Basic Characteristics of Cycloconverter-Type Commutatorless Motors

Cycloconverter-type commutatorless motors having shunt and series characteristics are treated. Though their principle of performance is almost the same as that of a polyphase separately excited inverter, there is commutation due to source voltage at the ac power source which does not exist with a polyphase separately excited inverter. Theoretical equations for rotational speed of the shunt-type and the series-type motors are derived, and it is shown that these characteristics are the same as for dc machines. Factors affecting commutation due to induced EMF, which is a key point in this type of commutatorless motor, are overlapping angle and armature reaction. In summary, for the shunt type these two increase as load current increases until commutation failure occurs. On the other hand, for the series type these two are independent of load current if the iron does not saturate. So the commutation failure cannot occur with the series type. These phenomena are treated in detail theoretically, and are proven by measuring the effective controlling angle ¿by means of new methods. Other basic characteristics are shown theoretically and experimentally.