# Menu 4 − Torque and Current control

Common Features

Open loop current control

In open loop mode it is possible to control the motor frequency or the motor torque. When the frequency of the motor is controlled (Torque Mode Selector (04.011) = 0) the Post Ramp Reference (02.001) is defined by the ramp system unless the current limits are active. The Post Ramp Reference (02.001) can directly define the output frequency of the drive or this can be modified to compensate for motor slip. If the current limits are active (Current Limit Active (10.009) = 1) the ramp system remains active, but the output of the current controller is added to the ramp output so that the frequency applied to the motor is modified to try and reduce the torque producing current in the motor. For example, if the Post Ramp Reference (02.001) is positive (i.e. motor is running forwards) and the motor is overloaded with a motoring load a positive Torque Producing Current (04.002) is generated that will exceed the Final Current Limit (04.018). This gives a negative error which attempts to reduce the ramp output causing the motor to slow down.

When motor torque is being controlled (Torque Mode Selector (04.011) = 1) The Final Torque Reference (04.003) is converted to a current reference and the current limits are applied giving the Final Current Reference (04.004). This is used as the reference input to the PI controller that regulates the torque producing current in the motor. The output of the PI controller is the Post Ramp Reference (02.001), and so the torque is controlled by increasing or decreasing the motor frequency. This system gives only moderate dynamic performance. For better torque control in a system without position feedback, closed loop current control should be used.

It is possible to disable the flux compensation by setting Flux Control Compensation Disable (05.028) to 1. This is only normally required to prevent motor instability when an inaccurate value for Motor Rated Speed (05.008) is being used in RFC-A mode.

Current Controller Kp Gain (04.013) and Current Controller Ki Gain (04.014) are the proportional and integral gains of the current controller. As already mentioned the current controller either provides current limits or closed-loop torque control by modifying the Post Ramp Reference (02.001). The control loop is also used in its torque mode during supply loss, or when the controlled mode standard ramp is active and the drive is decelerating, to regulate the flow of current into the drive. Although the default settings have been chosen to give suitable gains for less demanding applications it may be necessary for the user to adjust the performance of the controller. The following is a guide to setting the gains for different applications.

Current limit operation
The current limits will normally operate with an integral term only, particularly below the point where field weakening begins. The proportional term is inherent in the loop. The integral term must be increased enough to counter the effect of the ramp which is still active even in current limit. For example, if the drive is operating at constant frequency and is overloaded the current limit system will try to reduce the output frequency to reduce the load. At the same time the ramp will try to increase the frequency back up to the demand level. If the integral gain is increased too far the first signs of instability will occur when operating around the point where field weakening begins. These oscillations can be reduced by increasing the proportional gain. A system has been included to prevent regulation because of the opposite actions of the ramps and the current limit. This can reduce the actual level that the current limit becomes active by 12.5%. This still allows the current to increase up to the current limit set by the user.

However the current limit flag (Current Limit Active (10.009)) could become active up to 12.5% below the current limit depending on the ramp rate used.

Torque control
Again the controller will normally operate with an integral term only, particularly below the point where field weakening begins. The first signs of instability will appear around rated frequency, and can be reduced by increasing the proportional gain. The controller can be less stable in torque control mode compared to when it is used for current limiting. This is because load helps to stabilise the controller, and under torque control the drive may operate with light load. Under current limit the drive is often under heavy load unless the current limits are set at a low level.

Supply loss and standard ramp
The d.c. link voltage controller becomes active if supply loss detection is enabled and the drive supply is lost or standard ramp is being used (Ramp Mode Select (02.004) > 0) and the motor is regenerating. The d.c. link controller attempts to hold the d.c. link voltage at a fixed level by controlling the flow of current from the drive inverter into its d.c. link capacitors. The system is forced into current control mode and the output of the d.c. voltage controller is fed into the current controller as shown below.

Although it is not usually necessary, the d.c. link voltage controller gain can be adjusted with the Voltage Controller Gain (05.031). However, it may be necessary to adjust the current controller gains to obtain the required performance. If the gains are not suitable it is best to set up the drive in torque control first. Set the gains to a value that does not cause instability around the point at which field weakening occurs. Then revert back to open loop frequency control in standard ramp mode. To test the controller the supply should be removed whilst the motor is running. It is likely that the gains can be increased further if required because the d.c. link voltage controller has a stabilising effect, provided that the drive is not required to operate in torque control mode.

RFC current control

In RFC modes, closed-loop current control is provided for the torque and flux producing currents. The torque reference is normally provided by the frequency controller, or from the torque reference, or as a combination of both depending on the value of the Torque Mode Selector (04.011). During supply loss or when standard ramp mode is selected and the motor is regenerating it is possible that the torque producing current reference may be provided by the d.c. link voltage controller as shown above.

Current Controller Kp Gain (04.013) and Current Controller Ki Gain (04.014) are the proportional and integral gains of the current controllers It should be noted that when an auto-tune is performed that measures the Transient Inductance (05.024) and Stator Resistance (05.017) the Current Controller Kp Gain (04.013) and Current Controller Ki Gain (04.014) are automatically set to the levels defined in the description. These represent the maximum levels that are likely to be used with this mode in most applications.

The current controller gains can either be set using auto-tuning (see Auto-tune (05.012)) or the values can be set up manually by the user. The calculations given below are those used by the auto-tuning system and should give good performance without excessive overshoot.

The proportional gain, Current Controller Kp Gain (04.013), is the most critical value in controlling the performance of the current controllers. The required value can be calculated as

Current Controller Kp Gain (04.013) = (L / T) x (Ifs / Vfs) x (256 / 37.5)

where

T is the sample time of the current controllers. The drive compensates for any change of sample time, and so it should be assumed that the sample time is equivalent to the base value of 167μs.

L is the motor inductance. For a permanent magnet motor this is half the phase to phase inductance that is normally specified by the manufacturer. For an induction motor this is the per phase transient inductance (sLs). The inductance for either of these motors can be taken from the manufacturer’s data or it can be obtained from the value stored in the Transient Inductance (05.024) after auto-tuning.

Ifs is the peak full scale current feedback, i.e. full scale current x √2. The r.m.s. full scale current is given by Full Scale Current Kc (11.061), and so Ifs = Full Scale Current Kc (11.061) x √2.

Vfs is the maximum d.c. link voltage.

Therefore

Current Controller Kp Gain (04.013) = (L / 167μs) x (Kc x √2/ Vfs) x (256 / 37.5)

= K x L x Kc

where

K = [√2 / (Vfs x 167μs)] x (256 / 37.5)

There is one value of the scaling factor K for each drive voltage rating as shown in the table below.

Drive Rated Voltage (11.033) | Vfs | K
200V | 415V | 1045
400V | 830V | 522
575V | 990V | 438

The integral gain, Current Controller Ki Gain (04.014), is less critical. A suggested value which matches the zero with the pole caused by the electrical time constant of the motor and ensures that the integral term does not contribute to current overshoot is given by

Current Controller Ki Gain (04.014) = Current Controller Kp Gain (04.013) x 5 x T / tm

Where tm is the motor time constant (L / R). R is the per phase stator resistance of the motor (i.e. half the resistance measured between two phases).

Therefore

Current Controller Ki Gain (04.014) = (K x L x Kc) x 5 x 167μs x R / L

= 0.0427 x K x R x Kc

The above equations give the gain values that should give a good response with minimal overshoot. If required the gains can be adjusted to modify the performance as follows:

1. Current Controller Ki Gain (04.014) can be increased to improve the performance of the current controllers by reducing the effects of inverter non-linearity. These effects become more significant with higher switching frequency. These effects will be more significant for drives with higher current ratings and higher voltage ratings. If Current Controller Ki Gain (04.014) is increased by a factor of 4 it is possible to get up to 10% overshoot in response to a step change of current reference. For high performance applications, it is recommended that Current Controller Ki Gain (04.014) is increased by a factor of 4 from the auto-tuned values. As the inverter non-linearity is worse with higher switching frequencies it may be necessary to increase Current Controller Ki Gain (04.014) by a factor of 8 for operation with 16kHz switching frequency.
2. It is possible to increase Current Controller Ki Gain (04.014) to reduce the response time of the current controllers. If Current Controller Kp Gain (04.013) is increased by a factor of 1.5 then the response to a step change of reference will give 12.5% overshoot. It is recommended that Current Controller Ki Gain (04.014) is increased in preference to Current Controller Kp Gain (04.013).

As already stated, the drive compensates for changes of switching frequency and the sampling method used by the controller. The table below shows the adjustment applied to the proportional and integral gains.

Switching Frequency (05.037) | Current controller sample time | Current Controller Kp Gain (04.013) adjustment | Current Controller Ki Gain (04.014) adjustment
0.667kHz | 750μs | x 167 / 750 = 0.2 | x 1.0
1kHz | 500μs | x 167 / 500 = 0.3 | x 1.0
2kHz | 500μs | x 167 / 500 = 0.3 | x 1.0
3kHz | 333μs | x 167 / 333 = 0.5 | x 1.0
4kHz | 250μs | x 167 / 250 = 0.7 | x 1.0
6kHz | 167μs | x 167 / 167 = 1.0 | x 1.0
8kHz | 125μs | x 167 / 125 = 1.3 | x 1.0
12kHz | 167μs | x 167 / 167 = 1.0 | x 1.0
16kHz | 125μs | x 167 / 125 = 1.3 | x 1.0

Note: 0.667kHz and 1kHz switching frequencies are not supported on standard drives or by large drive pods.

Parameter | 04.001 Current Magnitude
--- | ---
Short description | Shows the instantaneous drive output current
Minimum | −VM_DRIVE_CURRENT | Maximum | VM_DRIVE_CURRENT
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 16ms
Display Format | Standard | Decimal Places | 2
Coding | RO, FI, VM, ND, NC, PT

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

Parameter | 04.002 Torque Producing Current
--- | ---
Short description | Shows the instantaneous level of torque producing current
Minimum | −VM_DRIVE_CURRENT | Maximum | VM_DRIVE_CURRENT
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 1ms
Display Format | Standard | Decimal Places | 2
Coding | RO, FI, VM, ND, NC, PT

Torque Producing Current (04.002) is the instantaneous level of torque producing current scaled so that it represents the r.m.s. level of torque producing current under steady state conditions. Torque Producing Current (04.002) is proportional to the torque produced by the motor provided field weakening is not active. For field weakening operation the Torque Producing Current (04.002) is boosted for a given level of torque to compensate for the reduction in the motor flux. The sign of Torque Producing Current (04.002) is defined in the table below.

Sign of Torque Producing Current (04.002) | Sign of frequency | Direction of motor torque
+ | + | Accelerating
- | + | Decelerating
+ | - | Decelerating
- | - | Accelerating

Parameter | 04.003 Final Torque Reference
--- | ---
Short description | Shows the final torque reference
Minimum | −VM_TORQUE_CURRENT | Maximum | VM_TORQUE_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 1ms
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, VM, ND, NC, PT

The Final Torque Reference (04.003) will display the same as Torque Reference (04.008) as a percentage.

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

The Final Torque Reference (04.003) is converted into the Final Current Reference (04.004) by applying a torque to current conversion and by applying the Final Current Limit (04.018). The torque to current conversion is applied as follows:

|Output Frequency (05.001)| ≤ Motor Rated Frequency (05.006)
Current reference = Final Torque Reference (04.003)

|Output Frequency (05.001)| > Motor Rated Frequency (05.006)
Current reference = Final Torque Reference (04.003) x Motor Rated Frequency (05.006) / Output Frequency (05.001)

It is possible to disable the flux compensation by setting Flux Control Compensation Disable (05.028) to 1. This is only normally required to prevent motor instability when an inaccurate value for Motor Rated Speed (05.008) is being used in RFC-A mode.

Parameter | 04.005 Motoring Current Limit
--- | ---
Short description | Defines the current limit used when the motor is being accelerated away from standstill
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 165.0 | Units | %
Type | 16 Bit User Save | Update Rate | 16ms
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

The Motoring Current Limit (04.005) limits the current when the motor is being accelerated away from standstill. The Regenerating Current Limit (04.006) limits the current when the motor is being decelerated towards standstill. If the Symmetrical Current Limit (04.007) is below the Motoring Current Limit (04.005) then it is used instead of the Motoring Current Limit (04.005). If the Symmetrical Current Limit (04.007) is below the Regenerating Current Limit (04.006) then it is used instead of the Regenerating Current Limit (04.006).

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 Regenerating Current Limit
--- | ---
Short description | Defines the current limit used when the motor is being decelerated towards standstill
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 165.0 | Units | %
Type | 16 Bit User Save | Update Rate | 16ms
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

See Motoring Current Limit (04.005).

Parameter | 04.007 Symmetrical Current Limit
--- | ---
Short description | Defines the symmetrical current limit
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | 165.0 | Units | %
Type | 16 Bit User Save | Update Rate | 16ms
Display Format | Standard | Decimal Places | 1
Coding | RW, VM, RA

See Motoring Current Limit (04.005).

Parameter | 04.008 Torque Reference
--- | ---
Short description | Defines the torque reference
Minimum | −VM_USER_CURRENT | Maximum | VM_USER_CURRENT
Default | 0.0 | Units | %
Type | 32 Bit User Save | Update Rate | 1ms
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

See Final Torque Reference (04.003).

Parameter | 04.011 Torque Mode Selector
--- | ---
Short description | Defines the torque mode used by the drive
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | 16ms
Display Format | Standard | Decimal Places | 0
Coding | RW

If Torque Mode Selector (04.011) = 0 the ramp system defines the Post Ramp Reference (02.001) unless the current limits are active, and so the motor is frequency controlled. If Torque Mode Selector (04.011) = 1 the torque controller defines the Post Ramp Reference (02.001), and so the motor is torque controlled.

Parameter | 04.013 Current Controller Kp Gain
--- | ---
Short description | Defines the current loop controller proportional gain
Minimum | 0.00 | Maximum | 4000.00
Default | 20.00 | Units |
Type | 32 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 2
Coding | RW

Current Controller Kp Gain (04.013) and Current Controller Ki Gain (04.014) are the proportional and integral gains of the current controller.

Refer to Torque and Current control .

Parameter | 04.014 Current Controller Ki Gain
--- | ---
Short description | Defines the current loop controller integral gain
Minimum | 0.000 | Maximum | 600.000
Default | 40.000 | Units |
Type | 32 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 3
Coding | RW

See Current Controller Kp Gain (04.013).

Parameter | 04.015 Motor Thermal Time Constant 1
--- | ---
Short description | Set to the thermal time constant for the motor
Minimum | 1 | Maximum | 3000
Default | 179 | Units | s
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

A single time constant thermal model is provided that can be used to estimate the motor temperature as a percentage of its maximum allowed temperature. The input to the model is the Current Magnitude (04.001). Throughout the following discussion Motor Rated Current (05.007) is used in the model assuming Select Motor 2 Parameters (11.045) = 0. If Select Motor 2 Parameters (11.045) = 1 then M2 Motor Rated Current (21.007) is used instead.

Percentage Losses
The losses in the motor are calculated as a percentage value, so that under these conditions the Motor Protection Accumulator (04.019) would eventually reach 100%.

Percentage Losses = 100% x [Load Related Losses]

where

Load Related Losses = I / (K1 x IRated)2

where
I = Current Magnitude (04.001)
IRated = Motor Rated Current (05.007)

The value of K1 defines the continuous allowable motor overload as a proportion of the Motor Rated Current (05.007) before the Motor Protection Accumulator (04.019) reaches 100%. The value of K1 can be used to model reduced cooling at low frequencies and to allow the motor to operate under rated conditions with a small margin to prevent spurious trips. K1 is defined in more detail later.

Motor Protection Accumulator
So far the steady state motor losses have been defined, but the motor model must estimate the temperature within the motor under dynamically changing conditions, and so the Motor Protection Accumulator (04.019) is given by the following equation.

T = Percentage Losses x (1 - e-t/τ1)]

where
T = Motor Protection Accumulator (04.019)
τ1 = Motor Thermal Time Constant 1 (04.015)

Reduced cooling with lower frequency
If Low Frequency Thermal Protection Mode (04.025) = 0 the characteristic is intended for a motor which can operate at rated current over the whole frequency range. Induction motors with this type of characteristic normally have forced cooling. If Low Frequency Thermal Protection Mode (04.025) = 1 the characteristic is intended for motors where the cooling effect of motor fan reduces with reduced motor frequency below half of rated frequency. The maximum value for K1 is 1.05, so that above the knee of the characteristics the motor can operate continuously up to 105% of rated current.

If Motor Rated Current (05.007) > Maximum Heavy Duty Rating (11.032) then K1 is defined as shown below. Two different characteristics are provided, but in both cases the motor performance is limited at lower frequencies and the permissible overload is reduced from 105% to 101%.

Time for Motor Protection Accumulator to reach 100%
The time for the Motor Protection Accumulator (04.019) to change from its initial value to 100% is given by the following equation:

Time to reach 100.0% = -τ1 x ln[(1 - C1) / (C0 - C1)]

C0 represents the conditions that have persisted for long enough for the Motor Protection Accumulator (04.019) to reach a steady state value. If the motor current and frequency are I0 and w0 then

C0 = [(1 - Kfe) x (I0 / (K1 x IRated)2] + [Kfe x (w0 / wRated)1.6]

C1 represents the conditions that begin at the start of the time being calculated. If the motor current and frequency are by I1 and w1 then

C1 = [(1 - Kfe) x (I1 / (K1 x IRated)2] + [Kfe x (w1 / wRated)1.6]

Example 1: Motor Thermal Time Constant 1 (04.015) = 89s, the initial current is zero, Motor Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) and the new level of current is 1.5 x Motor Rated Current (05.007).

C0 = 0
C1 = [1.5 / (1.05 x 1.0)]2 = 2.041

Time to reach 100.0% = -179 x ln(1 - 1/C1) = -179 x ln(1 - (1 / 2.041)) = 120s

This is the default setting for Open loop and Closed Loop modes allowing an induction motor to run at 150% rated current for 120s from cold.

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

Motor Protection Accumulator Power-up Value (04.036) | Motor 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 motor 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 Motor Protection Accumulator (04.019) is reset under the following conditions:

1. Motor Thermal Time Constant 1 (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. Select Motor 2 Parameters (11.045) is modified.
3. Motor Rated Current (05.007) is modified when Select Motor 2 Parameters (11.045) = 0, or M2 Motor Rated Current (21.007) is modified when Select Motor 2 Parameters (11.045) = 1.

Motor Protection Accumulator Warning
If Percentage Losses > 100% then eventually the Motor Protection Accumulator (04.019) will reach 100% causing the drive to trip or the current limits to be reduced. If this is the case and Motor Protection Accumulator (04.019) > 75.00% then a Motor Overload alarm indication is given and Motor Overload Alarm (10.017) is set to one.

Parameter | 04.016 Thermal Protection Mode
--- | ---
Short description | Set to the require thermal protection mode
Minimum | 0 (Display: 00) | Maximum | 3 (Display: 11)
Default | 0 (Display: 00) | Units |
Type | 8 Bit User Save | Update Rate | Background read
Display Format | Binary | Decimal Places | 0
Coding | RW

Thermal Protection Mode (04.016) defines the action taken by the drive when Motor Protection Accumulator (04.019) reaches 100% and/or the drive thermal monitoring parameters approach their trip levels. The bits in Thermal Thermal Protection Mode (04.016) are defined as follows:

Bit | Function
0 | 0 = Motor Too Hot trip is initiated when Motor Protection Accumulator (04.019) reaches 100% 1 = Motor Too Hot trip is disabled and current limiting on motor overload is active as described below
1 | 0 = Drive thermal monitoring current limiting is disabled 1 = Drive thermal monitoring current limiting is described is active

The required current limit is derived from the current limit parameters (Motoring Current Limit (04.005) to Symmetrical Current Limit (04.007) or 21.027 to 21.029) depending on the set-up and conditions. The current limit can be further limited by current limit on motor overload and/or drive temperature monitoring as shown below to give the Final Current Limit (04.018).

Current limiting on motor overload
When the Motor Protection Accumulator (04.019) reaches 100.0% the current limit is limited to (K - 0.05) x 100.0%. This limitation is removed when the Motor Protection Accumulator (04.019) falls below 95.0%.

Drive thermal monitoring current limiting
If any of the drive temperature monitoring parameters (Stack Temperature (07.004) and Auxiliary Temperature (07.005)) are above their trip threshold minus 10°C the one that is closest to its trip threshold is used to modify the current limits as follows:

Final Current Limit (04.018) = Current limit x (Trip threshold - T) / (Trip threshold - 10°C)

where T is the drive temperature monitoring parameter value.

If the Percentage Of Drive Thermal Trip Level (07.036) is above 90% then the final current limit is modified as follows:

Final Current Limit (04.018) = Current limit x (100% - Percentage Of Drive Thermal Trip Level (07.036)) / 10%

If both of the above attempt to reduce the final current limit the lowest calculated value of current limit is used. This system has the effect of reducing the current limit to zero at the point where the drive should be tripped because its thermal monitoring has reached a trip threshold. This is intended to limit the load on the drive to prevent it from tripping when supplying a load that increases with frequency and does not include rapid transients (i.e. a fan).

Parameter | 04.017 Magnetising Current
--- | ---
Short description | Shows the instantaneous level of magnetising current
Minimum | −VM_DRIVE_CURRENT | Maximum | VM_DRIVE_CURRENT
Default |  | Units | A
Type | 32 Bit Volatile | Update Rate | 1ms
Display Format | Standard | Decimal Places | 2
Coding | RO, FI, VM, ND, NC, PT

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

Parameter | 04.018 Final Current Limit
--- | ---
Short description | Shows the final current limit that is applied to the torque producing current
Minimum | −VM_TORQUE_CURRENT | Maximum | VM_TORQUE_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 16ms
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 torque producing current. See Thermal Protection Mode (04.016).

Parameter | 04.019 Motor Protection Accumulator
--- | ---
Short description | Shows the level of the motor protection accumulator
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 Motor Thermal Time Constant 1 (04.015).

Parameter | 04.020 Percentage Load
--- | ---
Short description | Shows the level of torque producing current as a percentage of rated torque producing current for the motor
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 Torque Producing Current (04.002) as a percentage of the rated torque producing current for the motor. Positive values indicate motoring and negative values represent regenerating.

Parameter | 04.024 User Current Maximum Scaling
--- | ---
Short description | Defines the maximum for the torque reference and percentage load parameters
Minimum | −VM_TORQUE_CURRENT_UNIPOLAR | Maximum | VM_TORQUE_CURRENT_UNIPOLAR
Default | 165.0 | 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/minimums VM_USER_CURRENT which is applied to Percentage Load (04.020). This is useful when routing these parameters to an analogue 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 | 04.025 Low Frequency Thermal Protection Mode
--- | ---
Short description | Set to enable low frequency thermal protection mode
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

See Motor Thermal Time Constant 1 (04.015).

Parameter | 04.026 Percentage Torque
--- | ---
Short description | Displays the torque producing current as a percentage or motor rated current
Minimum | −VM_USER_CURRENT | Maximum | VM_USER_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | Background read
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, VM, ND, NC, PT

Percentage Torque (04.026) gives the Torque Producing Current (04.002) as a percentage of the rated torque producing current for the motor, but with an additional adjustment above rated frequency so that it gives percentage torque. Below rated frequency, Percentage Torque (04.026) = Percentage Load (04.020). Above rated frequency, the Percentage Torque (04.026) is adjusted as follows:

Percentage Torque (04.026) = Percentage Load (04.020) x Motor Rated Frequency (05.006) / Output Frequency (05.001)

Parameter | 04.036 Motor Protection Accumulator Power-up Value
--- | ---
Short description | Defines the initial power-up value of the motor protection accumulator
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | Background write
Display Format | Standard | Decimal Places | 0
Coding | RW, TE

Value | Text
0 | Pr.dn
1 | 0

See Motor Thermal Time Constant 1 (04.015).

Parameter | 04.041 User Over Current Trip Level
--- | ---
Short description | Defines the trip level for the user over-current trip as a percentage of the drive over current trip level.
Minimum | 0 | Maximum | 100
Default | 100 | Units | %
Type | 8 Bit User Save | Update Rate | Background Read
Display Format | Standard | Decimal Places | 0
Coding | RW, RA

The User Over-Current Trip protection level in % of Full Scale Current Kc (11.061) which is the full scale current in r.m.s. Amps. The User Over-Current Trip may be used to limit the output current of the drive when supplying a motor with a lower current rating than the drive. If the value of User Over Current Trip Level (04.041) is set at 100%, the user over-current trip is disabled.