BEGA Starter/Alternator—Vector Control Implementation and Performance for Wide Speed Range at Unity Power Factor Operation

The Biaxial Excitation Generator for Automobiles (BEGA) is proposed as a solution for integrated starter/alternator systems used in hybrid electric vehicles. This paper demonstrates through experiments and simulations that BEGA has a very large constant power speed range. A vector control structure is proposed for BEGA operation during motoring and generating, at unity power factor with zero $d$ -axis current $(i_{d})$ and zero $q$-axis flux $(\Psi_{q})$ control. In such conditions, BEGA behaves like a separately excited dc brush(commutator) machine, in the sense that no stator inductance voltage drop occurs in such constraint control conditions. A high $i_{q}$ current is required in order to cancel the $q$-axis flux, during unity power factor operation. This engages higher copper losses in the machine under light load. In order to minimize the copper losses, for lower load levels, a current referencer is proposed. Due to higher dc field excitation time constant, the dc field current response is not very fast, particularly for high-current excursion. In order to increase the torque response quickness, the $d$-axis current $i_{d}$ is controlled with a nonzero reference value only during transients, when there is a difference between the reference and measured dc field currents. This way, high dynamic performance is secured. Implementation, digital simulation, and experimental results validate the proposed solutions.