ANALYSIS OF A SERIES RESONANT CONVERTER BY PWM CONTROL

Submarine optical-fiber transmission systems are finding greater appli cation in supporting an increasing volume of global-level data transmi ssions. As a result of this development, the power feeding equipment t hat supplies power to submarine repeaters now plays a key role in the operation of communication systems. To ensure that a constant cut-rent is maintained, pulse frequency modulation (PFM) is being used to cont rol series resonant converters commonly employed in power feeding [I]. Power feeding systems supply rated current during stable operation. H ow ever, when they start supplying current, power feeding systems must gradually increase current from zero to the rated current. If cable f ailures occur, a de current lower than the rated current or the de cur rent overlaid with an ac current is used to detect fault locations and wiring routes. PFM control must control operating frequencies from ze ro frequency to control output current from zero amperes. However, con trolling the frequency from zero leads to such problems as the require ment of large smoothing filters, saturation of the transformer core, a nd generation of acoustic noise. To date, a number of solutions have b een suggested. However, most of these solutions require the addition o f components that handle electric power [2-5]. This paper reports a se ries resonant converter that employs PFM around rated current, and pul se width modulation (PWM) below the rated current to avoid inverter tr ansformer saturation and acoustic noise at low frequencies and to make the use of small filler circuits practical [6, 7]. (C) 1998 Scripta T echnica.