Direct-phase modelling of isolated brushless exciter-alternator unit including the magnetic nonlinearities

Detailed accurate models for brushless alternator units are important for practice and design engineers. The paper presents a state space mathematical model for a standalone unit based on a circuit model in the direct-phase reference frame. Also, a state space mathematical model for an automatic voltage regulator is integrated with the machine model. Due to the existence of the rotating bridge rectifier of the exciter, the topology of the circuit is variable. Therefore, Kron´s tensor technique is applied using a variable connection matrix to develop the mathematical model. The model is complete in the sense that it covers all modes of operation of the bridge rectifier. Consequently, it is capable of simulating any loading conditions. To enhance the model accuracy, electromagnetic nonlinearity effects are introduced through developed saturation factors which consider the mutual saturation effects between the main and leakage fluxes. Also, a new saturation concept using dynamic and static inductances is applied. Various transient responses are computed and compared with test results to verify the validity of the presented model