Square-wave Operation Research Articles

1.9 μm square-wave passively Q-witched mode-locked fiber laser.

We propose and demonstrate the operation of Q-switched mode-locked square-wave pulses in a thulium-holmium co-doped fiber laser. By using a nonlinear amplifying loop mirror, continuous square-wave dissipative soliton resonance pulse is obtained with 4.4 MHz repetition rate. With the increasing pump power, square-wave pulse duration can be broadened from 1.7 ns to 3.2 ns. On such basis Q-switched mode-locked operation is achieved by properly setting the pump power and the polarization controllers. The internal mode-locked pulses in Q-switched envelope still keep square-wave type. The Q-switched repetition rate can be varied from 41.6 kHz to 74 kHz by increasing pump power. The corresponding average single-pulse energy increases from 2.67 nJ to 5.2 nJ. The average peak power is also improved from 0.6 W to 1.1 W when continuous square-wave operation is changed into Q-switched mode-locked operation. It indicates that Q-switched mode-locked operation is an effective method to increase the square-wave pulse energy and peak power.

Square-Wave Operation for a Single-Phase-PFC Three-Phase Motor Drive System Without a Reactor

This paper proposes a square-wave control strategy for a single-phase power factor correction with a new boost-up converter which uses the leakage inductance of a motor instead of a boost-up reactor. Since the power supply is connected to the neutral point of the motor, the current distortion in the power supply occurs when the inverter outputs square waveforms. First, this paper describes the characteristic of the proposed circuit and the problems in the square-wave operation. Next, a current control method for the square waveform is proposed to suppress the current distortion. Finally, the validity of the proposed converter and its control strategy are demonstrated by experimental results.

Five-level inverter scheme for an open-end winding induction machine with less number of switches

Higher level of inversion is achieved with a less number of switches in the proposed scheme. The scheme proposes a five-level inverter for an open-end winding induction motor which uses only two DC-link rectifiers of voltage rating of Vdc/4, a neutral-point clamped (NPC) three-level inverter and a two-level inverter. Even though the two-level inverter is connected to the high-voltage side, it is always in square-wave operation. Since the two-level inverter is not switching in a pulse width modulated fashion and the magnitude of switching transient is only half compared to the convention three-level NPC inverter, the switching losses and electromagnetic interference is not so high. The scheme is experimentally verified on a 2.5 kW induction machine.

Low-speed performance comparisons of back-EMF detection circuits with position-dependent load torque

Because of the widely used brushless DC motors (BDCMs) in high-efficiency variable-speed compressors, many sensorless controls with square-wave operation had been developed in the literatures. Recently, more and more low-production-cost BDCM-type compressors with position-dependent load torque, such as rotary compressors, are applied to the residential products, which lead to the importance of low-speed performance of sensorless control. The authors address the low-speed performance comparisons between two common back-EMF detecting circuits (BEDCs). Without using the actual refrigerant system, a Motor-Generator set coupled with a disk and copper cylinder are also built up to serve as the experimental position-dependent load torque. From the simulated and experimental results, one of the BEDCs is better than the other one for the low-speed application of position-dependent load torque.

Radio-Frequency Inverters With Transmission-Line Input Networks

A soft-switching inverter topology (the Class Phi ) is presented which draws dc source current through a transmission line or a lumped-network approximation of a distributed line. By aligning the inverter switching frequency just below the line's lambda/4-wave resonance, the Class Phi topology enforces odd-and even-harmonic content in its drain voltage and input current, respectively. The symmetrizing action of the transmission-line dynamics results in natural square-wave operation of the switch, reducing the inverter stresses (relative to a Class E) for a given power throughput. The inverter waveforms and normalized power-output capability are analyzed in simple terms, and supported by measurements of an inverter built around a length of distributed line, and an inverter incorporating a lumped L-C ladder network. The latter implementation is constructed with air-core magnetics and inter-layer capacitances that are integrated into the thickness of a printed-circuit board. A comparison with a Class E inverter of similar size and ratings demonstrates the small passive-component values and manufacturing advantages afforded by the Class Phi topology.

Diode lasers with optical feedback produce self-modulated square waves

Semiconductor laser diodes are popular and widely-used sources due to their high power, low cost, tunability, and easy integration with miniaturized electronics. They can also serve as flexible signal sources of high-frequency oscillations and pulsations. To generate waveforms while taking advantage of their high frequency capabilities, all-optical feedback methods are often simpler to use than high-speed electronics, which can be costly, inefficient, or operationally limited. In this context, a square-wave signal is a particularly useful waveform, since its rising and falling edges require high-frequency components in their creation. One method that can generate square waves from diode lasers is polarization self-modulation, meaning that the laser output switches regularly between its two natural polarization modes rather than simply switching on and off in total intensity. This self-modulation can be achieved entirely optically by injecting light from one laser polarization mode into the orthogonal mode. This requires that the optical feedback be rotated from its original orientation by some means, typically a waveplate. Square-wave operation has been observed in vertical-cavity surface-emitting lasers (VCSELs), but can be difficult to achieve: the specific VCSEL characteristics or operating parameters that are required for such outputs are not well-understood. Another limitation is that, if the feedback path is short, the VCSEL will exhibit chaotic fluctuations rather than regular square waves. In edge-emitting lasers however, short feedback delays still allow square-wave operation. In these devices, one polarization mode is typically suppressed, and accordingly requires relatively strong feedback to be activated. Our recent work has explored the dynamical mechanisms of this Figure 1. Top: Schematic of our experimental apparatus showing the laser diode feedback elements (blue) and the detection system components (green). Bottom: sample square-wave data.

矩形波点灯における冷陰極放電管の効率改善

矩形波点灯における冷陰極放電管の効率改善

AN EXPERIMENTAL STUDY OF CONCENTRATION FORCING APPLIED TO THE METHANOL SYNTHESIS REACTION

Abstract The effect of square-wave concentration-forcing operation on the rate of methanol production over two industrial catalysts was studied at 513 K and 2.86 MPa total pressure. Improvements as high as 25 percent relative to the optimal steady-state methanol production rate, in moles per gram catalyst per unit time, were obtained over BASF's S 3-85 catalyst. This occurred in a laboratory-scale fixed-bed reactor with gas mixing for a cycling time of τ = 12 seconds and for a cycle split relative to carbon monoxide of γCO = 0.20, the rest of the cycle being hydrogen. Improvements as high as 15 percent were also obtained over Imperial Chemical Industries ICI 51-2 catalyst, in a differential plug-flow reactor for τ = 24 seconds and γCO = 0.15. These improvements were obtained for pure-component steady cycling between carbon monoxide and hydrogen with a constant carbon dioxide molar concentration of 2 per cent (BASF catalyst) or 3 percent (ICI catalyst) present in both parts of the cycle. On the other hand,...

Cyclical-field field-flow fractionation: a new method based on transport rates

A new form of field-flow fractionation (FFF) is described in which the field strength is cycled up and down many times during a run. It is shown that this method, termed cyclical FFF (CFFF), leads to migration rates dependent on transport coefficients. After development of the general theory, results are obtained for coherent (no diffusion) square-wave operation. For the latter, migration rates are shown to depend on the generalized mobility of the particles and upon system parameters such as cycle time and field strength. Other variants of CFFF are noted and several advantages are indicated. A gravitational CFFF system operating according to sedimentation coefficients is described and certain programming options are discussed.

Square-Wave Operation of a Thermal Conductivity Detectort†

SUMMARY Equipment is described for the operation of thermal conductivity detectors with square-wave bridge current. The resulting ac output signal allows amplification without the need for low-level choppers. With phase-locked demodulation of the amplified signal, bridge unbalance signals of the order of 10 nV can be detected. This performance exceeds the requirements of presently available detector cells, which produce noise levels of the order of 100 nV. The instrument is compatible with most existing hot wire detectors and may be used with economical recorders. Air and other permanent gases can be reliably analyzed at levels of 0.02 μl, with detection limits of the order of 0.002 μl. This performance makes the instrument attractive in the field of air pollution and opens the way to further research in the design of low-noise detector cells.

The effect of supply frequency on a mercury-argon discharge

Measurements have been made of the 2537 and 1849 A resonance line intensities emitted from the positive column of a mercury-argon discharge contained in a 36 mm bore tube and operated at powers of 0.5-1.5 W cm-1, from d.c. and from 50 c/s to 20 kc/s a.c. supplies. At a constant positive column power input there is little variation of these intensities with frequency when sine wave a.c. supplies are used; their values are lower than those for d.c. and rise towards this level at frequencies above about 10 kc/s. On square-wave operation the intensities are the same as those for d.c. The power dissipated at the electrodes is found to fall with increase in frequency, becoming constant above about 500 c/s.

A design basis for silicon-controlled rectifier parallel inverters

The operation of the silicon-controlled rectifier in the basic form of parallel inverter circuits with resistive loads is investigated, and analysis is carried out to determine the conditions for optimum performance. Two fundamental parameters in terms of time-constants are introduced, one relating to the ballast inductance and the other to the commutating capacitance, as opposed to the method of defining design parameters in terms of a required triggering period hitherto employed in analysing thyratron circuits. The analysis shows that the basic circuit has three main modes of operation, two of which are undesirable. Within the range of the desirable mode square-wave and sine-wave operations are found to be feasible, and a procedure is given for determining the optimum triggering points in terms of time-constants. Expressions are derived for the maximum repetition rates for the generation of both types of waveforms in terms of relevant time-constants and turn-off times of the silicon-controlled rectifiers; with currently available high-current silicon-controlled rectifiers repetition rates of the order 6kc/s for square-wave operation and 12kc/s for sine-wave operation are found to be readily obtainable. With low-current diffused types, the corresponding repetition rates would be of the order of 35 and 70kc/s, respectively. The complete design procedure is illustrated by applying the analytical results to the practical design of a d.c./d.c. convertor, which is essentially an inverter followed by a bridge-rectifier filter unit.