Important problems of the theory and practice of the current electric drive include the problem of widening application area and effective usage of the asynchronous electric drive possessing a series of positive qualities. With the appearance of the digital signal processors new possibilities occurred for further development of the controlled and regulated electric drives of the alternating current, which are placed more high requirements on to provide speed of operation, reliability, accuracy and stability of controlling effects execution, as well as optimal energy consumption. Along with a wide application of the variable-frequency electric drives currently the devices of soft start are demanded. The given devices are three-phase thyristor adjusters of the voltage allowing one to increase softly the voltage at the asynchronous electric engine stator when starting in order to limit impact moment and starting current. The advantage of the similar systems compared with the frequency converters based on the completely controlled keys is cheapness of the power part elements, as well as capability to use thyristor systems for the engines of any power practically.