About PowerFlex 755

PowerFlex 755 is a variable-frequency AC drive designed by Allen-Bradley/Rockwell Automation, for ease of integration, high motor control performance, advanced safety and application flexibility. This high-power drive (power rating of up to 1500kW) builds on the common user experience and application flexibility of PowerFlex 750-Series, providing heavy industries with an option for state-of -the-art power control.

It is well suited for a wide variety of applications ranging from simple variable torque and variable speed control in demanding industrial systems that require constant torque control. Target applications for PowerFlex 755 AC drives include pumps, conveyors, fans, extruders, compressors and mixers control, as well as process control applications in tire and rubber, metals and mining, oil and gas, and refining industries.

The PowerFlex 755 drives are configured with instructions embedded in Allen-Bradley CompactLogix Programmable Automation Controllers (PACs). Hence, having an understanding of the drive’s parameter settings and functions is an essential prerequisite. This knowledge will enable you to properly program, configure and operate a PowerFlex 755 AC drive seamlessly.

Adjusting a Variable-Frequency PowerFlex 755 drive to perform a given motor control task, requires different parameter settings depending on the type of filter used at the output of the drive. This article provides a detailed list of the key parameters required when applying different types of Volts per Hertz (VHS) Control, or Adjustable Voltage Control through a filter used at the output of a PowerFlex 755 drive. Various types of output filters can be used with PowerFlex 755 drives, namely:

A) Sine-Wave Output Filter: This filter uses a resistor, capacitor, and inductor. It is designed to be used only with Volts per Hertz Control (VHz). Hence, it cannot be used with Sensorless Vector Control (SVC), or Flux Vector Control (FVC).

B) dV/dt Output Filters: These are a derivative of voltage concerning time or rate of voltage change over time filters. They control the voltage transients generated by variable frequency PowerFlex drives and long motor lead lengths. When left uncontrolled, high voltages on the motor leads can lead to premature failure and damage of the motor winding insulation, especially within the first few turns. The dV/dt filters that can be used at the output of a PowerFlex 755 drive include:

• LRC dV/dt Output Filter: This filter uses an Inductor(L), a Resistor(R), and a Capacitor (C). It is designed to be used only with Volts per Hertz Control (VHz). Hence, you cannot use this filter with Sensorless Vector Control (SVC), or Flux Vector Control (FVC).

• LR dV/dt Output Filter: This filter uses only an Inductor(L) and a Resistor(R), it doesn’t have a Capacitor. It is designed to be used with either Volts per Hertz Control (VHz), Flux Vector Control (FVC), or Sensorless Vector Control (SVC).