# Menu 4 − Torque and Current control

Mode: Open‑Loop

In Open-loop mode it is possible to control the motor speed or the motor torque. When the speed 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 Iq, 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 RFC-A mode should be used.

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, or it can have a no-overload rating. The duty rating is selected automatically by the drive based on the setting of Rated Current (05.007). See Maximum Heavy Duty Rating (11.032) for more details. The different duty ratings modify the motor protection characteristic (see Motor Thermal Time Constant 1 (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.

For more details of the current limit system and the calculation of the variable maximums that limit the current limit user parameters (VM_MOTOR1_CURRENT_LIMIT and VM_MOTOR2_CURRENT_LIMIT) see the "Drive Limits" document included in this parameter reference guide.

Parameter | 04.001 Current Magnitude
--- | ---
Short description | Shows the instantaneous drive output current
Mode | Open‑Loop
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

Instantaneous level of fundamental current at the drive output terminals in r.m.s. amps.

Parameter | 04.002 Torque Producing Current
--- | ---
Short description | Shows the instantaneous level of torque producing current
Mode | Open‑Loop
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

Iq, Torque Producing Current (04.002) is the instantaneous level of torque producing current scaled so that it represents the r.m.s. level of current under steady state conditions. Iq, 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 Iq, Torque Producing Current (04.002) is boosted for a given level of torque to compensate for the reduction in the motor flux.

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

Parameter | 04.003 Final Torque Reference
--- | ---
Short description | Shows the final torque reference
Mode | Open‑Loop
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 Torque Reference (04.003) is the sum of the Torque Reference (04.008), and Torque Offset (04.009) if enabled, as a percentage of rated motor torque.

Parameter | 04.004 Final Current Reference
--- | ---
Short description | Shows the final current reference after the current limits
Mode | Open‑Loop
Minimum | −VM_TORQUE_CURRENT | Maximum | VM_TORQUE_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 250µs write
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)| ≤ Rated Frequency (05.006)
Current reference = Final Torque Reference (04.003)

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

Parameter | 04.005 Motoring Current Limit
--- | ---
Short description | Defines the current limit used when the motor is being accelerated away from standstill
Mode | Open‑Loop
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | Default Open Loop Current Limit | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

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
Mode | Open‑Loop
Minimum | −VM_MOTOR1_CURRENT_LIMIT | Maximum | VM_MOTOR1_CURRENT_LIMIT
Default | Default Open Loop Current Limit | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

See Motoring Current Limit (04.005).

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

See Motoring Current Limit (04.005).

Parameter | 04.008 Torque Reference
--- | ---
Short description | Defines the torque reference
Mode | Open‑Loop
Minimum | −VM_USER_CURRENT_HIGH_RES | Maximum | VM_USER_CURRENT_HIGH_RES
Default | 0.00 | Units | %
Type | 32 Bit User Save | Update Rate | 250µs read
Display Format | Standard | Decimal Places | 2
Coding | RW, VM

The torque reference is produced as given in the table below. The result is the required torque reference as a percentage of rated motor torque.

Torque Offset Select (04.010) | Torque reference
Offset (-1) | Torque Offset (04.009)
Reference (0) | Torque Reference (04.008)
Ref + Offset (1) | Torque Reference (04.008) + Torque Offset (04.009)

Parameter | 04.009 Torque Offset
--- | ---
Short description | Defines the torque offset that can be added to the torque reference or selected as the torque reference.
Mode | Open‑Loop
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

See Torque Reference (04.008).

Parameter | 04.010 Torque Offset Select
--- | ---
Short description | Selects the final torque reference as a combination of the torque reference and torque offset.
Mode | Open‑Loop
Minimum | -1 | Maximum | 1
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | 4ms read
Display Format | Standard | Decimal Places | 0
Coding | RW, TE

Value | Text
-1 | Offset
0 | Reference
1 | Ref + Offset

See Torque Reference (04.008).

Parameter | 04.011 Torque Mode Selector
--- | ---
Short description | Defines the torque mode used by the drive
Mode | Open‑Loop
Minimum | 0 | Maximum | 1
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | 4ms read
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 speed 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
Mode | Open‑Loop
Minimum | 0 | Maximum | 30000
Default | 20 | 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 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 Active (10.009) flag 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 base speed, 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. bus voltage controller becomes active if supply loss detection is enabled and the drive supply is lost or standard ramp is being used (Ramp Mode (02.004) > 0) and the motor is regenerating. The d.c. bus controller attempts to hold the d.c. bus voltage at a fixed level by controlling the flow of current from the drive inverter into its d.c. bus capacitors. The system is forced into current control mode and the output of the d.c. bus voltage controller is fed into the current controller as shown below.

Although it is not usually necessary, the d.c. bus 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 speed 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. bus voltage controller has a stabilising effect, provided that the drive is not required to operate in torque control mode.

Parameter | 04.014 Current Controller Ki Gain
--- | ---
Short description | Defines the current loop controller integral gain
Mode | Open‑Loop
Minimum | 0 | Maximum | 30000
Default | 40 | 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 Motor Thermal Time Constant 1
--- | ---
Short description | Set to the thermal time constant for the motor
Mode | Open‑Loop
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 dual 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 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 Rated Current (21.007) is used instead. It should be noted that if the parameters that have been added in addition to those in Unidrive SP are left at their default values the model is a simple single time constant model as provided in Unidrive SP.

Percentage Losses
The losses in the motor are calculated as a percentage value.

Percentage Losses = 100% x [Load Related Losses + Iron Losses]

where:
Load Related Losses = (1 - Kfe) x (I / (K1 x IRated))2
Iron Losses = Kfe x (w / wRated)1.6

where:
I = Current Magnitude (04.001)
IRated = Rated Current (05.007)
Kfe = Rated Iron Losses As Percentage Of Losses (04.039) / 100%

The iron losses are relatively low in motors that have a rated frequency of 60Hz or less, and so the motor could be modelled based on load related losses alone. This can be done by setting Kfe to zero. In motors where iron losses are significant, Kfe defines the proportion of losses that are iron losses under rated conditions (i.e. rated current and rated frequency). For example if the iron losses are 30% of losses and other losses are 70% of losses under rated conditions Rated Iron Losses As Percentage Of Losses (04.039) should be set to 30%.

The value of K1 defines the continuous allowable motor overload as a proportion of the 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 speeds 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 − K2) (1 − e-t/τ1) + K2 (1 − e-t/τ2)]

where
T = Motor Protection Accumulator (04.019)
K2 = Motor Thermal Time Constant 2 Scaling (04.038) / 100%
τ1 = Motor Thermal Time Constant 1 (04.015)
τ2 = Motor Thermal Time Constant 2 (04.037)

[(1 − K2) (1 − e-t/τ1) + K2 (1 − e-t/τ2)] gives the effects of the thermal time constants in the motor. K2 defines the ratio of the contribution to the Motor Protection Accumulator (04.019) value from each of the time constants. If K2 is set to its default value of 0 then only Motor Thermal Time Constant 1 (04.015) is included and the model will give the temperature of the main mass of the motor body. To give better protection to the motor, the model can be used to model a particular point in the motor, for example the stator windings. This can be done by including an additional shorter time constant representing the thermal impedance between the windings and the main mass of the motor body which can be modelled with Motor Thermal Time Constant 2 (04.037).

Reduced cooling with lower speed
If Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) then K1 is defined as shown below. If Low Speed Thermal Protection Mode (04.025) = 0 the characteristic is intended for a motor which can operate at rated current over the whole speed range. Induction motors with this type of characteristic normally have forced cooling. If Low Speed Thermal Protection Mode (04.025) = 1 the characteristic is intended for motors where the cooling effect of motor fan reduces with reduced motor speed below half of rated speed. 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 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 speeds and the permissible overload is reduced from 105% to 101%.

Time for Motor Protection Accumulator to reach 100%
Assuming a single time constant model is being used (i.e. Motor Thermal Time Constant 2 Scaling (04.038), 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 speed 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 speed are by I1 and w1 then,

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

Example 1: The effect of iron losses are not modelled (Kfe = 0), Motor Thermal Time Constant 1 (04.015) = 89s, the initial current is zero, Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) and the new level of current is 1.5 x Rated Current (05.007).

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

Time to reach 100.0% = -89 x ln(1 − 1/C1) = -89 x ln(1 − 1/2.041) = 60s

This is the default setting for Open-loop and RFC-A modes allowing an induction motor to run at 150% rated current for 60s from cold.

Example 2: The effect of iron losses are not modelled (Kfe = 0), Motor Thermal Time Constant 1 (04.015) = 89s, the initial current is Rated Current (05.007), Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) and the new level of current is 1.5 x Rated Current (05.007).

C0 = [1.0 / (1.05 x 1.0)]2 = 0.907
C1 = [1.5 / (1.05 x 1.0)]2 = 2.041

Time to reach 100.0% = -89 x ln((1 − C1) / (C0 − C1)) = -89 x ln[(1 − 2.041) / (0.907 − 2.041)] = 7.6s

This is the default setting for Open-loop and RFC-A modes allowing an induction motor to run at 150% rated current for 7.6s after running under rated conditions for a significant period of time.

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. Rated Current (05.007) is modified when Select Motor 2 Parameters (11.045) = 0, or M2 Rated Current (21.007) is modified when Select Motor 2 Parameters (11.045) = 1.
4. Thermal Protection Mode (04.016) is modified.

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) > 70.0% then [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
Mode | Open‑Loop
Minimum | 0 | Maximum | 4
Default | 0 | Units |
Type | 8 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW, TE

Value | Text
0 | Motor Trip
1 | Motor Limit
2 | Drive Limit
3 | Both Limit
4 | Disabled

Thermal Protection Mode (04.016) defines the action taken by the drive when Motor Protection Accumulator (04.019) reaches 100% and/or Percentage Of Drive Thermal Trip Level (07.036) exceeds 90%. The actions for each mode are given in the table below.

Thermal Protection Mode (04.016) | Actions
Motor Trip (0) | Motor Too Hot trip is initiated when Motor Protection Accumulator (04.019) reaches 100%. No current limiting. Motor Protection Accumulator (04.019) is limited to 100.0%.
Motor Current Limit (1) | Motor Too Hot trip is disabled. Current limiting on motor overload as described below. Motor Protection Accumulator (04.019) is limited to 100.0%.
Drive Current Limit (2) | Motor Too Hot trip is initiated when Motor Protection Accumulator (04.019) reaches 100%. Current limiting on drive thermal monitoring as described below. Motor Protection Accumulator (04.019) is limited to 100.0%.
Motor and Drive Current Limit (3) | Motor Too Hot trip is disabled. Current limiting on motor overload and drive thermal monitoring as described below. Motor Protection Accumulator (04.019) is limited to 100.0%.
Disabled (4) | Motor Too Hot trip is disabled and Motor Overload alarm is disabled. No current limiting. Motor Protection Accumulator (04.019) is limited to 200.0%.

The current limit is derived from the current limit parameters (i.e. Motoring Current Limit (04.005), etc.) 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 (K1 – 0.05) x 100.0%. This limitation is removed when the Motor Protection Accumulator (04.019) falls below 95.0%. (K1 is defined in the description of Motor Thermal Time Constant 1 (04.015).)

Drive thermal monitoring current limiting
If Percentage Of Drive Thermal Trip Level (07.036) exceeds 90% the 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 speed and does not include rapid transients.

Parameter | 04.017 Magnetising Current
--- | ---
Short description | Shows the instantaneous level of magnetising current
Mode | Open‑Loop
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

Id, 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
Mode | Open‑Loop
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 give the Final Current Reference (04.004).

Parameter | 04.019 Motor Protection Accumulator
--- | ---
Short description | Shows the level of the motor protection accumulator
Mode | Open‑Loop
Minimum | 0.0 | Maximum | 200.0
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
Mode | Open‑Loop
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 Iq, Torque Producing Current (04.002) as a percentage of the rated torque producing current for the motor.

Sign of Percentage Load (04.020) | Sign of frequency or speed | Direction of motor torque
+ | + | Accelerating
- | + | Decelerating
+ | - | Decelerating
- | - | Accelerating

With synchronous reluctance or high saliency permenant motors it is difficult to predict the torque based on the motor current because the torque depends on the motor inductance which varies with current. To obtain an indication of torque (motor load) the rated motor torque should be set in Rated Torque (04.041) and Percentage Torque (04.026) should be used to give the torque or load indication.

Parameter | 04.021 Current Feedback Filter Disable
--- | ---
Short description | Disables the 4ms filter applied to current feedback parameters.
Mode | Open‑Loop
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 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.

Parameter | 04.024 User Current Maximum Scaling
--- | ---
Short description | Defines the maximum for the torque reference and percentage load parameters
Mode | Open‑Loop
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

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 or when using them as the destination for an analog input, as it allows the full scale 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 Speed Thermal Protection Mode
--- | ---
Short description | Set to enable low speed thermal protection mode
Mode | Open‑Loop
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 | Calculated torque as a percentage of rated torque
Mode | Open‑Loop
Minimum | −VM_USER_CURRENT | Maximum | VM_USER_CURRENT
Default |  | Units | %
Type | 16 Bit Volatile | Update Rate | 4ms write
Display Format | Standard | Decimal Places | 1
Coding | RO, FI, VM, ND, NC, PT

This parameter gives the motor torque with reasonable accuracy as a percentage of rated torque and is intended to be used to trim the torque reference to improve the relationship between the torque reference and the actual motor torque in RFC-A and RFC-S modes. It can also be used as an indication of the motor torque as a percentage of rated torque. The table below shows the parameters that are needed for Percentage Torque (04.026) to operate.

Parameter | Comments
Rated Torque (04.041) | Must be set up so the measured torque can be converted to a percentage.
Stator Resistance (05.017) | Required. Measured during auto-tuning.
Number Of Motor Poles (05.011) | Required.
No-load Core Loss (04.045) | Improves the measured torque accuracy. Measured during auto-tuning in RFC-A mode. Could be estimated during calibration tests with a torque transducer.
Rated Core Loss (04.046) | Further improves the measured torque accuracy. Could be estimated during calibration tests with a torque transducer.
Torque Estimation Minimum Frequency (04.042) | The default value of 5% of rated frequency should be suitable in most applications.
Torque Correction Time Constant (04.043) | Torque trimming is enabled if this is set to a non-zero value. (RFC-A and RFC-S modes only.)
Torque Correction Maximum (04.044) | The default value of 20% is suitable for most applications. (RFC-A and RFC-S modes only.)

The shaft torque of the motor is estimated by the drive and Percentage Torque (04.026) gives this torque as a percentage of the expected Rated Torque (04.041). The default value for Rated Torque (04.041) is zero which disables this feature so that Percentage Torque (04.026) is always zero. To enable this torque estimation system Rated Torque (04.041) should be set to the expected torque from the motor under rated conditions. The percentage torque is calculated as follows.

Torque(%) = [(Output power - Stator losses) / (2π x Output frequency / Motor poles/2)] ×100% / Rated Torque (04.041)
= [(Output Power (05.003) - Stator losses) / (2π x Output frequency / (Number Of Motor Poles (05.011)/2))] ×100% / Rated Torque (04.041)

The stator losses are split into resistance loss and core loss.

Stator losses = Resistance loss + Core power loss

Resistance loss = Current Magnitude (04.001)2 × Temperature Compensated Stator Resistance (05.050)

Core power loss = No-load Core Loss (04.045) + (Rated Core Loss (04.046) - No-load Core Loss (04.045)) x (Torque Producing Current / Rated Torque Producing Current)

If Rated Core Loss (04.046) ≤ No-load Core Loss (04.045) then only the no load value is used and Core power loss = No-load Core Loss (04.045). This provides some compensation for core losses, but not the load dependent component. The core loss power values can be difficult to obtain except by experimental measurement because the loss mechanisms within the motor are complex and are affected by the PWM frequencies applied to the motor by the drive. It is possible to obtain an estimate for No-load Core Loss (04.045) during auto-tuning for RFC-A mode, but not RFC-S mode. As the auto-tuning algorithm cannot measure Rated Core Loss (04.046) this is set to zero, so that it is not used. If power dependent core losses are to be included Rated Core Loss (04.046) must be set by the user.

At low output frequencies this estimate of torque is inaccurate. Torque Estimation Minimum Frequency (04.042) defines the frequency as a percentage of rated frequency where the calculated torque is too inaccurate to use.

For Open-loop and RFC-A modes: FThreshold = Rated Frequency (05.006) x Torque Estimation Minimum Frequency (04.042) / 100.

For RFC-S mode: FThreshold = Rated Speed (05.008) x number of motor poles / 120 x Torque Estimation Minimum Frequency (04.042) / 100.

The table below shows how Percentage Torque (04.026) is calculated at different frequencies.

Condition | Percentage Torque (04.026) RFC-A and RFC-S modes | Percentage Torque (04.026) Open-loop mode
|Output Frequency (05.001)| < FThreshold | Final Torque Reference (04.003)* | 0
FThreshold ≤ |Output Frequency (05.001)| < 2FThreshold | Changes linearly between Final Torque Reference (04.003) and calculated torque including core losses | 0
|Output Frequency (05.001)| ≥ 2FThreshold | Calculated torque including core losses | Calculated torque including core losses

*As the torque reference and actual torque may not align well with some motors, the ratio of the torque reference and measured torque is stored when the frequency is above 2FThreshold and this is then used when the frequency is below 2FThreshold to try and improve the estimated torque.

In RFC-A and RFC-S modes Percentage Torque (04.026) can be used to trim the torque reference and improve the relationship between the torque reference and the actual torque if Torque Correction Time Constant (04.043) is non-zero.

Parameter | 04.036 Motor Protection Accumulator Power-up Value
--- | ---
Short description | Defines the initial power-up value of the motor protection accumulator
Mode | Open‑Loop
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 Motor Thermal Time Constant 1 (04.015).

Parameter | 04.037 Motor Thermal Time Constant 2
--- | ---
Short description | Can be used to define an additional motor thermal time constant
Mode | Open‑Loop
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

See Motor Thermal Time Constant 1 (04.015).

Parameter | 04.038 Motor Thermal Time Constant 2 Scaling
--- | ---
Short description | Defines the ratio of the contribution to the motor protection accumulator value from each of the time constants
Mode | Open‑Loop
Minimum | 0 | Maximum | 100
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 | 04.039 Rated Iron Losses As Percentage Of Losses
--- | ---
Short description | Set to the rated iron losses of the motor as a percentage of the total losses for the motor
Mode | Open‑Loop
Minimum | 0 | Maximum | 100
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 | 04.041 Rated Torque
--- | ---
Short description | Rated motor torque used to calculate percentage torque.
Mode | Open‑Loop
Minimum | 0.00 | Maximum | 50000.00
Default | 0.00 | Units | Nm
Type | 32 Bit User Save | Update Rate | Background Read
Display Format | Standard | Decimal Places | 2
Coding | RW

See Percentage Torque (04.026).

Parameter | 04.042 Torque Estimation Minimum Frequency
--- | ---
Short description | Minimum frequency used by the torque correction system
Mode | Open‑Loop
Minimum | 0 | Maximum | 100
Default | 5 | Units | %
Type | 8 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 0
Coding | RW

See Percentage Torque (04.026).

Parameter | 04.045 No-load Core Loss
--- | ---
Short description | Defines the no-load core loss for the motor used by the torque correction system
Mode | Open‑Loop
Minimum | 0.000 | Maximum | 99999.999
Default | 0.000 | Units | kW
Type | 32 Bit User Save | Update Rate | Background Read
Display Format | Standard | Decimal Places | 3
Coding | RW

See Percentage Torque (04.026).

Parameter | 04.046 Rated Core Loss
--- | ---
Short description | Defines the rated core loss for the motor used by the torque correction system
Mode | Open‑Loop
Minimum | 0.000 | Maximum | 99999.999
Default | 0.000 | Units | kW
Type | 32 Bit User Save | Update Rate | Background Read
Display Format | Standard | Decimal Places | 3
Coding | RW

See Percentage Torque (04.026).