At present, the asynchronous electric motor has become the basic device in most electric drives of load lifting cranes.
The two main disadvantages of the asynchronous motor is the impossibility of a simple rotor speed of rotation, a very high starting current – five-/seven- fold higher than the nominal current. In case of using only mechanical regulation devices, the specified disadvantages will cause big energy losses and impact mechanical loads. It has an extremely negative effect on the service life period of the crane mechanisms.
As a result of scientific works in that direction, a new class of appliances has been born, allowing to solve these problems using the electronic method instead of the mechanical.
The frequency converter with pulse-width control (FC with PWM) decreases the starting currents by 4–5 times. It allows smooth start of the asynchronous motor and controls the drive according to the preset stress/frequency ratio formula.
The frequency converter gives energy consumption saving up to 50%. The possibility of switching on the feedbacks between the adjacent drives appears, i.e. of self-adjusting the equipment according to the assigned task and changing of the operating conditions in the whole system.