Week 4

  • The aim of week 4
The main task of this week is to connect the capacitors bank in series with the load components hence can be used to correct the power factor. The second objective is to test the programme complied in the ARM MCU of which the main functions was to detect the phase difference and to control the capacitors bank.
  • Experiment procedures
In the morning section, the main activity was to connect the capacitors bank in series with the load inductors. By converting the phase differences between the voltage and the current to the power factor, the required capacitance to correct the power factor can be calculated. Then the ARM MCU can give the active low signals to the certain branches of the capacitors which can then be enabled to compensate the power factor.

Figure 1. Test of the relay module
  • Trouble Shooting
The first problem encountered in this week was that the measured power factor using the oscilloscope was much higher than the calculated power factor. After using the RLC meter to measure the internal resistance of the inductor, it was found that the internal resistance of the inductor was quite high, which was approximately 40 Ω. Taking this factor account to calculation, the experimental results then conformed to the calculated results.
The second problem was that the ARM MCU was hard to recognize the input signals after rectified by the diodes. After removing the diode, the input signals were surprisingly recognized by the MCU. Hence, the phase difference between the voltage and current can be distinguished by the MCU.
  • Conclusions and Further Tasks
The main achievement of this week was constructed the whole circuit of the project. The function of each individual part of the circuit was tested to be successful. However, there are still some issues existed in the software part which the ARM MCU cannot recognize the power factor steadily. Also, some part of the circuit was connected in such disordered sequences. Hence, the emphasises of the next week are to adjust the programme while measuring the power factor using a better algorithm and reconstruct the circuit to make it clearer to be visualized.

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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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