I am having trouble visualizing the current ig. I think it would be similar to Figure 19.8, but since it is a half bridge, vs will not go negative, and therefore ig cannot go negative. Also, when vs is zero, ig would also be zero.
Is the current through Cb and L like a sin wave (positive and negative)?
If ig is zero for more than half the period, how does this correlate to the model derived in class? Do I need to determine an equation for the fundamental component, then integrate to get the average ig?
How do you find the value of the phase shift?
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(A) First comment is correct. I also say Ig is zero from DTs to Ts
(B) Yes, all the switching produces. Note that vs(t) in the problem (second figure) has an average value associated with it. Thus you need a blocking capacitor (Cb) in the circuit to remove this average value. By removing this "shift" in the graph, the voltage beyond vs(t) will oscillate above and below. You want a pure ac signal going into the resonant tank.
Not sure how to answer your 3rd set of questions (maybe the above clarified some things).
Regarding the phase shift, and from what i understand, we treat it as a variable. We know their is a face shift and carry it through the analysis. All you really care about is the transfer function across the resonant tank because this gives you the dynamics of the circuit. You also can't determine the phase shift because you don't know if the resonant tank is acting inductively or as a capacitance.....this depends on the transfer function and the switching frequency.
This is at least what I understand from flipping through this chapter so far.
Should we consider C_b part of the switching network and not the resonant tank? It seems we can still approximate the v_s waveform as the fundamental component shifted up. It also seems to me that the current going into C_b would the i_g waveform with a phase shift. Is this reasonable?
I am not sure how to compute the i_g waveform while v_s = V_g. I tried pushing the capacitor through the transformer and use the inductor and capacitor equations to determine the current, but I am stuck on how to do this.
19.1a ig-waveform:
Resonant tank looks inductive above the resonance (from resonant tank ||Zin(s)||). Voltage vs(t)_fundamental=vs1=(2Vg/pi)*sin(ws*t) is driving the resonant tank. Tank response is the current is1(t)=Is1*sin(ws*t-phi_s), since voltage vs1(t) lead the current is1(t).
0<t<Ts/2: ig(t)=is1(t)=current going into the Cb(ig and is1 are in phase), vs(t)=Vg
Ts/2<t<Ts ig(t)=0 (since Q1 and D1 are off), vs(t)=-Vg
Isn't vs(t) given and equal to zero when Ts/2<t<Ts? I would think that Voltage vs(t)_fundamental=vs1=(2Vg/pi)*sin(ws*t) + Vg/2 because it has a dc offset of Vg/2.
Does ig(t) go below zero during the phase shifted portion of the waveform? How do you handle the dc offset? If the voltage has a dc offset, does the current have a corresponding dc offset?
How do you calculate Is1?
Since ig(t) is zero during Ts/2<t<Ts, and we know current will continue to flow through is(t), how do I correlate is(t) to ig(t) to develop my dependent current source for my model?
I agree with your vs_fundamental Jessica.
Could we use a sinusiodal approximation for the i_g waveform to correlate it with the i_s1 waveform for the model, even though i_g is neither sinusoidal nor square?
I think the current source will be the same as in text that is (2Is1/pi)cos(phis). Because since ig=0 for Ts/2<t<Ts we still get avg(ig) by evaluating Is1*sin(wst-phis).
Yusuf, why would the current source be the same as the text? The waveform zero for Ts/2<t<Ts, and doesn't it have a dc offset?
Also, could somebody provide a refresher on how we build this model of dependent sources? How do you assign the voltage/current sources, and how do you pair them together? It doesn't seem to work the same as it did in the previous course.
Is the transformer included in the tank network? How do we account for that?
I basically walked through the first example from the class notes of how to build the model, and it seemed to work out very much the same way for the half bridge.
For my current source I took the average by integrating over the whole period, including the zero current half, and this gave me basically half of the previous answer.
Hi to all on campus students. I am off campus student and trying to keep up with you. For 19.1 a)the answer I see to be similar to fig. 19.8 but correlate to the simulation that has been provided to us (LT Spice). Vs point flies from +Vg to 0 however the current in Cb changes its flowing (voltage polarity). Run the simulation and u get the answer.
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