Small Vectors Research Articles

A Novel Three-Level Quasi-Switched Boost F-Type Inverter With High Voltage Gain and Self-Balanced Neutral-Point Voltage

This paper introduces a new topology of three-level quasi-switched boost F-type inverter (3L-qSBFTI) to improve voltage gain compared to traditional impedance-source inverters (ISIs). This topology uses a switched-capacitor (SC) structure to increase the boost factor to twice that of traditional ISIs. Unlike any conventional SC circuit, the current through capacitors when they are connected in parallel is limited by inductor current. Hence, there is no inrush current through capacitors and semiconductor devices in this operating state. Furthermore, this SC structure helps to obtain self-balanced neutral-point-voltage. The lower-shoot-through (LST) state, which is inserted into P-type small vectors, is used to boost the DC-link voltage. This insertion helps to increase modulation index utilization. As a result, the component voltage rating of the introduced inverter is significantly improved. The comparison study, simulation, and experimental validations have been presented to verify the proposed inverter.

Naomi Datta. 17 September 1922—30 November 2008

Naomi Datta was distinguished for her discovery of bacterial plasmids carrying genes giving resistance to antibiotics. She studied medicine and successfully combined a career with bringing up her family. Appointed to the Royal Postgraduate Medical School, she studied an outbreak of Salmonella at Hammersmith Hospital in 1959. She discovered genetic factors responsible for transfer of resistance between strains. Her publication on this was the first in Europe. Collaboration with Bill Hayes (FRS 1964) and others at the adjacent Medical Research Council Unit revealed that transfer was due to small replicating loops of DNA, later called plasmids. With Bob Hedges, Naomi classified plasmids into families; their work was recognized worldwide. Molecular analysis of plasmids revealed that drug resistance genes were carried on small vectors called transposons, which could transfer themselves between plasmids and bacterial chromosomes. This facilitated gene mapping and later gene cloning and genetic engineering, which became highly controversial.

Hybrid Space Vector Modulation Scheme to Reduce Common-Mode Voltage Magnitude and Frequency in Three-Level Quasi-Z-Source Inverter

The three-level quasi-Z-source inverter (TLQZSI) is an attractive topology that is suitable for voltage buck and boost operation. This article further presents a hybrid space vector modulation (HSVM) scheme to reduce the common-mode voltage (CMV) magnitude and frequency simultaneously. At first, the selection of basic vectors is optimized. Six medium vectors, six small vectors that have low CMV magnitudes, one zero vector, and three shoot-through vectors are utilized to produce the ac output voltage. The shoot-through state is properly inserted within the zero vector without affecting the normal ac output voltage. The effective small vector is selected according to the neutral-point voltage (NPV). Duty cycles of the adopted vectors are updated accordingly, and the restriction of the duty cycle of effective small vector is also derived. When comparing with the conventional SVM method, the CMV magnitude for the proposed scheme is suppressed by half. Furthermore, the CMV frequency is reduced by comparison to the conventional CMV reduction method. The feasibility of the proposed scheme has been tested by using the Simulink platform and a hardware-based test rig.

Robust DC-Link Voltage-Balancing Strategy Based on Model Predictive Control

For single-phase three-level inverters, the neutral-point (NP) voltage balance problem must be solved to ensure normal operation. This brief proposes a robust voltage balance control method based on the model predictive control. The relative tracking errors of the grid current are used to judge which split capacitor voltage is larger. Then, the larger (smaller) split capacitor voltage will be used as the small vector when releasing power to the grid (absorbing power from the grid). Consequently, there is no need sampling the split capacitor voltages and the voltage sensors can be reduced. Besides, the NP voltage balance is well achieved even when the parameter drift happens to the grid inductor, which enhances the robustness. Finally, a T-type single-phase three-level grid-tied inverter platform is built to verify the effectiveness of the proposed control method.

FPGA‐based control strategy of five‐phase induction motor drives

Here, a novel control technique for Five-Phase Induction Motor (FPIM) drives using a field-programmable gate array (FPGA) controller is proposed. Open-loop control is analysed in terms of the performance and measurement of various power quality factors, such as voltage harmonics, current harmonics, total harmonic distortion, crest factor, unbalanced, short and long-term flickering, K-factor, real power, reactive power, apparent power, and power factor. This study experimentally demonstrated a closed-loop system with both PID and DTC controls for the FPIM. Diminished torque pulsation is obtained by efficiently utilizing the voltage vectors from the total states of 25 = 32. A novel EG voltage vector sequence was proposed for DTC techniques and compared with small, medium, and large voltage vector sequences. Proposed innovative control programming techniques in spartan-6 XC6SLX25 series FPGA for switching the five-phase two-level inverter to reduce the total harmonics distortion by less than 2%.

A novel neutral-point potential balance control method based on voltage feedback for neutral-point clamped three-level inverter

Neutral-point potential imbalance is not only an inherent problem of neutral-point clamped three-level converters, but also the key factor affecting their performance. The traditional capacitor neutral-point potential balance control methods based on space vector modulation, such as VSVPWM, have several shortcomings including the uncompensated region of neutral-point voltage and the slow dynamic response. A novel voltage feedback control method on neutral-point potential balance is proposed in this paper. A coefficient is introduced to define the degree of neutral-point potential imbalance. The composite signal composed of this coefficient and neutral point current is designed. Based on the improved reasonable sectors’ division, the suitable small vectors are selected by this composite signal to obtain the switching sequence of power devices. The voltage feedback control method is employed to realize accurate neutral-point potential balance of NPC three-level inverter. The experimental results show that this method can quickly balance the neutral-point potential fluctuation caused by disturbance. It has the advantages of low switching loss, stable output voltage and current waveform, and good dynamic performance.

A Novel Model-Free Predictive Control for T-Type Three-Level Grid-Tied Inverters

The model-free predictive control (MFPC) scheme is an effective scheme to enhance the parameter robustness of model predictive control. However, the MFPC scheme can be affected by the current gradient updating frequency. This paper proposes an improved MFPC scheme for a T-type three-level inverter. First, a novel current gradient updating method is designed to estimate all current gradients per control period, which uses the current gradient relationship between different voltage vectors and eliminates the effect of current gradients updating stagnation. Moreover, a sector judgment method based on the current gradient is proposed. Redundant small vectors are accurately judged and the computational burden is greatly reduced. Finally, simulation and experimental comparisons on a T-type three-level inverter verify the effectiveness of the proposed MFPC scheme.

Hybrid Space Vector PWM Strategy for Three-Phase VIENNA Rectifiers.

Vienna rectifiers are widely used, but they have problems of zero-crossing current distortion and midpoint potential imbalance. In this paper, an improved hybrid modulation strategy is proposed. According to the phase difference between the reference voltage vector and the input current vector, the dynamic current crossing distortion sector is divided at each phase current crossing, and the discontinuous pulse width modulation strategy is adopted in the sector to suppress the redundant small vector mutation and improve the current crossing distortion. To solve the problem of midpoint potential balance, a space vector modulation strategy is adopted outside the sector to control the midpoint potential balance by allocating the time of small vector action by voltage balance factor. Finally, the effectiveness of the proposed method is verified by simulation and experiment.

Optimizing creation operators for charmonium spectroscopy on the lattice

Smearing the bare quantum fields in lattice calculations before applying composite hadron creation operators has a long record of substantially improving overlaps onto low-lying energy eigenstates. A technique called distillation which defines smearing for quark fields as a low-rank linear projection operator into a small vector space of smooth gauge-covariant fields has proven to be both effective and versatile in hadron spectroscopy calculations albeit with significant computational cost . In this paper, more general operators in this space of smooth fields are introduced and optimised, which enhances the performance of the method when tested on systems of heavy quark-anti-quark pairs close to the charmonium energy scale.

Small angles vector magnetometer based on anisotropic ferromagnetic nanofluid functionalized fiber interferometer

As factories and vehicles become more automated, accurate and low-latency sensing of motor shaft speed and position is critical for process control, system reliability, and safety. To address these needs, a highly precise and fast vector magnetometer is required that has the capability to detect magnetic field variations also at tiny angles. We present the development of an ultrathin tapered fiber interferometer-based highly accurate sensor suspended in a magnetorheological fluid film, which holds the capability of simultaneously detecting magnetic field intensity and its direction in three-dimensional space. The sensing mechanism counts on the magnetism-regulatable effective index amendment of exciting asymmetric cladding modes in a nonadiabatic biconical tapered fiber interferometer. Based on the azimuth-dependent anisotropic distribution of nanoparticles surrounding the fiber, such a magnetometer has achieved the maximum magnetic field sensitivity of ∼16.4 pm mT−1 at 0° whereas at small angles of ±1° and ±2° the sensitivities are observed of ∼ ±14.6 pm mT−1 and ∼ ±11.7 pm mT−1, respectively over a larger span of 0–567 mT.

Advances in utilizing the endogenous CRISPR-Cas system for genome editing of lactic acid bacteria

The CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated proteins) system is an efficient and precise gene editing tool. The development of this technology has promoted genome editing into a rapid development stage. The most widely used Cas9 protein is SpyCas9 from Streptococcus pyogenes. As a "gene scissors", the SpyCas9 protein is widely used in eukaryotes including mammals and plants. However, the application of this protein in some lactic acid bacteria (LAB) is still hampered by many factors. It has been identified that LAB genomes possess many types of CRISPR system and are rich in uncharacterized Cas proteins. Genome editing of LAB is possible by repurposing the endogenous CRISPR-Cas systems in LAB combined with exogenous single guide RNA (sgRNA) and homologous recombination template. This method employs its endogenous CRISPR-Cas system for gene editing, which has the advantages including easiness for transformation due to the relatively small targeting vector, and no concern about the toxicity of heterologous Cas9 to host cells. Compared to CRISPR-SpyCas9, the endogenous CRISPR-Cas system is more suitable for genome editing of LAB, and it may become the main genome editing tool for some LAB in the future. This article summarizes the advances in this field.

A Single-Stage Boost-Derived T-Type Inverter With Self-Balanced Capacitor Voltage

This article proposes a novel single-stage three-level buck–boost inverter based on voltage multiplier cells. The characteristics of the proposed topology are listed as 1) providing buck–boost operation in a single-stage power conversion, 2) reducing the number of components, 3) low component rating, and 4) automatic capacitor voltage balance without requiring any voltage sensors. A space-vector modulation (SVM) technique is introduced to control the proposed inverter and improve the quality of the output voltage waveform. In the SVM scheme, three nearest vectors are used to generate the output voltage vector in any switching period. The upper shoot-through switching state is adopted to provide buck–boost operations. This state is added within the small N-type vectors. The operating states, steady-state analysis, component selections, and comparison analysis are detailed. A 1-kVA laboratory prototype is built to validate the effectiveness of the proposed inverter. The experimental results show that the switch operates under a zero-voltage switching conditions for both turning- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and - <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> . Moreover, the capacitor voltage self-balanced characteristic keeps the voltage difference within 3.8% of the average capacitor voltage.

Improved Model Predictive Current Control of NPC Three-Level Converter Fed PMSM System for Neutral Point Potential Imbalance Suppression

For the neutral point clamped (NPC) three-level converter fed permanent magnet synchronous motor (PMSM) system, the performance of the conventional model predictive current control (MPCC) algorithm will be deteriorated if the amplitude of the neutral point potential (NPP) is large. Additionally, the adjustment process of the weighted coefficients of the conventional MPCC algorithm is complex because of numerous control terms in the cost function. To solve the above issues, an improved MPCC algorithm is proposed in this paper. Firstly, Newtonian iteration is used to transfer the stator current into stator voltage in the cost function. Then, the NPP term in the conventional cost function can be eliminated by introducing the partition control of the NP potential, which also eliminates the whole adjustment process of weighting coefficients. Finally, based on the amplitude of the NPP, the amplitude and phase angle of medium and small vectors are modified to improve the control performance of the torque and flux. Experimental results show that the fluctuation of the neutral point potential can be suppressed rapidly. Meanwhile, the performance of the torque, flux and current are also improved compared with the conventional MPCC.

An Improved LMSVM Method for Leakage Current Suppression and Neutral-Point Voltage Control in Transformerless NPC Three-Level Inverters

Transformerless three-level inverters have many advantages over two-level inverters in photovoltaic (PV) systems. However, in transformerless systems, except for the inherent unbalanced neutral voltage of the three-level inverter, the leakage current also needs to be limited strictly. Concerning the defects of the conventional common-mode voltage (CMV) suppression methods, an improved LMSVM (ILMSVM) method is proposed. Unlike the conventional CMV suppression method, the ILMSVM method no longer just abandons the high CMV small vectors to limit the range of CMV to ±1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6U_{\mathrm {dc}}$ </tex-math></inline-formula> , but limits CMV variation to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta 1/6U_{\mathrm {dc}}$ </tex-math></inline-formula> in all switching cycles. So, high CMV small vectors also can be used in some sequence to help controlling neutral point (NP) while keeping leakage current well suppressed. Moreover, medium vector sequences are also used as an independent control sequence to help achieving bidirectional control on NP potential. Compared with LMP/NSVM strategy, the ILMSVM method has advantages in regulating NP potential, and leakage current spikes of the LMP/NSVM method are also eliminated. In comparison with the conventional SVPWM (CSVPWM) method, leakage current in the ILMSVM method is also well restrained. Simulations and experiment results verify that the ILMSVM method can well restrain leakage current and maintain good control of NP in comparing with LMP/space vector modulation (SVM) method and CSVPWM method.

Common-Mode Voltage Reduction and Neutral-Point Voltage Control Using Space Vector Modulation for Coupled Ten-Switch Three-Phase Three-Level Inverter

Space vector pulsewidth modulation (SVPWM) provides enhanced performance for the coupled ten-switch three-phase three-level inverter (TP-TLI). However, it suffers from high common-mode voltage (CMV) and unbalanced neutral-point voltage (NPV). To solve this problem, a CMVR_SVPWM with CMV reduction and NPV control (NPVC) is proposed in this article. By using suitable vectors with lower CMVs and sequences, the amplitude of CMV is suppressed to 50% of the previous strategies for ten-switch TP-TLI. A newly control degree is explored to regular the NPV through the two pairs of newly virtualized vectors in each sector. The dwell time of each selected vector is indirectly calculated to cooperate the NPVC with the CMVR_SVPWM. By enhancing the dwell time of the desired small vector, the NPV can be balanced while maintaining the almost same output quality. The dead-time effect is analyzed, and the resulting CMV spikes is eliminated by increasing the dwell time of the vector which is less than twice the compensation time. It preferentially attempts to eliminated the CMV spikes based on volt-second balance. This minimizes the effect of the proposed compensation method on output quality. A 3-kVA experimental prototype is built up to verify the feasibility and performance of the proposed CMVR_SVPWM.

Codon Optimization of saCas9 Gene Enhances Protein Expression in Human Kidney Cells to Compensate for Difficulties in Delivery Vectors to Boost CRISPR‐Cas9 in vivo Therapeutic Application

The novel gene editing technology CRISPR‐Cas9 shows great promise in revolutionizing treatments of genetic disorders; however, currently the only practical treatments are ex vivo, limited to blood diseases. In vivo treatment can substantially extend the clinical reach of the technology, but is limited by a challenging delivery process. The large size of the Cas9 gene (~4500bp) inhibits delivery by the small viral vectors and lipid nanoparticles used. We hypothesize that a Cas9 gene codon optimized for human cells will support significantly higher protein expression than the presently used genes; this can compensate for the low delivery efficiency and has great potential to improve the viability of in vivo CRISPR‐Cas9 therapies.To investigate our hypothesis, we selected a commonly used parent saCas9 Addgene’s public plasmid database. We engineered a novel, codon‐optimized gene sequence from the parent using GenScript’s OptimumGene™ algorithm. We will compare protein expression via ELISA assay and Western Blot analysis. In this poster we will present the data gleaned from these assays.

A Unified Carrier-Based Pulsewidth Modulation for Three-Phase Vienna-Type Rectifiers

Compared with space-vector pulsewidth modulation (SV-PWM) schemes, carrier-based PWM (CB-PWM) schemes feature less digital calculation burden. Unfortunately, since different CB-PWM schemes were not represented by a unified expression and the relationship between the injected zero-sequence components (ZSCs) and the switching-state sequences is not revealed, the CB-PWM has poor flexibility in designing the switching-state sequences. In this article, a unified carrier-based PWM (UCB-PWM) is proposed to unify the expressions of different CB-PWM schemes. The ZSC of the proposed UCB-PWM is classified into a basic ZSC (B-ZSC) and a redundant ZSC (R-ZSC). The B-ZSC is a shared component of all CB-PWM schemes, and the dwelling time of redundant small vectors can be distributed by injecting different R-ZSCs. Also, the neutral-point voltage balance control based on either continuous PWM or discontinuous PWM (DPWM) can be achieved by injecting R-ZSCs. Besides, not only the existing carrier-based DPWM schemes but also new carrier-based DPWM schemes are derived by the proposed UCB-PWM. Finally, experimental results verify the correctness and advantages of the proposed UCB-PWM.

A Novel Low-Frequency Virtual Space Vector Modulation With the Improved Continuity of Output Average-Voltage and Bus Voltage Utilization for Single-Phase Neutral Point Clamped Three-Level Inverter

In the high-power superconducting fusion converter, the single-phase neutral point clamped (NPC) three-level converter is applied to replace the traditional thyristor converter using an integrated gate-commutated thyristor (IGCT) as a power device. The operating frequency of IGCT is usually lower, only a few hundred Hz. An optimized hybrid space vector pulsewidth modulation (SVPWM)-8H is proposed to solve the problems of discontinuous output average voltage, low dc bus voltage utilization rate, dead time compensation, and neutral point potential balance. The new sectors are inserted to make the range of output average voltage of adjacent sectors intersect, which improves the continuity of output average voltage. Furthermore, some sectors are composed of four vectors to reduce the minimum working time of redundant small vectors, improving the dc bus voltage utilization ratio and the converter’s performance. Moreover, by analyzing the influence of dead time on redundant small vectors, redundant vectors are rearranged to make redundant small vectors’ working time synchronously in sector and sector switching, which reduces the influence of dead time on neutral point potential balance. Finally, by analyzing the influence of dead time on the output average voltage, dead time compensation is applied, which reduces the difficulty of compensation implementation. Simulations and experiments verify the rationality of the optimized hybrid SVPWM-8H.

Three-Layer Double-Vector Model Predictive Control Strategy for Current Harmonic Reduction and Neutral-Point Voltage Balance in Vienna Rectifier

Vienna rectifier, which is a nongenerative-boost-type rectifier, is widely employed in electric vehicle charging systems. Nevertheless, the Vienna rectifier faces the challenge of current distortion elimination, current ripple mitigation, and neutral-point (NP) voltage balance. As these problems are mutually coupled, the conventional finite control set model predictive control (FCS-MPC) methods cannot solve these problems properly. To address these issues, a three-layer double-vector FCS-MPC method is proposed. In the first layer of the proposed FCS-MPC method, the sectors are divided and the candidate vectors are selected to reduce the current distortion. In the second layer of the proposed FCS-MPC method, the double vectors with optimal duty cycles are adopted to reduce the current ripples. In the third layer of the proposed FCS-MPC method, the NP voltage is balanced by selecting the redundant p-type small vector or n-type small vector. Through the proposed method, the current distortion elimination, current ripple mitigation, and NP voltage balancing are realized at the same time. The effectiveness of the proposed method has been verified by simulation and experiment.

Novel NK1R-Targeted 68Ga-/177Lu-Radioconjugates with Potential Application against Glioblastoma Multiforme: Preliminary Exploration of Structure-Activity Relationships.

Locoregionally administered, NK1 receptor (NK1R) targeted radionuclide therapy is a promising strategy for the treatment of glioblastoma multiforme. So far, the radiopharmaceuticals used in this approach have been based on the endogenous agonist of NK1R, Substance P or on its close analogues. Herein, we used a well-known, small molecular NK1R antagonist, L732,138, as the basis for the radiopharmaceutical vector. First, 14 analogues of this compound were evaluated to check whether extending the parent structure with linkers of different lengths would not deteriorate the NK1R binding. The tested analogues had affinity similar to or better than the parent compound, and none of the linkers had a negative impact on the binding. Next, five DOTA conjugates were synthesized and used for labelling with 68Ga and 177Lu. The obtained radioconjugates turned out to be fairly lipophilic but showed rather limited stability in human plasma. Evaluation of the receptor affinity of the (radio)conjugates showed that neither the chelator nor the metal negatively impacts the NK1R binding. The 177Lu-radioconjugates exhibited the binding characteristics towards NK1R similar or better than that of the 177Lu-labelled derivative of Substance P, which is in current clinical use. The experimental results presented herein, along with their structural rationalization provided by modelling, give insight for the further molecular design of small molecular NK1R-targeting vectors.