# Menu 4 − Current Control

Mode: Regeneration

In Regen mode separate current control is provided for the active and reactive currents. The active current reference is normally produced by the d.c. bus voltage controller and power feed-forwards system, although it is possible for the user to define the active current reference if required. The reactive current reference is either defined directly from the Reactive Current Reference (04.008) or from the Reactive Power Input kVAR (03.020). See Menu 3 for more details.

Drive rating information

Current rating

The drive output currents can be represented as a vector. The limits and the scaling applied to the drive output currents are defined by the magnitude of this vector as shown below.

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Throughout this section Rated Current (05.007) and other parameters related to motor 1 are used. It should be noted that this applies if Select Motor 2 Parameters (11.045) = 0. If Select Motor 2 Parameters (11.045) = 1 then M2 Rated Current (21.007) and other parameter associated with motor 2 should be used instead.

The full scale current is the maximum current that the drive can measure and if the current exceeds this level the drive produces an over current trip. Kc is the current scaling for the drive and is used in determining the control performance of the drive. This is given in Full Scale Current Kc (11.061) and Kc is equal the full scale current in r.m.s. Amps. (Note that this is a change from Unidrive SP which used the full scale current multiplied by 0.45 for Kc.)

The maximum current reference is the highest magnitude of the current reference vector in the drive under any circumstances. The area between the maximum current reference and the full scale current provides headroom to allow for overshoot in the current controllers without tripping the drive. In all modes except Open-loop mode, the current limits can be adjusted so that the maximum current reference vector (IMaxRef) is equal to 0.9 x Kc provided Rated Current (05.007) is set to the Maximum Heavy Duty Rating (11.032) or less. If Rated Current (05.007) is set to a higher level then the current limits can be adjusted so that the maximum current reference vector (IMaxRef) is equal to 1.1 x Maximum Rated Current (11.060) or 0.9 x Kc whichever is lower.

In Open-loop mode the current is limited by the peak limit system to a maximum level of 0.8 x Kc. The peak limit controls the total current, however the Open-loop control system current limit only applies to the torque producing current and would limit the maximum current to IMaxRef if the magnetising current remains constant at its rated level. IMaxRef must give headroom below the peak limit and is set at 0.7 x Kc, provided Rated Current (05.007) is set to the Maximum Heavy Duty Rating (11.032) or less. If Rated Current (05.007) is set to a higher level then the current limits can be adjusted so that the maximum current reference vector (IMaxRef) is equal to 1.1 x Maximum Rated Current (11.060) or 0.7 x Kc whichever is lower.

The drive can have a heavy duty rating intended for applications where high overload current may be required under transient conditions, or it can have a normal duty rating where a lower level of overload current is required. The duty rating is selected automatically by the drive based on the setting of Rated Current (05.007). The Maximum Heavy Duty Rating (11.032) and Maximum Rated Current (11.060) are fixed for each drive size and the table below shows the possible duty ratings that can be selected depending on the levels of these parameters.

Conditions | Possible duty ratings
Maximum Heavy Duty Rating (11.032) = 0.00 | Normal duty operation only
Maximum Heavy Duty Rating (11.032) < Maximum Rated Current (11.060) | Heavy duty operation if rated current > MAX, otherwise normal duty operation
Maximum Heavy Duty Rating (11.032) = Maximum Rated Current (11.060) | Heavy duty operation only

The different duty ratings modify the motor protection characteristic (see Motor Thermal Time Constant 1 (04.015) for motor control modes, and Inductor Thermal Time Constant (04.015) for Regen mode). The different duty ratings can also change the level of IMaxRef as described previously.

In a drive that contains multiple power modules Full Scale Current Kc (11.061) is the full scale current of an individual module multiplied by the number of modules. Maximum Heavy Duty Rating (11.032) and Maximum Rated Current (11.060) are the value for an individual module multiplied by the number of modules.

Variable Maximums applied to the current limits

The variable maximums applied to the current limit parameters are VM_MOTOR1_CURRENT_LIMIT for motor map 1 and VM_MOTOR2_CURRENT_LIMIT for motor map 2. The calculations given below are used in each drive mode to define VM_MOTOR1_CURRENT_LIMIT. Similar calculations based on the equivalent motor map 2 parameters are be used to define VM_MOTOR2_CURRENT_LIMIT.

Regen mode

In Regen mode the drive orientates the output current vector to align with the voltage vector that represents the voltage at its terminals, and so unless specifically required, all the current is active current and there is no reactive current. Therefore the maximum value for the current limit parameters is calculated in the same way as for RFC-S mode:

VM_MOTOR1_CURRENT_LIMIT = (IMaxRef / IRated) x 100%

where

IRated = Rated Current (05.007)

A maximum is applied to the reactive current reference parameter so that the combined current reference for the active and reactive currents does not exceed IMaxRef.

VM_REGEN_REACTIVE = √(VM_MOTOR1_CURRENT_LIMIT2 – ILimit2)

where

ILimit is gives the highest level of the active current reference that can occur. This value is defined by the current limit values. If the current limits are all set to their maximum values (i.e. VM_MOTOR1_CURRENT_LIMIT) then there is no current capability left for the reactive current. However, if the current limits are reduced the resulting headroom can be used for the reactive current. ILimit is defined by a combination of all the current limits excluding any reduction of the current limit due to the motor thermal model, It should be noted that if Island Detection Enable (03.030) = 1 then VM_REGEN_REACTIVE is reduced by 5% to allow for the islanding system injection current.

Parameter | 04.001 Current Magnitude
--- | ---
Short description | Shows the instantaneous drive output current
Mode | Regeneration
Minimum | −VM_DRIVE_CURRENT_UNIPOLAR | Maximum | VM_DRIVE_CURRENT_UNIPOLAR
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 4ms write
Display Format | Standard | Decimal Places | 3
Coding | RO, FI, VM, ND, NC, PT

Current Magnitude (04.001) is the instantaneous regen drive output current scaled so that it represents the r.m.s. phase current in Amps under steady state conditions.

Parameter | 04.002 Active Current
--- | ---
Short description | Shows the instantaneous level of active current
Mode | Regeneration
Minimum | −VM_DRIVE_CURRENT | Maximum | VM_DRIVE_CURRENT
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 250µs write
Display Format | Standard | Decimal Places | 3
Coding | RO, FI, VM, ND, NC, PT

Active Current (04.002) is the instantaneous level of active current scaled so that it represents the r.m.s. level of active current under steady state conditions. The Active Current (04.002) is positive when power is flow from the supply and negative when power is flowing into the supply.

Parameter | 04.004 Final Active Current Reference
--- | ---
Short description | Shows the final current reference after the current limits
Mode | Regeneration
Minimum | −VM_TORQUE_CURRENT | Maximum | VM_TORQUE_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 250µs read
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, VM, ND, NC, PT

The Final Active Current Reference (04.004) is the active current reference from the d.c. bus voltage controller and power feed-forward system or user defined value with the current limits applied.

Parameter | 04.005 Power From Supply Current Limit
--- | ---
Short description | Defines the current limit used when power is being taken from the supply
Mode | Regeneration
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

The Power From Supply Current Limit (04.005) limits the active current when power is being taken from the supply. The Power To Supply Current Limit (04.006) limits the active current when power is being fed back into the supply. If the Symmetrical Current Limit (04.007) is below the Power From Supply Current Limit (04.005) then it is used instead of the Power From Supply Current Limit (04.005). If the Symmetrical Current Limit (04.007) is below the Power To Supply Current Limit (04.006) then it is used instead of the Power To Supply Current Limit (04.006). It should be noted that if the current limits become active it is no longer possible for the d.c. bus voltage to be controlled.

The maximum possible current limit (VM_MOTOR1_CURRENT_LIMIT [MAX]) varies between drive sizes with default parameters loaded. For some drive sizes the default value may be reduced below the value given by the parameter range limiting.

Parameter | 04.006 Power To Supply Current Limit
--- | ---
Short description | Defines the current limit used when power is being fed back into the supply
Mode | Regeneration
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

See Power From Supply Current Limit (04.005).

Parameter | 04.007 Symmetrical Current Limit
--- | ---
Short description | Defines the symmetrical current limit
Mode | Regeneration
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

See Power From Supply Current Limit (04.005).

Parameter | 04.008 Reactive Current Reference
--- | ---
Short description | Defines the reactive current reference
Mode | Regeneration
Minimum | −VM_REGEN_REACTIVE | Maximum | VM_REGEN_REACTIVE
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 250µs read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

Reactive Current Reference (04.008) can be used to define a level of reactive current other than the default value of zero, so that the regen drive can be made to produce or consume reactive power. Reactive Current Reference (04.008) defines the level of reactive current as a percentage of the Rated Current (05.007). Positive reactive current produces a component of current flowing from the supply to the regen that lags the respective phase voltage, and negative reactive current produces a component of current that leads the respective voltage.

The variable maximum applied to Reactive Current Reference (04.008) is used to ensure that the total current does not exceed the maximum allowed. If the current limits are at their maximum values then no reactive current is allowed and VM_REGEN_REACTIVE_REFERENCE[MIN] = 0 and VM_REGEN_REACTIVE_REFERENCE[MAX] = 0. As the Final Current Limit (04.018) is reduced then more reactive current is allowed.

Parameter | 04.009 Active Current Reference
--- | ---
Short description | Defines the active current reference
Mode | Regeneration
Minimum | −VM_USER_CURRENT | Maximum | VM_USER_CURRENT
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 250µs read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

If Active Current Reference Selector (04.010) = 0 then the active current reference is defined by the d.c. bus voltage controller and the power feed-forward system. If Active Current Reference Selector (04.010) = 1 then the user can define the active current reference. The polarity of Active Current Reference (04.009) is the same as Active Current (04.002), and so a positive value causes power to flow from the supply to the regen drive, and a negative values causes power to flow from the regen drive to the supply. It should be noted that the regen drive can no longer control its own d.c. bus voltage, and so this must be controlled by some external system.

Parameter | 04.010 Active Current Reference Selector
--- | ---
Short description | Set to enable the user active current reference
Mode | Regeneration
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 1 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 0
Coding | RW

See Active Current Reference (04.009).

Parameter | 04.013 Current Controller Kp Gain
--- | ---
Short description | Defines the current loop controller proportional gain
Mode | Regeneration
Minimum | 0 | Maximum | 30000
Default | 90 | Units |
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

Current Controller Kp Gain (04.013) and Current Controller Ki Gain (04.014) are the proportional and integral gains of the current controllers. Either standard or high performance modes, selected with Current Controller Mode (04.030), can be used for a regen drive. In many applications the default gains can be used, but under certain supply conditions it is necessary to reduce the Current Controller Kp Gain (04.013) to prevent instability.

Parameter | 04.014 Current Controller Ki Gain
--- | ---
Short description | Defines the current loop controller integral gain
Mode | Regeneration
Minimum | 0 | Maximum | 30000
Default | 2000 | Units |
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

See Current Controller Kp Gain (04.013).

Parameter | 04.015 Inductor Thermal Time Constant
--- | ---
Short description | Set to the inductor thermal time constant
Mode | Regeneration
Minimum | 1.0 | Maximum | 3000.0
Default | 89.0 | Units | s
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 1
Coding | RW

A single time constant thermal model is provided that can be use to estimate the temperature of the regen inductors connected between the regen drive and the supply. The input to the model is the Current Magnitude (04.001). The Inductor Protection Accumulator (04.019) is given by the following equation.

T = 100.0% x [I / (K1 x IRated)]2 x (1 − e-t/τ)

where:
T = Inductor Protection Accumulator (04.019)
I = Current Magnitude (04.001)
IRated = Rated Current (05.007)
τ = Inductor Thermal Time Constant (04.015)

If Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) then K1 = 1.05, otherwise K1 = 1.01.

Inductor Protection Accumulator Reset
The initial value in the Inductor Protection Accumulator (04.019) at power-up is defined by Inductor Protection Accumulator Power-up Value (04.036) as given in the table below.

Inductor Protection Accumulator Power-up Value (04.036) | Inductor Protection Accumulator (04.019) at power-up
Power Down | The value is saved at power-down and is used as the initial value at power-up.
Zero | The value is set to zero.
Real Time | If a real-time clock is present and if Date/Time Selector (06.019) is set up to select the real-time clock then the value saved at power-down is modified to include the effect of the inductor thermal protection time constants over the time between power-down and power-up. This modified value is then used as the initial value at power-up. If no real time clock is present then and this option is selected then the value saved at power-down is used as the initial value.

The Inductor Protection Accumulator (04.019) is reset under the following conditions:

1. Inductor Thermal Time Constant (04.015) is set to 0.0. Note that this is not possible in the standard product as the minimum parameter value is 1.0.
2. Rated Current (05.007) is modified.

Inductor Protection Accumulator Warning
If [I / (K1 x IRated)]2 > 1.0 then eventually the Inductor Protection Accumulator (04.019) will reach 100% causing the regen drive to trip. If this is the case and Inductor Protection Accumulator (04.019) > 75.0% then [Ind Overload] alarm indication is given and Inductor Overload Alarm (10.017) is set to one.

Parameter | 04.017 Reactive Current
--- | ---
Short description | Shows the instantaneous level of reactive current
Mode | Regeneration
Minimum | −VM_DRIVE_CURRENT | Maximum | VM_DRIVE_CURRENT
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 250µs write
Display Format | Standard | Decimal Places | 3
Coding | RO, FI, VM, ND, NC, PT

Reactive Current (04.017) is the instantaneous level of reactive current scaled so that it represents the r.m.s. level of reactive current under steady state conditions.

Parameter | 04.018 Final Current Limit
--- | ---
Short description | Shows the final current limit that is applied to the active current
Mode | Regeneration
Minimum | −VM_TORQUE_CURRENT | Maximum | VM_TORQUE_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 4ms write
Display Format | Standard | Decimal Places | 1
Coding | RO, VM, ND, NC, PT

Final Current Limit (04.018) is the current limit level that is applied to the active current.

Parameter | 04.019 Inductor Protection Accumulator
--- | ---
Short description | Shows the level of the inductor protection accumulator
Mode | Regeneration
Minimum | 0.0 | Maximum | 100.0
Default |  | Units | %
Type | 16 Bit Power Down Save | Update Rate | Background write
Display Format | Standard | Decimal Places | 1
Coding | RO, ND, NC, PT

See Inductor Thermal Time Constant (04.015).

Parameter | 04.020 Percentage Load
--- | ---
Short description | Shows the level of active current as a percentage of rated current
Mode | Regeneration
Minimum | −VM_USER_CURRENT | Maximum | VM_USER_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | Background write
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, VM, ND, NC, PT

Percentage Load (04.020) gives the Active Current (04.002) as a percentage of the Rated Current (05.007). Positive values indicate power flow from the supply to the regen drive and negative values indicate power flow from the regen drive to the supply.

Parameter | 04.021 Current Feedback Filter Disable
--- | ---
Short description | Disables the 16ms filter applied to current feedback parameters
Mode | Regeneration
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 1 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

If Current Feedback Filter Disable (04.021) = 0 a 4ms filter is applied to the current feedback components measured by the drive to be used in Active Current (04.002) and Reactive Current (04.017). This filter removes ripple components associated with the PWM switching. If Current Feedback Filter Disable (04.021) = 1, the filter is disabled and the user parameters are based on the current components sampled every 250us.

Parameter | 04.024 User Current Maximum Scaling
--- | ---
Short description | Defines the maximum for the active current reference and percentage load parameters
Mode | Regeneration
Minimum | −VM_TORQUE_CURRENT_UNIPOLAR | Maximum | VM_TORQUE_CURRENT_UNIPOLAR
Default | 175.0 | Units | %
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

User Current Maximum Scaling (04.024) defines the variable maximum/minimum VM_USER_CURRENT which is applied to Percentage Load (04.020) and Active Current Reference (04.009). This is useful when routing these parameters to an analog output as it allows the full scale output value to be defined by the user.

The maximum value (VM_TORQUE_CURRENT_UNIPOLAR [MAX]) varies between drive sizes with default parameters loaded. For some drive sizes the default value may be reduced below the value given by the parameter range limiting.

Parameter | 04.036 Inductor Protection Accumulator Power-up Value
--- | ---
Short description | Defines the initial power-up value of the inductor protection accumulator
Mode | Regeneration
Minimum | 0 | Maximum | 2
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | Background write
Display Format | Standard | Decimal Places | 0
Coding | RW, TE

Value | Text
0 | Power down
1 | Zero
2 | Real time

See Inductor Thermal Time Constant (04.015).

Parameter | 04.040 Final Reactive Current Reference
--- | ---
Short description | Shows the final reactive current reference
Mode | Regeneration
Minimum | -200.0 | Maximum | 200.0
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 250µs write
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, ND, NC, PT

Final Reactive Current Reference (04.040) gives the reactive current reference that is defined by the user plus any current that is injected by the island detection system.