Synchronous PWM control of triple transformer-connected inverters for photovoltaic system

Abstract: This paper presents results of research of modulation processes in power conversion system with triple voltage source inverters, supplied by photovoltaic (PV) strings, and connected to a four-winding transformer. The transformer has in this case specific connections between the secondary windings and inverters, allowing providing of multilevel voltages at secondary windings of the transformer. Specialized space-vector-based strategy of pulsewidth modulation (PWM) has been used for control of inverters, insuring quarter-wave symmetry of winding voltages for any modulation indices and switching frequency of inverters. Analysis and comparison of harmonic composition of winding voltages and output voltages of inverters has been done. The validity of the analyzed processes has been verified by simulations: three basic variants of the scheme of modulation have been applied for control of inverters

Multiphase quad-inverter system with feedforward synchronous PWM and nonlinear voltage regulation

Abstract: This manuscript presents modified scheme of synchronous space-vector modulation allowing providing nonlinear dependences between the fundamental voltage and fundamental frequency of dual three-phase open-winding ac drive with four modulated inverters. Behavior of the system with six control modes (characterized by different dc-voltages and switching frequencies of inverters) and two nonlinear Voltage/Frequency ratios has been analyzed and simulated by the means of MATLAB-software

Zero voltage switching used for a reversible DC-DC converter

Abstract A novel bi-directional dc-dc converter with Zero Voltage Switching (ZVS) and interleaving for dual voltage systems in automobiles is presented. A variable frequency extended band hysteretic current control method is proposed. In comparison with classical fixed frequency current control PWM, the reverse polarity peak current needed for ZVS operation is kept constant. Inductor current ripple decreases with load reduction. Automatic changes in operation between buck and boost modes are accomplished without transient currents. Converter simulations are carried out using Matlab/Simulink platform

Reversible DC-DC converter for a dual voltage automative system using zero voltage switching techniques

Abstract: A novel hysteretic controller for a bi-directional dc-dc converter with ZVS and interleaving for dual voltage systems in automobiles is presented. A variable frequency extended band hysteretic current control method is proposed. In comparison with classical fixed frequency current control PWM, the reverse polarity peak current needed for ZVS operation is kept constant. Inductor current ripple decreases with load reduction. Automatic changes in operation between buck and boost modes are accomplished without transient currents. Converter simulations are carried out using Matlab/Simulink platform

Comparative analysis of modulation techniques in frequency converter

Abstract: A generalized frequency converter has been realized which makes use of a cyclo-converter in newer form AC-AC converter. An attempt has been made to operate this converter both in a conventional low frequency AC-AC converter and a new high frequency AC-AC converter. The ability to directly affect the frequency conversion of power without any intermediate stage involving DC power is a huge advantage of the system. The output of this converter has a frequency either fo = fi × Nr or fo = fi / Nr. where Nr is an integer and fi is the source frequency. A methodology is developed to generate the required trigger signal for any integer multiple/sub multiple of the output frequency. The undesirable harmonic components in the output of the frequency converter have been minimized using four modulation techniques namely; sinusoidal pulse width modulation (SPWM), delta modulation (DM), trapezoidal modulation (TM) and space vector modulation (SVM) technique. The converter is simulated using well known software package MATLAB. Comparative simulation analysis is presented for a single phase frequency converter (SPFC) topology with all these modulation techniques when the converter is operating both step up as well as for step down mode

From master-slave to down-conversion optical coherence tomography

We present here advances on the Master Slave (MS) concept, applicable to spectral/Fourier/frequency-domain optical coherence tomography (OCT) technology. Instead of obtaining an A-scan from the sample investigated via a Fourier Transform (FT) or equivalent, the amplitude of the A-scan for each resolvable point along the depth is obtained along a separate output. A multiplier produces the product of the photo-detected signal from the OCT system with that generated by an Electrical or an Optical Master. This allows acquisition at a frequency comparable to that of the sweeping, much inferior to the frequency bandwidth of the channeled spectrum. 3 advantages of the down-conversion method are demonstrated here: (a) real time delivery of an en-face image; (b) axial optical path difference (OPD) range at the level of the source’s dynamic coherence length and (c): tolerance to fluctuations in the sweep of the swept source. The most important advantage of the down-conversion method is that it reduces the signal bandwidth considerably, to the level of the sweeping rate. This facilitates real-time operation. Conventional A-scan production can only be performed real-time if the FT processing is carried out in a time comparable to or less than the sweep time, which depending on the number of sampled points and dynamic range determines a limit of ∼ MHz sweep rate. Before even calculating a FT, acquisition may also be limited by the sampling rate of the digitiser. In conventional SS-OCT, the number of depth points can exceed 1,000, which for a sweeping time of 1 μs would determine signals in the GHz range. Using long coherence length swept sources, this number of depths could be even larger, hence the conventional FT-based method faces a bottleneck due to the time needed to calculate the FT, combined with the need to acquire data at many GS/s

Giant duodenal lipoma: clinical presentation, diagnostic approach, and therapeutic management

Scopul studiului. De a îmbunătăți cunoștințele despre lipoma duodenală; de a studia metodele utile în diagnosticul și tratamentul lipomei duodenale gigante. Materiale și metode. Cercetarea literaturii de specialitate în limba engleză în baza de date PubMed, folosind următorii MeSH termeni: „gastrointestinal lipoma”, „duodenum”, „giant lipoma”, „complications”, „endoscopic excision” și „surgical excision”, în perioada aa. 2010‒ 2022. Rezultate. Lipoamele gastrointestinale (GI) reprezintă 4% din toate tumorile gastrointestinale benigne, cele mai multe dintre ele sunt observate în colon (64%) sau intestinul subțire (26%), însă localizări rare, ca duoden (4%), stomac (3%) și esofag. (2%), sunt de asemenea descrise. Literatura privind lipoamele duodenale (LD) este reprezentată de cazuri clinice, fiind identificate doar 7 publicații relevante. LD sunt caracterizate prin creșterea lentă, majoritatea sunt asimptomatice, descoperite accidental, cel mai frecvent localizate în D2 (n=6;85.7%), dar pot cauza plângeri specifice sau nespecifice gastrointestinale, inclusiv sațietate precoce, disconfort abdominal, durere și senzație de plenitudine (n=4;57.1%). Complicații severe sunt înregistrate în cazul lipoamelor gigante (>4,0 cm), ca anemie prin ulcerație și sângerare (n=3;42.8%), ocluzie intestinală prin invaginație (n=1;14.3%). Investigațiile clinice necesare pentru diagnosticul LD sunt: esofagogastroduodenoscopia (n=6;85.7%), CT (n=3;42.8%) și ecoendoscopia (n=4;57.1%). Nu există tratament standardizat; recomandările existente sunt controversate. Pentru leziunile mai mari excizia endoscopică poate fi asociată cu risc crescut de hemoragie și perforație; este dificil de efectuat în cazul leziunilor localizate în D2, care este o porțiune îngustă si curbată, excizia chirurgicală fiind mai sigură (n=3;42.8%). Concluzii. LD gigante sunt extrem de rare. Simptomele sunt nespecifice, iar instrumentele imagistice sunt utile pentru diagnostic. Tratamentul depinde de dimensiunea și poziția leziunii.Aim of study. To enhance the knowledge of duodenal lipoma; to study the diagnosis and treatment of giant duodenal lipoma. Materials and methods. The English literature search was conducted in PubMed database, using the following MeSH-terms: “gastrointestinal lipoma”, “duodenum”, “giant lipoma”, “complications”, “endoscopic excision”, and “surgical excision”, time period 2010‒2022. Results. Gastrointestinal (GI) lipomas account 4% of all benign GI tumors, most of them are seen in colon (64%) or small intestine (26%), rare localizations, as duodenum (4%), stomach (3%) and oesophagus (2%), are also described. Literature on duodenal lipomas (DLs) is scarce, only 7 relevant publications were identified. The are slow-growing, most of them asymptomatic, incidentally discovered, most frequently localized in D2 (n=6;85.7%), but may cause a set of specific or non-specific upper GI complaints, including early satiety, abdominal discomfort, pain, and fullness (n=4;57.1%). Severe complications are registered in case of giants lipomas (>4,0 cm), as anemia because of ulceration and bleeding (n=3;42.8%), intestinal obstruction due to intussusception (n=1;14.3%). Clinical investigations necessary for diagnosis include esophagogastroduodenoscopy (n=6;85.7%), CT (n=3;42.8%), and endoscopic ultrasound (n=4;57.1%). No standard of care to treat symptomatic lessions is accepted; the existing recommendations are controversial. For the larger lesions endoscopic removal may be associated with high risk of hemorrhage and perforation; it is difficult to be applied in case the lesion is localized in D2 which is narrow and curved, surgical excision being preferred (n=3;42.8%). Conclusions. Giant DLs are extremely rare. The symptoms are nonspecific and imaging tools are useful for diagnosis. The treatment depends on the size and position of the lesion

Harmonic minimization in modulated frequency single-phase matrix converter

Abstract: This Field Programmable Gate Array (FPGA) based digital controller has been developed to improve the output of the frequency converter using Hardware Description Language. An attempt has been made to analyze converters using three modulation techniques namely sinusoidal pulse width modulation (SPWM), delta modulation (DM) and trapezoidal modulation (TM) to reduce the harmonics. It has been found that for the Sine PWM, the total harmonic distortion factor (THD) is high when the output frequency is greater than input frequency. The output is improved with delta modulation scheme where the total harmonic distortion is found minimum as compare to the SPWM and TM techniques. The circuit has been tested qualitatively by observing various waveforms on digital storage oscilloscope (DSO). The overall system is compact and no external memory system is required. Tests have been carried out to show the effectiveness and flexibility of the proposed method

Primary tumors of jejunum and ileum: one center experience

Introduction: Primary benign and malignant tumors of jejunum and ileum are rare. They are very often diagnosed by accident or as a cause of acute abdomen. Purpose: The aim of study was to analyze the cases of primary tumors of jejunum and ileum admitted for surgical procedures in an emergency and elective setting. Materials and Methods: Retrospective review of all patients referred to our institution and diagnosed with primary tumors of jejunum and ileum and its complications during the last 7 years. Results: There were 15 pts (F-9, M-6) with mean age of 52.9 ±5.1 years (range from 17 to 79). Intussusceptions (n=6), intestinal obstruction (n=3), perforation (n=2), intussusceptions/ perforation with GI bleeding (n=2) were the most common clinical presentations. In 2 cases primary tumors of jejunum and ileum were detected as incidental findings during surgical procedure. Most tumors (n = ll, 73.3%) were located in the ileum. In 15 pts intestinal resection (R()-12, R ,-l) with end-to-end (n=7), side-to-side (n=6), Maydl procedure (n=l) and terminal ileostomy (n=l) were performed. There were 9 benign tumors (leiomyoma-4, angioleiomyoma- 2, fibrolipoma -2, fibroid polyp-1) and 6 malignant (c-KIT/CD 117 positive GISTs-2, lymphomas-2, neuroendocrine tumor-1, adenocarcinoma-1). Conclusion: Primary tumors of jejunum and ileum are rare, the symptoms often non-specific, and the accuracy of different diagnostic tests needs to be improved. Timing and type of the intervention to the process and biological behavior of the pathological cells predict the prognosis