Low-Frequency Signal Sampling Method Implemented in a PLC Controller Dedicated to Applications in the Monitoring of Selected Electrical Devices
| Autor: | Tomasz Gebarowski, Marcin Jaraczewski, Maciej Sułowicz, Ryszard Mielnik |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Computer Networks and Communications
Computer science low-frequency sampling method power measurement lcsh:TK7800-8360 measurement of current 02 engineering and technology Signal power Root mean square Electric power system Sampling (signal processing) Aliasing 0202 electrical engineering electronic engineering information engineering Electronic engineering Nyquist–Shannon sampling theorem Electrical and Electronic Engineering Total harmonic distortion Observational error compact PLC lcsh:Electronics Sampling (statistics) 020206 networking & telecommunications controllers AC power 021001 nanoscience & nanotechnology Hardware and Architecture Control and Systems Engineering Harmonics voltage Signal Processing 0210 nano-technology measurement errors |
| Zdroj: | Electronics Volume 10 Issue 4 Electronics, Vol 10, Iss 442, p 442 (2021) |
| ISSN: | 2079-9292 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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