SECOND ORDER CIRCUITS. Prepared by: Ertuğrul Eriş Reference book: Electric Circuits, Nielsson, Riedel Pearson, Prentence Hall,2007. Update 1: October 2011. RLC CIRCUITS. Second order circuits Two inductors, two capacitors, one inductor one capacitor DC Independent source /AC later
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SECOND ORDER CIRCUITS Prepared by: Ertuğrul Eriş Reference book: Electric Circuits, Nielsson, Riedel Pearson, Prentence Hall,2007 Update 1: October 2011
RLC CIRCUITS • Second order circuits • Two inductors, two capacitors, one inductor one capacitor • DC Independent source /AC later • Serial or parallel • Second order differential equation • At most second order derivative OR • Two first order differential equations, matrices Ertuğrul Eriş
PARALLEL RLC CIRCUIT ANALYSIS • MATHEMATICAL • Second order single differential equation, or first order two differential equations • Homogenous solution: independent sources deactivated. • Particular solution: independent source type solution • General solution= Homogenous solution + particular solution • CIRCUIT BASED • Natural response • Independent sources are deactivated, initial conditions exsist • Forced solution • Independent sources active (step, basamak); initial conditions are(0) • General solution (Tam, genel çözüm)=Natural response+forced solution Ertuğrul Eriş
SECOND ORDER CIRCUITS Paralel RLC Mathematical Homogenous+particular Circuit based Natural+forced + V0 _ I0 Seri RLC Mathematical Homogenous+particular Circuit based Natural+forced I0 + V0 _ Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-1 + V0 _ I0 Second order single differential equation (capacitor voltage, inductor current): Two first order differential equations state equations (Durum Denklemleri ) Would it be enough to solve only one of the above equations? How could we find the other unknowns? Compare left and right hand equations Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-2 + V0 _ I0 General (Tam) solution: = Homogenous (Homojen) solution + particular (Özel) solution independent sources deactivated for DC type souces it is a constant, For AC type sources, it is a sinusoidal function How do we know that the sum of homogenous and particular solution is general solution? Linearity!! Difference of homogenous and natural response? Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-3 Tam çözüm (General)= = Homojen çözüm (Homogenous) + Özel çözüm (particular) The two unknown parameters in homogenous solution will be calculated by using the two initial conditions on the general solution = Transient state (Geçici hal,rejim) + Steady state (Sürekli hal,rejim) How do we know that the sum of homogenous and particular solution is general solution? Linearity!! Difference of homogenous and natural response? Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-4 + V0 _ I0 I(t) independent current source If it is DC source then its derivative is (0) For Vc(t) general solution is equal to homogenous solution while particular solution is (0) A1 and A2 parameters will be calculated by vc(0), iL(0) initial conditions. dvc(0)/dt; diL(0)/dt can be calculated in terms of vc(0), iL(0) Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-5 + V0 _ I0 If current source is a DC source then particular solution is estimated as a constant D and calculated. A1 and A2 parameters will be calculated by the known vc(0), iL(0) initial conditions. dvc(0)/dt; diL(0)/dt will be found by vc(0), iL(0) initial conditions Compare Vc(t) in previous slide and iL(t) (this slide)? Steady state (particular solution) is I, What does this mean? Difference of homogenous and natural response? Ertuğrul Eriş
CHARACTERISTIC ROOTS • Four cases: • Reel roots α2>ω20, Overdamped • Complex conjugate roots α2<ω20, underdamped • Multiple roots α2=ω20, critically damped • Imaginary rootsα=0 Could the charecteristic roots be imaginar in a second order circuit? Why? Ertuğrul Eriş
PARALLEL RLC CIRCUIT MATHEMATICAL ANALYSIS-7: REAL ROOTS EXAMPLE VC(0+)=12V, iL(0+)=30 mA C=0,2 μF L=50 mH R=200Ω I=1 A + V0 _ I0 α = - (1/RC) = 12500 ω0 = 1/√LC = 10000 α > ω0 iL(0-) = iL(0) = iL(0+) = 30 mA iC = C (dv/dt) diL(0+)/dt = vc(0+)/L =240 A/s s1 = - 5000r/s s2 = - 20000r/s A1 = -1,277 A2 = 0,307 iL(t) = -1,277e-5000t + 0,307 e-20000t +1 A, t≥0 v(t) = 319 e-5000t - 307 e-20000t V, t≥0 iR(t) = 1,59 e-5000t - 1,53e-20000t A, t≥0 iC(t)= (-0,323e-5000t +1,223e-20000t) A, t≥0 Ertuğrul Eriş
GENERAL SOLUTION FOR REAL ROOTS + V0 _ I0 VC(0+)=12V, iL(0+)=30 mA C=0,2 μF L=50 mH R=200Ω I=1 A s1 = - 5000r/s, s2 = - 20000r/s iL(t) = -1,277e-5000t + 0,307 e-20000t +1 A, t≥0 Transient and stady state solution, which elements will be short/open circuits, why? Ertuğrul Eriş
GENERAL SOLUTION FOR COMPLEX ROOTS + V0 _ I0 VC(0+)=0 V, iL(0+)=-500 mA C=0,125 μF L=8mH R=20KΩ I=1 A Transient and stady state solution, which elements will be short/open circuits, why? Ertuğrul Eriş
GENERAL SOLUTION FOR MULTIPLE ROOTS + V0 _ I0 VC(0+)=0 V, iL(0+)=-500 mA C=0,125 μF L=8 H R=4KΩ I=1 A Transient and stady state solution, which elements will be short/open circuits, why? Ertuğrul Eriş
SERIAL RLC CIRCUIT ANALYSIS NATURAL RESPONSE EXAMPLE iL(0)=0 Vc(0)=100V What can we say about roots by looking the solutions? Stability? Aynı sonuçlara başka hangi diferansiyel denklemle ulaşılabilir? Ertuğrul Eriş
SERIAL RLC CIRCUIT ANALYSIS FORCED RESPONSE EXAMPLE iL(0)=0 Vc(0)=0 100mH 560Ω 0.1 μF What can we say about roots by looking the solutions? Can we find the same solution by using different differential equation? Which one is it? Which part of the above solution is homogenous and particular? Which part of the above solution is transient and steady state? Ertuğrul Eriş
SERIAL RLC CIRCUIT ANALYSIS FORCED RESPONSE EXAMPLE iL(0)=0 Vc(0)=0 100mH 560Ω 0.1 μF What can we say about roots by looking the solutions? Can we find the same solution by using different differential equation? Which one is it? Which part of the above solution is homogenous and particular? Which part of the above solution is transient and steady state? Ertuğrul Eriş