A Four-Switch Three-Phase SEPIC-Based Inverter Diab, Mohamed S.; Elserougi, Ahmed; Massoud, Ahmed M. ...
IEEE transactions on power electronics,
09/2015, Letnik:
30, Številka:
9
Journal Article
Recenzirano
The four-switch three-phase (FSTP) inverter has been proposed as an innovative inverter design to reduce the cost, complexity, size, and switching losses of the dc-ac conversion system. Traditional ...FSTP inverter usually operates at half the dc input voltage; hence, the output line voltage cannot exceed this value. This paper proposes a novel design for the FSTP inverter based on the topology of the single-ended primary-inductance converter (SEPIC). The proposed topology provides pure sinusoidal output voltages with no need for output filter. Compared to traditional FSTP inverter, the proposed FSTP SEPIC inverter improves the voltage utilization factor of the input dc supply, where the proposed topology provides higher output line voltage which can be extended up to the full value of the dc input voltage. The integral sliding-mode control is used with the proposed topology to optimize its dynamics and to ensure robustness of the system during different operating conditions. Derivation of the equations describing the parameters design, components ratings, and the operation of the proposed SEPIC inverter is presented in this paper. Simulation model and experimental setup are used to validate the proposed concept. Simulations and experimental results show the effectiveness of the proposed inverter.
The integration of renewable energy sources in Medium-/High-voltage DC grids has called up continuous research to develop DC-DC conversion systems. This paper presents a hybrid modular multilevel ...DC-DC converter topology which successfully overcomes the issue of capacitors voltage imbalance during DC-DC conversion. In the proposed topology, single MMC leg is employed with half-bridge submodules in the upper arm and full-bridge submodules in the lower arm along with soft-switched high-voltage valves. The proposed hybrid modular multilevel converter has inherited arm energy equalization with the help of the parallel connectivity of involved arms’ capacitors. During the equalization period, the series-connected upper arm capacitors are connected in parallel to the series-connected lower arm capacitors to transfer the energy between the involved arms which results in operating with balanced capacitors voltages. The proposed modular DC-DC converter is a bidirectional converter which allows power flow from high-voltage side to low-voltage side and vice versa, i.e., it can be operated successfully as a DC transformer. The operational concept of the proposed configuration, control strategy, and parameters design are presented. Simulation results are presented along with experimental results of a scaled-down prototype to validate the proposed approach. Simulation and experimental results show the viability of the suggested approach.
This paper presents an indirect vector control scheme with an improved flux pattern using third harmonic injection. The control objective is to independently control both flux and torque and to ...generate a nearly rectangular air-gap flux, resulting in improved machine power density. If there is a proportional relation between the third harmonic and fundamental plane currents, variable misalignment between fundamental and third air-gap flux components occurs with varying mechanical loading. Due to this misalignment, saturation may take place. Accordingly, the total flux is saturated and iron loss increases. Hence, coupling results between different sequence planes. Instead of a proportional relation between the current components, direct and quadrature current components of the injected third harmonic current reference are a function of the fundamental direct and quadrature reference current components, respectively. These functions ensure that the air-gap flux is near rectangular with a maximum value of 1 p.u. from no load to full load. Moreover, this controller guarantees complete decoupling between the sequence planes. An eleven-phase induction machine is used to validate the proposed controller experimentally, while supporting simulation results and theoretical analysis use both MATLAB and finite element platforms.
Purpose
To evaluate the clinical outcomes of primary or revision ACL reconstruction (ACLR) after contralateral hamstring autografts versus ipsilateral hamstring autograft harvest.
Methods
Three ...databases (MEDLINE, PubMed and EMBASE) were searched from inception to April 27th, 2023 for studies investigating contralateral hamstring autografts in primary or revision ACLR. The authors adhered to the PRISMA and R-AMSTAR guidelines as well as the Cochrane Handbook for Systematic Reviews of Interventions. Data on demographics, strength measures, patient-reported outcome measures (PROMs), and rates of positive Lachman test, positive pivot-shift test and graft rupture were extracted. PROMs included Lysholm, International Knee Documentation Committee (IKDC) and Tegner scores.
Results
Nine studies comprising 371 patients were included in this review. In primary ACLR, there were no significant differences between contralateral and ipsilateral groups in isokinetic hamstring torque in the non-ACLR limb or isokinetic quadriceps torque in both limbs when tested at 60, 90, 120 or 180 degrees/second. Isokinetic hamstring torque in the non-ACLR limb was significantly weaker in the contralateral group at six months for primary ACLR; however, these deficits did not persist. There were no significant differences in postoperative median Tegner scores and Lysholm scores between contralateral and ipsilateral groups in primary ACLR. There were no significant differences in postoperative median Tegner, mean Lysholm and IKDC scores between groups in revision ACLR. There were no significant differences in positive Lachman, positive pivot-shift and rupture rates in primary ACLR between groups. Rates of positive Lachman and pivot-shift were slightly higher in the contralateral than ipsilateral group for revision ACLR.
Conclusion
Contralateral hamstring autografts results in comparable muscle strength to ipsilateral hamstring autografts, with the exception of weaker hamstring strengths in the early postoperative period. Patient-reported outcome measures were similar between the two groups across both primary and revision ACLR, with rates of instability and failure being similar between groups for primary ACLR. Contralateral hamstring grafts do not provide additional benefit when compared to ipsilateral options for either primary or revision ACLR, and should be used only in select circumstances including insufficient ipsilateral hamstring grafts or situations where quadriceps or patella autografts are not optimal.
Level of evidence
Level IV.
•We studied the performance of single loop control of the Inverter Based Distributed generators at faults, we found it not stable.•We made a Matlab model to study how the different fault current ...generated by the IBDG affect the power system protection.•We proposed with mathematical analysis an additional control loop to solve the problems at faults.•We built the necessary experimental setup using two voltage source inverters connected to the grid.•The results of the proposed method are presented.
Inverter-based distributed generation (IBDG) is characterized by its negligible fault current contribution compared with synchronous generators due to its inherent non-overload capabilities. Thus, IBDG hardly affects the fault current level; this shadows the conventional protection schemes resulting in improper system protection especially with a high penetration of IBDGs at high power levels and/or in island operation mode. This paper presents an experimental investigation of two scenarios for IBDG fault current contribution under different fault conditions. In the first scenario, the inverter is controlled to produce zero output current or is disconnected upon fault occurrence, which is the case for most commercial grid-connected inverters. In the second scenario, the inverter contributes its rated current to the fault. The practical selection may be questionable and is affected by the fault level, employed protection scheme, and the penetration level of IBDGs. The introduction of double-loop proportional-resonant (PR) current controller is investigated using three case studies applying the previously described fault current contribution scenarios. The double-loop PR controller is found favorable when the inverter is designed to contribute its rated current to the fault. This conclusion is verified experimentally in this work.
•A steady-state model based on symmetrical components theory is used to estimate machine currents and developed torque under open circuit phase(s).•The performance of the multiphase IM under open ...circuited phase(s) is assessed.•A genetic algorithm is used to generate to achieve the optimum current distribution in the healthy phases.•Derating factor is calculated during faults to avoid increase of DC-link voltage.•Eleven-phase machine is used as a prototype model to achieve these derating factors.
Multiphase machines have become a promising candidate in high-power applications as they offer many advantages over their three-phase counterparts. The main salient feature is the high fault tolerance capability. During faults, two alternatives for machine operation are possible, namely; open loop control and optimal current control. While the former corresponds to higher torque ripple and unbalanced winding currents, the latter option necessitates unbalanced phase voltages and typically an increased DC-link voltage to source the required optimal currents. Consequently, an increase in the employed semiconductor device rating is required, which is a critical design factor especially in medium voltage applications. This paper investigates an eleven-phase induction machine with concentric windings under fault conditions. An unbalanced steady-state machine model based on symmetrical components theory is developed as a mathematical tool to estimate different machine currents and total developed torque under open circuit phase(s). The effect of different sequence planes is also included in the derived model. This model is then experimentally verified. It is shown that the application of optimal current control in multiphase induction machines with open circuited phase(s) optimizes torque production while maintaining minimum stator copper loss and torque ripples. This optimization problem usually incorporates solving complicated nonlinear equations that increase in complexity with higher numbers of phases. Alternatively, a genetic algorithm is used in this paper to provide a simple method to obtain the optimum currents in the remaining healthy phases. Based on the derived optimal currents, the steady-state model is used to estimate the required DC-link voltage reserve that ensures no machine de-rating. Finally, the required derating factors to avoid machine overheating are calculated for different numbers of disconnected phases when DC-link voltage limitation is introduced.
The aim of this systematic review was to evaluate the impact of bone grafting of patellar defects on reported anterior knee morbidity and subjective outcomes after bone–patellar tendon–bone autograft ...reconstruction of the anterior cruciate ligament.
A systematic electronic search of MEDLINE, Embase, Web of Science, and the Cochrane Library was carried out. All English-language prospective randomized clinical trials published from January 1, 2000, to July 24, 2020, were eligible for inclusion. All studies addressing patellar defect grafting were eligible for inclusion regardless of the timing of surgery, graft type, surgical technique, or rehabilitation protocol.
A total of 39 studies with 1,955 patients were included for analysis. There were 796 patients in the no patellar grafting (NPG) group, with a mean age range of 22.7 to 33.0 years, and 1,159 patients in the patellar grafting (PG) group, with a mean age range of 17.8 to 34.7 years. The visual analog scale pain score ranged from 1.2 to 5.1 in the NPG group compared with 0.3 to 3.7 in the PG group. The proportion of patients with anterior knee pain ranged from 19% to 81% in the NPG group and from 15% to 32% in the PG group. Moderate to severe kneeling pain was reported in 22% to 57% of patients in the NPG group and 10% of those in the PG group. The percentage of patients with at least 3° of extension loss ranged from 4% to 43% in the NPG group and from 2% to 11% in the PG group.
PG favors decreased anterior knee pain, kneeling pain, and extension loss compared with non-grafted defects; however, the functional outcomes are comparable. Owing to the heterogeneity in reporting, statistical conclusions could not be drawn.
Level II, systematic review of Level I and II studies.
An interline dynamic voltage restorer (IDVR) is invariably employed in distribution systems to mitigate voltage sag/swell problems. An IDVR merely consists of several dynamic voltage restorers (DVRs) ...sharing a common dc link connecting independent feeders to secure electric power to critical loads. While one of the DVRs compensates for the local voltage sag in its feeder, the other DVRs replenish the common dc-link voltage. For normal voltage levels, the DVRs should be bypassed. Instead of bypassing the DVRs in normal conditions, this paper proposes operating the DVRs, if needed, to improve the displacement factor (DF) of one of the involved feeders. DF improvement can be achieved via active and reactive power exchange (PQ sharing) between different feeders. To successfully apply this concept, several constraints are addressed throughout the paper. Simulation and experimental results elucidate and substantiate the proposed concept.
Our group has recently developed and studied "finger"-type divertors that are a simplified version of the helium-cooled modular divertor with multiple jets (HEMJ) using coupled computational fluid ...dynamics and thermal stress simulations. Such a simplified geometry could reduce complexity and cost given the large number of fingers required to cover the total divertor target area. Previous experimental studies for this simplified flat design reported lower heat transfer coefficients and higher pressure drops than the HEMJ, contrary to numerical predictions. Subsequent measurements determined that the original test section had significant dimensional variations in the jet exit holes. A new test section was therefore manufactured and tested in the Georgia Tech (GT) helium loop. The experimental results presented here for this test section at maximum heat flux of 7.1 MW/m
2
are in good agreement with numerical predictions. Correlations developed from these experimental data are extrapolated to predict the maximum heat flux that can be accommodated by the flat design and the coolant pumping power requirements under prototypical conditions. Finally, numerical simulations are used to estimate the sensitivity of the flat design to geometric variations typical of manufacturing tolerances and variations in the gap width.
► An indirect vector controlled multiphase induction motor drive with harmonic injection to obtain a near rectangular air-gap flux is introduced. ► The proposed controller, avoids multiple ...PI-controllers; only two PI-controllers are used. ► An eleven-phase induction machine is used as a prototype. ► A comparison between the conventional controller, using multiple PI controllers, and the proposed controller is made for third harmonic injection.
Torque enhancement by stator current harmonic injection is one possible use of the additional degrees of freedom offered by multiphase machines yielding a near rectangular air-gap flux. The number of injected harmonics depends on the phase order and the corresponding sequence planes. As the number of machine phases increases, the injected harmonic order can be increased where each plane requires two PI controllers, to control its current components, resulting in a complicated tuning process. Moreover, the deployment of conventional indirect vector control with multiple PI controller fails to maintain a near rectangular air-gap flux with different loading conditions due to synchronization problem between different planes. In this paper, the conventional indirect vector control based on multiple PI-controllers is replaced by only two PI-controllers to develop the fundamental dq voltage components from which the dq voltage components for other planes are determined using offline optimized constant gains. The proposed controller makes the tuning process is easier and achieve near rectangular air-gap flux during loading conditions. The proposed controller tested using a prototype eleven-phase induction machine where injection up to the ninth harmonic can be engaged. A comparison between the conventional controller, using multiple PI controllers, and the proposed controller is made for third harmonic injection. Practical results are introduced as a conformance to simulation results.
