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Unformatted text preview: EL 625 Lecture 2 1 EL 625 Lecture 2 State equations of finite dimensional linear systems Continuoustime : ˙ x ( t ) = A ( t ) x ( t ) + B ( t ) u ( t ) y ( t ) = C ( t ) x ( t ) + D ( t ) u ( t ) Discretetime : x ( t k +1 ) = A ( t k ) x ( t k ) + B ( t k ) u ( t k ) y ( t k ) = C ( t k ) x ( t k ) + D ( t k ) u ( t k ) state x ( t )  vector of length n × 1 input u ( t )  r × 1 output y ( t )  m × 1 A,B,C and D are matrices of sizes n × n, n × r, m × n and m × r respectively. If A,B,C,D are functions of time ⇒ timevarying If these matrices are constant with time ⇒ timeinvariant EL 625 Lecture 2 2 State Differential equations of circuits basic elements → resistor,capacitor, inductor Resistor : v R ( t ) = R ( t ) i R ( t ) v R ( t ) : the voltage across the resistor i R ( t ) : the current through the resistor R ( t ) : the resistance A resistor is a ‘zeromemory’ element. B B B B B B B B B B B B B B R h h + – v R i R Any circuit with only resistors (a purely resistive network) has zeromemory and is of zero order (needs no states to describe it). EL 625 Lecture 2 3 Capacitor : i C ( t ) = ˙ q C ( t ) , q C ( t ) = C ( t ) v C ( t ) where: i C ( t ) : the current through the capacitor q C ( t ) : the electrical charge in the capacitor v C ( t ) : the voltage across the capacitor C ( t ) : the capacitance C ( t ) dv C ( t ) dt = i C ( t ) dC ( t ) dt v C ( t ) If the capacitance does not change with time, C dv C ( t ) dt = i C ( t ) C h h + – v C i C EL 625 Lecture 2 4 Inductor : v L ( t ) = ˙ φ ( t ) , φ ( t ) = L ( t ) i L ( t ) where: i L ( t ) : the current through the inductor v L ( t ) : the voltage across the inductor φ ( t ) : the flux stored in the inductor L ( t ) : the inductance L ( t ) di L ( t ) dt = v L ( t ) dL ( t ) dt i L ( t ) If the inductance does not change with time, L di L ( t ) dt = v L ( t ) L h h + – v L i L EL 625 Lecture 2 5 Example : L C 1 P P P P P P P P P P P R 1 C 2 P P P P P P P P P P P R 2 &% '$ &% '$ + – e 1 ( t ) e 2 ( t ) + – + – + – + – i L ( t ) v L ( t ) ? ? i 1 ( t ) i 2 ( t ) v 2 ( t ) v 1 ( t ) Applying Kirchoff’s current and voltage laws, i L = i 1 + i 2 e 1 = v L + i 1 R 1 + v 1 e 1 = v L + v 2 + i 2 R 2 + e 2 From the terminal relationships of the capacitors and the inductor, ˙ v 1 = 1 C 1 i 1 ˙ v 2 = 1 C 2 i 2 ˙ i L = 1 L v L EL 625 Lecture 2 6 The inputs are e 1 and e 2 . The output is the voltage across the inductor, v L . Choosing as our states, i L , v 1 and v 2 , x = i L v 1 v 2 , u = e 1 e 2 , y = [ v L ] Need to express ˙ x in terms of x and the inputs, e 1 and e 2 ,. . ....
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This note was uploaded on 12/06/2010 for the course EL 625 taught by Professor Khorami during the Spring '10 term at NYU Poly.
 Spring '10
 khorami

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