Menu 4 − Current Control

Mode: Regeneration

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.

The different duty ratings modify the inductor protection characteristic (see Inductor Thermal Time Constant (04.015)), and also change the maximum settings for the current limits. 

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.

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. Current limits are applied to the active current reference. For more details of the current limit system and the calculation of the variable maximum that limits the current limit user parameter (VM_MOTOR1_CURRENT_LIMIT) see the "Drive Limits" document included in this parameter reference guide.

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.

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 flowing from the supply and negative when power is flowing into the supply.

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.

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.

See Power From Supply Current Limit (04.005).

See Motoring Current Limit (04.005).

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.

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. The following should be noted:

1. When the regen drive first becomes active the d.c. bus voltage controller will be active and will raise the d.c. voltage to the reference level defined by Voltage Set Point (03.005). Once the required level is reached the d.c. voltage controller is disabled and the active current reference can be controlled with  Active Current Reference (04.009).
2. If the d.c. bus controller is not active then either the d.c. bus voltage must be defined by another system connected to the d.c. bus or some form of control must be provided by the user.

See Active Current Reference (04.009).

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.

See Current Controller Kp Gain (04.013).

A single time constant thermal model is provided that can be used 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 I_Rated)]² x (1 − e^-t/τ)

where:
T = Inductor Protection Accumulator (04.019)
I = Current Magnitude (04.001)
I_Rated = 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.

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 I_Rated)]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.

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.

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

See Inductor Thermal Time Constant (04.015).

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.

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 Iq, Torque Producing Current (04.002) and Id, Magnetising 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.   

User Current Maximum Scaling (04.024) defines the variable maximum/minimums VM_USER_CURRENT and VM_USER_CURRENT_HIGH_RES which are applied to Percentage Load (04.020), Torque Reference (04.008) and Torque Offset (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.

See Inductor Thermal Time Constant (04.015).

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.