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EEE8147- Advanced Power Electronics and Applications
FLYBACK DC-DC CONVERTER SIMULATION ASSIGNMENT 1. AIM AND OBJECTIVE: Flyback converters are very popular in low power applications such as phone adaptor and other household appliances. The aim of this simulation exercise is to evaluate the operation of Flyback dc dc converter in various operating modes and to observe the resultant operating waveforms. Some calculations are required to compare the measurements with the idealised theory that is covered in the lectures. Some design considerations are also required to account for some nonidealities in the system. Fig. 1 circuit schematic of isolated Flyback SMPS 2. EXPERIMENTS Students are required to build a simulation model of the Flyback dc dc converter shown in Fig. 1 using PSIM software (other simulation software are also acceptable) and perform the following FIVE tasks: Note: use an ideal transformer with an inductance in parallel with the primary to represent the coupled inductor Task 1: continuous conduction mode (CCM) operation Build the simulation model for a Flyback converter with the following specifications: , varies between140 − 325 , a constant output voltage, = 5 with a maximum ripple of ∆ = 2% and a switching frequency of = 100 . The magnetizing inductance is found to be 5 and the transformer turns ratio, 1/2 = 15 i. Calculate the range of the duty cycle. SW D C VO L o a d VS EEE8147- Advanced Power Electronics and Applications ii. Plot the current AND voltage across the magnetizing inductance (), noting all amplitudes and timing. Compare the value of ∆ obtained from the simulation waveform with the theoretical value. iii. Plot the voltage across the output capacitor. Measure ∆ and compare it with the theoretical value. (comment on your results) iv. Now increase the frequency to 150 and discuss any impact that might have on the converter operation. Task 2: discontinuous conduction mode (DCM) operation Rebuild the simulation model described in task 1. Calculate the critical load resistance (.) that set the boundary between CCM and DCM. i. Plot the inductor current waveform showing the minimum value. ii. Now, use THREE times of . and re-run the simulation model again. Evaluate the following: o Plot the input source current waveform and compare it with the current source in task 1. o Show the voltage waveforms across the output resistance, the main switch and diode 1. Task 3: impact of non-ideal components on the converter operation Rebuild the simulation model as in task 1 using the following parameters: Input source () 325 V Ideal transformer 1/2 = 15 Magnetizing inductance = 5 with a series resistance of 0.1Ω MOSFET switch (model level, ideal) Saturation voltage =2V, transistor resistance = 3mΩ, diode forward voltage = 0.7V and diode resistance = 0.1mΩ Diode 1 forward voltage =0.7V and diode resistance = 0.5mΩ Output capacitor = 100 with an ESR of 0.2Ω Duty ratio = 0.1875 Show the output voltage and magnetizing inductance current waveforms and critically discuss your observation with reference to the results obtained in task