Electrical drives have found their way into every industrial application which has motors and movement of personnel and material. Hardly anyone can find a motor circuit nowadays that is not equipped with a drive. The most common variant here is the variable frequency drive (or VFD). Why variable frequency? Let's dive into this complex topic.
The majority of residential and industrial power systems run on alternating power or short "AC". AC power is generated when you have a magnetic field cutting a wire in a swift motion. You could try to replicate this by holding a magnet and wire in your hand. The results would be minuscule, so you'd have to employ a sensitive meter to pick up small amounts of current generated. The way to experience greater measurable power is by using stronger magnetic fields, sitting on a rotating shaft, and cutting a multitude of wires (coils) that are wound in a specific fashion, resting in a stator. This arrangement of a turbo generator may have the size of a small submarine and can easily produce hundreds of Megawatts of power. Take a few of those in parallel, add boilers, steam generation, and cooling towers, and you have a full-fledged power plant.
Now, note that earlier we mentioned there are magnets (fields) on a rotor hitting stator coils with their magnetic field. We actually said "cutting," but that does not mean cutting in a literal sense, it means that the magnetic field is rushing through the coil, hence producing electron flow. Imagine a magnet rotating and its field is rushing by wire coils, similar to a clock, where the magnet is the rotating hand in the center, and the coils represent numbers 1 through 12. This current flow is directional - we won't go into right-hand and left-hand rules here, but just note that the orientation of the magnetic field and the direction of the attack determine which direction the electrons go.