Design of Fixed Frequency Sliding Mode Controllers for Fourth Order Class-D Amplifier

Abstract

In sound amplification, mostly in audio power amplifiers, the Signal to Noise Ratio (SNR) and efficiency of the amplifier carries vital significance. In most switching devices, switching losses and the parasitic voltage ringing cause problems at higher frequency spectrum. Higher order LC (Inductor- Capacitor) circuit is used as a filter for removal of above mentioned issues by providing us more attenuation at cutoff frequency resulting in improvements within total harmonic distortion (THD) of an amplifier. The proposed control approach is based on two different sliding mode controller types’ namely terminal sliding mode controller and arbitrary order sliding mode controller. The controller uses capacitor current feedback and inductor current feedback for proposed control law. The control laws are derived from Sliding surface equations for proposed controller respectively. Differentiators are also used for the purpose of noise rejection using their state approximation property. Simulations show that controllers outperformed according to expectations with better results in the form of efficiency, SNR, and frequency response. Performance of controllers in terms of resolving issues like overshoot settling time and steady state error has been excellent. However, further improvements in terms of frequency response and robustness of system, the addition of differentiator proved to be useful. This thesis also presents a detailed comparison between proposed controllers, in terms of their distinctive features and performance.