Robust control of PWM power amplifier by approximate 2-degree-of-freedom digital controller with bumpless mode switching

Robust PWM power amplifiers whose transient response characteristics do not deteriorate against extensive load changes and/or direct-current power-supply voltage changes are needed. In this paper, a digital robust controller with bumpless mode switching for PWM power amplifiers which can satisfy such demands and can extend the range of capacitive load wider is proposed. It is necessary to measure the value of load to implement this bumpless mode switching automatically according to the load range. Thus, the method of estimating capacitive load is shown. Although it is necessary to use current for estimating capacitive load, it is expensive if a current sensor is used. Therefore, an easy current estimating method which can be performed more cheaply is shown. The current estimated by this method is used for capacity estimation and current feedback. The bumpless mode switching is automatically performed by estimating a capacitive value, without specifying the value of capacitive load beforehand. That is, the value of capacitive load is estimated during DDC execution, and the control mode is automatically switched bumplessly according to this estimated value. The digital controller equipped with capacity estimation and the bumpless mode switching is realized by a DSP. An experiment shows that the digital controller with the proposed bumpless mode can satisfy larger specifications.