Power Electronics Lab 1

Lecture 13ECEN 4517/5517

Experiment 4 Part 3

Part III—Closed loop transient analysis:

Use averaged model to simulate (and fix) startup transientUse averaged model tosimulate load transientresponseUse switching model to simulate startup transient

Part 3 employs both libraries of models:• switching4517.lib• average4517.lib

Power Electronics Lab 2

New Schedule

Part First week Second week

Part 1: open-loop system

March 16-20 March 30 – April 3

Report due April 3

Part 2: closed-loop, averaged model

April 6-10 April 13-17

Report due April 17

Part 3: closed-loop, switching model

April 20-24 April 27 – May 1

Report due May 1

Power Electronics Lab 3

Step 1: Closed-loop startup transient

Use your closed-loop averaged model from Part 2Replace power source Vg with the current-limited power supply usedin Part 1Use averaged PWM model and averaged switch models• Be sure to correctly set CCM-DCM1 parameters to those used in

your converter• Likely you will need to adjust the PWM Dmax and soft start• Use your saturating inductor modelsStart all voltages and currents at zero

Can you get your closed-loop converter to start up, and reach regulation at V = 200 V ± 5 V?

Power Electronics Lab 4

average4517.lib

PWMavg CCM-DCM1

Parameters:L=valuefs=value

Parameters:Dmax=valueDmin=0.02Voffset=1VM=2.3

Power Electronics Lab 5

Bench power supply with current limiting

Use current-limited power supply (from switching4517.lib) in your closed-loop averaged simulation

Vlim = 13Ilim ≤ 12

In current limit mode, LTspice probably won’t converge when directly driving an inductor. Capacitor bypassing is needed. You may adjust Ilim to any value no greater than 12 A

Power Electronics Lab 6

Step 2: Evaluate Load Transient Response

The resistor value starts at 470 ΩAt t = 20 ms, the resistor value changes (in 1 µs) to 4.7 kΩ

Using a piecewise linear source to make the load resistance change

PWL(t1 v1 t2 v2 …)

Power Electronics Lab 7

The Step 2 Simulation

Start all signals at zero, and go through a startup transition as in Part 1 with a load resistance of 470 Ω (85 W at 200 V)

Wait until system reaches steady state at V = 200 V ± 5 V, then change load resistance to 4.7 kΩ (8.5 W at 200 V)

Observe closed loop response of output voltage to step change in load resistance.

Load resistance changes here

Output voltage

L1 inductor current

Steady state here

Power Electronics Lab 8

Step 3: Switching Simulation of Startup

Start with your result from Step 1: averaged model that successfully starts up and reaches steady state at V = 200 V ± 5 V

Convert this LTspice circuit to a switching model:• Replace CCM-DCM1 averaged switch models with MOSFETs and

diodes (from Exp 4 Part 1)• Add gate drivers• Replace averaged model PWMavg with switching model PWM3525

Set parameters such as Dmax, Ilim, etc. to the same values that worked inStep 1

Perform transient simulation of start up. Does it reach steady state of 200 V ± 5 V? How do the averaged and switching waveforms compare? Do the inductors saturate during the start up transient?

Power Electronics Lab 9

Exp 4 Part 3 Due Date

Upload your Part 3 Report to Canvas by 5:00 pm on Friday May 1