China
Africa
Explore chapters and articles related to this topic
Hello World!
Published in Syed R. Rizvi, Microcontroller Programming, 2016
In the field of Digital Image Processing, a Laplace filter is a filter that seeks out points in the signal stream where the digital signal of an image passes through a pre-set “0” value and marks this out as a potential edge point. Because the signal has crossed through the point of zero, it is called a zero-crossing. We are interested in writing a program that counts the number of times a signal crosses zero. For the sake of simplicity, we assume that the signal values are stored in an array. Create a program flow and describe what kind of branch tests would be performed to accomplish this task.
Impact of Nonlinear Loads on Power System and Equipment
Published in Shoaib Khan, Industrial Power Systems, 2018
Power electronic equipment is susceptible to misoperation if there are significant levels of harmonic distortion. Some of the control systems for power electronic devices use zero crossing detection to control switching. Harmonic distortion can result in shifting of the voltage zero crossing points, and these changes can be critical for many types of electronic control circuits. Also, if incorrect switching occurs, more harmonics can be produced, compounding the problem.
Electric Machines and Power Systems
Published in Mohd Hasan Ali, Wind Energy Systems, 2017
Zero-point quenching—contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. The zero crossing occurs at twice the line frequency (i.e., 100 times per second for 50 Hz and 120 times per second for 60 Hz AC)
Performance Investigations of Novel PWM Control Strategies for Fundamental Fortification in Single-Phase Matrix Converter for Cyclo-Conversion Operation and FPGA Implementations
Published in Electric Power Components and Systems, 2022
S. Thamizharasan, C. Krishnakumar
The proposed methods have been realized using a base PWM generator, phase synchronization unit followed by logical circuits. Figure 3 illustrates the block diagram representation of the base PWM generator. The base PWM block comprising of square pulses (S and Q) of input supply (fs) and output (fo) (load voltage) frequencies. The main function of zero crossing detector (ZCD) is to convert input sinusoidal supply voltage (scaled down through step down transformer) to digital square wave of the same frequency using comparator circuits for phase synchronization of pulses obtained using digital logic circuits in response to supply voltage for proper switching of power devices. The signal (Q) should be synchronized with the input voltage response to trigger the switches at either square pulse or PWM over one complete fundamental cycle in the respective sector following the proposed PWM patterns. The signal (P) is a PWM pulse acquired through a direct comparison of modulating sinusoid and triangular carrier function. The signals (P, Q and S) generate the proposed patterns (I and II) using the multiplexer circuit depicted in Figure 4 which consists of logic gates to generate the required gating pattern to turn on/off each switching device (S1–S4) in the matrix converter.
State-of-the-art research on micro grid stability: a review
Published in International Journal of Ambient Energy, 2019
A. Nageswara Rao, P. Vijayapriya, M. Kowsalya
Observes phase difference between inverter terminal voltage and its output current that occurs during islanding due to Q mismatch.Phase angle can change faster than frequency, so faster island detection is possible than earlier.Can be implemented easily using zero-crossing detection synchronous methods.Nowadays, fast PLLs are used for synchronisation, so the phase locked loop forces the current to resynchronise with the voltage after islanding.The solution is to have two PLLs: For fast synchronisation (with settling time of 50–100 ms)Very slow for islanding detection (with settling time of 1–2 s) which filters out phase jump. So, comparing both PLLs gives the phase jump.
Adaptive phasor estimation technique during off-nominal frequency for numerical relays
Published in Journal of Information and Telecommunication, 2018
Omar Sami Thiab, Łukasz Nogal, Ryszard Kowalik
On this algorithm, zero-crossing method is used to calculate frequency before any phasor estimation process. The zero-crossing technique can be implemented either in hardware or software on the numerical relay. The time between two consecutive zero crossing is used to find the time of one cycle and frequency. The fundamental frequency is estimated on this method bywhere M is the number of zero crossings;tM time of the mth zero crossing;t1 is the time of the first zero crossing;f is the estimated frequency.