The Variable Frequency Drive (VFD), also called Adjustable Speed Drive (ASD) or Adjustable Frequency Drive (AFD) in some applications, has been enhanced to include models for motor starting control schemes, rectifier/inverter/DC-link dynamics, and harmonic spectrum. It can be used to simulate VFD behavior in normal speed control operation, during motor acceleration, and under disturbances to study its impact on system dynamics.
ETAP provides flexible representation and modeling for VFD systems. It can be inserted between a motor and its terminal bus or connected to a motor through transformers and cables to simulate long distance subsea power system. On the input side of VFD, it can be connected to multiple transformers directly to represent 12, 18 or 24 pulse VFDs.
To simulate normal operating conditions, VFD has ten operating categories allowing the user to specify different output frequency values and corresponding output voltage according to user specified V/Hz ratio. The VFD load is calculated based on VFD output frequency and load frequency characteristics. Three options for VFD input power factor are provided: VFD rated power factor, VFD output load power factor and user-specified power factor.
Two control types are provided to simulate VFD operations during motor starting for all available control schemes in today’s applications. The Frequency control scheme allows the user to freely specify VFD output frequency and Volt/Hz as functions of time. This control type can be easily used to model constant power control, constant torque control, and any other forms of controls. The Torque control scheme allows the user to specify motor torque as function of time with a maximum current limit. Voltage boost effect is also simulated in Motor Starting simulation.
The rectifier/inverter/DC-link and dynamic control modeling allows the user to simulate the impact of VFD operations on power system under disturbances, such as sudden load variations, VFD frequency change, or faults in the system.