Sigma Delta modulation is a technology stemming from modern signal processing and is mainly known from audio systems, ADCs and DACs. The basic idea behind sigma delta modulation is that the quantiser output is fed back (see Figure). Thus, the quantisation error influences all following errors. This method is described as noise shaping conversion, i.e. the quantisation noise can be shaped by a filter H(s) in the feedback path. The transfer function G(s) in the forward path consists in most cases of one or more integrators.
When it comes to convert a continuous signal into a power signal, Pulse Width Modulators (PWMs) are mainly used in industry. They run at a fixed carrier frequency and map a continuous signal with a certain bandwidth to a high frequency switched signal with two states, corresponding to two opposite voltages. The resulting signal then drives some power electronics such as IGBT modules which finally driv a load. That type of power electronics is well known.
The idea persued in this work is to apply sigma delta modulation techniques instead, replacing a PWM chip by a sigma delta modulator. Both DAC and PWM are replaced by a digital circuit which can directly built into a digital circuity of a controller.
Wurmsdobler, P., H. Jörgl and M. Buyle: Digital current control using a switching power amplifier and sigma delta modulation. In Proceedings of the Fourth European Control Conference, Brussels, Belgium, 1997.
Wurmsdobler, P. : Sigma delta modulation for class D power amplifiers for the use in digital audio or other indutive loads. Project description, 1999.