ANALYSIS AND CONTROL OF BIDIRECTIONAL DC-DC CONVERTERS

Abstract

This thesis introduces the design and implementation of 350W conventional bidirectional dc-dc converter with hard switching operation. A more accurate modeling of non-ideal elements of bidirectional dc-dc converter (BDDC) using state space averaging technique is presented. Steady state and small signal analytical expressions are derived individually for both boost and buck mode of BDDC in continuous conduction mode. Type III error amplifier for boost mode and PID controller for buck mode are designed to achieve the desired loop bandwidth of the converter system. Transient performance of the converter is simulated for both boost mode and buck mode to achieve precise regulation against the line and load abrupt change using MATLAB/SIMULINK software package. Hardware prototype of converter is implemented and tested for performance evaluation. The dynamic performance of the converter is then tested against the load variation. With the experimental measurement, the corresponding design has been verified. Results show that the model is accurate and offers a significant improvement in the computation. Ringing effect due to parasitic impedance across MOSFET switching device at 100 kHz is substantially reduced by proper selection of snubber circuit elements and sophisticated gate drive mechanism. Analysis of three-phase interleaved bidirectional dc-dc converter (IBDDC) in continuous conduction mode using state space averaging method has been presented in this thesis. Analytical expression of small signal control to duty ratio has been derived for the three-phase IBDDC operates either in boost mode or in buck mode. Two or more identical converters are connected in parallel to reduce both input and output ripple currents, hence size of the capacitor decrease. Non-isolated three-phase IBDDC offers many advantages like equal current sharing capability among individual converter, increased output power, better utilization of switches, lower switching loss, increased efficiency, fast dynamic response, lower per phase ripple, reduced input and output ripple. The basic operation of three-phase IBDDC, steady state, small signal analysis, and voltage mode control of IBDDC are clearly described. Simulation of type 3 error amplifier and fuzzy logic controller based three-phase IBDDC is carried out in Simulink/SimPowerSystem and load dynamic performance is compared with the experimental results.