scholarly journals Low-Frequency Signal Sampling Method Implemented in a PLC Controller Dedicated to Applications in the Monitoring of Selected Electrical Devices

Electronics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 442
Author(s):  
Marcin Jaraczewski ◽  
Ryszard Mielnik ◽  
Tomasz Gębarowski ◽  
Maciej Sułowicz

High requirements for power systems, and hence for electrical devices used in industrial processes, make it necessary to ensure adequate power quality. The main parameters of the power system include the rms-values of the current, voltage, and active and reactive power consumed by the loads. In previous articles, the authors investigated the use of low-frequency sampling to measure these parameters of the power system, showing that the method can be easily implemented in simple microcontrollers and PLCs. This article discusses the methods of measuring electrical quantities by devices with low computational efficiency and low sampling frequency up to 1 kHz. It is not obvious that the signal of 50–500 Hz can be processed using the sampling frequency of fs = 47.619 Hz because it defies the Nyquist–Shannon sampling theorem. This theorem states that a reconstruction of a sampled signal is only guaranteed possible for a bandlimit fmax < fs, where fmax is the maximum frequency of a sampled signal. Therefore, theoretically, neither 50 nor 500 Hz can be identified by such a low-frequency sampling. Although, it turns out that if we have a longer period of a stable multi-harmonic signal, which is band-limited (from the bottom and top), it allows us to map this band to the lower frequencies, thus it is possible to use the lower sampling ratio and still get enough precise information of its harmonics and rms value. The use of aliasing for measurement purposes is not often used because it is considered a harmful phenomenon. In our work, it has been used for measurement purposes with good results. The main advantage of this new method is that it achieves a balance between PLC processing power (which is moderate or low) and accuracy in calculating the most important electrical signal indicators such as power, RMS value and sinusoidal-signal distortion factor (e.g., THD). It can be achieved despite an aliasing effect that causes different frequencies to become indistinguishable. The result of the research is a proposal of error reduction in the low-frequency measurement method implemented on compact PLCs. Laboratory tests carried out on a Mitsubishi FX5 compact PLC controller confirmed the correctness of the proposed method of reducing the measurement error.

2013 ◽  
Vol 391 ◽  
pp. 271-276
Author(s):  
Peng Li ◽  
Ning Bo Wang ◽  
De Zhi Chen ◽  
Xiao Rong Zhu ◽  
Yun Ting Song

Increasing penetration level of wind power integration has a significant impact on low-frequency oscillations of power systems. Based on PSD-BPA simulation software, time domain simulation analysis and eigenvalue analysis are employed to investigate its effect on power system low-frequency oscillation characteristic in an outward transmitting thermal generated power bundled with wind power illustrative power system. System damping enhances markedly and the risk of low-frequency oscillation reduce when the generation of wind farm increase. In addition, dynamic reactive power compensations apply to wind farm, and the simulation result indicates that it can improve dynamic stability and enhance the system damping.


2015 ◽  
Vol 2 (3) ◽  
pp. 140550 ◽  
Author(s):  
Isaac Amidror

Sampling moiré effects are well known in signal processing. They occur when a continuous periodic signal g ( x ) is sampled using a sampling frequency f s that does not respect the Nyquist condition, and the signal-frequency f folds over and gives a new, false low frequency in the sampled signal. However, some visible beating artefacts may also occur in the sampled signal when g ( x ) is sampled using a sampling frequency f s which fully respects the Nyquist condition. We call these phenomena sub-Nyquist artefacts . Although these beating effects have already been reported in the literature, their detailed mathematical behaviour is not widely known. In this paper, we study the behaviour of these phenomena and compare it with analogous results from the moiré theory. We show that both sampling moirés and sub-Nyquist artefacts obey the same basic mathematical rules, in spite of the differences between them. This leads us to a unified approach that explains all of these phenomena and puts them under the same roof. In particular, it turns out that all of these phenomena occur when the signal-frequency f and the sampling frequency f s satisfy f ≈( m / n ) f s with integer m , n , where m / n is a reduced integer ratio; cases with n =1 correspond to true sampling moiré effects.


2021 ◽  
Vol 252 ◽  
pp. 02001
Author(s):  
Ping He ◽  
Mingming Zheng ◽  
Zhao Li ◽  
Qiyuan Fang ◽  
Xiaopeng Wu

The new energy represented by strong random wind power connecting to the power system may make the problem of inter-area low-frequency oscillation more serious. In this paper, a DFIG-PSS controller based on virtual impedance is constructed to solve the low-frequency oscillation problem in the wind power system. The step response of PSS-VI was carried out to test the effect of the controller to verify the advantages of PSS-VI than traditional PSS. The input signal of PSS-VI which is a controller based on PSS installed virtual impedance is the active power of DFIG. The output signal of PSS-VI is added to the reactive power control loop of rotor side controller of DFIG. DFIG-PSS-VI was built in Digsilent/Powerfactory software, and the simulation was carried out on the system of 4 machines and 2 regions. It is verified that PSS-VI can improve the low-frequency oscillation of wind power system.


2012 ◽  
Vol 12 (15) ◽  
pp. 6757-6773 ◽  
Author(s):  
M. Saunois ◽  
L. Emmons ◽  
J.-F. Lamarque ◽  
S. Tilmes ◽  
C. Wespes ◽  
...  

Abstract. Measurements of ozone vertical profiles are valuable for the evaluation of atmospheric chemistry models and contribute to the understanding of the processes controlling the distribution of tropospheric ozone. The longest record of ozone vertical profiles is provided by ozone sondes, which have a typical frequency of 4 to 12 profiles a month. Here we quantify the uncertainty introduced by low frequency sampling in the determination of means and trends. To do this, the high frequency MOZAIC (Measurements of OZone, water vapor, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) profiles over airports, such as Frankfurt, have been subsampled at two typical ozone sonde frequencies of 4 and 12 profiles per month. We found the lowest sampling uncertainty on seasonal means at 700 hPa over Frankfurt, with around 5% for a frequency of 12 profiles per month and 10% for a 4 profile-a-month frequency. However the uncertainty can reach up to 15 and 29% at the lowest altitude levels. As a consequence, the sampling uncertainty at the lowest frequency could be higher than the typical 10% accuracy of the ozone sondes and should be carefully considered for observation comparison and model evaluation. We found that the 95% confidence limit on the seasonal mean derived from the subsample created is similar to the sampling uncertainty and suggest to use it as an estimate of the sampling uncertainty. Similar results are found at six other Northern Hemisphere sites. We show that the sampling substantially impacts on the inter-annual variability and the trend derived over the period 1998–2008 both in magnitude and in sign throughout the troposphere. Also, a tropical case is discussed using the MOZAIC profiles taken over Windhoek, Namibia between 2005 and 2008. For this site, we found that the sampling uncertainty in the free troposphere is around 8 and 12% at 12 and 4 profiles a month respectively.


Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2435
Author(s):  
Ming Yang ◽  
Wu Cao ◽  
Tingjun Lin ◽  
Jianfeng Zhao ◽  
Wei Li

Low frequency oscillations are the most easily occurring dynamic stability problem in the power system. With the increasing capacity of power electronic equipment, the coupling coordination of a synchronous generator and inverter in a low frequency range is worth to be studied further. This paper analyzes the mechanism of the interaction between a normal active/reactive power control grid-connected inverters and power regulation of a synchronous generator. Based on the mechanism, the power system stabilizer built in the inverter is used to increase damping in low frequency range. The small-signal model for electromagnetic torque interaction between the grid-connected inverters and the generator is analyzed first. The small-signal model is the basis for the inverters to provide damping with specific amplitude and phase. The additional damping torque control of the inverters is realized through a built-in power system stabilizer. The fundamentals and the structure of a built-in power system stabilizer are illustrated. The built-in power system stabilizer can be realized through the active or reactive power control loop. The parameter design method is also proposed. With the proposed model and suppression method, the inverters can provide a certain damping torque to improve system stability. Finally, detailed system damping simulation results of the universal step test verify that the analysis is valid and effective.


Sign in / Sign up

Export Citation Format

Share Document