Unformatted text preview: College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4 Alternating Current (AC) SteadyState Analysis EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
In this chapter, the analysis of the steadystate forced response (ergo the partial solution) of circuits with alternating current (AC) input sources will be studied. In AC circuits, the input function is sinusoidal in nature. Because the transient response rapidly decays to zero, steadystate analysis is more significant.
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis i (t ) = I M cos( t + i ) amperes v ( t ) = V M cos( t + v ) volts
IM and VM are the amplitude, maximum, or peak values of the current or voltage. is the angular frequency (measured in radians per seconds) I and V are the phase angles for the current or voltage.
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP Sinusoidal current and voltage are given by the corresponding equations: College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis i (t ) = I M cos( t + i ) amperes v ( t ) = V M cos( t + v ) volts
Sinusoidal waveforms are periodic, that is they repeat the same pattern of values after a certain point in time, t. This specific point in time is called the period, T.
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP Sinusoidal current and voltage corresponding equations (continued): College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
Periodicity can be expressed in general for a function p(t) with a period T as p (t + nT ) = p (t ) n = 1, 2,3 K
for all values of t Cosine and sine functions complete one cycle when the argument (t) increases by 2 radians. Hence: T = 2
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis i (t ) = I M cos( t + i ) amperes v ( t ) = V M cos( t + v ) volts
The frequency (f) of a sinusoidal, which is measured in Hertz (Hz), is related to the period, T, by the equation: 1 Sinusoidal current and voltage corresponding equations (continued): f = EECE 310 Preston D. Frazier, Ph.D., P.E., PMP T College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
Two sinusoidal cosine voltage functions: v1 (t ) = V M 1 cos( t + v1 ) volts v 2 (t ) = V M 2 cos( t + v 2 ) volts
If v1 = v2, then the waveforms are in phase. If v1 v2, then the waveforms are out of phase. If v1 < v2, then the v2(t) leads v1(t) or v1(t) lags v2(t). If v1 > v2, then the v1(t) leads v2(t) or v2(t) lags v2(t).
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
Sine and cosine function relationships: sin( t ) = cos( t  2  A sin( t + ) = A sin( t + )
 A cos( t + ) = A cos( t + )
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP cos( t ) = sin( t + 2 ) ) College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
Sinusoidal functions and complex numbers are related through Euler's equation. e j t = cos( t ) + j sin( t )
j t The complex function may be broken into its real and imaginary parts: Re( e ) = cos( t ) j t Im( e ) = sin( t )
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
Sinusoidal current and voltage corresponding equations: i (t ) = I M cos( t i ) amperes v ( t ) = V M cos( t v ) volts j I The complex representation of the current and voltage sinusoidal may be written as: i (t ) = I M e amperes j V v (t ) = V M e volts
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis
i (t ) = I M cos( t i ) = I M i v ( t ) = V M cos( t v ) = V M v
The phasor transformation of sinusoidal sine current and voltage functions: The phasor transformation of sinusoidal cosine current and voltage functions: i ( t ) = I M sin( t i ) = I M ( i 
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP 2 v ( t ) = V M sin( t v ) = V M ( v  ) 2 ) College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 4AC SteadyState Analysis The phasor identities for a voltage function: r V =rV M i volts Re( V ) = V M cos( v ) r Im( V ) = jV M sin( v )
VM r 2 r 2 = (Re( V )) + (Im( V )) r 1 Im( V ) r ) v = tan ( Re( V )
EECE 310 Preston D. Frazier, Ph.D., P.E., PMP College of Engineering, Architecture, and Computer Sciences Department of Electrical and Computer Engineering Chapter 5 SteadyState Sinusoidal Analysis
Important Note about Phasors: If the number falls to the left of the imaginary axis (i.e., if the real part is negative), then add 180 degrees to the arctangent (imag/real) to obtain the correct angle. EECE 310 Preston D. Frazier, Ph.D., P.E., PMP ...
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 Fall '08
 FRAZIER
 Computer Science, Electrical Engineering, Steady State, Alternating Current, Computer Sciences Department of Electrical and Computer Engineering, Preston D. Frazier

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