An AC motor operates using alternating current through its field windings to create and electromechanically magnet which in turns drives the rotor assembly via north/south pole attraction. The basic AC motor designs are induction, synchronous and three phase industrial. Some AC motors will allow a limited amount of speed control by varying input voltage but, usually it is a only on the top 20% of its speed range.
The motion control industry has adopted the use on three phase motors for not only their ability to run across three phase line voltage (230VAC,460VAC) but because they can be used in conjunction with variable frequency drives (VFD).
Typically, an AC Controller consists of three basic parts: the rectifier, inverter, and the DC link to connect the two. The rectifier converts AC input into DC (direct current), while the inverter switches the DC voltage to an adjustable frequency AC output voltage. The inverter can also be used to control output current flow if needed. Both the rectifier and inverter are directed by a set of controls to generate a specific amount of AC voltage and frequency to match the AC motor system at a given point in time.
There are three common Variable Frequency Drives (VFDs) that offer both advantages and disadvantages depending on the application they are used for. The three common VFD designs used include: Current Source Inverter (CSI), Voltage Source Inverter (VSI), and Pulse Width Modulation (PWM). However, there is a fourth type of VFD called Flux Vector Drive, which is emerging in popularity among end-users for its closed-loop control feature. Each VFD consists of a Converter, DC Link and Inverter section but how each one is constructed varies from drive to drive. Although the sections of each VFD are similar, they require a variation in circuitry in how they supply the frequency and voltage to the motor.
If you would like to have us prepare a competitive quote on AC controls, please contact one of our sales representatives or contact our office directly at (949) 369-8000.