Frequency converter current-compounding excitation systems
Static current-compounding excitation schemes that provide an isolated synchronous generator with a field current that increases both with increasing load and with worsening power factor have been in existence for many years. Such schemes, while capable of maintaining the on-load terminal voltage substantially constant, require brushes to carry the excitation current to the generator field winding and in some practical applications these brushes may present serious maintenance problems. In a recent development, a new brushless frequency-converter type of excitation system was introduced. This system, while using only passive components, can furnish a loaded synchronous generator with a compounded excitation current such that its terminal voltage is maintained to within a reasonably close tolerance, irrespective of the load power factor. The central unit of the system is a special purpose exciter, the rather unconventional stator windings of which make the concept of an automatically-regulated and brushless generator a practical reality.