Applications of a mathematical similarity to converter control systems

An invariant control system of PWM (pulse-width modulation) converters is discussed. Such a system ensures the stabilisation of the output quantities (such as voltage, current or a certain time interval) even in open control systems. This control system is obtained by using the carrier voltage with a more complicated form than a simple linear (triangular) form that is usually used in common PWM systems. In the systems discussed here, the carrier voltage follows the form or characteristic of the output quantity, having a mathematical expression, which is similar to those of the output quantity. For this reason the authors call this kind of regulation a mathematical similarity. The general approach of creation of such a carrier voltage and its application in such invariant regulation systems is formulated. Examples of specific invariant PWM systems for a control rectifier, a DC DC converter in continuous and discontinuous operating mode, the power factor corrector and the resonant inverter are given.