Using the sliding-mode control approach for analysis and design of the boost inverter

A cascade control strategy is employed in the boost inverter to generate a sinusoidal signal at grid frequency with very low distortion. The internal loop of the cascade employs a switching surface based on the difference of the inductor currents to induce sliding motions in the power stage. The outer loop in turn establishes the reference of the internal loop and ensures the tracking of an external sinusoidal signal at 50 Hz. The reported approach is analytical and is based on the equivalent control method. The root locus of the capacitor voltages at the equilibrium point of the inner loop is obtained assuming a constant value of the loop reference. In the particular case of a zero reference, sinusoidal variations at grid frequency are superposed to the corresponding equilibrium point and the resulting ideal dynamics are linearised yielding the control to output transfer function of the system. A proportional-integral (PI) compensator is designed for both large bandwidth and small phase error. Experimental results in a 500 W prototype are in perfect agreement with the analytical predictions.