ECEN 45171Lecture 4ECEN 4517/5517DC-DC converterBattery charge controllerPeak power trackerExperiment 3ECEN 45172Upcoming deadlinesQuiz 2 on Exp 2: last 15 minutes today This week in lab:Continue Exp. 3 Part 1.Get your converter running open-loop, and take data outsideNext week in lab:Finish Exp. 3 Part 1, including simulationsExp. 3 Part 1 report will be due Feb 28Exp. 2 prelab 2 (sensing circuitry + MPPT code) due Feb 24Exp. 2 on-line modules and quizzes coming up – keep an eye on D2LECEN 45173Converter modeling and simulationConduction modes– Continuous conduction mode (CCM)– Discontinuous conduction mode (DCM)Equivalent circuit modeling– The dc transformer model: CCM– DCM modelSimulation– Averaged switch model in CCM– Averaged switch model in DCM– A combined automatic model for PSPICE (or Simulink, optional)– Exp. 3 Part 1: simulation model for your system, including PV panel and converterECEN 45174Averaged switch modelingBasic approach (CCM)D1Q1R+V–+–CLVgGiven a switching converter operating in CCMBuck converter exampleSeparate the switching elements from the remainder of the converterDefine the terminal voltages and currents of the two-port switch networkR+V–+–CLVgD1Q1+v1–+v2–Switchnetworki1i2ECEN 45175Terminal waveforms of the switch networkRelationship between average terminal waveforms:ECEN 45176Averaged model of switch networkSoModeling the switch network viaaveraged dependent sourcesECEN 45177Switch Library FileSpice simulation of averaged waveforms.subckt CCM1 1 2 3 4 5Et 1 6 value={(1-v(5))*v(3,4)/v(5)}Vdum 6 2 0Gd 4 3 value={(1-v(5))*i(Vdum)/v(5)}.endsECEN 45178Basic CCM SEPIC ExampleFrequency ResponseIdeal SEPIC frequency response.lib switch.libVg 1 0 dc 120VL1 1 2x 800uHRL1 2x 2 1UC1 2 3 100uFL2 3 0 100uHC2 4 0 100uFRL 4 0 40Vc 5 0 dc 0.4 ac 1Rc 5 0 1MXswitch 2 0 4 3 5 CCM1.ac DEC 201 10 100kHz.PROBE.endECEN 45179AC analysis in SpiceGiven a nonlinear time-invariant circuit, as on the previous slide, we can get Spice to automatically perturb, linearize, and plot small-signal ac transfer functions:• Use DC sources to set up the correct quiescent operating conditions• Include an AC source having amplitude 1• Perform an AC analysis: Spice will• Do a DC analysis to find the quiescent operating point• Linearize all nonlinear elements at this point, to construct a linear model• Perform an AC (phasor) analysis at specified frequencies to find the magnitudes and phases of all signals• Construct Bode plots of selected signals. With an input amplitude of 1, the signal magnitude and phase plot is the transfer function.ECEN 451710AC analysisSEPIC Example: Control-to-output transfer functionMagnitudePhaseECEN 451711Discontinuous Conduction ModeR+V–+–CLVgD1Q1+v1–+v2–Switchnetworki1i2• Again find average values of switch network terminal voltages and currents• Eliminate variables external to the switch network• Results on next slidesECEN 451712Input (transistor) portAveraged equivalent circuiti1(t)Ts=d12(t)Ts2Lv1(t)Tsi1(t)Ts=v1(t)TsRe(d1)Re(d1)=2Ld12Tsv1(t)Tsi1(t)TsRe(d1)+–ECEN 451713Output (diode) portAveraged equivalent circuiti2(t)Ts=d12(t) Ts2Lv1(t)Ts2v2(t)Tsi2(t)Tsv2(t)Ts=v1(t)Ts2Re(d1)= p(t)Tsp(t)+v(t)–i(t)ECEN 451714Averaged modeling of CCM and DCM switch networks+–1 : d(t)i1(t)Tsi2(t)Ts+–v2(t)Tsv1(t)TsAveraged switch modelSwitch networkCCM+v2(t)–+v1(t)–i1(t) i2(t)i2(t )Ts+–v2(t )Tsv1(t)Tsi1(t)TsRe(d1)+–DCM+v2(t)–+v1(t)–i1(t) i2(t)p(t)TsECEN 451715Spice model CCM-DCM1Combined CCM/DCM switch model• This is one of the models inside switch.lib• It automatically switches between CCM and DCM as necessaryECEN 451716LTspice simulationExp. 3 Part 1: open loop• Use your PV model from Exp. 1• Replace buck converter switches with averaged switch model• CCM-DCM1 and other Spice model library elements are linked on the course web page• Online module and quiz on
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