Control Techniques Unidrive SP Part Numbers and Modes

To better understand your UNIDRIVE SP Model, look at the part number. The guide below breaks down SP range numbers for you and explains each section individually.

The Control Techniques Unidrive SP is designed in order to operate in multiple modes, all of which are explained below:

• Open Loop Mode: Power is applied to the motor by the drive at frequencies that change according to the operator. The speed of the motor comes from the output frequency of the drive and slip (a result of the mechanical load). Slip compensation allows the drive to improve the speed control of the motor. Depending on whether V/F mode or open loop vector mode is selected will determine the motor’s performance at a lower speed.
  • Vector Mode: Voltage applied to the motor is directly proportional to the frequency, except at low speed – the drive uses motor parameters to apply accurate voltage. This keeps the flux constant under conditions of changing loads. (100% torque is usually available down to 1 Hz for a 50 Hz motor).
  • Fixed V/F Mode: Voltage is directly proportional to the frequency, except at low speed – where voltage boost is provided. (100% torque is usually available down to 4 Hz for a 50 Hz motor).
  • Quadratic V/F Mode: Voltage is directly proportional to the square of the frequency except at low speed – voltage boost is provided and set by the operator. Quadratic V/F Mode can be used for running fan or pump apps with quadratic load characteristics, or multi-motor apps. However, it is not suitable for apps that require a high starting torque.
• RFC Mode: RFC stands for Rotor Flux Control. It provides closed loop control without position feedback. It uses current, voltages and key motor parameters for estimating motor speed and prevents instability that is usually associated with open loop control.
• Closed loop vector mode: These are used with induction motors that have a feedback device installed. The speed of the motor is controlled by the drive to ensure the rotor speed is exact. Full torque, all the way down to zero speed, is provided by consistently accurate and controlled motor flux.
• Servo: This mode is used with permanent magnet, brushless motors that have a feedback device installed. The speed of the motor is controlled by the drive through used of the feedback device. This ensures accurate rotor speed. Flux control is not required in this mode because the magnets which form part of the rotor cause the motor to self-excite. To ensure the output voltage is matched accurately to the back EMF of the motor, absolute position information from the feedback device is required.
• Regen: Used as a regenerative front end for four quadrant operation. This mode allows bi-directional power flow back and forth from the AC supply. Energy conservation is more efficient as a result, whereas other applications dissipate energy in the form of heat in a braking resistor. Because of the sinusoidal nature of the waveform, the harmonic content of the input current is insignificant, as compared to a conventional bridge rectifier, or an SCR/thyristor front end.

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