PowerFlex 755 Parameter List and Uses

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). 

1. PowerFlex 755 Parameter Settings for use with a Sine-wave Output Filter

The table below outlines the default and required parameter settings for using a PowerFlex 755 drive with a sine-wave output filter. 

No.Parameter DescriptionDefault SettingRequired Setting
P35Motor Control Mode0 “Sensorless Vector” 0 (Induction VHz)
P38Pulse-Width Modulation (PWM) Frequency2 kHz or 4 kHzSet to match with the filter’s frequency tuning
P40Reflected Wave: 5-Bit1 “Turned On”0 (Turned Off)
P40PWM Level-Type Select: 7-bit1 “Full-time three-phase”  1 (Full-time three-phase)
P40Asynchronous PWM Lock: 8-Bit0 “Turned Off” 1 (Turned On)
P40PWM Frequency Lock: 9-Bit0 “Turned Off”1 (Turned On)
P40Electric Stab-Lok: 11-Bit 
(Voltage Stability Gain Off) 
(Angle Stability Gain Off)
1 “Enabled”0 (Disabled)
P40Transistor Diagnostics: 12-Bit1 “Turned On”0 (Turned Off)
P43Flux Up Mode1 “Automatic”0(Manual)
P44Flux Up TimeReference Frame – Dependent0.0000 seconds
P420Drive Overload Mode3-Level “Single Channel PWM”Option 1 (Reduce Current Limit)
P1153  Dead-Time Compensation100%Adjust from 100% to 0%
P1154  DC Offset Control0 “Turned Off”1 (Turned On)

Table 1.1: PowerFlex 755 Parameter Settings for use with Sine-Wave Output Filters

1.2 Parameters Description

P35[Motor Control Mode]: This parameter has to be set to Volts per Hertz Control (VHz) since the sine-wave output filter includes resistive, capacitive, and inductive components between the PowerFlex 755 drive and the motor being controlled. The VHz setting prevents the load from resembling an equivalent of a motor circuit to the drive, used in Sensorless Vector Control (SVC) or Flux Vector Control (FVC). Hence, with this setting, the PowerFlex 755 drive will only operate in a simple VHz control mode.
Note, do not autotune the drive on applying this setting. Because an autotune function may fail to complete whenever the VHz setting is applied.

P38[PWM Frequency]: Guidelines on how to set the Pulse-Width Modulation (PWM) frequency are as per the usage instructions of the sine-wave filter. Also, the settings of this parameter depend on the PWM rating of the PowerFlex 755 drive being used. 

P40 [Motor Configuration Options]:

  • Reflected Wave: The reflected wave 5-bit parameter is turned off so that the output voltage waveform does not have any missing pulses. Also, turning off this parameter minimizes any DC offsets that might appear. 
  • PWM Level-Type Select: This 7-bit parameter is maintained at its default value of 1 “full-time three-phase modulation” (space vector) without an option to switch over to 2-phase modulation. A two-phase modulation mode is likely to degrade the filter’s performance.
  • Asynchronous PWM Lock: The asynchronous PWM 8-bit lock has to switch on since the sine-wave filter is tuned to the carrier frequency. This setting requires the carrier to be fixed, as changes in the carrier frequency would make the filter not function. Also, the PWM frequency must be set to whatever value the filter frequency is tuned to; which can be either 2 kHz or 4 kHz. 
  • PWM Frequency Lock: The 9-bit pulse-width modulation frequency lock is turned on because the sine-wave filter is tuned to the carrier frequency. The PWM frequency setting should match the output filter design. 
  • Electric Stab-Lok: This 11-bit Lok affects the Voltage and Angle stability. When the electrical stability is set to 0(Disabled), the voltage stability gain and angle stability gain are automatically set to 0. That means that the two gains will not try to compensate for the current flowing into the capacitors in the filter. 
  • Transistor Diagnostics: The 12-bit transistor diagnostics parameter should be turned off. This is because the sequence that switches the transistors off and on also charges the filter’s capacitors. This can bring about an Instantaneous Over- Current (IOC) fault trip or an F12 [Hard Ware (HW) Over Current] fault. The F12 fault indicates that the PowerFlex 755 drive is drawing in current that is 2-times higher than its rating (mainly around 250%). 

P43 [Flux Up Mode]: The Flux Up Mode parameter is set to 0 (Manual) in order to accommodate motor control that is not equivalent to a motor circuit to the drive.

P44 [Flux Up Time]: The Flux Up Time is set to 0.0000 seconds because the output load does not resemble a motor circuit to the PowerFlex 755 drive. Also, building a stator flux independently before accelerating would be less effective.

P420 [Drive Overload Mode]: The Drive Overload Mode is set to 1 (reduce current limit), which is different from its default setting of 3-Level Single Channel PWM frequency. This is because the frequency of the sine-wave output filter is tuned to the carrier frequency. And if the carrier frequency changes, the output filter would not work. Hence, the carrier frequency must be fixed at a given value.

P1153 [Dead-Time Compensation]: In PowerFlex 755 drives, it is best to set the Dead-Time Compensation parameter to 0% if the output of the sine-wave filter is used as the input to the load transformer. This prevents or reduces the occurrence of DC Offset voltages.

P1154 [DC Offset Control]: This parameter is turned on, so as to enable the DC to offset control whenever the output of the Pulse-Width Modulation inverter is used for non-motor loads. This parameter also disables any offset controls programmed in the drive’s firmware. Note, if you turn on the P1154 parameter then the P1153 parameter should be disabled.

2. PowerFlex 755 Parameter Settings for use with dV/dt Output Filters

As previously mentioned, PowerFlex 755 drives can be used with both LRC dV/dt output filters and LR dV/dt output filters. The required parameter settings when using a PowerFlex 755 with either of the two dV/dt Filters are similar. The only difference is in setting the Motor Control Mode parameter [P35]. The LRC dV/dt filters can only be used with Volts per Hertz (VHz) Control, while the LR dV/dt output filters can be used with either Volts per Hertz (VHz) Control, Flux Vector Control (FVC), or Sensorless Vector Control (SVC). 

The table below provides a list of the required parameter settings when using a PowerFlex 755 drive with LRC dV/dt filters and LR dV/dt filters. 

No.  Parameter Description  Default Setting  Required Setting 
P35Motor Control Mode0 “Sensorless Vector”0 (Induction VHz) for LRC dV/dt Filter 
 VHz, FVC, SVC for LR dV/dt Filter 
P38Pulse-Width Modulation (PWM) Frequency2 kHz or 4 kHzSet to match with the filter’s frequency tuning
P40 Reflected Wave: 5-Bit1 “Enabled” 0 (Disabled)
P40 PWM Type Select: 7-bit1“Full-time three-phase”
1 (Full-time three-phase)
P40 Asynchronous PWM Lock: 8-Bit0 “Disabled”
1 (Enabled)
P40 PWM Frequency Lock: 9-Bit0 “Disabled”1 (Enabled)
P40 Electric Stab-Lok: 11-Bi
(Voltage Stability Gain Off)
(Angle Stability Gain Off)
1 “Enabled”0 (Disabled)
P40Transistor Diagnostics: 12-Bit1 “Enabled”0 (Disabled)
P43Flux Up Mode1 “Automatic”0(Manual)
P44Flux Up TimeReference Frame – Dependent0.0000 seconds
P420Drive Overload Mode3-Level “Single Channel PWM”Option 1 (Reduce Current Limit)

Table 2.1: PowerFlex 755 Parameter Settings for use with dV/dt Output Filters

Note, the operation theory behind the setting of each of the parameters listed in this table (Table 2.1), is as discussed in the “Parameters Description” section 1.2 above.
When using a PowerFlex 755 drive with an LRC dV/dt output filter, it’s very important that you set the Motor Control Mode [P35] parameter to the specific settings of LRC DV/dt filters. Failure to do so would make the drive more prone to F12 [Hard Ware (HW) Over Current] faults, especially for the PowerFlex 755 drives with lower spectrum current capacity rating. Therefore, in case you are using an LRC DV/dt filter at the output of a PowerFlex 755 and there are frequent occurrences of instantaneous over current (IOC) faults; be sure to check the Motor Control Mode settings.

3. PowerFlex 755 Parameter Settings Required when applying Adjustable Voltage Control with a Sine-Wave Output Filter

In PowerFlex 755 drives, Adjustable Voltage Control is enabled by setting the Motor Control Mode[P35] parameter to Option 9 [the Adjustable Voltage Control Mode]. This feature provides either single-phase or three-phase output voltage. Its default setting is a three-phase output voltage, which is selected by parameter P1131 [Adjustable Voltage Configuration].

Note, in single-phase mode, the PowerFlex 755 drive is not designed to operate single-phase motors; as the output load is considered to have a unity power factor comprising of inductance and resistance for non-motor or specially designed motor applications. Rather the output is said to be lagging.

Also, with Adjustable Voltage Control, the reference sources of the input voltage to the PowerFlex 755 drive can be configured using parameter P1133[Adjustable Voltage Select]. The input voltage source can be scaled upwards when the lower limits are applied. Also, the P1136[Adjustable Voltage Trim-Source Select] parameter allows you to select a trim source. Note, the trim voltage is either subtracted from or added to the reference voltage.

The table below lists the required settings of the major parameters used when applying Adjustable Voltage Control through a sine-wave filter at the output of a PowerFlex 755 Variable-Frequency Drive (VFD).

No.Parameter DescriptionDefault SettingRequired Setting
P35Motor Control Mode0 “Sensorless Vector”Option 9 (Adjustable Voltage Control Mode)
P38Pulse-Width Modulation (PWM) Frequency2 kHz or 4 kHz  Set to match with the filter’s frequency tuning
P40Reflected Wave: 5-Bit 1 “Turned On”0 (Turned Off)
P40PWM Level-Type Select: 7-bit1 “Full-time three-phase”1 (Full-time three-phase) 
P40Asynchronous PWM Lock: 8-Bit0 “Turned Off”1 (Turned On)
P40Electric Stab-Lok: 11-Bit
(Voltage Stability Gain Off)
(Angle Stability Gain Off)
1 “Enabled”0 (Disabled)
P40Transistor Diagnostics: 12-Bit1 “Turned On”0 (Turned Off)
P40Jerk Select: 15-Bit1 “Turned On”0 (Turned Off)
P43Flux Up Mode1 “Automatic
(Forced to Automatic) 
0(Manual)
P44Flux Up TimeReference Frame – Dependent0.0000 seconds
P60Start/Acceleration BoostReference Frame-dependent0.00
P61Runtime BoostReference Frame-dependent0.00
P62Breakdown VoltageReference Voltage-dependent0.00
P63Cut-off FrequencyReference Frequency-dependent0.00
P420Drive Overload Mode3-Level “Single Channel PWM”1 (Reduce Current Limit)

Table 3.1 PowerFlex 755 Parameter Settings for use with Adjustable Voltage Control with a Sine-Wave Output Filter

3.2 Parameters Description 

The use of some of the parameter settings listed in the table above (Table 3.1) is as per the previously described operational theory in section 1.2. The aforementioned parameter settings are: (i) P38 [PWM Frequency], (ii) P40 [Motor Configuration Options] including Reflect Wave; PWM Level-Type Select; Asynchronous PWM Lock; Electric Stab-Lok and Transistor Diagnostics, (iii) P43[Flux Up Mode], (iv) P44[Flux Up Time], and (v) P420[Drive Overload Mode].  

Jerk Select: This 15-bit parameter is used when a PowerFlex 755 Variable-Frequency drive with sine-wave output filter is used with LIMs (Linear Induction Motors) having a short-lived acceleration rate.  Set the Jerk bit to 0 “Disabled” to allow for smooth and unlimited acceleration rates of 0.1 seconds in the frequency channel. This setting applies to Volts per Hertz (VHz) and Sensorless Vector motor control modes, in positioning type applications. When set to 1 “Enabled” this parameter prevents 0.0 seconds ramp time. 

Parameters P60 to P63 are set whenever there are DC offset voltages at the input windings of the load transformer.  Their specific uses are as follows: 

P60[Start/Acceleration Boost]: This parameter is used to build-up additional torque for starting off the motor from zero speed, and accelerating heavy motor loads at lower speeds. 

P61 [Runtime Boost]: This parameter is used to create additional torque to allow the PowerFlex 755 drive to operate at slower speeds. The output torque that is generated when this parameter is enabled is typically lower than the required acceleration torque. Hence, the drive will reduce the boost voltage to this level whenever it’s not accelerating (operating at low speeds). This prevents excessive motor heating, which could occur in case the higher Start/ Acceleration boost level was used. 

P62 [Breakdown Voltage] and P63 [Cut-off Frequency]: These parameters are used to provide additional torque to the PowerFlex 755 drive, by increasing the lower portion of the Volts (Voltage) versus Hertz (Frequency) curve. 

The table below provides a list of the parameters that can be adjusted by the user when applying Adjustable Voltage Control through a sine-wave filter at the output of a PowerFlex 755 Variable Frequency Drive (VFD). 

No. Parameter Description Default Setting Required Setting 
P1131 Adjustable Voltage Configuration 1 “Three-Phase” 1 (Three-Phase) or  0 (Single-Phase) 
P1133 Adjustable Voltage Select 0 “Disabled” Preset 1 (Enabled) 
P1134 Adjustable Voltage High Reference 0% 100% 
P1140 Adjustable Voltage Acceleration Time 0 seconds Set the required acceleration seconds 
P1141 Adjustable Voltage Deceleration Time0 Seconds Required seconds (Application dependent) 
P1142 Adjustable Voltage Preset 1 0 VAC (Volts AC) n VAC (Application dependent) 
P1153 Dead-Time Compensation 100% Varies from 100% to 0% 
P1154 DC Offset Control  0 “Turned Off” 1 (Turned On)  

Table 3.2 User Adjustable PowerFlex 755 Parameters for use with Adjustable Voltage Control with a Sine-wave Output Filter

Conclusion

The PowerFlex 755 drive parameter settings described in this article can be used to modify Modulation Mode, Stability Gains, and to prevent over-reaction of the charging current flowing into the capacitors of a Sine-Wave output filter (which is the most commonly used output filter). 

Also, even though motor control applications can be unique and require specific parameter settings for the PowerFlex 755 drive used. This article has listed examples of setups for different types of Volts per Hertz (VHz) Control methods, and the Adjustable Voltage Control mode applied through various output filters. The provided examples can be a great starting point for configuring your PowerFlex 755 drive. For more information or to discuss which PLC Control and Instrumentation solution might be best for your application, please visit our website here, or contact us at sales@dosupply.com or 1-800-730-0292.

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