Stall Protection
Overview
The stall protection feature protects inverter outputs, as well as the motor, from high current values that occur during (near) standstill situations.
When a stall condition occurs, due to the low rotation speed, the current in all three phases is not balanced. The stall may be caused by the three phases exceeding the permissible load even though the maximum inverter or motor power has not been exceeded. Additionally, a high current can flow in one phase while the current in the other phases remains at an acceptable level. These situations can cause damage to an inverter or motor.
Detailed Description
Internally, the servo drive measures the motor current and each phase’s current individually. At high speeds, e.g., greater than 1Hz, the motor current can be effectively used to calculate the motor load; however, below 1Hz the current at each phase can vary and must be measured separately.
Each phase’s output has a permissible maximum heat load. An algorithm calculates the thermal load based on the measured current for each phase; depending on the user setting, it either limits the current or triggers an error.
The current limit is lifted when the accumulated heat capacity for all phases is reduced to 50% of the maximum heat capacity. Additionally, when the protection is activated, it is indicated by the subitem “Protection active” 0x200A:4. The sub index value remains at 1 until the current limit is present.
Stall Protection Configuration
Stall protection can be configured with the following options via the object 0x200A I2t and Stall protection, subitem “Enabled” 0x200A:1.
|
Option |
Description |
|---|---|
|
0 (FET only stall protection - Error Reaction) |
Protects the inverter solely based on the internal inverter settings. |
|
1 (Motor i2t and combined stall protection - Current Limit) |
For low rotation speed (<1 Hz), the motor and the inverter are protected. The current limit is generated from the lowest current limit (from either the motor or the inverter). The calculation is per phase. For high rotation speed (>1 Hz), the I2t protection is active. It works the same as <1 Hz; however, the algorithm calculates the effective “RMS” current, not the current in each phase separately. If the limit is reached, the servo drive limits the current. |
|
2 (Motor i2t and combined stall Protection - Error Reaction) |
This option is the same as 1; however, when the limit is reached an error is raised and the drive stops. |
|
3 (Combined Stall Protection - Current Limit) |
With this option, both the inverter and motor are protected in a stall condition. The protection is only active in stall conditions (<1 Hz or 10 Hz). |
|
4 (Combined Stall Protection - Error Reaction) |
This option is the same as 2; however, this is used for all rotation speeds, with subsequent error. |
When stall protection is triggered, the protection feature limits the maximum allowed reference current value to either the motor rated, or drive rated, current value (mARMS) depending on which Enabled option is selected.
Parameters
| Object ID | Name | Description |
|---|---|---|
| 0x6075 | Motor rated current | The RMS value of motor phase currents which can continuously pass through motor windings without overheating the motor |
| 0x6073 | Max current | The configured maximum permissible torque-creating current in the motor. |
| 0x200A:2 | Peak Time | How long the motor can operate while peak rms current is flowing in its windings. The motor manufacturer should determine this value. |