The synchronous machines are the primary generating units of power systems , from the load side , synchronous motors will also be used . This indicates that the synchronous machine one of the most important components of electric power systems . Synchronous ac machines find application as motors in constant speed applications and when interfaced to the energy source with a variable-frequency converter system , in variable-speed applications . High-performance variable-speed motor drives are often constructed employing a permanent-magnet synchronous motor .