Current mode control of frequency controlled resonant converters

This paper examines an implementation of the average current mode control (ACMC) in a frequency controlled series resonant converter used in a telecommunication rectifier. This control mode provides very fast output overcurrent protection and improves reliability of the series resonant converter. In addition it improves significantly the dynamic response of the output voltage control loop to meet the toughest telecommunication standards as well as the dynamic response of the current sharing loop of parallel connected rectifiers. Various telecom standards regarding output voltage dynamic response are analysed and the control loop bandwidth necessary to meet these requirements is identified. The transfer functions of the converter system are identified by measurements and curve fitting methods. An appropriate compensation for the current and voltage loop is selected and designed. Experimental results verifying the design are presented. This control method is practically implemented in a 58 V/100 A, telecom rectifier. It operates at 300 kHz with more than 92% efficiency and has a current control loop bandwidth of 20 kHz.