Robust design of PWM power amplifier by approximate 2-degree-of-freedom digital control with suitable sampling

A robust PWM power amplifier whose transient response characteristics do not deteriorate against an extensive load change and/or direct-current power-supply voltage change is needed. In this paper, a method for designing a digital robust controller for PWM power amplifier which can satisfy such demands is proposed. First, a nominal model of PWM power amplifier is derived from the linear approximation. The controlled object is described by discrete-time systems with consideration of the input dead time. It is shown that a digital controller can be designed in almost the same way as the previously proposed analog controller and then 2-degree-of-freedom digital robust systems are constituted. An integral-type control system is built by carrying out an equivalent conversion. The LC filter and the digital controller which satisfy the design specifications are determined by the proposed design procedure. Especially, the sampling period of the digital controller is determined suitably. A DSP is used to realize the digital controller obtained here. An experiment demonstrates that the proposed digital controller can satisfy all the specifications.