Uday Kumar M (EE13D054)
There is a huge demand for reduction in the size and increase in the power output of the permanent magnet generator. Different rotor configurations are also proposed more specifically for increasing the power density of permanent magnet generator. Few applications like defense applications require an alternator with multiple outputs which can provide different voltage levels at different frequencies. Few applications like wind generator applications require hybrid excited alternators for flux regulation. Whatever may be the application, there is a demand for alternators to be compact and to have high power density. A novel high power density parallel hybrid excitation alternator is proposed for wind generator applications and a novel high power density hybrid flux multiple output permanent magnet alternator is proposed for defense applications in this research work.
In the case of a conventional synchronous alternator, the desired terminal voltage can be achieved either by reducing or increasing the field excitation. On the contrary, air gap flux density of a permanent magnet alternator cannot be regulated easily as compared to conventional alternator. This is due to the fact the magnetic field of the permanent magnet cannot be varied by external means. They are indeed permanent by nature. In order to regulate the terminal voltage of the permanent magnet alternator, many studies on hybrid excitation alternators have been reported in the literature. The Hybrid Excitation Alternator (HEA) uses both permanent magnets and excitation windings as sources of excitation to achieve the advantages of both permanent magnet alternator and conventional synchronous alternator.
Based on the coupling relation between magnetic flux of excitation winding and that of the permanent magnet, hybrid excitation alternators are classified into Series Hybrid Excitation Alternators (SHEA) and Parallel Hybrid Excitation Alternators (PHEA). The flux regulation capability in the case of SHEA is limited because the reluctance offered by the permanent magnets to the excitation winding flux path is high. Double-rotor parallel hybrid excitation alternators are proposed in the literature to achieve wide flux regulation but they are large in size as they consist of two rotors. However, very little attempt has been made in order to have wide flux regulation in a parallel hybrid excitation alternator with single rotor structure.
An innovative rotor excitation topology comprising of permanent magnets and field windings in one rotor for Parallel Hybrid Excitation Alternator (PHEA) is proposed. The proposed rotor configuration of PHEA achieves wide flux regulation with a single rotor structure. In this configuration, some part of the permanent magnet flux is allowed to leak in the rotor itself. The increase or decrease in amount of this leakage magnetic flux is controlled through excitation field control. As a result the air gap magnetic flux is controlled through excitation field control. In this way a wider flux regulation is achieved for the proposed PHEA. The concept is verified with FEM simulation and the concept is explained with required mathematical modeling. A 1.8 kW prototype has been manufactured and experimentally verified in the laboratory.
To address the applications that need multiple outputs, a conventional multiple output PMA is proposed in the literature by having different sets of isolated windings in the stator core but it increases the stator frame length. To address the requirement of not only multiple outputs of an alternator but also high power density of an alternator, a novel hybrid flux multiple output PMA is proposed by utilizing radial and axial flux technologies. The proposed hybrid flux multiple output PMA can provide three AC outputs of 3-phase supply with required voltage levels and frequency levels. At the same time, the proposed hybrid flux multiple output PMA offers higher power density compared to the conventional multiple output PMA. A 6.1 kW prototype has been manufactured and tested to prove the concept.