Rotary electrical machine

A rotary electrical machine comprising:

• an annular stator having a stator core around which an armature winding is wound, and
• a rotor arranged on an inner circumference side of the stator, wherein
• the rotor includes a field core and a field winding that generates a magnetomotive force by supplying a field current, wherein
• the field core includes:
• a cylindrical boss part provided closer to an inner circumference side of the rotor than the field winding;
• a plurality of disk parts extending outward in a radial direction of the boss part from an axial one end of the boss part and provided at a predetermined angular interval in the circumferential direction of the boss part;
• and
• a plurality of claw-like magnetic pole parts extending in an axial direction of the boss part so as to surround the field winding from tips of the disk parts and having magnetic poles with alternately different polarities formed in the circumferential direction of the rotor, wherein
• when a value obtained by dividing a sectional area of the boss part when the boss part as seen in its axial direction by the number of pole pairs of the rotary electrical machine is Ab, a sectional area of the disk part is Ad, a sectional area of an annular yoke constituting the stator core is Acb, and a sectional area of a tooth per magnetic pole of the plurality of teeth constituting the stator core is At, a smaller one of Ab and Ad is made larger than a smaller one of Acb and At, wherein
• the rotary electrical machine further comprising:
• a switch provided so as to supply power from a power source to the field winding by being turned on and stop supplying power from the power source to the field winding by being turned off;
• and
• a controller that, in a case where a ratio of an on-time to one switching cycle of the switch is defined as a duty ratio, sets the duty ratio on the condition that an upper limit of the duty ratio is set as a predetermined value and turns on/off the switch based on the set duty ratio, wherein
• the predetermined value is set to a value which is larger than the duty ratio corresponding to the field current that gives the maximum reduction amount of the inductance of the field winding with respect to an increasing amount of the field current in a range that the field current can take and which is less than 100%.