PWM Sequence Research Articles

A Discontinuous PWM Strategy to Control Neutral Point Voltage for Vienna Rectifier With Improved PWM Sequence

Vienna rectifier is a boost-type rectifier with unidirectional energy flow, which is widely used in industrial applications. To improve the power density of the Vienna rectifier, the high switching frequency is seen as an inevitable cause of larger switching losses. To reduce switching losses, discontinuous pulsewidth modulation (DPWM) is usually used. But this will cause dc offset and ac ripple on neutral point (NP) voltage. To overcome these problems, a carrier-based DPWM (CB_DPWM) method suitable for a Vienna rectifier with simple implementation is proposed to simultaneously reduce switching losses and control NP voltage. By selecting the proper clamping mode, NP voltage can be well controlled. To avoid unnecessary switching actions while switching clamping mode, an improved PWM sequence based on carrier type is given. The comparisons among space vector PWM, DPWM 1–3 presented by Zhang <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , and the proposed CB_DPWM are presented with the corresponding simulation and experimental results, and the superiority of the proposed strategy is verified in terms of reducing switching loss and controlling NP voltage.

Aging Detection and State of Health Estimation of Live Power Semiconductor Devices Using SSTDR Embedded PWM Sequence

Power semiconductor switches undergo degradation due to environmental and electro-thermal stresses resulting in an impedance variation within the device. This impedance variation can be characterized using reflectometry, which is a well-known technique in electromagnetics. A condition monitoring algorithm for power devices in a live power converter using spread spectrum time domain reflectometry (SSTDR) method has been introduced in this article. SSTDR has been successfully used for locating transmission line faults and detecting device degradation in power converters while running at static condition. However, the rapid variation in impedance throughout the entire live converter circuit caused by fast switching makes condition monitoring more challenging while using SSTDR. This article addresses these shortcomings by proposing a novel solution that can be successfully used to identify the aging of the power devices in a live converter. SSTDR test signal was applied at various test nodes in three different circuits: a single-phase H-bridge photovoltaic inverter, a dc–dc buck converter, and a three-phase inverter. The experimental results demonstrate that the SSTDR test data are consistent with the aging of the power devices and do not affect the switching performance of the modulation process even the test signal is applied across the gate-source interface of the power mosfet . This implies that the SSTDR technique can be integrated with the gate driver module, thereby creating a new platform for an intelligent gate-driver architecture that enables real-time health monitoring of power devices while performing features offered by a commercially available driver.

Improving the quality of the output quasi-sinusoidal voltage in a bridge inverter

When forming the output voltage of the bridge inverter, a specific trapezoidal law was used with partial modulation of the PWM sequence at the fronts playback intervals. For this reason, there are a number of features that affect the selection of the envelope in the filtering process. The spectral and temporal models of the ripple of the input current and the output voltage of the LC filter are investigated. A filter optimization criterion is justified, taking into account the presence of the third harmonic and the group structure of the PWM spectrum spectrum. By a rational combination of spectral and temporal models, simple engineering formulas were obtained for determining the filter parameters and the harmonic coefficient of the output voltage of the inverter. It has been established that the mass and dimensional indicator of the filter with trapezoidal modulation is reduced by 1.5 times as compared with the sinusoidal one. An example of calculating the filter parameters is given.

A Novel Discontinuous PWM Strategy to Control Neutral Point Voltage for Neutral Point Clamped Three-Level Inverter With Improved PWM Sequence

In order to reduce switching loss of neutral point clamped three-level inverter (NPC TLI), generally discontinuous pulsewidth modulation (DPWM) is used. But it can result in dc offset and ac ripple on neutral point (NP) voltage. So a novel pulse sequence DPWM (NPSDPWM) is proposed to reduce switching loss and control NP voltage simultaneously in this paper. NP voltage is controlled by choosing proper clamping modes. To avoid unexpected switching action during changing clamping mode, an improved pulse sequence is also presented. The switching loss and NP voltage ripple of NPSDPWM, traditional and proposed DPWM in previous literature are compared, respectively. The experimental results show that NPSDPWM has well NP voltage control ability and the switching losses are reduced effectively.

A Predictive Hybrid Pulse-Width-Modulation Technique for Active-Front-End Rectifiers

Nowadays, active-front-end rectifiers are increasingly used as grid connected devices. Their efficiency and performances have become relevant for reducing the overall grid losses. This paper thus introduces a predictive hybrid pulse-width-modulation (PH-PWM) technique, adaptable to any space-vector PWM (SVPWM) controller. As opposed to hybrid PWM techniques based on sector partitioning, the PH-PWM technique selects the appropriate PWM sequence online with the help of a predictive algorithm. This selection is based on a cost-function where users can define a tradeoff between various criteria, such as the reduction of current distortion and switching losses, as presented in this paper. The use of the PH-PWM technique increases performances in comparison with the conventional PWM techniques. The simulation and experimental results are presented to confirm the effectiveness of the proposed PH-PWM technique. Aside from the tradeoff capacity of the proposed PH-PWM technique, the simulation results validate a reduction of the switching losses for the converter up to 23 $\%$ as compared with the conventional SVPWM technique.

Optimally choosing PWM motif databases and sequence scanning approaches based on ChIP-seq data.

BackgroundFor many years now, binding preferences of Transcription Factors have been described by so called motifs, usually mathematically defined by position weight matrices or similar models, for the purpose of predicting potential binding sites. However, despite the availability of thousands of motif models in public and commercial databases, a researcher who wants to use them is left with many competing methods of identifying potential binding sites in a genome of interest and there is little published information regarding the optimality of different choices. Thanks to the availability of large number of different motif models as well as a number of experimental datasets describing actual binding of TFs in hundreds of TF-ChIP-seq pairs, we set out to perform a comprehensive analysis of this matter.ResultsWe focus on the task of identifying potential transcription factor binding sites in the human genome. Firstly, we provide a comprehensive comparison of the coverage and quality of models available in different databases, showing that the public databases have comparable TFs coverage and better motif performance than commercial databases. Secondly, we compare different motif scanners showing that, regardless of the database used, the tools developed by the scientific community outperform the commercial tools. Thirdly, we calculate for each motif a detection threshold optimizing the accuracy of prediction. Finally, we provide an in-depth comparison of different methods of choosing thresholds for all motifs a priori. Surprisingly, we show that selecting a common false-positive rate gives results that are the least biased by the information content of the motif and therefore most uniformly accurate.ConclusionWe provide a guide for researchers working with transcription factor motifs. It is supplemented with detailed results of the analysis and the benchmark datasets at http://bioputer.mimuw.edu.pl/papers/motifs/.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-015-0573-5) contains supplementary material, which is available to authorized users.

Novel Loss and Harmonic Minimized Vector Modulation for a Current-Fed Quasi-Z-Source Inverter in HEV Motor Drive Application

The recently proposed current-fed quasi- Z-source inverter (QZSI) can buck and boost voltage and provide bidirectional power flow . A crucial criterion for the size of three-phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation at certain operating points. In the modified space vector PWM method (SVPWM) control method for this circuit, different PWM sequences can lead to different switching loss, current ripple, total harmonic distortion, and also the voltage spike on the switching devices. In order to select the best PWM sequence to obtain the best performance and efficiency, a complete analysis and calculation for the four mentioned criterions are presented for different sequences. For each criterion, the best sequences are selected to obtain better performance. Finally, the optimized PWM sequence in the modified SVPWM control for this circuit is selected with the optimized hardware design together to achieve the best efficiency at the full operation range. The optimized hardware design has been built in the lab, including the optimal design of the coupled inductor, optimal design and selection of Z-source capacitors and output capacitors, the selection of Z-source diode, and the final layout of the hardware. In order to bring the prototype into real application in a hybrid electrical vehicle , the inverter efficiency is measured according to the motor P-V curve. The estimated efficiency curve and experiment results are plot and compared. The best efficiency at 15 kW reaches 97.6% at unity voltage gain.

Control Strategy for Input-Series–Output-Parallel High-Frequency AC Link Inverters

This paper presents a control strategy for input-series-output-parallel (ISOP) modular inverters. Each module is a high-frequency (HF) ac link (HFACL) inverter composed of an HF inverter, an HF transformer, and a cycloconverter. A PWM sequence generation based on DSP control is given, with which the circulating currents among all the constituent modules can be avoided automatically. To achieve input voltage sharing (IVS) and output current sharing (OCS) among the constituent inverter modules, a stable OCS scheme, which consists of one common output voltage regulation (OVR) loop and individual inner currents loops, is proposed. The OVR loop provides a common reference for all individual inner current loops, in which the current feedback for an individual module is the sum of all the other output currents instead of its own. The compensator designs of the OVR loop and individual inner current loops are also presented. With this control strategy, excellent IVS and OCS can be obtained. The effectiveness of the proposed control strategy is verified using the simulation and experimental results of a 1100-VA ISOP two-HFACL inverter system.

Research on SVPWM Method and its Neutral Point Potential Control

Neutral-point potential unbalance is an inherent problem of Neutral-point-clamped three-level PWM rectifiers. If the problem of neutral point can’t be controlled appropriately, the harm of input current will increase, and even the dc-link capacitor and switches will be destroyed. Thus domestic and foreign experts have done lots of research on the balance control of Neutral-point-clamed and put forward many effective control methods. This paper proposes a novel SVPWM strategy for the three-level neutral-point-clamped voltage source inverter, based on the particular disposition of all the redundant voltage vectors. The new modulation approach shows superior performance for the harmonic voltage and the control of neutral-point potential compared to the popular eight-stage centered SVPWM and realizes the balancing control of inverter neutral-point potential by modifying redundant small vectors pairs’ distribution factor accurately, only requiring the information of dc-link capacitor voltages and three-phase load currents, which is convenient to apply and is compatible of digital computer realization. The feasibility of the proposed control approach has been verified via simulation and experiment results. In the strategy of software control, domestic and foreign scholars propose numerous neutral point potential control schemes. When carrier modulation is used, the balance control is achieved by injecting zero-sequence component into the three-phase modulated wave. When space vector modulation methods are adopted, they can be divided into three categories: passive control, hysteresis control and active control. there is also a new algorithm based on the intrinsic relationship between SVPWMs for two—level inverters and three．1evel inverters．a novel SVPWM control algorithm is proposed for three．1evel．The dwell time of voltage vector for three-level inverter can be acquired from counterpart for two-level inverter by using a linear transformation．Aiming to analysis the output PWM sequence of three-level inverter, a novel classification standard of voltage vector is proposed．Based on evaluating the PWM sequences, a novel PWM sequence is given，that can reduce the total harmonics distortion of inverter output.