LTspice simulation of damped RLC discharge

Thread Starter

frustratedgrape20

Joined Mar 3, 2020
19
Hi,

I am trying to design a RLC discharge circuit such that 2 paralleled capacitors are connected to a coaxial pulse transformer, which in turn, is connected to a RL load. To ensure that the maximum energy is discharged into the RL load, the pulse transformer's primary resistance is matched to the equivalent capacitors' ESR. The pulse transformer is supposed to amp up the current pulsed through the RL load.

After running a simulation, I noticed 4 problems that I can't solve:-

1. the charge voltage of the capacitor is 360V, but yet when I simulate the voltage of the capacitors, I get this:
voltage.jpg

2. the current in the secondary winding should be larger than that in the primary, but the simulation shows otherwise:
current amplification problem.jpg

3. the secondary current doesn't terminate at 0 long after the pulse whereas the primary current does

4. the integration of instantaneous power across the primary winding shows that only 35.86 J is supplied to the primary winding (vs. initial capacitive energy = 388.8 J), which suggests very high impedance mismatch

Individual component parasitics were included into this circuit. However, even if the pulse transformer's parasitics were to be removed, the same 4 problems persist. Could anyone please tell me what I am not doing right?

I have attached the schematic for your reference and thank you for taking the time to read this.
 

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Thread Starter

frustratedgrape20

Joined Mar 3, 2020
19
I am not sure why that's the case, but I am going to reinstall the program now. Meanwhile, here's a screenshot:
Untitled.jpg
N.B.
  • 'Lp' and 'Ls' in the spice directives refer to the respective self-inductance of the primary and secondary windings, whereas​
  • Lpri. and Lsec. refer to the mutually coupled inductance of the primary and secondary winding respectively (smaller than self-inductance due to imperfect coupling); and​
  • K1 and K2 refer to the coupling coefficients of the primary and secondary windings respectively​
 
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Thread Starter

frustratedgrape20

Joined Mar 3, 2020
19
Yes, the picture you posted looks correct. However, shouldn't the secondary current be higher at every point during the discharge, not just when t>0.7 ms? It is my understanding transformers of any kind convert voltages and current so as to preserve power input. Why is this not observed for t<0.7 ms?

The pulse transformer considered has a turn ratio of 6:1. In the absence of parasitics, it will amp up the primary current by a factor of 6. However, the main problem I see is that the current in the secondary is actually lower than the primary's.
 
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