Week 2

  • The aim of Week 2
In this week, we need to find out how to use zero crossing detector and design a circuit to measure the   phase difference between voltage and current on the transmission line. We decided to simulate the circuit on Proteus first and then build the actual circuit on the board.
  • Time arrangement 
Feb. 5th-Feb. 6th: Try to apply a zero crossing detector (AQ-H) to find out the zero points of voltage and current on the transmission line. However, after several experiments, we found out that this item could not achieve the function as expected, so we started to look for other methods of measurement.

Feb.7th: Group discussion and find a possible method of phase difference measurement by using to voltage comparator.

Feb.8th: Use software Proteus to design and simulate an appropriate circuit and arrange a group meeting with our academic advisor.

Feb.9th: Try to add some electrical components to the basic detector circuit to avoid unexpected interference and build an actual circuit on the breadboard according to the simulation results.
  • Achievements
Before the experiment, we first searched on the Internet to find some possible ways to realize the function of phase difference detector. After that, we chose a certain circuit shown in figure 1 to realize the function.
Figure 1. Comparator connection

The upper part of this diagram is a circuit used to find out zero points of input voltage and generate a square wave which reach high level at zero points, while the lower part of this diagram is a circuit used to find out zero points of input current, because the oscilloscope could only detect voltage signal, a small register should be connected in the circuit. In this way, as a result of the register will not change the phase, the phase of  input current is the same as the voltage across the register. As a result, we used the Proteus to simulate this kind of circuit and the results of simulation was shown below and two types of comparator was applied to qualify whether the results was the same as expected.

The design circuit using LM358N is displayed in figure 2.
Figure 2. Simulation Circuit Connection of LM358N 


   The simulation result in Proteus is shown below.

Figure 3. Simulation Result of Proteus

After the success of simulation, we started to build the actual circuit. However, it is a difficulty that there are a large amount of elements affecting the experimental results. The oscilloscope only showed some square waves with some unexpected clips and curves. Next week, we need to find out the solutions to avoid interference and try to complete other parts of the circuit.

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Week 1

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The aim of Week 1 In the first week, the basic circuit model and theoretic information were determined. Several tests were conducted which indicated that the method to realize power factor correction needed to reconsidered and  improved.  Background theory Power factor is defined as the ratio of real power to the apparent power which is utilized to measure the efficiency of the power system. An triangle could be used to demonstrate the relationship between these parameters in the figure 1.  Figure 1. Triangle relationship of Power The value of power factor will tend to 1 if the efficiency of the system is high enough. Therefore, in order to improve the operating efficiency, the reactive power ought to be reduced to minimize the theta in the triangle.  Testing and Results The most straightest way to increase PF is to add capacitors to reduce Q. In this project, capacitor banks controlled by BJT were utilized to compensate the negative rea...
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Week 5

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The aim of week 5 The aim of this week is to combine the two sections of the project and improve the compensation section.  Procedure All components related to this project have been ­connected together and tested in this week.  Initially, the internal resistance of the previous inductor was far bigger than the pure resistors in the load. This led that the phase difference would be too small to be corrected. In this week, a transformer was utilized as an 7.5 mH inductor. Therefore, the measured power factor before the capacitor is 0.9106 which is displayed in the figure 1. Figure 1. Measured Power Factor without Capacitors In the next step, the value of the capacitors was not large enough to correct the phase difference. Hence, capacitors were changed to larger ones. Therefore, four 2.2mF compensation capacitors were utilized and connected into the circuit.  Finally, the program of measuring the power factor and controlling the capacitors bank w...
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Week 3

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The aim of Week 3 The aim of this week is to complete the circuit design of the control circuit with MOSFET and test the code measurement. Achievements The voltage comparators (LM358N) were successfully applied to the whole circuit in this week. The phase difference between the voltage and current displayed on the oscilloscope is shown in the figure below.  Figure 1. Phase Difference between the Voltage and Current Hence, the next step of this project is to connect capacitors to the load in parallel so as to eliminate the inductive power factor. In other words, the phase difference between the current and voltage should be approximately zero. An updated circuit produced by software Proteus 7.8 can be observed in Figure 2. Figure 2: Updated Circuit with Capacitors and Switch Testing It can be seen that the circuit on the right hand side aimed to eliminate the inductive power factor with capacitors connected in parallel. In addition, the circuit on the left ha...
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