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

Biaxial excitation generator for automobile (BEGA) is proposed as a solution for integrated starter/alternator systems used in hybrid electric vehicles (HEVs). This paper demonstrates through experiments and simulations that BEGA has a very large constant power speed range (CPSR), theoretically to infinite. 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 truly dc. brush machine (with zero reactance in steady state !). 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. 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, especially for high current excursion. In order to increase the torque response quickness, the d- axis current i_d is controlled with non-zero reference value only during transients, when there is a difference between the reference and measured dc field current. This way high dynamic performance is secured. Implementation and extensive experiments validate the proposed solutions.