Projects:2019s1-191 Microcontrollers for the Measurement of Power Quality
Contents
Introduction
Power quality is a measurement of standard reliability of voltage, frequency, pure sinusoidal waveform and uninterrupted supply in electric power systems. As power network evolves, involving the usage of non-linear loads in power networks which made the power quality problem becomes more acute which is the possible of a part of power network become disengaged or known as "islanded". The islanding power network may cause issues on voltage and frequency which the problem in electric power system can be indicated by the changes of Rate of Change of Frequency (RoCoF) which could indicate instability in power systems. On the other hands, the recent development of microelectronics which made powerful computational power available at very low cost. There are much more possible ways to reduce this problems and one of those is by early detection which this project is to make an early indicator to detect Rate of Change of Frequency (RoCoF) using a microcontroller with embedded Phase-Locked Loop integrated circuit to estimate Rate of Change of Frequency (RoCoF) by measuring Real and Reactive Power, Power Factor, Power Angle and Harmonics.
Project Team
Students
- Tony Chen
- Hafiz Syahmi Hanizar
- Muhammad Haziem Rosdi
Supervisor
Dr. Andrew Allison
Definitions and Abbreviations
- RoCoF = Rate of Change of Frequency
- PLL = Phase Locked Loop
Aim
To measure Real and Reactive Power, Power Factor, Phase difference for estimating Rate of Change of Frequency. This project is also intended for proposing possible alternative for measuring RoCoF at low costs by implementing analog electronics with micro-controller.
Background
Power Quality
Power Quality is a standard requirement for measuring the reliability of the power delivered to consumers, which the parameters are voltage, frequency, harmonics in waveform, and service availability including Real and Reactive Power, Power Factor and Phase Angle.
Signal Processing
This project implemented Walsh Function which is known as square-wave function where the maximum and minimum amplitude would be at +1 and -1 respectively. Walsh Function helps to reduce the amount of computational load, where the calculation involved is simpler than Fourier Transform for signal measurement.
Phase-Locked Loop
Phase-Locked Loop is a feedback control loop circuit which is used to adjust and match the frequency of input signal. The Phase-Locked Loop consists of three main component which are Phase Detector, Low-Pass Filter and Voltage-Controlled Oscillator.
A signal is injected to one of the input pin of Phase Detector. The Phase Detector compares the phase difference between two signals from external sources and the output from the oscillator. The Phase detector will produce average dc error voltage, Ue when there is phase difference between two signals. The error voltage will be fed into Low-Pass Filter to filter out any higher frequency components and clean the dc output. The filtered signal, Uf is then fed into the Voltage-Controlled Oscillator which it generates pulse signals based on the external RC components programmed on the Phase-Locked Loop circuit and voltage input from the filtered signal. The VCO output is then fed into the phase detector which completes the feedback loop operations.
Analog Circuit Design
The component used for design is consists of capacitors, resistors, LM393N dual comparator and CD4046B Phase-Locked Loop.
Signal Theory
The time requirement for the PLL circuit to settle in the transient response is about 10 seconds. The reason for the long settling time is to ensure that the PLL will stable in the determined frequency range.
Micro-controller
Micro-controller used for this project is Arduino UNO. The model is one of the most popular used by the developer. We believe that this Arduino has the ability to carry out the aim of this project and try to maximise it's potential.
In order to protect the Arduino board from damage, it will stacked with a shield board. The PLL circuit will be placed and embedded to the shield board instead.
References
[1] Best, R. (2003). Phase-Locked Loops Design, Simulation and Applications. 5th ed. Oberwill, Switzerland: McGraw-Hill, pp.7-109, 327-337.
[2] Berlin, H. (1989). Design of phase-locked loop circuit, with experiments. 1st ed. Indianapolis, Indiana: Sams.
[3] Roberts, M. (2012). Signals and systems. 2nd ed. New York: McGraw-Hill.
[4] T. Gönen, Electric power distribution system engineering, 1st ed. New York, McGraw Hill: 1986.
[5] J. Smith, Modern communication circuits, 1st ed. Boston, Massachusetts, WCB/McGraw-Hill: 1998.
