Exact solution of the p+ip pairing Hamiltonian and a hierarchy of integrable models

Using the well-known trigonometric six-vertex solution of the Yang-Baxter equation we derive an integrable pairing Hamiltonian with anyonic degrees of freedom. The exact algebraic Bethe ansatz solution is obtained using standard techniques. From this model we obtain several limiting models, including the pairing Hamiltonian with p+ip-wave symmetry. An in-depth study of the p+ip model is then undertaken, including a mean-field analysis, analytic and numerical solution of the Bethe ansatz equations, and an investigation of the topological properties of the ground-state wavefunction. Our main result is that the ground-state phase diagram of the p+ip model consists of three phases. There is the known boundary line with gapless excitations that occurs for vanishing chemical potential, separating the topologically trivial strong pairing phase and the topologically non-trivial weak pairing phase. We argue that a second boundary line exists separating the weak pairing phase from a topologically trivial weak coupling BCS phase, which includes the Fermi sea in the limit of zero coupling. The ground state on this second boundary line is the Moore-Read state.Comment: 65 pages, 11 figures, 3 table

A new hybrid cycloconverter with smooth output voltage generation capability and accurate control of the circulating current

Nowadays, power electronic converters based exclusively on IGBTs deliver excellent load side performance up to megawatt powers in the low voltage range (200-690V) and are steadily gaining performance in the medium voltage range as well. However, the medium and high voltage/high power range remains dominated by converters using naturally commutated thyristors (i.e. cycloconverters, current source inverters), which offer poorer output side performance. This paper proposes a new hybrid arrangement, targeting the medium and high-power range, comprising a naturally commutated cycloconverter connected to a PWM Voltage Source Inverter, able to offer improved output voltage quality and accurate control of the circulating current. The feasibility of the newly proposed concept is validated by Saber simulation results

Assessing the benefits of hybrid cycloconverters

Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first to be used in driving electrical motors with variable speed, but now, due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices are not yet competitive. Hybrid cycloconverters proposed recently are capable of improving the performance of cycloconverters by adding an auxiliary forced commutated inverter with reduced installed power. It will be shown that the new topology is not only able to improve the quality of the output voltage but is also able to enhance the control over the circulating current and, therefore, for some of the cycloconverter arrangements, to improve the input power quality. This paper evaluates the performance of a few standard and hybrid cycloconverter arrangements using both simulation and experimental results

Constraints Perceived by Students in School Vegetable Gardening

The study was conducted in Thiruvananthapuram district of Kerala to identify the constraints experienced by students in the course of engaging in school vegetable gardening programme. Ten schools were selected for data enumeration. A total of 130 respondents with 100 students comprising ten students each and 30 teachers comprising three each, from each school were selected for meeting the objectives of the study. The reaction to each constraint was obtained on a four-point continuum namely most important, important, less important and least important with the score 4, 3, 2 and 1 respectively. Mean rank cumulative index for each constraint was worked out and the constraints were ranked and catalogued. The major constraints as perceived by students in school vegetable garden projects were, high input cost followed by lack of student’s participation, lack of teacher’s involvement, non-availability of implements, high labour cost, poor storage facilities and lack of knowledge about gardening

Experimental evaluation of hybrid cycloconverters

Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first used in driving electrical motors with variable speed but now due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices is not competitive yet. Hybrid cycloconverters proposed recently improve the performance of cycloconverters by adding an auxiliary forced commutated inverter with reduced installed power that enhances the control over the circulating current and improves the quality of the output voltage. This paper evaluates the performance of a few standard and hybrid cycloconverter arrangements using simulation and experimental results

Control and grid integration of MW-range wind and solar energy conversion systems

Solar-based energy generation has increased by more than ten times over the same period. In total, worldwide electrical energy consumption increased by approximately 6340 TWh from 2003 to 2013. To meet the challenges created by intermittent energy generation sources, grid operators have increasingly demanded more stringent technical requirements for the connection and operation of grid-connected intermittent energy systems, for instance concerning fault ride through capability, voltage and frequency support, and inertia emulation. Ongoing developments include new or improved high-voltage converters, power converters with higher power density, control systems to provide ride-through capability, implementation of redundancy schemes to provide more reliable generation systems, and the use of high-voltage direct current (HVdc) links for the connection of large off-shore intermittent energy systems

Direct Nitrous Oxide Emissions From Tropical And Sub-Tropical Agricultural Systems : A Review and Modelling of Emission Factors

We acknowledge the financial support from the CGIAR Research Programs on Climate Change, Agriculture and Food Security (CCAFS). Grant ref. n. P25.Peer reviewedPublisher PD

Fast convergence delayed signal cancellation method for sequence component separation

Delayed Signal Cancellation (DSC) is one of the methods used to separate the negative and positive sequence components in unbalanced 34 systems. In this paper a DSC methodology with a fast convergence time is proposed and is shown that an improved separation of the positive and negative sequences is feasible. Experimental results are presented to demonstrate the performance of the proposed methodology

Repetitive control for high-performance resonant pulsed power supply in radio frequency applications

This paper presents a novel three phase series resonant parallel loaded (SRPL) resonant converter topology for radio frequency (RF) applications. The proposed converter is capable to produce as output voltage a series of “long pulses”, each one lasting 1ms in time. Three individual single phase resonant stages are able to operate independently in conjunction with three separate single phase output rectification stages. Due to this important feature, the converter has a strong ability of rejecting the influence of unbalance in the resonant tanks. A PI + Repetitive Control (RC) strategy has been used for the output pulsed voltage regulation, resulting in a fast rise time, reduced overshoot, and constant amplitude. The soft-switching of semiconductor devices is ensured at full power by a combined frequency and phase shift modulation (CFPS), even in the presence of large tank unbalances

An enhanced dq-based vector control system for modular multilevel converters feeding variable speed drives

Modular multilevel converters (M2C) are considered an attractive solution for high power drive applications. However, energy balancing within the converter is complex to achieve, particularly when the machine is operating at low rotational speeds. In this paper, a new control system, based on cascaded control loops and a vector-power-voltage (vPV) model of the M2C, is proposed. The control system is implemented in a dq-synchronous frame rotating at ωe rad/s with the external loop regulating the capacitor voltages using proportional-integral (PI) controllers. The internal loop controls the converter currents using PI and resonant controllers. In addition, the control systems required to operate the machine at other points, i.e., at medium and high rotational speeds, are also discussed in this paper. Experimental results obtained with an M2C-based drive laboratory prototype with 18 power cells are presented in this paper