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Rotational speed detection is important for alternator-voltage-regulator (AVR) to starts-up and generates regulated electric power for vehicles. However, the rotational speed detection in standby mode for self-start is challenging with low loss rectifier, such as the Schottky diode. In this paper, a novel rotational speed detection method by sensing phase voltage or field voltage at specific modes is proposed to solve the issue without extra wiring or external components. The analysis of phase voltage in standby mode considering rectifier leakage current explains the challenges of conventional detection. The derivation of field voltage in standby mode with ANSYS Maxwell simulation verifies the proposed method. The experimental platform with a three-phase six-pole pairs alternator verified that the proposed method can detect rotational speed even in self-start and low speed of 200 rpm.

In this paper, a fast response voltage control circuit is presented which integrates a boost converter and an H-bridge driving circuit. As compared with the traditional voltage control circuit, the proposed one features faster transient response. In the proposed voltage control circuit, the boost converter provides a high voltage for the H-bridge driving circuit. According to Faraday's law, with the assistance of the higher input voltage, the slope of the rotor current can be faster during the excitation period. Similarly, with a high input voltage in the opposite direction across the rotor, the de-magnetizing time can be shortened. Therefore, the alternators can achieve fast response during the load transient.