Invt GD10 Frequency Control Rotary EncoderFrequency Control Using Invt GD10 Rotary Encoder Understanding Frequency Control Using Invt GD10 Rotary Encoder is likely to be a variable frequency drive (VFD) manufactured by the Chinese company INVT. Variable frequency drives are used to control the speed and torque of electric motors. Rotary encoder feedback is a common method used in variable frequency drives to accurately monitor the speed and position of the motor. How Rotary Encoder Feedback Work