Y2 Project Week 3

Week 3

The aim of this week's group project

In this week, we need to solve the problem of the circuit in last week and then finishing the design of the whole circuit.  In addition, we need to think the basic logic of the code for the ARM to realize the function and the code can ensure the ARM can run automatically.

The design of the circuit

Firstly, we discussed the reason why the branch cannot work.  We concluded the reason is that the current of the BJT may be ignored because we just focused on the voltage. In addition, the βof the BJT was ignored as well.  Therefore, we tried to change the value of resistors Rc and Re to test the circuit can work or not.  Secondly, we followed the Teaching Assistant's advice, we simulated the circuit on the computer by using the PSPICE software.  It was found that the circuit can work regularly.  After the simulation, we checked the real circuit and finally found that there is a wrong connection on the breadboard.

After the correction, we designed the whole circuit which will be displayed in the figure 1 and figure 2:

Figure 1

Figure 2

After the connection, we tested this circuit and found it still exist a problem is that the voltage of resistor in cascade circuit is 0 and another resistor have the whole voltage of the cascade circuit.  This problem will be discussed in next week with the supervisor's help.

The code for the ARM 

In this week, we have designed the basic logic of the code.  Firstly, input the voltage and current to the ARM.  Secondly, the ARM will calculate the phase difference and then calculate the power factor.  Thirdly,the output voltage will be added to the BJT in open circuit in order to connect the capacitor to the circuit.  Fourthly, the ARM will repeat the second and third step to find the most suitable power factor value and choose the best capacitor.

The theoretical foundation for the basic logic are that the phase difference can be calculate by the difference value between two signals in time domain and the ARM can provide voltage for BJT by its port.

However, there still exist some problems in details when we tested the code. Firstly, the time cannot be read because it cannot be displayed on the computer screen due to the problem of the port.  Secondly, we did not know the accuracy and the interval time between the detecting the difference value of two different signals in time domain.  Therefore, the code part still need us to work more hard in order to solve these problems.

Figure 3: one part of the code

Y2 Project Week 2

Week 2

Revision:

In this week's lab time, we do the revision for the week 1 in order to remember the key point.  We simulate the circuit in week 1 and then display the wave in oscilloscope to prove the feasibility of this circuit.  The figure is displayed to show the power factor correction:

Figure 1

Design circuit:

After the tutorial with supervisor, we have designed a circuit to the realize the function of change different capacitor to select the best capacitor to ensure the value of power factor is the closest to the 1.  The idea is that we can design three branches in parallel and all of them are controlled by the capacitor.  When the voltage of the bipolar junction transistor reach the specific value, the branch can be connected.  The figure of the branch in the circuit is displayed in the figure 2 and figure 3:

Figure 2

Figure 3

However, when we used this circuit in the real circuit, we found a problem is that there is no change for the voltage of BJT when we changed the supply voltage.  Therefore, we need more discussion and practice in next week in order to solve this problem.

The code for the ARM 

In this week's lab time, we also discussed the code for the ARM in order to realize the function of the ARM can select the best capacitor after the calculation of the power factor.  We searched the Internet and found some similar code in Arduino language which is similar to the ARM.  Therefore, we decided to transfer the code into the ARM language in next week.  

Y2 Project Week 1

Week 1: Basic preparation for the project

Introduction:

This week,we made some preparation for the project.  The aim of this project is to find the solution to improve the efficiency which means the value of power factor should be close to 1.

What we did in this week:

With the guidance of the supervisor, we created a basic structure to realize this function.  The basic structure is displayed in the figure 1.  In this structure, students need to input code to the ARM microcontroller to realize the function of detecting the most suitable capacitor form C1 to C3 in order to obtain the most suitable value which is close to the 1.  In addition, the ARM microcontroller need to have the function of calculating the power factor of the circuit.

Figure 1

After knowing the basic structure, we discussed the method to calculate the power factor.  We found that the voltage and current between ARM and circuit can be used to calculate the power of the circuit.  Then the power factor can be obtained by the equation: Real Power/Apparent Power.
In order to prove this method is practicable or not, we designed a simple circuit which is displayed in the figure2:

Figure 2

Using the oscilloscope to display the voltage and current between ARM and circuit, we found that it is practicable to calculate the apparent power of the circuit.
We will focus on the code of the ARM and the circuit in next week.