Single-phase Square Research Articles

Fast synchronization with enhanced switching control for grid-tied single-phase square wave inverter using FPGA

Research on grid synchronization has been conducted worldwide by researchers in conjunction with the development of innovative technologies, such as dedicated short-range communication (DSRC) and cellular vehicle-to-everything (C-V2X). However, grid-connected inverters face several challenges, mainly the mismatch in voltage amplitude, frequency, and phase angle, as well as grid voltage disturbance and grid faults. Thus, the control algorithm of this research mainly focused on a half-cycle algorithm to design an enhanced digital switching control for fast synchronization using an FPGA. The control algorithm was developed based on zero-crossing detection (ZCD) and digital phase-locked loop (PLL) modeling techniques using the hardware description language (HDL) and a combination of digital logic blocks in Quartus II software, where the proposed switching was applied using the square-wave switching technique through a 300-watt full-bridge experimental prototype. The performance of the proposed technique was studied, where the total harmonic distortion (THD) for voltage and current resulted in a percentage reduction of 89.29% and 78.05% for voltage and current, respectively, after filter implementation. Also, the resulting signal synchronized in every half cycle and matched the voltage amplitude, frequency, and phase angle of the grid signal in 10 ms.

Wind Turbine Generation System Implemented with a Car Alternator for Use in Isolated Locations

This work presents a wind driven AC electrical generator system for use in isolated locations. The mechanical energy is provided by a vertical axis wind turbine, connected to a standard car alternator. This arrangement requires no mechanical speed control and, as far as possible, can be produced and serviced in many workshops in third word countries, without special tooling and using locally available materials and parts. Controlling the alternator field current a regulated 12 Vdc supply is generated. The 12 Vdc (nominal) output is fed to the power electronic block formed by a chopper up-converter and an inverter stage. Four different output units are available, providing four different quality outputs: a simple non-filtered single phase square wave inverter; a filtered PWM-controlled single phase inverter providing a line-line AC supply (115 V rms, 60 Hz, for Venezuela); a standard low power UPS; and a filtered PWM-controlled three-phase AC supply (208 V rms, 60 Hz, for Venezuela). This work presents the initial test results, using the alternator and the power electronic blocks, and emulating the wind turbine with an AC motor.

Dynamics of a single-phase natural circulation system under harmonic excitation.

A natural circulation system (NCS) has a broad application in the sector of thermal engineering, for example, in nuclear reactors due to its capability in transferring heat without any support of external power or a mechanical device. NCSs, although designed for steady operation, have been found to exhibit dynamical behavior, such as periodic oscillations, depending on the input heater power. The heater power, otherwise assumed to be steady, can be fluctuating in practice. The present study focuses on the dynamics of a single-phase square NCS, which exhibits periodic dynamics and is subjected to an external harmonic perturbation (chosen as the simplest form of fluctuation) over the steady heater power. The objective of the study is to study the dynamics of NCS under external (harmonic) disturbances using the framework of forced synchronization. Toward that, a 1D transient model of a square-shaped NCS is simulated with harmonically forced input power. The transition in the nature of synchronization between mass flux oscillations and the external forcing has been characterized by varying the frequency and amplitude of external perturbation independently. We find different nonlinear effects of the harmonic forcing, such as exhibition of quasiperiodic dynamics, frequency pulling/pushing, and frequency locking or forced synchronization. The aforementioned characterization techniques open up an avenue for detailed analysis of the more complex type of fluctuating input heat in real systems.

Turbulent cylinder-stirred flow heat and momentum transfer research in batch operated single-phase square reactor

Heat transfer and momentum transfer due to water flow in a cylinder-stirred reactor of square cross section were investigated. Important industrial processes like mixing depend on combined effects of heat transfer and fluid flow which can be understood by analyzing the turbulence structure. A reactor of aspect ratio η = 0.21 (diameter of cylinder to tank side wall) was considered. It uses a small-diameter cylinder to stir the water in batch condition with rotating Reynolds number in a range 1.68 × 104 <Re < 10.1 × 104. The cylinder released a constant heat flux rate of 158 W/m2 through its surface. The steady state mean flow was numerically simulated using two models for turbulence, isothermally with a k-ε and thermally with the RSM model. The results revealed a fluid motion like Taylor-Couette vortex which was validated with PIV streamlines for Re = 6.1 × 104 and 10.1 × 104. Turbulent angular momentum and shear rate revealed differences for the corner direction as the Re number increased compared with the wall direction. Temperature fluctuations and thermal gradient in the gap allowed to analyze the turbulent heat diffusivity coefficient and the ratio to predicted diffusivity for momentum. The results revealed that heat and momentum diffusivity increase for higher Re number and show that heat diffusivity is faster than momentum in the gap. The main frequencies of fluid motion showed large-scale structures and secondary cells of fluid motion. The averaged heat transfer as a function of Re number indicate that this reactor is an enhanced mean for mixing process compared to concentric cylinders reactors.

Flow reversal prediction of a single-phase square natural circulation loop using symbolic time series analysis

Flow reversal prediction of a single-phase square natural circulation loop using symbolic time series analysis

Flow dynamic study of a single-phase square NCL using recurrence plot and recurrence quantification

Flow dynamic study of a single-phase square NCL using recurrence plot and recurrence quantification

Dynamic characterization of a single phase square natural circulation loop

Natural circulation loop (NCL) has many applications in the energy sector as a passive heat transfer system. The passive nature of its operation increases the reliability of natural circulation loops and makes them crucial for the safety of the system. However, depending on the operating conditions, the dynamics of the system can vary significantly. For this reason proper analysis of the fluid flow dynamics in the NCL is very important. In this paper instability associated with the loop fluid flow in the NCL is investigated from a dynamical systems perspective with the help of phase plot, Fast Fourier Transform (FFT), correlation dimension and largest Lyapunov exponent. From the numerical analyses it is found that with the increase in heater power, dynamics of the fluid flow in the loop changes significantly. Loop characteristics remain steady up to a certain heater power level but with the increase in heater power level first it shows periodic oscillations and then it shows chaotic behavior. The existence of periodic and chaotic regimes is established using tools of dynamic systems analysis.

Detection of the Source of the Incipient Faults Produced by Single Phase Inverter using Feed- Forward Back-Propagation Neural Network

With the increasing usage of solar Photovoltaic (PV) system in Malaysia, the condition aspect of solar PV system especially inverter system needs to be given full attention. Detection of faults at earlier stage is very important in order to avoid the extended period of down-time caused by inverter failure. Thus, this paper aims to detect the source of the incipient faults produced by a single phase inverter of a PV system. The incipient faults were generated by modifying the pulse wave control signal. A total of 100 incipient faults and one set of normal condition waveform are collected at the output of the single phase square wave inverter. These waveforms are then used to train the feed-forward backpropagation neural network. One hidden layer feed-forward backpropagation neural network of 9 neurons was trained and MSE of 6.13 × 10-4 was obtained. It was shown that the trained feed-forward backpropagation neural network was able to detect which IGBT of the single phase square wave inverter produced the incipient faults.

The effects and mechanism of electrical stimulation on esophageal muscle in rat: an experimental study

Objective To explore the correlation between smooth muscle contraction and stimulation parameters, and mechanism of electrical stimulation on the esophageal body muscle strips in normal rats. Methods A segment of lower part esophagus of 20 healthy male WISTAR rats was obtained. Single phase square wave(width 25 ms)was used and the electrical stimulation lasted for 3 s with varied electrical parameter(current: 1.5 V, 3.0 V, 5.0 V, 8.0 V; frequency: 5 Hz, 10 Hz, 20 Hz). The correlation between tension and stimulation parameters was studied.Fifty healthy male rats were divided randomly into control group(n=10), ATR group(n=10), PHT group(n=10), L-NNA group(n=10), TTX group(n=10). Respective drugs were given 10 minutes before lower part of esophagus was stimulated with single phase square wave(5.0 V; 20 Hz; width 25 ms), the tension was recorded and compared among groups. Results At frequency 20 Hz and width 25 ms, the peak value of contraction in 1.5 V group was 0 g. The peak value of contraction in 5.0 V group was more than 3.0 V group and less than 8.0 V group(P 0.1, P 0.1, P 0.05). Conclusion The electrical stimulation of esophageal muscle in normal rats could cause effective contraction immediately. The peak value of contraction is correlated positively with volgage and frequency of electrical stimulation. The effect of electrical stimulation on esophageal muscle is not influenced by nurontransmeters. Key words: Achalasia; Mechanism; Neurotransmitter; Electrical stimulus; Esophageal muscle

The effect of alternating current stimulation on the esophageal motility of rabbits

Objective To observe the effect of electrical stimulation on the movement of rabbits esophagus, and to promote effective esophageal peristalsis and determine the best electrical pacing parameters. Methods After anesthesia, 24 healthy rabbits underwent open surgery and the lower esophagus was exposed. The esophagus was stimulated with the multi-channel signal generator, and the changes of esophagus pressure and the length of esophageal contraction with high resolution manometry were recorded.(1) The effects on contraction pressure of esophagus body and lower esophageal sphincter (LES) after single site electrical stimulation under different parameters were observed.The stimulation modes utilized were electric current 3 mA, 5 mA and 8 mA, frequency 5 Hz, 10 Hz and 20 Hz, pulsewidth 0.25 ms, 25 ms and 50 ms, waveform of single phase and double phase.(2)The esophagus was sequentially stimulated. The stimulation mode utilized was electric current 5 mA, frequency 20 Hz, pulsewidth 25 ms, stimulation duration 3 s, single phase square wave. Results At electrical stimulation on the esophagus body and LES, contraction delay was 13.00±1.54 ms and 12.00±0.73 ms respectively. The contraction pressure of esophageal body was significantly positively related tothe electric current (R=0.968, P<0.01), the pulse width(R=0.971, P<0.01), and the frequency (R=0.947, P<0.01). The length of contraction in 10 Hz group was shorter than that of the 20 Hz group(1.33±0.06 cm VS 1.80±0.00 cm, P<0.05). The contraction pressure of LES was also significantly positively related to the electric current(R=0.965, P<0.01), the pulse width (R=0.973, P<0.01), and the frequency (R=0.842, P<0.01). The pressure of lower esophageal sphincter of single phase square wave was greater than that of the double phase square group (P<0.05). Under the same parameters, the contraction pressure of LES group was lower than that of the esophageal body group (27.33±1.15 mmHg VS 104.00±6.00 mmHg, P<0.05). Esophageal sequential contraction was induced by multi-points sequential electrical stimulation. Conclusion Single point electric stimulation can cause esophageal contraction immediately without obvious delay. Within a certain range, the esophageal contraction pressure is positively correlated with electric current, frequency and pulse width. The contraction pressure of single square phase wave is greater than that of the double square phase wave. The contraction pressure of esophageal body is greater than that of LES after electric stimulation. Multi-points sequential electrical stimulation can promote sequential movement of esophagus. Key words: Electrostimulation; Achalasia; Gastroesophageal reflux; High resolution manometry; Low esophageal sphincter

Experimental and Numerical Investigation of a Single-Phase Square Natural Circulation Loop

Experimental and numerical analyses are carried out for a natural circulation loop (NCL) under low and moderate heater power. The effect of ambient temperature variation on the loop thermal behavior has been taken into account in present study. The effect of liquid inertia has a role in the initial transience, as revealed by the numerical and experimental observations. The steady-state results from the present analyses are validated with the reported dimensionless results for NCL. The experimental steady-state results are in fair agreement with the developed lumped numerical models. At moderate power, the numerical and experimental results indicate periodic oscillations.

보조전원장치에 의한 12-펄스정류기의 고조파 저감

Abstract: Diode rectifiers have been widely used for an AC to DC converter. But a big problem is that they include large harmonics components in the input currents. A 12-pulse configuration with phase shifting trans-former is useful for reducing them. however, it still includes the (12m±1)th (m; integer) harmonics in the in-put currents. In this paper, we propose a single-phase square wave auxiliary voltage supply which is inserted in the middle DC bus. It reduces harmonics especially the 11th and 13th and the harmonic characteristic be-comes almost equivalent to a 24-pulse rectifier. Theoretical analysis of the combined 12-pulse diode rectifier with the auxiliary supply is presented and a control method of the auxiliary supply is proposed. The reduction in the input current harmonics is verified by simulation using software PSIM. Keywords: 12-pulse Diode rectifiers, Auxiliary Voltage Supply, Harmonics, Square Wave Voltage Supply 1. 서 론 최근에 다양한 전력변환소자의 개발에 힘입어 이러한 소자들을 채용한 전력전자장비들이 각종 선박뿐 아니라 해양플랜트 등에도 등장하고 있다. 그러나 이런 장비들을 사용할 경우 선박이나 플랜트내의 전력품질을 현저히 저하시켜 다른 장비나 시스템에 악영향을 끼칠 수 있다

An Auxiliary-Supply-Assisted Harmonic Reduction Scheme for 12-Pulse Diode Rectifiers

Diode rectifiers have been widely used for an ac-to-dc converter. A big problem is that they include large harmonic components in the input currents. A 12-pulse configuration is useful for reducing them, but it still includes the (12 mplusmnl)th (m: integer) harmonics in the input currents. In order to further reduce the input current harmonics a single-phase square wave auxiliary voltage supply is inserted in the middle dc bus. It reduces harmonics especially the 11th and 13th and the harmonic characteristic becomes almost equivalent to a 24-pulse rectifier. Theoretical analysis of the combined 12-pulse diode rectifier with the auxiliary supply is presented, and a control method of the auxiliary supply is proposed. The reduction in the input current harmonics is verified by simulation and experimental results. The auxiliary supply is also applied to a 12-pulse thyristor rectifier.

An Auxiliary Supply Assisted Input Current Harmonic Reduction for 12-pulse Diode Rectifiers

Diode rectifiers have been widely used for an ac-to-dc converter. One of their problems is that they include large lower-order harmonics in the input current. A 12-pulse diode rectifier is useful for reducing them but it still includes the (12m ± 1)th (m: integer) harmonics. In order to further reduce the input current harmonics a single-phase square wave auxiliary voltage supply is inserted in the middle dc bus of a 12-pulse diode rectifier. The purpose is to obtain a 12-pulse diode rectifier whose harmonic contents are equivalent to those of a 24-pulse diode rectifier. Theoretical analysis of the auxiliary supply assisted 12-pulse diode rectifier is presented and a control method of the auxiliary supply in relation to the dc load current is proposed. Effectiveness of an auxiliary supply is verified by simulation and experimental results.

Frequency-Dividing-Type Three-Phase Inverter with Adjusting Capacitor

Frequency-dividing three-phase inverters, which consist of a single-phase square wave inverter and a three-phase ferroresonant circuit, have excellent efficiency, constant voltage characteristics, and three-phase balance. These advantages make them suitable for use as dc-ac converters and uninterruptible power supplies (UPS). However, when such three-phase inverters are used as UPS devices, a startup circuit with a complicated sequence is needed to reduce the capacitance of the single-phase inverter. If the sequence is simplified a separate problem emerges-the phase sequence of the voltage cannot be determined. In this work, the relationship between circuit imbalance and the phase sequence of three-phase voltages is clarified through both experiments and analyses. The results provide useful information on circuit constants which can be used to reduce costs through simplification of startup circuits for these applications.

調整容量をもつ分周形三相インバータ装置

The frequency-dividing-type three-phase inverter, Which consists of a single-phase square wave inverter and a three-phase ferro-resonant circuit, has excellent efficiency, constant-voltage characteristics, and three-phase balance. These advantages make it suitable for use as a DC-AC converter and a UPS. However, When this three-phase inverter is used as a UPS, a start-up circuit with a complicated sequence is needed to reduce the capacity of the single-phase inverter. If the sequence is simplified, the phase sequence of the voltage cannot be determined, Which creates another problem. In this paper, the relationship between circuit imbalance and the phase sequence of three-phase voltage is reviewed through experiment and analysis. In consequence, the relationship between circuit imbalance and phase sequence is clarified. The results given in this paper provide useful information on circuit constants that can reduce costs by simplifying the start-up circuit of a frequency-dividing-type.

鉄共振回路の分周機能を利用した三相インバータ装置

The ferro-resonant type power supply has high reliability, and is therefore used for power supply to electronic devices. Recently, a three phase inverter has been proposed (called the phase conversion type), which is a combination of a single phase squarewave inverter and a phase converter utilizing the phase conversion function of the ferro-resonant circuit. However, the phase conversion type causes difficulties in that the output voltages are not balanced and that the efficiency remains at about 60%. This paper reports experiments, analysis and review made on a three phase inverter (called the frequency divide type) having a phase converter utilizing the frequency divide function and a single phase square wave inverter in a combination. As a result, the characteristics of the device are clarified, and a high output balance and system efficiency are realized.