Commutation Problem Research Articles

A family of single‐phase boost AC‐AC converters based on impedance network cells with symmetric bipolar operation

SummaryIn this paper, a family of single‐phase boost AC‐AC converters based on impedance network cells with symmetric bipolar operation is proposed. The proposed converters exhibit a range of voltage gains as a result of non‐inverting and inverting boost operations, which are influenced by the input voltage and various impedance source cells. The converters leverage inherent commutation to address the commutation problem without requiring snubber circuits and safe commutation strategy. Additionally, high‐speed switching is achieved by preventing power MOSFETs' body diode conduction and related poor reverse recovery issues. The design incorporates a simple and flexible switching strategy to produce step‐change frequency at the output, using only four switches to achieve both step‐changed frequency operation and output voltage regulation. Furthermore, by reducing the total stored energy of passive components, the proposed converters effectively decrease volume, weight, and cost. The operational modes of the converters are elucidated, and their key relationships are summarized in tabular format. Finally, experimental validation through a laboratory prototype confirms the performance accuracy of the proposed converters at frequencies 25, 50, and 100 Hz.

Integrated Departure Time and Parking Location Choices in a Morning Commute Problem under a Partially Automated Environment

This study formulates the joint decisions of commuters on departure time and parking location choices in a morning commute problem where the commuters travel with autonomous vehicles (AVs) or human-driven vehicles (HVs). Under a mixed traffic environment, we aim to explore the impacts of parking capacity and parking pricing on the equilibrium travel pattern and the system performance. We build a dynamic equilibrium model for the morning commute problem by assuming that the parking slots can be grouped into central and peripheral clusters based on the distance between the parking location and the workplace. We first analyze the parking location preferences of commuters towards the two parking clusters under a mixed traffic environment. We then examine the equilibrium conditions and identify all the equilibrium travel patterns. We further analyze the system performance measured by the total travel cost with respect to the parking prices and the capacity of the central cluster. The optimal parking pricing scheme is also derived to minimize the total travel cost. We conduct numerical analysis to demonstrate the change in the total travel cost against the parking capacity of the central cluster and its parking price. Sensitivity analysis is performed to show the impacts of the network configuration on the total travel cost.

A Bidirectional Direct AC-AC Resonant SCC

A direct ac-ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant voltage regulator (CVR), and constant current regulator (CCR). Zero voltage switching (ZVS) and zero current switching (ZCS) operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference (EMI) noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

Dual Toeplitz operators on the orthogonal complement of the harmonic Bergman space

&lt;p&gt;This paper aimed to give some partial answers to the zero-product problem and commutativity problem concerning dual Toeplitz operators with nonharmonic symbols on the orthogonal complement of the harmonic Bergman space. Using the symbol map, we described the necessary condition for $ S_{\varphi_1}S_{\varphi_2}\cdots S_{\varphi_N} = 0 $ with radial symbols. Furthermore, we established the sufficient and necessary conditions for $ S_{\varphi}S_{ \psi} = S_{\psi}S_{\varphi} $ with $ \varphi(z) = az^{p_1}\overline{z}^{q_1}+bz^{p_2}\overline{z}^{q_2} $ and $ \psi(z) = z^{s}\overline{z}^{t} $.&lt;/p&gt;

On a Particular Solution of the σ-Commutation Problem () for Toeplitz and Hankel Matrices

A unified approach is proposed to the construction of matrix pairs (T,H) that solve the ‑commutation problem for Toeplitz and Hankel matrices. For a certain particular case, a family of solutions is derived.

A New Four-Step Commutation Method for Indirect Matrix Converter With Active-Voltage Vectors Being Applied

The existing two commutation methods of the rectifier stage for indirect matrix converter (IMC) are zero-current commutation and four-step commutation. The premise of zero-current commutation is that the inverter stage of IMC uses a zero-voltage vector, but when the inverter stage cannot use zero-voltage vectors (such as space overmodulation, common mode suppression modulation, etc.), the four-step commutation is adopted. The conventional four-step commutation method has a complex switching sequence and requires additional sensors. Based on the natural freewheeling characteristic of IMC and the switching sequence of zero-current commutation, a new four-step commutation method is proposed when active-voltage vectors are applied in the inverter stage, first turn off the two switches at 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> and 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> steps, and then turn on the two switches at 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> and 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> steps. The switching sequence of the new four-step commutation is not affected by the polarity of input voltage or output current direction, thus solving the complexity switching sequence problem of the conventional four-step commutation, and does not require additional voltage or current sensors, making the IMC commutation process safer and more reliable. Finally, this paper verifies the effectiveness of the new four-step commutation method of IMC through experiments.

A novel control method for enhanced performance of single‐phase matrix converters

AbstractThe conventional topology of direct single‐to‐single‐phase matrix converter (SSMC) is widely adopted in industrial and power system‐related applications owing to its desired features. Current control methods in the literature either limit the voltage transfer ratio (VTR) or prohibit their utilization to drive inductive (RL) loads. In this study, we propose a novel control method that overcomes these limitations by enabling the SSMC to achieve relatively high VTRs while driving RL loads with negligible output voltage spikes and without current commutation problems. Further, the proposed control method improves the overall performance by reducing output voltage and source input current total harmonic distortion (THD) and offering soft‐switching at the commutation instances. The rigidity of the proposed control method over the counterpart methods in the literature is verified through simulation and experimental case studies over a wide range of synthesized output frequencies and modulation indexes. A 530‐W laboratory prototype is built for the experimental study. Results demonstrated the ability of the proposed method in enabling the SSMC to drive an RL load without current commutation issues and with mitigated output voltage spikes while achieving relatively high VTRs and suppressing the output voltage and source input current THD.

A single-phase direct buck-boost AC–AC converter with minimum number of components

In this paper, a single-phase direct pulse width modulation (PWM) buck-boost AC–AC converter is proposed. The proposed converter utilizes a minimum number of semiconductor switches and passive components that decreases the converter power losses and offers high efficiency. It can be operated with simple PWM control and doesn’t require soft-commutation strategies. It does not suffer from input source shoot-through and commutation problems. Moreover, it supplies both continuous input and output currents. The common sharing ground of the input and output gives the proposed converter the feature that it can be utilized for voltage sag and swell compensation. A comparison of the proposed converter performance with similar existing converters is presented. Also, detailed circuit analysis, component design guidelines, and simulation results using the MATLAB/Simulink environment are demonstrated. A laboratory prototype has been built and tested to validate the converter performance and confirm the results obtained by computer simulation.

Common-Ground-Structured High-Reliability Single-Phase AC–AC Converters

This paper proposes enhanced single-phase pulse width modulation buck, boost, and buck-boost-type ac-ac converters. The proposed converters, in which input and output voltages share a common ground, require no isolated voltage sensor and have no leakage current problem. The commutation problem is solved with series-connected switching cell structures without using a RC snubber. In addition, switching patterns are determined using only the polarity of input voltage, allowing the inductor currents to flow through switching devices during all operational modes. Because two switches are always turned on during a half-period of the input voltage, the switching loss is significantly reduced. Detailed analysis and experimental results are provided to verify the performance of the proposed converter.

Single-Stage Isolated AC/AC Converter With Phase-Shifted Controller

This article proposes a single-stage ac/ac converter with a high-frequency link, which is suitable for multilevel converters. The proposed topology is a direct ac/ac converter without commutation problems, which solves the common issue of direct ac/ac converters. Moreover, four-quadrant switches commonly used in matrix converters, and unfolding bridges normally essential in conventional circuits, are unnecessary in the proposed circuit, which enhances the efficiency and cost. The converter control strategy is adapted based on a single-phase shift technique with constant switching frequency and 50% duty cycle. The control strategy achieves a wide range of zero-voltage-switching (ZVS) turn-on without any auxiliary circuit. Furthermore, the high-frequency transformer (HFT) is free from line-frequency components with minimized rms value of current. Hence, an HFT with reduced size can be realized. The converter also has a low total harmonic distortion (THD) load current. A new continuous-time transient model of the proposed converter is proposed based on the generalized average model (GAM). The derived model is used to design the proposed phase shift controller. Moreover, a detailed closed-loop transient analysis is presented. A prototype circuit is implemented to validate the theoretical analysis and the feasibility of the proposed converter.

Nonisolated Dual-Output Single-Phase Boost Inverter With Reduced Active and Passive Components

This article proposes a nonisolated dual- output single-phase boost inverter with reduced active and passive components. The suggested inverter can serve two single-phase ac loads independently like two full-bridge inverters, but owing to the use of a pair of three-switch legs in the inverter bridge, it has a 25% reduction in active switches. The proposed inverter is capable of obtaining a boost output voltage while employing fewer passive components compared to the traditional impedance source inverter. And the high-frequency current commutation problem of diodes in the traditional split-source inverter is solved by replacing the diodes with two complimentary switches. A hybrid sinusoidal and constant pulsewidth modulation control strategy is elaborated, which enables the proposed inverter to operate in equal frequency mode and different frequency mode. Comprehensive working principles, modulation strategy, steady-state analysis, and parameter design guideline are introduced, both simulation and experimental results are presented to confirm the characteristics of the proposed topology.

Research on ZVS Phase-Shifted Full-Bridge Broadband Inverter Based on Auxiliary Current Source

Phase-shifted full-bridge topologies are widely used in medium- and high-power DC/DC converters due to their small size and high switching frequency. However, there are few studies on the application of broadband inverters. In the traditional phase-shift full-bridge inverter with a fully resonant load, the problem of current commutation which leads to hard switching is often encountered, to overcome such an issue, an auxiliary current source network is introduced to realize the zero-voltage turn-on of the lagging bridge arm. The working modes of the converter are analyzed in detail, and the parameters of the auxiliary current source network are designed. The simulation verification is carried out by MATLAB/Simulink in a wide frequency range from 10 kHz to 500 kHz. Finally, an experimental circuit board is designed, and the experimental results show that the topology can achieve soft switching in a frequency range from 10 kHz to 200 kHz and has a certain applicability.

Managing the Morning Commute Problem with Tradable Credit Schemes under a Fully Autonomous Vehicle Environment

This study investigates the morning commute problem in a single corridor with a bottleneck under a fully automated vehicle environment. By extending Vickrey’s bottleneck model, we formulate the joint decisions on departure time and parking choices of morning commuters who make trade-offs among travel cost, the cost associated with parking, and the cost of tradable credits. To alleviate traffic congestion and improve social welfare, we propose a time-varying tradable credit scheme and integrate it with the morning commute problem. We explore the travel patterns and the optimal design of tradable credit schemes for the morning commute problem with homogeneous and heterogeneous commuters, respectively. For the homogeneous case, we derive the conditions on the tradable credit scheme to ensure the existence of equilibrium. The system-wide travel cost decreases with parking density after tradable credits are incorporated. Additionally, the efficiency of the tradable credits scheme can be improved by increasing the rate of credit charge rate. For the heterogeneous case, we propose an initial distribution strategy and combine it with the optimal tradable credit in order to guarantee social equity. The commuters with a low value of time (VOT) should be allocated more credits and the commuters with high VOT should be charged more credits. For both cases at system optimum, we find that the equilibrium price of tradable credits increases with parking density and decreases with the total amount of tradable credits.

Single-Stage Isolated AC-AC Converter Without Commutation Problem

A single-stage isolated ac–ac converter without the commutation problem is proposed. The proposed converter has the step-up/down function dependence on the phase shift control which provides zero-voltage switching zero-voltage switching (ZVS) for all switches in rated condition. Also, the commutation paths of the secondary side switches are provided for any switching case by adding a single capacitor; originally, a filter capacitor is used for the switching mode power supply input, and in this case, this filter capacitor also solves the primary-side commutation problem. The ZVS and solving the commutation problem increase the power efficiency and reliability. The proposed converter achieves high power quality with a simple control algorithm. A 1 kW/ 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> prototype is implemented to verify the theoretical analysis and performance of the proposed converter. The California energy commission efficiency is 97.3%, the total harmonic distortion (THD) of the input current is 2.45% at full load, and the THD of the output voltage is 1.07% at full load.

Performance Analysis of Single Phase AC-AC Voltage Converter for Compensation of Voltage Issues in Power Distribution System

The power quality of the power distribution system is highly concerned with the use of renewable sources, solid-state electronic devices, and power electronic processors. This results in voltage fluctuations, voltage sag, and swell issues. The voltage source converter (dc-to-ac) can resolve these issues but there is a problem with high rating storage devices. The Dual converter (ac- to-dc) will be useful for energy-storing devices but due to complex circuit arrangement and high conversion losses, this converter is not favorable. The direct AC-AC voltage converter is a matter of research due to simple conversion. This paper presents the performance analysis of a single-phase ac-to-ac voltage converter operating in inverting and non-inverting modes with no current commutation problems. The performance analysis of the proposed converter is been done in MATLAB/Simulink 2019b. Keywords-Voltage sag and swell, voltage control, inverting mode, non-inverting mode, power distribution system

Stillbirth in COVID-19 Affected Pregnancies: A Double Whammy for the Mother.

IntroductionPregnant women represent a high-risk group especially during the COVID-19 pandemic, suffering at the expense of pandemic restrictions and landing up in adverse maternofetal outcomes including stillbirth. Fetal demise along with COVID-19 disease acts as a double blow to these mothers. Literature is still limited on its impact on maternofetal outcomes.MethodsA prospective, observational study was conducted in a tertiary care hospital in Delhi, India from April 15, 2020 to April 14, 2021, wherein all pregnant mothers with SARS-CoV-2 infection in the hospital who delivered a stillborn baby were enrolled and analyzed for incidence of stillbirth. These women were evaluated for risk factors and causes for stillbirth.ResultsOut of 15859 deliveries in the institute, there were 330 viable births among COVID-19 affected pregnancies. The incidence of stillbirth was 7.2% (24/330). The institutional delivery rate fell by 43% during the pandemic. The majority of cases were unbooked, from rural areas and of low socioeconomic status (p<0.01). The most significant risk factor and cause for stillbirth was an associated comorbidity (75%, p<0.001), notably severe forms of hypertensive disorders of pregnancy (HDP, 41.6%, p=0.002), followed by preterm labour (58.3%) and preterm premature rupture of membranes (PPROM, 29.1%, p<0.001). HDP remained the main cause of macerated stillbirths while maternal fever (50%, p<0.001) was the main cause of fresh stillbirth. Major modifiable factors were lack of awareness of when to seek care (83.3%), financial reasons (75%), commutation problems (87.5%), distance to hospitals (50%) and delayed referral (41.6%).ConclusionImproved policy-making, with an emphasis on telemedicine, COVID-19 preparedness alongside amped up vaccination and healthcare workers training will help reduce adverse maternofetal outcomes.

On the Morning Commute Problem in a Y-shaped Network with Individual and Household Travelers

This paper examines the morning commute problem when both household commuters and individual commuters are considered in a Y-shaped network with two upstream links and a single downstream link. The household parents daily pass through an upstream bottleneck with a limited capacity before a school and drop off their children. Then, they traverse the downstream bottleneck common to both household and individual commuters and arrive at the workplace. We explore the effects of staggering policy, that is, staggering work and school start times, on the distribution of traffic congestion and social welfare. We analytically solve all the equilibrium cases and reveal all the traffic congestion patterns. The results reveal that the staggering policy may be harmful in certain cases. When the demand of individuals is relatively low, the staggering policy may not improve social welfare. When the demand of individuals is high, social welfare can be significantly improved if the schedule gap between the work start time and school start time is optimized. The effects of the staggering policy on system performance are examined. We derive a Pareto frontier, which provides a good candidate set for policymakers when the two system performance measures, that is, the total system cost and the total congestion cost, are considered. Our results show that the optimal staggering policy on system performance depends on the demand distribution of the two groups. When the demand of individuals is high, there exists a unique optimal staggering policy that optimizes system performance. However, when the demand of individuals is low, the optimal staggering policy should be selected from the Pareto frontier. Furthermore, we re-examine the capacity expansion paradox under the staggering policy. Our study shows the capacity expansion at the downstream bottleneck can always reduce the total system cost. However, the paradoxical phenomenon may arise when the capacity of the upstream bottleneck is expanded, but it can be eliminated if the schedule gap is properly designed.

Effect of Transit Capacity onto Morning Commute Problem with Competitive Modes and Distributed Demand

A lane exclusively for transit is one measure to reduce urban congestion and intelligent transportation systems (ITSs) are expected to make this policy more effective. However, the advantage may be limited if a transit agency does not provide sufficient vehicles. This study evaluates the effect of transit capacity on a dedicated transit lane policy by examining the morning commute problem, by defining user equilibrium and system optimisation considering transit capacity. It was confirmed that reduced transit capacity under user equilibrium smoothly increases the transit cost per person, which decreases the duration period of the dedicated transit lane and increases the number of early and delayed car commuters. However, the effect of reducing transit capacity under a system optimum depends on the initial solution of the system optimum.

A comparative analysis of converters performance using various control techniques to minimize the torque ripple in BLDC drive system

Because of its high consistent quality, essential edge, high capability, rapid dynamic reaction, preservationist estimation, and cheap maintenance independently, the BLDC motor is widely utilised in military, industrial, and business applications. In comparison to conventional machines, the torque ripples of a BLDC motor are greatly impacted by the speed and transient line current in the commutation interval. This study investigates the value of torque ripple reduction in a BLDC motor drive system by looking at speed, current, and commutation problems. The FOPID and MRPID controllers were used to reduce torque ripple in BLDC motors caused by mistake tuning optimum gain controllers. The FOPID and MRPID controllers are offered for controlling the motor's current and speed. This suggested suppression circuit employs a modified Landsman converter and a modified Luo converter, with the obligation cycle adapted to get the optimal DC-bus voltage based on the BLDC motor's speed. The proposed method is used to hold the supported converter in place by reducing ripples by regulating the yield torque. The performance of the speed, current, and torque regulating systems is improved by modelling a BLDC motor drive system based on a modified Luo converter. In this work, a novel technique combining Elephant Herding Optimization (EHO) and Adaptive Neuro Fuzzy Inference System (ANFIS) based on the MRPID controller scheme is suggested and compared, including EHO-ANFIS with FOPID, GA-ANFIS with PID, and PSO with PID. The suggested EHO ANFIS technique's major goal is to reduce and regulate speed, current, and torque problems in BLDC motor drive systems. Simulation is carried out in the MATLAB SIMULINK model to achieve the goal.

Departure time choice behavior in commute problem with stochastic bottleneck capacity: experiments and modeling

ABSTRACT The effect of environmental uncertainty on equilibrium patterns is of vital importance to understand travel choice behavior. This paper conducted a laboratory experiment to investigate the effects of stochastic bottleneck capacity on departure time choice behavior. In the experiment, the bottleneck capacity varied stochastically from round to round, and two different scenarios with different information feedback were investigated. Our experimental results showed that the relationship between the mean travel cost and the standard deviation of travel cost on each departure time was fitted approximately linearly with a positive slope , indicating subjects were more likely to minimize their travel cost budget rather than their mean travel cost. Also, we found that the feedback on costs of all departure times resulted in a smaller than the feedback on the subjects’ own travel cost only. We propose a reinforcement learning model to reproduce the main experimental findings.