# 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.

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 may produce 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 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 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)). 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.

The diagram shows a motor operating with a current equal to IMaxRef, which was defined in the previous section. The magnetising and torque producing motor currents are defined for rated conditions as follows.

IRated = Rated Current (05.007)

cos φ = Rated Power Factor (05.010)

The angle between the total current vector and the torque producing current (cos φ) is assumed to be equivalent to the power factor. The power factor is really the angle between the voltage and current vectors. Normally for Open-loop operation the difference between the power factor and cos f is small and can be neglected. Therefore

Rated magnetising current IMrated = IRated sin φ

Rated torque producing current ITrated = IRated cos φ

Assuming that the magnetising current does not change with load then when the motor operates with maximum allowed current (IMaxRef) the torque producing current is given by:

ITlimit = IMaxRef x cos(sin-1(IMrated / IMaxRef))

The maximum required current limit setting is given by:

VM_MOTOR1_CURRENT_LIMIT = (ITlimit / ITrated) x 100%

As mentioned previously the magnetising current does vary slightly with load, but the headroom between IMaxRef and the peak limit should allow for this.

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

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
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 | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
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
Mode | Open‑Loop
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 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 | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | 4ms read
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
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

Gives the required torque reference as a percentage of rated motor torque.

Parameter | 04.009 Torque Offset
--- | ---
Short description | Defines the torque offset to be added to 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 | 4ms read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

The torque offset added to Torque Reference (04.008) if Torque Offset Select (04.010) = 1.

Parameter | 04.010 Torque Offset Select
--- | ---
Short description | Set to add the torque offset to the torque reference
Mode | Open‑Loop
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 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.

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) > 75.0% 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 (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 Percentage Of Drive Thermal Trip Level (07.036) exceeds 90%. The bits in 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 as described below is active

The required current limit is derived from the current limit parameters (04.005 to 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 (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 | 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
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. Positive values indicate motoring and negative values represent regenerating. It should be noted that if Active Saliency Torque Mode (05.066) = 1 indicating that the high saliency motor control system is being used in RFC-S mode that compensation is provided to give a linear relationship between the torque reference and the actual motor torque. This has the effect of making Percentage Load (04.020) higher than the torque reference between zero and rated torque reference.

Parameter | 04.021 Current Feedback Filter Disable
--- | ---
Short description | Disables the 16ms 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, RA

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.

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 | Sows the 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

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 torque defined by 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 the torque estimation system Rated Torque (04.041) should be set to the expected torque from the motor under rated conditions. For accurate torque estimation, and consistent results for both motoring and regenerating conditions, it is necessary to provide the drive with the core losses under no-load and rated load conditions at rated speed (i.e. No-load Core Loss (04.045) and Rated Core Loss (04.046) respectively). The drive will then include the core power loss in the torque calculation as

PCoreLoss = 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 PCoreLoss = 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 algortihm 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.

Parameter | 04.027 Low Load Detection Level
--- | ---
Short description | Defines the low load detection level
Mode | Open‑Loop
Minimum | 0.0 | Maximum | 100.0
Default | 0.0 | Units | %
Type | 16 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 1
Coding | RW

If Low Load Detection Level (04.027) is set to 0.0 the low load detection system is disabled, otherwise the low load detection system is enabled. The low load detection system is provided so that loss of load can be detected and action taken. So that the detector can be used with fan and pump type loads, where the load is relatively light at low motor speed, the detector is only active when the output frequency or speed is above the level defined by Low Load Detection Speed/Frequency Threshold (04.028). The detector is also only enabled when the motor is at the required speed (i.e. not accelerating or decelerating), and so it is only active when At Speed (10.006) = 1. Once the detector is active, the low load condition is detected when the Percentage Load (04.020) falls below the threshold defined by Low Load Detection Level (04.027). Therefore the condition for detecting low load is given by,

At Speed (10.006) = 1 AND |Output Frequency (05.001)| > Low Load Detection Speed/Frequency Threshold (04.028) AND |Percentage Load (04.020)| Low Load Detection Level (04.027)

The diagram below shows a typical fan type load and the shaded areas define where low load is detected.

Enable Trip On Low Load (04.029) defines the action taken when low load is detected. If Enable Trip On Low Load (04.029) = 0 a Low Load warning is displayed and Low Load Detected Alarm (10.062) is set to one. If Enable Trip On Low Load (04.029) = 1 no warning is given, but a Low Load trip is initiated.

Parameter | 04.028 Low Load Detection Speed/Frequency Threshold
--- | ---
Short description | Defines the low load detection speed/frequency threshold
Mode | Open‑Loop
Minimum | −VM_SPEED_FREQ_REF_UNIPOLAR | Maximum | VM_SPEED_FREQ_REF_UNIPOLAR
Default | 0.0 | Units |
Type | 32 Bit User Save | Update Rate | Background read
Display Format | Standard | Decimal Places | 1
Coding | RW, VM

See Low Load Detection Level (04.027).

Parameter | 04.029 Enable Trip On Low Load
--- | ---
Short description | Defines the action taken when low load is detected
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

See Low Load Detection Level (04.027).

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 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

The estimated torque (Percentage Torque (04.026)) is given as a percentage of Rated Torque (04.041). If Rated Torque (04.041) is left at the default value of zero then Percentage Torque (04.026) will remain at zero under all conditions.

Parameter | 04.042 Torque Estimation Minimum Frequency
--- | ---
Short description | Torque Estimation Minimum Frequency
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

The drive estimates the motor shaft torque (Percentage Torque (04.026)), but at low output frequencies this estimate is very inaccurate. Torque Estimation Minimum Frequency (04.042) defines the point where the estimate of torque is too inaccurate to use and when the modulus of frequency is below this level Percentage Torque (04.026) is zero. The default value of 5% normally prevents a very inaccurate value of estimated torque at low frequencies, but if the stator resistance is very high it may be necessary to increase this threshold.

Parameter | 04.045 No-load Core Loss
--- | ---
Short description | No-load Core Loss
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 | Rated Core Loss
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).