail. In this paper, the impact of pulsewidth modulation (PWM) strategies on the CMV of interleaved two-level VSCs is analyzed. The analysis is conducted based on the double Fourier integral theory and in a generalized way considering an arbitrary number of interleaved converters. Five PWM schemes are considered, including the interleaved sinusoidal PWM (ISPWM), the interleaved space vector modulation (ISVM), the interleaved discontinuous PWM (IDPWM), and the recently proposed interleaved carrier phase-shift PWM (ICPS PWM), and interleaved carrier phase-shift SVM (ICPS SVM). Both magnitude and harmonic content of CMV are examined for each method. The analysis reveals that with ISPWM, ISVM, ICPS PWM, and ICPS SVM, the CMV can be reduced. In contrast, interleaving has little impact on the CMV with IDPWM, which is always at VDC/2 due to high low-order harmonics, making it less attractive for drive applications using coupled architecture. For modular architecture, ICPS PWM and ICPS SVM are more desirable considering their low-ZSCC peak value. The study is verified through experimental results. [ABSTRACT FROM AUTHOR]

The matrix converter (MxC) is a bidirectional direct ac–ac power conversion topology that can generate variable voltage and variable frequency output. It has low harmonics in input current and power factor control capability. In this paper, MxC concept is extended to medium-voltage (MV) level to provide a high-power drive that has bidirectional power flow capability and very low harmonics in input current and output voltage. MV MxC is implemented by connecting power cells in series which consist of three-phase input and single-phase output MxC. In this paper, detailed design of the MV MxC topology is described and the performance of the proposed topology is explained through experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents an experimental study on the ageing of insulated-gate bipolar transistor (IGBT) power modules. The aim is to identify the effects of power cycling on these devices with high baseplate temperatures (60 ^\circ\C to 90 ^ \circ\C) and wide temperature swings (60 ^\circ \C to 100 ^\circ\C). These values for thermal stresses have been defined according to automotive applications. The test conditions are provided by two types of test benches that will be described in this paper. The changes in electrical and thermal indicators are observed regularly by a monitoring system. At the end of the test (reaching damage criterion or failure), different analyses are performed (acoustic scanning and SEM imaging), and the damage is listed systematically. Nineteen samples of 600-V 200-A IGBT modules were thus aged using five different power-cycling protocols. The final summary of results shows that ageing mechanisms mainly concern wire bonds and emitter metallization, with gradual impact depending on protocol severity. [ABSTRACT FROM AUTHOR]

Two three-level inverters driving an open-end winding induction motor can generate equivalent voltage waveforms as a single five-level inverter-based drive. In addition, it can bring in benefits such as reduced dc-link voltage, less number of devices, and fault-tolerant capability, which is favored in high-power motor drive applications. The main challenge with this type of configuration is the appearance of large zero-sequence current circulating between the two inverters, which generates extra losses in the switching devices and the motor as well as affects the normal operation of the machine. Another challenge is to balance the dc-link neutral point voltage of the two three-level inverters. This paper has proposed a simplified decoupled space-vector pulsewidth-modulation (PWM) strategy to eliminate the averaged zero-sequence voltage in each switching cycle by the placement of redundant vectors of each individual inverter using a time shift. Neutral point voltage balance is further achieved by adjusting the time duration of the redundant vectors. In this paper, it is shown that it is possible to operate this kind of drive configuration with a single dc power supply and achieve averaged zero-sequence voltage elimination and neutral-point voltage balancing at the same time. Experimental results of a 5.5-kW dual three-level inverter drive using the proposed PWM strategy are presented, which validates the control method and drive configuration. [ABSTRACT FROM PUBLISHER]

A new pulsewidth modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is proposed in this paper. A three-level NPC inverter is completely mature and very well-established topology in high-power applications. However, the three-level NPC inverter has an inheritance problem of the neutral-point voltage unbalancing due to the split dc-link capacitors. This structure can cause large neutral-point voltage ripple. Furthermore, output currents of the three-level NPC inverter are distorted by the neutral-point voltage ripple. Therefore, the neutral-point voltage must be controlled. In this paper, a new DPWM method using two different offsets for the neutral-point ripple reduction is proposed and the effectiveness of the proposed DPWM method is verified by using the simulation and the experimental results. [ABSTRACT FROM PUBLISHER]

A conventional asymmetrical half-bridge (AHB) converter is widely used for dc–dc stage in low-to-medium power system. However, since the asymmetric operation of AHB converter causes the low efficiency over entire load condition, the conventional AHB converter is not usually considered for the candidate of server power system. In order to overcome the problems of the conventional AHB converter, a wide zero-voltage-switching (ZVS) range AHB converter with a clamp switch and a clamp diode is proposed in this paper. The proposed AHB converter (PAHBC) replaces a low-side clamp diode with a MOSFET switch and adds an auxiliary winding, which changes the transformer turns-ratio. From these modifications and the pulsewidth-modulation (PWM) control of clamp switch, the PAHBC can be designed optimally at nominal input condition and obtains additional dc gain at hold-up time condition. These advantages achieve the high conversion efficiency over the entire load condition. The operational principle and analysis of the PAHBC are presented in this paper and verified by a 340–400 V input and 50 V/500 W output laboratory prototype. [ABSTRACT FROM PUBLISHER]

Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector (SV) structures have advantages like extension of linear modulation range, elimination of fifth and seventh harmonics in phase voltages and currents for the full modulation range including extreme 12-step operation, reduced device voltage ratings, lesser dv/dt stresses on devices and motor phase windings resulting in lower EMI/EMC problems, and lower switching frequency—making it more suitable for high-power drive applications. This paper proposes a simple method to obtain pulsewidth modulation (PWM) timings for a dodecagonal voltage SV structure using only sampled reference voltages. In addition to this, a carrier-based method for obtaining the PWM timings for a general N-level dodecagonal structure is proposed in this paper for the first time. The algorithm outputs the triangle information and the PWM timing values which can be set as the compare values for any carrier-based hardware PWM module to obtain SV PWM like switching sequences. The proposed method eliminates the need for angle estimation, computation of modulation indices, and iterative search algorithms that are typical in multilevel dodecagonal SV systems. The proposed PWM scheme was implemented on a five-level dodecagonal SV structure. Exhaustive simulation and experimental results for steady-state and transient conditions are presented to validate the proposed method. [ABSTRACT FROM PUBLISHER]

It is known that the ripple-based control of a switching dc–dc converter benefits from a faster transient response than a conventional pulse width modulation (PWM) control switching dc–dc converter. However, ripple-based control switching dc–dc converters may suffer from fast-scale oscillation. In order to achieve fast transient response and ensure the stable operation of a switching dc–dc converter over a wide load range, based on a conventional pulse train (PT) control technique, a peak capacitor current PT (PCC-PT) control technique is proposed in this paper. With a buck converter as an example, the operating modes, steady-state performance, and transient respond performance of a PCC-PT controlled buck converter are presented and assessed. To eliminate fast-scale oscillation, circuit and control parameter design considerations are given. An accurate discrete iteration model of a PCC-PT controlled buck converter is established, based on which the effects of circuit parameters on the stability of the converter operating in a discontinuous current mode (DCM), mixed DCM-continuous conduction mode (CCM), and CCM are studied. Simulation and experimental results are presented to verify the analysis results. [ABSTRACT FROM PUBLISHER]

A four-level five-phase open-end winding (OeW) drive topology is introduced in this paper. The drive comprises a five-phase induction machine with open-end stator windings, supplied using two two-level voltage-source inverters with isolated and unequal dc-link voltages, in the ratio 2 : 1. The topology offers the advantages of a modular structure with fewer semiconductor components and has a greater potential for fault tolerance, as compared with an equivalent single-sided four-level drive. Due to the large number of switching states, development of a suitable space vector pulsewidth-modulation (PWM) method can be challenging. Hence, this paper examines the implementation of two-level-shifted carrier-based PWM methods. The effect of dead time on the drive performance is discussed, and it is shown that simultaneous PWM switching of both inverters can lead to degraded output phase voltage waveforms. Detailed analysis of this phenomenon is presented, a solution is proposed, and the modified modulation techniques are incorporated in an experimental setup, at first in conjunction with $V/f$ control. Once the proof of concept has been provided, full field-oriented control is implemented in this OeW drive topology for the first time; detailed experimental testing is conducted, and results are reported. [ABSTRACT FROM AUTHOR]

This paper shows how the problem of estimating the initial rotor position in permanent-magnet sensorless drives can benefit from the availability of a direct measurement of motor phase voltages. Two different estimation methods are presented for this purpose. The first is a readjustment of a classic procedure based on the detection, by means of the injection of voltage test pulses, of inductance variations due to motor saliencies, from which it is then possible to infer the position of the rotor. Since the application of irregular test pulses may increase the estimation uncertainties, the available voltage measurement is exploited to implement a closed-loop amplitude control of the test pulses. The second method is introduced both to overcome an issue related to the digital measurement approach adopted in this paper and to allow position estimation even in a motor with no relevant saliency, a case for which the first method is inappropriate. The effectiveness of the proposed solutions is validated by several experimental tests, which are carried out on two motors with different saliency properties. [ABSTRACT FROM PUBLISHER]

This paper proposes a modular isolated dc–dc converter, based on the input-series and output-series association of the full-bridge PWM dc–dc converter with capacitive filter. The main attribute of the proposed architecture is its ability to provide self-balance of the input and output voltages across the individual converters, without voltage loop control scheme, both in the steady-state and transient operations. Circuit operation, theoretical analysis, and modeling are included in this paper, along with experimental results taken from a laboratory prototype with four modules, 1600-Vdc total input voltage, 1600-Vdc total output voltage, 4-kW output power, and 40-kHz switching frequency. Possible applications include high-voltage power supplies, solid-state transformers, dc current distribution systems, and renewable electric energy systems. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) is increasingly becoming popular for multi-MW drive systems. One of the main technical challenges associated with the operation of MMC for adjustable-speed drives is the large magnitude of submodule (SM) capacitor voltage ripple under constant-torque low-speed operation. This paper proposes two new control strategies to reduce the magnitude of the SM capacitor voltage ripple in the MMC-based adjustable-speed drive systems under constant-torque low-speed operation. The proposed control strategies are based on injecting a square-wave common-mode voltage at the ac-side and a circulating current within the phase-legs to attenuate the low-frequency components of the SM capacitor voltages. The frequency spectrum of the injected circulating current consists of components in the vicinity of either the common-mode frequency or the common-mode frequency and third harmonic of the common-mode frequency. This paper also provides: i) a theoretical comparison of the proposed control strategies with the existing ones; ii) a controller design methodology to systematically determine the controller gains of the proposed control strategies; and iii) a theoretical proof of stability of the proposed control strategies and their design methodology based on Lyapunov analysis of singularly perturbed nonlinear non-autonomous systems. A set of experimental results for various case studies on a laboratory-scale prototype are provided to support the theoretical proof of stability of the proposed control strategies and their design methodology, and to show the superior performance of the proposed strategies over the existing strategy. [ABSTRACT FROM PUBLISHER]

This paper proposes a technique to suppress low-order harmonics for an open-end winding induction motor drive for a full modulation range. One side of the machine is connected to a main inverter with a dc power supply, whereas the other inverter is connected to a capacitor from the other side. Harmonic suppression (with complete elimination of fifth- and seventh-order harmonics) is achieved by realizing dodecagonal space vectors using a combined pulsewidth modulation (PWM) control for the two inverters. The floating capacitor voltage is inherently controlled during the PWM operation. The proposed PWM technique is shown to be valid for the entire modulation range, including overmodulation and six-step mode of operation of the main inverter. Experimental results have been presented to validate the proposed technique. [ABSTRACT FROM PUBLISHER]

By combining the conventional switched-mode power converters with advanced switched capacitor (SC) techniques, a plurality of single-switch current-balancing circuits is developed to drive multiple light-emitting diode (LED) strings in this paper. Compared with the existing current-balancing LED drivers, the proposed drive circuits exhibit their attractive advantages in size and cost efficiency because just one active switch and one magnetic device are required. LED strings' current can be regulated by controlling the duty ratio of the switch in pulsewidth-modulation mode. Both advanced resonant and nonresonant SC methods are introduced to optimize the performance of the proposed LED drivers. The feasibility and theoretical analysis are verified with a 9-W dual-channel nonisolated prototype and a 25-W four-channel isolated prototype. [ABSTRACT FROM PUBLISHER]

This paper develops an electric vehicle switched-reluctance motor (SRM) drive powered by a battery/supercapacitor having grid-to-vehicle (G2V) and vehicle-to-home (V2H)/vehicle-to-grid (V2G) functions. The power circuit of the motor drive is formed by a bidirectional two-quadrant front-end dc/dc converter and an SRM asymmetric bridge converter. Through proper control and setting of key parameters, good acceleration/deceleration, reversible driving, and braking characteristics are obtained. In idle condition, the proposed motor drive schematic can be rearranged to construct the integrated power converter to perform the following functions: 1) G2V charging mode: a single-phase two-stage switch-mode rectifier based charger is formed with power factor correction capability; 2) autonomous V2H discharging mode: the 60-Hz 220-V/110-V ac sources are generated by the developed single-phase three-wire inverter to power home appliances. Through the developed differential mode and common mode control schemes, well-regulated output voltages are achieved; 3) grid-connected V2G discharging mode: the programmed real power can be sent back to the utility grid. [ABSTRACT FROM PUBLISHER]

In this paper, a simplified pulsewidth modulation with switching constraint control scheme is proposed to eliminate the circulating currents for bidirectional paralleled ac/dc converters in grid-tied system. The proposed control scheme can reduce the circulating currents and does not need additional current sensors and communication device among paralleled converters compared with conventional methods. Therefore, the paralleled system cost can be reduced. In addition, the current shaping and sharing between the paralleled converters can be well accomplished so that the overall performance of the paralleled converter system can be raised. Furthermore, the dc, ac, and self-generated circulating currents are clearly analyzed by graphics, and the synchronous circulating currents are first explored. Finally, a prototype system is constructed, and the proposed control scheme is implemented using a Spartan-3E XC3S250E FPGA. Both simulation and experimental results verify the validity of the proposed theory and control scheme. [ABSTRACT FROM PUBLISHER]

The parameters of electrical machines can change considerably during operation due to thermal effects. Therefore, the corresponding models and the estimates of parameters can be subject to a significant bias and uncertainty, which degrade the performance of the system. In this paper, a method is developed to estimate the resistance of the coil of a linear electromagnetic actuator, i.e., of a single-coil linear solenoid. In the electrical model of the solenoid actuator, the inductance depends on the current. The inductance is identified from the transient waveform of the current (step response), and an estimate of the resistance is provided by extrapolating to the steady state of the current. Thus, the resistance can be estimated before the system reaches the steady state. The presented method is generalized to pulsewidth-modulation (PWM) drive conditions by considering the average of the current of the coil in the successive PWM cycles. This improves the suppression of measurement noise. The developed approach is demonstrated through numerical and experimental analyses. [ABSTRACT FROM PUBLISHER]