Cell Shunt Resistor Verification

This test is designed to test whether the value of resistance in shunt with the cell capacitor is correct or not. To achieve the test purpose, we can charge the cells with a certain arm current, and then observe whether the final V_cap of the cell equals to the mathematic calculation value. This test is just like test in section 3.4.

System initialization.
For easy testing, set the value of resistance in shunt with the cell capacitor in MMC Parameter block to 10ohm.
Set the number of cell per arm wanted to be tested in MMC Parameter block, and change Vb correspondingly.
Change the V_cap mode to 0: normal operation.
Give ON signal to the gate of MMC cells need to be test in MMC pulse block.
To generate an arm current pulse with magnitude 0.1 and duration 25s, set up the Arm Current Generation block as Table 8.

Table 8: Arm Current Generation block setup

variables	Set value	reason
DC current	ones(6,1)*0.1	(More details are related in section 2.1.1)
AC magnitude	ones(6,1)*0
Frequency	ones(6,1)*50
Form of the current	1: Current with a duration
Pulse duration	25

7. Check the box for current in each valve to generate a current pulse. Pay attention to the arm current scope and the V_cap display block. When the arm current is set to 0.1, the MMC cells are charged. When the arm current return to 0, the MMC cells are discharged through the resistance in shunt with the cell capacitor. If the final value of the V_cap is 1 when the arm current is 0.1 (as shown in Figure 30), it shows the value of the resistance in shunt with the cell capacitor can be set correctly. If the value of V_cap can return to 0, it shows the connection of the resistance in shunt with the cell capacitor is correct.

It should be noted that the mathematic calculation of the final V_cap value is below:

V_{cap_final}=i_{arm_DC}*R_{cell_C}

In our test, R_{cell_C}=10; I_arm is “A pulse with magnitude of 0.1 and duration of 25s” so during 25s, the i_arm can be treated as a DC current i_{arm_DC}, and i_{arm_DC} = 0.1;

So the final V_cap during 25s is: V_cap = 10*0.1=1.

For An order RC circuit, there is a time constant (t) describing the charging and discharging time of the capacitor.

t=R*C

According to the mathematical function of the order RC circuit, during the charging process, after 5t time, the difference between the capacitor current voltage value and final voltage value is just 0.7% of the final value. So the charging process can be thought as having been finished. Here the time constant t=10*0.01=0.1s, which is much less than 25s. So at the end of 25s, the capacitor is almost charged to full.

The better way to check whether the value of the resistance in shunt with the cell capacitor is correct or not in this test is the V_cap-time curve. Due to the asynchronous communication between the target and console, it is hard to see a complete V_cap-time curve in the console. So the observation of the final value of V_cap become the only way here.