Unterschiede
Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
Beide Seiten der vorigen Revision Vorhergehende Überarbeitung Nächste Überarbeitung | Vorhergehende Überarbeitung | ||
electrical_engineering_2:inductances_in_circuits [2022/05/23 01:59] – tfischer | electrical_engineering_2:inductances_in_circuits [2024/06/06 11:08] (aktuell) – [Exercises] mexleadmin | ||
---|---|---|---|
Zeile 1: | Zeile 1: | ||
- | ====== | + | ====== |
- | ===== 5.1 Basic Circuits ===== | + | ===== 6.1 Basic Circuits ===== |
Focus here: uncoupled inductors! | Focus here: uncoupled inductors! | ||
- | ==== 5.1.1 Series Circuits ==== | + | ==== 6.1.1 Series Circuits ==== |
- | Based on $L = {{ \Psi(t)}\over{i}}$ and Kirchhoff' | + | Based on $L = {{ \Psi(t)}\over{i}}$ and Kirchhoff' |
- | Since the current must stay constant in the series circuit, the following applies for the equivalent inductor of a series connection of signle | + | |
- | \begin{align*} | + | \begin{align*} L_{\rm eq} &= {{\sum_i \Psi_i}\over{I}} = \sum_i L_i \end{align*} |
- | L_{eq} &= {{\sum_i \Psi_i}\over{I}} = \sum_i L_i | + | |
- | \end{align*} | + | |
- | A similar result can be derived from the induced voltage $u_{ind}= L {{di}\over{dt}}$, when taking the situation of a series circuit (i.e. $i_1 = i_2 = i_1 = ... = i_{eq}$ and $u_{eq}= u_1 + u_2 + ...$): | + | A similar result can be derived from the induced voltage $u_{ind}= L {{{\rm d}i}\over{{\rm d}t}}$, when taking the situation of a series circuit (i.e. $i_1 = i_2 = i_1 = ... = i_{\rm eq}$ and $u_{\rm eq}= u_1 + u_2 + ...$): |
\begin{align*} | \begin{align*} | ||
- | & u_{eq} | + | & u_{\rm eq} |
- | & L_{eq} | + | & L_{\rm eq} {{{\rm d}i_{\rm |
- | & L_{eq} | + | & L_{\rm eq} {{{\rm d}i }\over{{\rm d}t}} & = &L_{1} {{{\rm d}i }\over{{\rm d}t}} & + &L_{2} {{di |
- | & L_{eq} | + | & L_{\rm eq} |
\end{align*} | \end{align*} | ||
- | ==== 5.1.2 Parallel Circuits ==== | + | ==== 6.1.2 Parallel Circuits ==== |
- | For parallel circuits one can also start with the principles based on Kirchhoff' | + | For parallel circuits, one can also start with the principles based on Kirchhoff' |
- | \begin{align*} | + | \begin{align*} u_{\rm eq}= u_1 = u_2 = ... \\ \end{align*} |
- | u_{eq}= u_1 = u_2 = ... \\ | + | |
- | \end{align*} | + | |
- | and Kirchhoff' | + | and Kirchhoff' |
- | \begin{align*} | + | \begin{align*} i_{\rm eq}= i_1 + i_2 + ... \\ \end{align*} |
- | i_{eq}= i_1 + i_2 + ... \\ | + | |
- | \end{align*} | + | |
Here, the formula for the induced voltage has to be rearranged: | Here, the formula for the induced voltage has to be rearranged: | ||
\begin{align*} | \begin{align*} | ||
- | u_{ind} &= L {{di}\over{dt}} \quad \quad \quad \quad \bigg| \int()dt | + | u_{\rm ind} &= L {{{\rm d}i}\over{{\rm d}t}} \quad \quad \quad \quad \bigg| \int(){\rm d}t \\ |
- | \int u_{ind} | + | \int u_{\rm ind} {\rm d}t &= L \cdot i \\ |
- | i &= {{1}\over{L}} \cdot \int u_{ind} | + | i &= {{1}\over{L}} \cdot \int u_{\rm ind} {\rm d}t \\ |
\end{align*} | \end{align*} | ||
Zeile 49: | Zeile 41: | ||
\begin{align*} | \begin{align*} | ||
- | i_{eq} | + | |
- | {{1}\over{L_{eq}}} \cdot \int u_{eq} | + | {{1}\over{L_{\rm eq}}} \cdot \int u_{\rm eq} {\rm d}t &=& {{1}\over{L_1}} \cdot \int u_{1} {\rm d}t &+& {{1}\over{L_2}} \cdot \int u_{2} {\rm d}t &+& ... \\ |
- | {{1}\over{L_{eq}}} \cdot \int u dt | + | {{1}\over{L_{\rm eq}}} \cdot \int u {\rm d}t &=& {{1}\over{L_1}} \cdot \int u {\rm d}t &+& {{1}\over{L_2}} \cdot \int u {\rm d}t &+& ... \\ |
- | {{1}\over{L_{eq}}} | + | {{1}\over{L_{\rm eq}}} &=& {{1}\over{L_1}} |
\end{align*} | \end{align*} | ||
- | <callout icon=" | + | <callout icon=" |
- | The inductor behaves in the parallel and series circuit similar to the resistor. | + | |
- | </ | + | |
- | ==== 5.1.3 in AC Circuits ==== | + | ==== 6.1.3 in AC Circuits ==== |
- | For AC circuits (i.e. with sinosidal | + | For AC circuits (i.e. with sinusoidal |
- | \begin{align*} | + | \begin{align*} \underline{Z} = {{\underline{u}}\over{\underline{i}}} |
- | \underline{Z} = {{\underline{u}}\over{\underline{i}}} | + | |
- | \end{align*} | + | |
- | With the induction $u_{ind}= | + | With the induction $u_{\rm ind}= L {{{\rm d}i}\over{{\rm d}t}}$ we get: |
- | \begin{align*} | + | \begin{align*} |
- | \underline{Z} &= {{ L {{d\underline{i}}\over{dt}} | + | \underline{Z} & |
- | & | + | |
\end{align*} | \end{align*} | ||
- | Without limiting the generality, one can assume the current $i$ to be: $i = I \cdot \sqrt{2} \cdot e^{j \cdot \omega t + \varphi_0}$. \\ | + | Without limiting the generality, one can assume the current $i$ to be: $i = I \cdot \sqrt{2} \cdot {\rm e}^{{\rm j} \cdot \omega t + \varphi_0}$.\\ |
- | Therefore: | + | Once inserted, the formula gets: |
- | \begin{align*} | + | \begin{align*} |
- | \underline{Z} & | + | \underline{Z} &= {{1} \over {I \cdot \sqrt{2} \cdot {\rm e}^{{\rm j} \cdot \omega t + \varphi_0}}} \cdot L {{ {\rm d}} \over {{\rm d}t} } \left( I \cdot \sqrt{2} \cdot {\rm e}^{{\rm j} \cdot \omega t + \varphi_0} |
- | & | + | &= {{1} \over {I \cdot \sqrt{2} \cdot {\rm e}^{{\rm j} \cdot \omega t + \varphi_0}}} \cdot L I \cdot \sqrt{2} \cdot {{ {\rm d}} \over {{\rm d}t} } \left( {\rm e}^{{\rm j} \cdot \omega t + \varphi_0} |
- | & | + | &= {{1} \over {\qquad\quad\; |
- | & | + | &= {{1} \over {\qquad\quad\; {\rm e}^{{\rm j} \cdot \omega t + \varphi_0}}} \cdot L |
- | &= L \cdot j \cdot \omega | + | \underline{Z} |
\end{align*} | \end{align*} | ||
- | <callout icon=" | + | <callout icon=" |
- | In AC calculations the inductor is described with a complex impedance $\underline{Z} = L \cdot j \omega | + | |
- | </ | + | |
+ | ===== 6.2 Charging and Discharging ===== | ||
- | ===== 5.2 Charging and Discharging ===== | + | Charging and discharging an $RL$ circuit is comparable to the RC-circuit in chapter [[: |
- | Charging and discharging an $RL$ circuit is comparable to the RC-circuit in chapter [[electrical_engineering_1: | + | < |
- | Details are not covered here; see [[https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/ | + | |
- | < | + | ===== 6.3 Resonance Phenomena ===== |
- | </ | + | |
+ | Similar to last semester' | ||
- | ===== 5.3 Resonance Phenomena ===== | + | ==== 6.3.1 RLC - Series Resonant Circuit ==== |
- | + | ||
- | Similar to the approach last semester we now focus on circuits with inductors $L$. For preparation, | + | |
- | + | ||
- | ==== 5.3.1 RLC - Series Resonant Circuit ==== | + | |
As seen last semester, the circuits with complex impedances can be interpreted as four-terminal networks. There, we will again look at " | As seen last semester, the circuits with complex impedances can be interpreted as four-terminal networks. There, we will again look at " | ||
- | In this chapter we look at combination where all three components resistor $R$, capacitor $C$ and inductance $L$ are used. | + | In this chapter, we look at a combination where all three components resistor $R$, capacitor $C$, and inductance $L$ are used. |
< | < | ||
- | If a resistor $R$, a capacitor $C$ and an inductance $L$ are connected in series, the result is a **series resonant circuit**. | + | If a resistor $R$, a capacitor $C$, and an inductance $L$ are connected in series, the result is a **series resonant circuit**. In this case, it is not clearly defined, what the output voltage is. Consequently, |
- | In this case, it not clearly defined, what the output voltage is. Consequently, | + | |
- | \begin{align*} | + | \begin{align*} \underline{U}_I = \underline{U}_R + \underline{U}_L + \underline{U}_C \end{align*} |
- | \underline{U}_I = \underline{U}_R + \underline{U}_L + \underline{U}_C | + | |
- | \end{align*} | + | |
Since the current in the circuit must be constant, the total impedance can be determined here in a simple way: | Since the current in the circuit must be constant, the total impedance can be determined here in a simple way: | ||
\begin{align*} | \begin{align*} | ||
- | \underline{U}_I | + | \underline{U}_I |
- | \underline{U}_I | + | \underline{U}_I |
- | \underline{Z}_{ges} & | + | \underline{Z}_{\rm eq} & |
\end{align*} | \end{align*} | ||
- | By this, the magnitude of the (input) voltage $U_I$, the (input or total) impedance $Z$ and the phase result to: | + | By this, the magnitude of the (input) voltage $U_I$, the (input or total) impedance $Z$, and the phase result to: |
\begin{align*} | \begin{align*} | ||
- | U_I &= \sqrt{U_R^2 + (U_Z)^2} = \sqrt{U_R^2 + (U_L - U_C)^2} | + | U_I &= \sqrt{U_R^2 + (U_Z )^2} |
+ | = \sqrt{U_R^2 + (U_L - U_C)^2} | ||
\end{align*} | \end{align*} | ||
\begin{align*} | \begin{align*} | ||
- | Z &= \sqrt{R^2 + (Z)^2} = \sqrt{R^2 + (\omega L - \frac{1}{\omega C})^2} | + | Z &= \sqrt{R^2 + X^2} |
+ | = \sqrt{R^2 + (\omega L - \frac{1}{\omega C})^2} | ||
\end{align*} | \end{align*} | ||
\begin{align*} | \begin{align*} | ||
- | \varphi_u = \varphi_Z &= arctan \frac{\omega L - \frac{1}{\omega C}}{R} | + | \varphi_u = \varphi_Z |
+ | & | ||
\end{align*} | \end{align*} | ||
Zeile 143: | Zeile 124: | ||
* If $U_L > U_C$ the whole setup behaves like an ohmic-inductive load. This is the case at high frequencies. | * If $U_L > U_C$ the whole setup behaves like an ohmic-inductive load. This is the case at high frequencies. | ||
- | * If $U_L=U_C$, the total input voltage $U$ is applied to the resistor. In this case, the total resistance $Z$ is minimal and only ohmic. \\ Thus, the current $I$ is then maximal. If the current is maximum, then the responses of the capacitance and inductance - their voltages - are also maximum. This situation is the **resonance case**. | + | * If $U_L = U_C$, the total input voltage $U$ is applied to the resistor. In this case, the total resistance $Z$ is minimal and only ohmic. \\ Thus, the current $I$ is then maximal. If the current is maximum, then the responses of the capacitance and inductance - their voltages - are also maximum. This situation is the **resonance case**. |
* If $U_L < U_C$ then the whole setup behaves like a resistive-capacitive load. This is the case at low frequencies. | * If $U_L < U_C$ then the whole setup behaves like a resistive-capacitive load. This is the case at low frequencies. | ||
- | Again, there seems to be an excellent | + | Again, there seems to be a singular |
\begin{align*} | \begin{align*} | ||
- | \frac{1}{\omega_0 C} & = \omega L \\ | + | \frac{1}{\omega_0 C} & = \omega_0 |
- | \omega_0 | + | \omega_0 |
- | 2\pi f_0 | + | 2\pi f_0 & = \frac{1}{ |
+ | \rightarrow \boxed{ f_0 = \frac{1}{2\pi \sqrt{LC}} } | ||
\end{align*} | \end{align*} | ||
The frequency $f_0$ is called **resonance frequency**. | The frequency $f_0$ is called **resonance frequency**. | ||
- | ^ ^ $\quad$ | + | ^ ^ $\quad$ |
- | |voltage $U_R$ \\ at the resistor | + | |voltage $U_R$ \\ at the resistor |
- | |voltage $U_L$ \\ at the inductor | + | |voltage $U_L$ \\ at the inductor |
- | |voltage $U_C$ \\ at the capacitor | | + | |voltage $U_C$ \\ at the capacitor | | $\boldsymbol{\LARGE{U}}$ \\ because $\frac{1}{\omega C}$ becomes very large | | $\boldsymbol{\frac{1}{\omega_0 C} \cdot I = \frac{1}{\omega_0 C} \cdot \frac{U}{R} = \color{blue}{\frac{1}{R}\sqrt{\frac{L}{C}}\cdot U}}$ | | $\boldsymbol{\small{0}}$ \\ because $\frac{1}{\omega C}$ becomes very small | |
- | The calculation in the table shows that in the resonance case, the voltage across the capacitor or inductor deviates from the input voltage by a factor $\color{blue}{\frac{1}{R}\sqrt{\frac{L}{C}}}$. This quantity is called **quality or Q-factor** | + | The calculation in the table shows that in the resonance case, the voltage across the capacitor or inductor deviates from the input voltage by a factor $\color{blue}{\frac{1}{R}\sqrt{\frac{L}{C}}}$. This quantity is called **quality or Q-factor** |
\begin{align*} | \begin{align*} | ||
- | \boxed{ \left.Q_S = \frac{U_C}{U} \right\vert_{\omega = \omega_0} = \frac{U_L}{U} | + | \boxed{ Q_{\rm S} = \left.\frac{U_C}{U} \right\vert_{\omega = \omega_0} |
+ | | ||
+ | | ||
\end{align*} | \end{align*} | ||
- | The quality can be greater than, less than or equal to 1. | + | The quality can be greater than, less than, or equal to 1. The quality $Q_{\rm S}$ does not have a unit and should not be confused with the charge $Q$. |
- | * If the quality is very high, the overshoot of the voltages at the impedances becomes very large in the resonance case. This is useful and necessary in various applications, | + | * If the quality is very high, the overshoot of the voltages at the impedances becomes very large in the resonance case. This is useful and necessary in various applications, |
- | * If the Q is very small, overshoot is no longer seen. Depending on the impedance at which the output voltage is measured, a high-pass or low-pass is formed similar to the RC or RL element. However, this has a steeper slope in the blocking range. This means that the filter effect is better. | + | * If the $Q$ is very small, overshoot is no longer seen. Depending on the impedance at which the output voltage is measured, a high-pass or low-pass is formed similar to the $RC$ or $RL$ element. However, this has a steeper slope in the blocking range. This means that the filter effect is better. |
- | The reciprocal of the Q is called **attenuation** | + | The reciprocal of the $Q$ is called **attenuation** |
- | \begin{align*} | + | \begin{align*} \boxed{ |
- | \boxed{ | + | |
- | \end{align*} | + | |
~~PAGEBREAK~~ ~~CLEARFIX~~ | ~~PAGEBREAK~~ ~~CLEARFIX~~ | ||
Zeile 182: | Zeile 164: | ||
< | < | ||
- | < | + | < |
- | <panel title=" | + | <panel title=" |
- | < | + | < |
- | </ | + | </ |
<panel title=" | <panel title=" | ||
- | < | + | < |
- | </panel> | + | </ |
- | <panel title=" | + | |
- | <WRAP>{{url> | + | |
- | </panel> | + | |
- | <panel title=" | + | |
- | < | + | |
- | </ | + | |
- | <panel title=" | + | |
- | < | + | |
- | </ | + | |
- | </ | + | |
- | ~~PAGEBREAK~~ ~~CLEARFIX~~ | + | <panel title=" |
+ | < | ||
+ | </ | ||
+ | <panel title=" | ||
+ | < | ||
+ | </ | ||
+ | |||
+ | <panel title=" | ||
+ | < | ||
+ | </ | ||
+ | |||
+ | ~~PAGEBREAK~~ ~~CLEARFIX~~ | ||
- | ===== 5.4 Applications of Inductors | + | ===== 6.4 Applications of Inductors ===== |
* ferrite bead | * ferrite bead | ||
* Decoupling | * Decoupling | ||
* Filter | * Filter | ||
- | * unwanted coupling and cirucit | + | * unwanted coupling and circuit |
- | + | ===== 6.5 Examples ===== | |
- | ===== 5.5 Examples ===== | + | |
=== Decoupling Capacitor on the Microcontroller === | === Decoupling Capacitor on the Microcontroller === | ||
Zeile 223: | Zeile 206: | ||
[[https:// | [[https:// | ||
- | Simulation in Time Domain | + | Simulation in Time Domain < |
- | < | + | |
- | </ | + | |
- | + | ||
- | Simulation in Frequency Domain | + | |
- | < | + | |
+ | Simulation in Frequency Domain < | ||
[[https:// | [[https:// | ||
+ | |||
+ | ===== Exercises ===== | ||
+ | |||
+ | <panel type=" | ||
+ | |||
+ | A $R$-$L$-$C$ series circuit uses a capacity of $C=100 ~\rm µF$. A voltage source with $U_I$ feeds the circuit at $f_1 = 50~\rm Hz$. | ||
+ | |||
+ | - Which values does $R$ and $L$ need to have, when the resonance voltage $|\underline{U}_L|$ and $|\underline{U}_C|$ at $f_1$ shall show the double value of the input voltage $U_I$? | ||
+ | - The components of question 1. shall now be used. What would be the value of ${{|\underline{U}_C|} \over {|\underline{U}_I|}} $ for $f_2 = 60~\rm Hz$? | ||
+ | |||
+ | </ | ||
+ | |||
+ | <panel type=" | ||
+ | |||
+ | A given $R$-$L$-$C$ series circuit is fed with a frequency, $20~\%$ larger than the resonance frequency keeping the amplitude of the input voltage constant. In this situation, the circuit shows a current $30~\%$ lower than the maximum current value. | ||
+ | |||
+ | Calculate the Quality $Q = {{1}\over{R}}\sqrt{{{L}\over{C}}}$. | ||
+ | |||
+ | # | ||
+ | The solution looks hard at first since no insights for the values of $R$, $C$, and $L$ are given. | ||
+ | |||
+ | However, it is possible and there are multiple ways to solve it. \\ \\ | ||
+ | |||
+ | <fs large> | ||
+ | |||
+ | But first, add some more info, which is always true from resonant circuits at the resonant frequency: | ||
+ | - $\omega_0 = {{1}\over{\sqrt{LC}}}$ | ||
+ | - $X_{C0} = - X_{L0}$ | ||
+ | - $Z = \sqrt{R^2 + (X_L + X_C)^2}$, based on the sum of the impedances $\underline{Z}_{\rm eq} = \underline{X}_R + \underline{X}_C + \underline{X}_L$ and the Pythagorean theorem$ | ||
+ | \\ | ||
+ | From the task, the following is also known. | ||
+ | - Using "a frequency, $20~\%$ larger than the resonance frequency": | ||
+ | - $f = 1.2 \cdot f_0 $ and | ||
+ | - $\omega = 1.2 \cdot \omega_0 $ | ||
+ | - The circuit shows a current $30~\%$ lower than the maximum current value: | ||
+ | - The maximum current for the series resonant circuit is given for the minimum impedance $Z$. \\ The minimum impedance $Z$ is given at resonance frequency, and is $Z_{\rm min} = R$ | ||
+ | - Therefore: $Z = {{1}\over{0.7}} \cdot R$ | ||
+ | \\ | ||
+ | <fs large> | ||
+ | |||
+ | We start with $Z = \sqrt{R^2 + (X_L + X_C)^2}$ for the cases: (1) at the resonant frequency $f_0$ and (2) at the given frequency $f = 1.2 \cdot f_0 $ | ||
+ | |||
+ | \begin{align*} | ||
+ | (1): && Z_0 &= R \\ | ||
+ | (2): && Z & | ||
+ | \end{align*} | ||
+ | |||
+ | In formula $(2)$ the impedance $X_L$ and $X_C$ are: | ||
+ | * $X_L= \omega \cdot L$ and therefore also $X_L = 1.2 \cdot \omega_0 \cdot L = 1.2 \cdot X_{L0}$ | ||
+ | * $X_C= - {{1}\over {\omega \cdot C}}$ and therefore also $X_C = - {{1}\over {1.2 \cdot \omega \cdot C}} = - {{1}\over {1.2}} \cdot X_{C0}$ | ||
+ | |||
+ | With $X_{C0} = X_{L0}$ we get for $(1)$: | ||
+ | |||
+ | \begin{align*} | ||
+ | Z &= \sqrt{R^2 + \left(1.2\cdot X_{L0} - {{1}\over{1.2}} X_{L0} \right)^2} \\ | ||
+ | &= \sqrt{R^2 + X_{L0}^2 \cdot \left(1.2 - {{1}\over{1.2}} \right)^2} \\ | ||
+ | \end{align*} | ||
+ | |||
+ | Since we know that $Z = {{1}\over{0.7}} \cdot R$ and $Z_0 = R$, we can start by dividing $(2)$ by $(1)$: | ||
+ | |||
+ | \begin{align*} | ||
+ | {{(2)}\over{(1)}} : && | ||
+ | && | ||
+ | && | ||
+ | && | ||
+ | && | ||
+ | && {{X_{L0}^2}\over{R^2}} | ||
+ | && {{X_{L0}}\over{R}} | ||
+ | && {{1}\over{R}}\cdot \sqrt{ {L} \over {C} } & | ||
+ | |||
+ | \end{align*} | ||
+ | |||
+ | # | ||
+ | |||
+ | |||
+ | # | ||
+ | |||
+ | \begin{align*} | ||
+ | Q & | ||
+ | &= 2.782... \\ | ||
+ | \rightarrow Q &= 2.78 | ||
+ | \end{align*} | ||
+ | |||
+ | |||
+ | # | ||
+ | |||
+ | |||
+ | </ | ||
+ | |||
+ |