Variable-frequency drive based on salient pole synchronous motor is considered in the article. The subject of research is described. A functional diagram and an integrated structural diagram of mathematical model of synchronous drive vector control system are presented. The task of the electric drive study in intermittent operational modes is formulated. Methods of synchronous drive modeling which enable to define the maximum motor temperature loads are described. The results of computer modeling of intermittent operational modes of the motor with continuous and optimal regulation of armature magnetic flux are given. The service life of the salient pole synchronous motor in respect of maximum allowable motor temperature and torque is defined. Comparative analysis of power losses in synchronous motor during operation of frequency-variable synchronous motor in intermittent modes with continuous and optimal regulation of armature magnetic flux is carried out. The conclusion is made about the efficiency of use of optimal armature magnetic flux regulation in vector control systems of synchronous drives that operate in intermittent modes.