Sliding Mode Control in Power Converters

Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.4 Fixed-Frequency SM Controller in Power Converters . . . . . . . . . . . 453.4.1 Pulse-Width Modulation-Based Sliding Mode Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.4.2 Duty-Ratio Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.5 Some Design Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Step 1: To Meet Hitting Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Step 2: To Meet Existence Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Step 3: To Meet Stability Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.6 Practical Issues in Analog Implementation . . . . . . . . . . . . . . . . . . . . . . 51The SM control is naturally well suited for the control of variable structure systems. Characterized by switching, power converters are inherently variable structure systems. It is, therefore, appropriate to apply SM control on power converters [105]. Moreover, SM control offers excellent large-signal handling capability, which is important for DC-DC converters. Since the design of conventional pulse-width modulation (PWM) controllers is small-signal based, the converters being controlled operate optimally only for a specific condi-of Switching Powerfail to perform under large parameter or load variations (i.e., large-signal operating condition) [25, 36, 58]. By replacing linear PWM controllers with SM (nonlinear) controllers, power converters can achieve better regulation and dynamical performance for a wider operating range.