Design of Low-Cost Voltage Sensing Method of Three-phase Synchronous Rectifier with High-Efficiency for Automotive Alternator

Design of low-cost voltage sensing method of three-phase synchronous rectifiers with high-efficiency for automotive alternators is proposed in this paper. A new control strategy and low-cost circuitry topology are applied. There are many control methods for Power MOSFETs of synchronous rectifiers to replace the conventional rectifier diodes for the improvement of the efficiency of AC/DC rectifier. Most of those methods for such synchronous rectifiers based on operational amplifiers which are sensitive and easy interfered by electronic noise, the proposed circuitry for voltage sensing in this paper is low-cost with diodes and resistors are used to sense the positive and negative voltage of each phase for determining when to switch the synchronous rectifiers thereby emulate the operation of conventional rectifier diodes. Sensing three-phase voltage and controlling Power MOSFETs state are done by micro-controller so this method is more stable. Measurements are taken on a prototype of proposed synchronous rectification compared to a conventional diode rectification for a standard automotive alternator. The experiment shows that the efficiency of the alternator system has been raised to 95.3% in comparison with 83.5% of the conventional diode-rectified alternator at the load of 700 W.