A simple nonlinear gain scheduling method in digital PWM converter control

In this paper, we analyze a simple, yet effective nonlinear digital control approach-gain scheduling of the A/D converter, in PWM converters to achieve system stability and improved dynamic performance. It is shown that a nonlinear gain scheduling could be conveniently realized and implemented, e.g. right after the A/D converter in digital controlled PWM converters. Several simple gain scheduling schemes are analyzed with describing function method, and associated gains are derived and provided. Experimental results on a FPGA system showed that the buck converter transient response could be improved via nonlinear gain scheduling method. However, in boost and buck-boost converters, it is necessary to make proper controller adjustment (pole and zero) so that the system stability is guaranteed not only with normal gain, but also with reduced gain.