MODELING OF MULTILEVEL CONVERTERS

In this paper, the imbricated cells multilevel converters are studied kind modeled from a control view point, These converters make use of s everal switches connected in a series, which allows using switches wit h reduced voltage ratings; these low voltage switches have lower condu ction losses and can switch at higher frequency, In addition to this f eature common to all converters using series connected switches, the c ontrol signals of multilevel converters can be phase shifted to increa se the apparent switching frequency and improve the dynamic performanc es of the whole converter, It will be shown that a multilevel inverter leg, composed of p pairs of switches and p - 1 capacitors, forms a mu ltivariable nonlinear system that cannot be properly modeled by standa rd methods such as state-space averaging, The transient behavior of th is system depends on the current harmonics and their phase shift with the different control signals, A specific model will be detailed, stud ied, and used to illustrate the properties of these converters, In par ticular, the natural balancing of the voltage across the switches will be demonstrated and the time constants involved in this process will be determined.