The purpose of this test is to determine whether the cell capacitance is correct. To achieve the purpose of test, we can charge the cells with a certain arm current, and then observe if the final Vcap of the cell equals to the mathematic calculation value. So this test can also test whether the cells can be charged at normal work state.

There are 2 kinds of arm currents can be used here to verify the cell capacitance: 1) a pulse arm current; 2) a sin wave arm current.

Test Based on a Pulse Arm Current

1. System initialization.
2. Set the number of cell per arm wanted to be tested in MMC Parameter block, and change Vb correspondingly.
3. Change the V_cap mode to 0: normal operation.
4. Give ON signal to the second cell gate switch in MMC pulse block (for easy testing).
5. Set up the arm current waveform in console as Table 3.
6. Turn on the current switch to create the current pulse. Pay attention to the V_cap display block. If every time we check or uncheck the boxes for triggering valve currents the V_cap increases 0.1 approximately, the test result is correct, as shown in Figure 28.

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

V_cap=1/C_cell* integral (iarm) +V_{cap_initial}

In this test, C_cell=0.01; I_arm is “A pulse with magnitude of 0.1 and duration of 0.01 s” so integral i_arm =0.1*0.01=0.001; and V_{cap_initial} = 0;

So after the pulse, V_cap = 1/0.01*0.001+0=0.1.

Test Based on a Sine Wave Arm Current

1. System initialization.
2. Set the number of cell per arm wanted to be tested in MMC Parameter block, and change Vb correspondingly.
3. Change the V_cap mode to 3: V_cap reset to a fixed value, at the same time change the V_cap fixed value to 1. After this operation, the V_cap of each cell should be set to 1, the Total V_cap should be set to 10, and the V_mmc still remain 0.
4. Give ON signal to the 2^nd gate switch of cell in MMC pulse block (for easy testing). After this operation, the V_mmc should be changed to 1.
5. To generate a sin wave arm current with magnitude 0.1 and frequency of 50 Hz, set up the Arm Current Generation block as Table 7.

Table 7: Sin Wave Arm Current Generation block setup

   6. Change the V_cap mode to 0: normal operation. After this operation, the V_cap of the 2^nd cell, V_mmc and Total V_cap become sinusoidal (dc component + ac component). For the ac component, the frequency is 50 Hz and magnitude is 0.1.

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

V_cap=1/C_cell* integral (i_arm) +V_{cap_initial}

In this test, C_cell=1/(2*pi*50); I_arm =0.1sin(100*pi*t); so integral i_arm =-0.1cos(100*pi*t)/(100*pi); and V_{cap_initial} = 1;

So after the pulse, V_cap = -0.1cos(100*pi*t)+1=1-0.1cos(100*pi*t).