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Why does the repeatable damped sinusoidal controlled current signal deliver AC with an increasing DC signal across the capacitor?

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Lucas Machado
Lucas Machado on 23 Sep 2020
Edited: Aman Vyas on 7 Oct 2020
I am trying to charge a capacitor using repeatable damped sinusoid current signals from a piezoelectric bender (Figure at left) - Result of the free vibration of the piezo beam (Current source plus piezoelectric capacitance in parallel - Figure at Right). The current from the piezo bender is rectified and used to charge a capacitor. I have simulated it Matlab/Simulink [See model in Figure 1] but it yields a weird behaviour when the input is a damped sinusoid current signals. The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely.
[See Figure 2]- >This is the expected behaviour (From a sinusoidal no-damped current input): Graph1: Voltage Across Cp1(Piezo Bender) Graph2: Voltage Across Capacitor that is being charged.
[See Figure 3]->However, this is what I get (The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely): Graph1: Voltage Across Cp1(Piezo Bender) Graph2: Voltage Across Capacitor that is being charged.
Would you have any suggestion or hint about what is happening here? Thank you very much for your help in advance.
Best wishes, Lucas

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Answers (1)

Aman Vyas
Aman Vyas on 7 Oct 2020
Edited: Aman Vyas on 7 Oct 2020
Hi,
This problem could occur as a result of many things:
1) The value of capacitor could be wrongly set may be reduced too much because of which before discharging takes place next set of cycle with greaat surge might be coming.
2) May be both of them might be correct and fig 1 may be zoomed version of fig 2 as time values are not visible.
Model appears fine to me, you will try to check the values given to the blocks in the model and also some timing stuff like sample time or simulation time.
Hope it helps !

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