Abstract:
Inductor inductor capacitor (LLC) series resonant converter is used for high frequency and high
voltage applications. The converter operates in zero voltage swithching (ZVS) region to reduce
swithching loss happened in swithches used to turn ON and OFF the system. This operation makes
the output voltage to be regulated for wide input voltage and load resistance variation with small
variation of switching frequency. This is the main advantage of LLC resonant converter compared
to other resonant converters. But, LLC series resonant DC-DC converter have a problem of the
voltage regulation due to nonlinearity, the uncertainity and disturbance which is caused by the
deviation of input voltage (300-400)V, load resistance (3-8)kΩ and resonant components from the
nominal value. Extended describing function and Jacobian Linearization methods is used to
develop small signal modeling of the converter. But, the linearized system has seven states wich
are not measurable and needs obsrever for controller design. Hence, seven state small signal
modeling of the converter is reduced to two measurable states using the relationship between the
state variables. Model reference adaptive sliding mode controller is designed for simplified second
order system of LLC converter to control the output voltage and rectifier current. The lyapunov
adaptive method is used to estimate the sliding mode controller parameters to solve the disturbance
caused by parameter variation in the converter. The stabilty of controller is checked using
Lyapunov stability criteria. The converter is designed for 4kV output voltage, 0.5A output current
and 2kW output power. The simulation is done using MATLAB/SIMULINK® software. The
simulation result indicates that the adaptive sliding mode controller has better performance
compared to supper twiting sliding mode controller. The setling (ts) is reduced to 2.5msec and rise
time (tr) is increased to
334.24
sec respectively, while the steady state error (ess) is reduced to
0.2%.
