Elevator and Escalator problem

Since the beginning of 21st century variable frequency drive (VFD) has become the preferred choice of controlling elevators and escalators. It replaced the erstwhile legacy of a motor generator (MG set) system which had been used practically through the entire 20th century. It used an AC motor to drive a DC generator for feeding power to a DC motor in a configuration called the Ward-Leonard system. The VFD drives have considerably reduced the lift room footprint, simplified commissioning, and improved energy efficiency.