Week 3

  • 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 hand side aimed to test a MOSFET switch with a capacitor connected in parallel.

 The simulation about eliminating inductive power factor seemed to be successful, as the phase difference was disappeared in the digital oscilloscope (see Figure 3).
Figure 3: Resulting Waveform in Digital Oscilloscope

It can be observed from Figure 3 that there was no phase difference between two wave forms in digital oscilloscope.
  • MOSFET
 The MOSFET was applied to perform a switch functionality in the capacitor bank. To be precise, the capacitor would be short circuited if a DC voltage was applied to the gate of the MOSFET, on the contrary the capacitor would be connected to the load if no DC voltage was applied to the gate. However, as for the simulation about MOSFET switch testing appeared to be failed. The result implies that MOSFET switches may not be used in AC condition, since the waveform of load would be changed to be non-sinusoidal (the yellow waveform in digital oscilloscope). Hence, another method of relay switch was proposed to this project (see Figure 4).
Figure 4: Working Principle of Relay

 The switch would be closed if a DC voltage was applied to the relay, and hence the capacitor could be connected to the load. Nevertheless, various relay has different operating voltage, the maximum DC voltage which ARM Cortex M3 can provide is about 3.7 Volts. Therefore, a specific type of relay will be chosen in the next week. 



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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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