Last part: The development of the AC load part

After the other stages were designed successfully and tested well, it was not difficult to design and test the AC load part. The final designed circuit is shown below:

The RLC AC load value is given: the active power P is: 500 W; the inductive reactive Power QL is 200VAr; the capacitive reactive power QC is: 500VAr.

It was simulated successfully. The curve of the line to line voltage at the output of the inverter and the voltage at ac load is shown below:

Another scope was also added to display the three phase line to line voltage:

The output at dc load part is also display in the following figure:

Test for the output of the universal bridge

Before developing the AC load part circuit, we began to design another circuit to test the universal bridge output which is connected to a 6 pulses PWM Generator. The designed circuit was shown below:

The line to line voltage and the line to line current in the three phase system is shown below:

Simulation model of the dc load part

After the dc load part was built successfully which is shown in the former blog, we begun to simulate the photovoltaic voltage output and the dc load output.

The curve of the current-voltage characteristics of PVA and the power-voltage characteristic of PVA is shown below:

Then the curves of the Time response of the PVA voltage, PAV current, PAV power and voltage at the dc load is also displayed below:

Test the model to supply for the DC load.

After the PVA model is built successfully, we can use it as a generator to supply power to a simple DC load. Today we were tried to design the dc load circuit and connect it to the PVA model. The designed circuit is shown below:

At the beginning, when we tested this circuit, the result is terrible and we can’t get stable output and the curves we obtained changed too much. They were far away from what we expected. Then we discussed this problem with our supervisor Dr Tang. After that, we found that the problem may caused by the wrong design in the filter so the next work we should do is to improve the design in filter.

In the above figure, it can be seen that in front of the filter, there is a diode.  It also has a little affect on the output voltage so we designed a circuit to test the output of this diode. The circuit is shown below:

When we simulated this design, the following figure can be obtained.

In the figure, it can be seen that at the beginning the voltage in diode increase fast and then it remains stable and to be 0.8 voltage. Thus at the dc load, the voltage should decrease fast at the beginning and then immediately the voltage reaches at a stable state. The initial value of the current is assigned to 0. In this case, the voltage has its maximum value. 

The development of the PVA functional model for the Simulink environment

Recently we are mainly contributed to design the PVA MODEL for GUI environment. It is the main part and the objective of this project is to develop the PVA functional model to simulate the photovoltaic solar cell output. This part uses the modeling stage 2 as a subsystem. The design circuit is shown below:

The Powergui block is used and necessary for any simulink model which contains SimPowerSystems blocks. It can store the equivalent simulink circuit. The other part in this model is mainly used to assign values to each variable in the photovoltaic cell voltage. In the above figure, it can be seen that Ns represents the number of the solar cells in series and is 8 in this model. Np represents the number of the solar cells in parallel and is 1. Tx and Sx are used to represent current value of temperature and solar irradiation and they are 15.9908 centigrade and 102.9493. The temperature is converted into Kelvin in equation of this model. The referent temperature Tc and irradiation Sc is given in the modeling stage 2 and the value is 20 centigrade and 100. According to the equation 1 which is:

It can be calculated that the maximum current is I_c=I_ph+I₀=5.1352 and the minimum current is: I_c=0. To make the voltage positive we use a Saturation component to limit the current in the range of 0 to 5.1. Then it can be obtained that the maximum voltage is: V_c=229.57 and the minimum voltage is: V_c=116.87.

The development of the modeling stage 2

Today, we were tried to design the modeling stage 2. The modeling stage 1 is a subsystem of the modeling stage 2 so this stage should contain the block of stage 1. This stage is used to multiply the cell voltage to form the full array voltage and then divide the array current by the number of the cell in parallel to obtain the cell current. And solar cells which we researched have 8 photovoltaic cells in series and only 1 line in parallel. The block circuit is shown below:

In this circuit, there are several new blocks used. This afternoon, we met our supervisor Dr Tang to discuss the problems we encountered when we assigned value to these blocks parameters. For the controlled voltage source is just used to change the input value into voltage value so the parameter in this block doesn’t need to change. For the Saturation part, only the current flow into this part, so the maximum and minimum value of the current should the calculated. According to the voltage equation, it can be found that the maximum value of current is 5.135 and the minimum value of the current is 0. Then for the transport delay part, Mr Tang suggested us to set the time delay to be 0.0001 so that enough test points can be got.

The development of the Modeling stage 1

Today, we used the Matlab-Simulink Gui Environment to build the first part of the model. The first modeling stage is used to simulate the output voltage and current of one single solar cell. This part is masked as one of subsystems of the last stage. The first stage was built successfully and the Simulink circuit is shown below.

For the Equation1 block and the Effect of Temperature & Solar Irradiation block, we also had two methods to build this part: One is to use Matlab Fun block to build this part and the other method is to use the math operation model in the Simulink to build the output voltage equation and the equation for the effect of the temperature and solar irradiation.

The code by using the first method is shown below:

The connection by using the second method is displayed:

Then this afternoon, we met with our supervisor Dr Tang to discuss about these two methods. We want to find which method is better. Mr. Tang advised us to use the Matlab function block to build this part because there is less component used in the method and this will occupy less CPU space and thus the processing speed can be improved. After the meeting, we tested these two circuits and it was observed that the first design circuit has high performance and faster processing speed. Thus we adopted the first method to develop this part.