| Abstract |
3-level Pulse-Width Modulation is peculiarly adapted to the control of high-power GTO inverters for variable speed asynchronous machines. It enables to use the GTO technology with high voltage levels, while maintaining a low harmonic contents of wave forms. This paper describes the different modulation modes (asynchronous, synchronous and precalculated) that can be combined to design a modulation strategy in the frequency voltage plane. We introduce in this paper a new method of synchronous dipolar modulation. Its harmonic spectrum has been computed by means of a double Fourier series. A programmed-logic modulator has been developed. For the moment only the dipolar asynchronous and synchronous modulation have been implemented in C language. This modulator has been tested on two prototypes of inverters: the first one is based upon bipolar transistors and is rated 8 kVA, the second one uses GTO and has got a maximum power of 500 kVA. Those tests have confirmed the interesting properties of the 3-level dipolar modulations and the validity of the chosen strategy. |
