Chap. 9 Sinusoidal Steady-State Analysis. C ontents. 9.1 The Sinusoidal Source 9.2 The Sinusoidal Response 9.3 The Phasor 9.4 The Passive Circuit Elements in the Frequency Domain 9.5 Kirchhoff’s Laws in the Frequency Domain 9.6 Series, Parallel, and Delta-to-Wye Simplifications - PowerPoint PPT Presentation
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Chap. 9 Sinusoidal Steady-State Analysis
Contents9.1 The Sinusoidal Source 9.2 The Sinusoidal Response9.3 The Phasor9.4 The Passive Circuit Elements in the Frequency Domain9.5 Kirchhoff’s Laws in the Frequency Domain9.6 Series, Parallel, and Delta-to-Wye Simplifications 9.7 Source Transformations & Thévenin-Norton Equivalent Circuits9.8 The Node-Voltage Method 9.9 The Mesh-Current Method9.10 The Transformer 9.11 The Ideal Transformer9.12 Phasor Diagrams
均方根值 (Root Mean Square, rms, Value): the square root of the mean value of the squared periodic function
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弦波電源的 rms值或稱有效值 (effective value),可經推導得:
EX 9.1 Finding the Characteristics of a Sinusoidal Current
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A sinusoidal current has a maximum amplitude of 20 A. The current passes through one complete cycle in 1 ms. The magnitude of the current at zero time is 10 A.
a) What is the frequency of the current in hertz (Hz)?b) What is the angular frequency in radians per second?c) Write the expression for i(t) using the cosine function. Express in degrees.d) What is the rms value of the current?
a)
b)
c)
d)
&
rms value =
EX 9.2 Finding the Characteristics of a Sinusoidal Voltage
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A sinusoidal voltage is given by the expression
a) What is the period of the voltage in milliseconds?b) What is the frequency in hertz?c) What is the magnitude of v at t = 2.778 ms?d) What is the rms value of v ?
a)
b)
c)
d)
.30120cos300 πtv
&
f =
& 2.778=
EX 9.3 Translating a Sine Expression to a Cosine Expression
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Translate the sine function to the cosine function by subtracting 90◦ (π/2 rad) from the argument of the sine function.
a) Verify the above translation.b) Express sin(ωt + 30◦) as a cosine function.
a)
b)
Let &
EX 9.4 Calculating the rms Value of a Triangular Waveform
EX 9.13 Analyzing a Linear Transformer (Frequency Domain)
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The parameters of a certain linear transformer are R1 = 200 , R2 = 100 ,
L1 = 9 H, L2 = 4 H, and k = 0.5. The transformer couples an impedance
consisting of an 800 resistor in series with a 1 µF capacitor to a sinusoidal voltage source. The 300 V (rms) source has an internal impedance of 500 + j 100 and a frequency of 400 rad/s.
EX 9.14 Analyzing an Ideal Transformer Ckt. (Frequency Domain)
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If vg = 2500 cos 400t V, find the steady-state expressions for (a) i1 ; (b) v1 ; (c) i2 ; and (d) v2 .
a)
rad/s 400
&
Also,
EX 9.14 (Contd.)
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c)
d)
b)
The Use of an Ideal Transformer for Impedance Matching
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將理想變壓器二次側負載阻抗反射至一次側時,須乘上 1/a2 。
9.12 Phasor Diagrams
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A graphic representation of phasors.
The complex number −7 − j 3.
A phasor diagram shows the magnitude and phase angle of each phasor quantity in the complex-number plane.
Phase angles are measured counterclockwise from the positive real axis, and magnitudes are measured from theorigin of the axes.
Two different magnitude scales are necessary, one for currents and one for voltages.
EX 9.15 Using Phasor Diagrams to Analyze a Circuit
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Find the value of R that will cause the current through that resistor, iR , to lag the source current, is , by 45◦ when = 5 krad/s.
By KCLΩ3
1 31 R /R
EX 9.16 Analyzing Capacitive Loading Effects
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Use phasor diagrams to explore the effect of adding a capacitor across the terminals of the load on the amplitude of Vs if we adjust Vs so that the amplitude of VL remains constant.
Utility companies use this technique to control the voltage drop on their lines.
EX 9.16 Analyzing Capacitive Loading Effects (Contd.)