Frequency response analysis of a two-axis commutator machine for the development of improved equivalent circuits

• Main Author: Banerjee, Hironmoy
• Published: Imperial College London 1963
• Subjects: 621.381
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602244

An investigation has been made to explore the possibility of representing a two-axis commutator machine by means of lumped parameter equivalent circuits derived on the basis of results of direct-current and steady-state alternating current tests (referred to, in this thesis, as the frequency-response tests) conducted on a dynamo-electric amplifier operating at constant speed. The d.c. resistances and the generative parameters (determined by d.c. excitation tests) have provided thei zeros of the impedance-frequency functions. A variable-speed constant excitation test (d.c.) has been performed; this has established the existence of the parasitic brush currents and has shown their effects on the performance of the machine. A method of analysing the linear operation of the machine by using the signal flow diagrams is presented. The frequency response of the machine has been determined by a series of variable frequency (1-120 c.p.s.) alternating current excitation tests (steady-state), conducted on each 'port' of the machine, in turn. An improved form of Rectangular Co-ordinate Potentiometer has been used. A testing technique has been applied whereby simultaneous measurement of the driving point impedance and all the transfer impedances, pertaining to a particular port, could be made without major circuit modification. The following types of operation of the test-machine have been experimented upon:- (a) Variable speed ant constant excitation; (b) constant speed anal (i) constant applied voltage, try or(ii) constant current excitations or(iii)constant voltage-per-unit frequency. Among the various types of excitation applied and tested, the constant current excitation has been considered as a necessary condition of the frequency response tests from the point of view of evaluating the constant parameters equivalent circuits of the machine when operating at constant speed. The analytical expressions of the impedance-frequency functions are derived by applying the Bode's Attenuation-Phase-Frequency Technique to the impedance-frequency loci. The parameters of the equivalent circuits are evaluated from the impedance functions by applying Brune's method of Network Synthesis. An electronic analogue, formed by the duals of the equivalent circuits, is described. The design, construction and testing of a gyrator is described.