FOC control is also named Vector Control, it's full name is Field-Oriented Control (FOC), it is an important technology for motor systems, particularly those using permanent magnets (PM). In general, FOC provides an efficient way to control BLDC motor in adjustable speed drive applications that have quickly changing loads, and can improve the power efficiency of an AC induction motor, especially at lower speeds. For this reason, some designers mistakenly associate FOC for use only with AC motors. While it is true that today’s brushless DC (BLDC) motors tend to very efficient, up to 96 percent even without FOC, the value FOC brings to these systems is reduced torque ripple, resulting in smoother motor performance and quieter operation.
In simple terms, FOC is a motor control technique where the system is trying to orient the stationary or “stator” flux vector to a specific degree relative to the rotor flux vector (see Figure 1). The optimal degree of orientation depends upon what characteristic of the motor needs to be maximized. The most common use of FOC is to maximize the motor’s torque per amp. This is achieved when the stator flux vector is 90 degrees to the rotor flux vector unless the motor has a variable reluctance, such as a motor with a magnet buried inside it. In this case, the degree of orientation is typically 115 to 120 degrees.
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