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Ramp timings hints and tips?

SINAMICS G & SINAMICS S

FAQ July 2013

Question

2 Ramp timings hints and tips

1.0, Item-ID: FAQ-DF829163

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Question Hints and tips for ramp timing issues

Answer The instructions and notes listed in this document provide a detailed answer to this question.

Table of content

Ramp timings hints and tips 1.0, Item-ID: FAQ-DF829163 3

Table of content 1 Introduction .................................................................................................... 4 2 Resolution of issues....................................................................................... 5

2.1 Oversizing the Inverter ....................................................................... 5 2.2 Why is my Inverter not following the set points I enter? ...................... 5 2.3 Why do I get over currents F7801? .................................................... 6 2.4 Why do I get over speed F7901? ....................................................... 6 2.5 The motor holding brake de-energized before it ramps down? ........... 7 2.6 Key parameters for ramp timings ....................................................... 8

1 Introduction

4 Ramp timings hints and tips

1.0, Item-ID: FAQ-DF829163

1 Introduction Ramp timings control the time that is taken to either start the motor and ramp it up to the required speed (ramp-up) or the time it takes to slow the motor down, normally to a standstill (ramp-down). The default ramp timings for both ramp-up and ramp-down is typically 10 seconds, but this timing may not be suitable for your particular application. The ramp timings can be adjusted using the following parameters:

P1120: Ramp-function generator ramp-up time P1121: Ramp-function generator ramp-down time

If the ramp timings are set too short, the Inverter will protect the system by tripping with an overcurrent or overvoltage fault. If the ramp-up timing is too short it will produce an overcurrent condition. If the ramp-down timing is too short it will produce an overvoltage condition. If the Inverter is forced to an overcurrent or overvoltage condition continually it could eventually cause damage to the Inverter..

NOTE When using telegram 900, the safety inputs in the drive must be set to “enable” to prevent a configuration fault (F1653). This will be explained in a later step. Likewise, if using telegram 30, the safety inputs must be set to “Inhibit” in the drive or a configuration fault will be generated. Again, telegram 900 can only be used in the –F safety control units..

2 Resolution of issues

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2 Resolution of issues 2.1 Oversizing the Inverter

When the Inverter keeps tripping on overcurrent or overvoltage because of ramp timings, but the set ramp timings are essential to the application, then oversizing the Inverter may be a better option. Oversizing the Inverter means selecting the next highest power rating of the Inverter so it can cope the high voltage or current generated by the ramp timings of the application. For example, if you are using a 3kW Inverter with a 3 kw motor, then you would replace the 3 kW Inverter with a 4 kW Inverter.

2.2 Why is my Inverter not following the set points I enter?

As previously stated, the Inverters will protect itself and the motor when short ramp time is used so the time maybe longer than the values set in P1120 and P1121. Limiting factors can be the Inverter current, power and torque. Simply setting the ramp times to zero will not give you the quickest ramp times and could cause damage with long term use.

If the motor is smaller than the Inverter it will allow up to 4 times the motor current for a limited time, the motor thermal protection should be configured, using parameter P0601 => 0. For the SINAMICS PM240 enter the value of the braking resistor in kilowatts ((P0219) (FW4.6 or higher)). This will automatically disable the Vmax controller P1280 VF P1240 SLVC. In SLVC after the setpoint changes or the speed limit changes, for example P1120 or P1082, a speed optimization should be performed again using parameter P1900=1.

NOTE Entering the correct motor data* from the rating plate is essential for motor protection and speed control. *some non-Siemens motors may calculate high inertia figures limiting the ramp times. You can improve this by reducing P0341.

2 Resolution of issues

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1.0, Item-ID: FAQ-DF829163

2.3 Why do I get over currents F7801?

Fast ramp times in VF control can give rise to high currents and undesirable ramp curves. This problem can be rectified by the using one of the following actions:

Increase the ramp time rates. Select SLVC. Enabling compound braking can increase ramp down rates but at the

expense of extra heat loss in the motor. Increase parameter P0640 to allow for higher currents.

Figure 1. Screenshot showing a high start-up current being drawn by the Inverter

2.4 Why do I get over speed F7901?

In Sensorless Vector mode (SLVC) after a speed optimization (P1960=1) the ramp curve will be improved. You may get over speed with fast ramp-up times. To decrease the problems with fast ramp timings the following solutions should be considered:

Increasing the value of P1082 will allow over shoot. Set P0322 to a higher speed. This will allow you to increase the over

speed hysteresis in P2162. Increasing the speed controller P gain P1470 may increase the ramp time

but also cause high speed overshoot. Increase the pre-controller scaling P1496 * . R0333 = rated motor torque. Increase P0640. Increase the ramp timings.

High start-up currents can reduce the life of the motor and inverter

2 Resolution of issues

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Figure 2. Screenshot showing the field weakening/saturation of the motor

2.5 The motor holding brake de-energized before it ramps down?

If the power limit is reached, and the ramp-down speed cannot meet the setpoint, then the Inverter will stop pulses and engage the EM brake (if one is fitted), as the Inverter can no longer control the output speed. P1531 is limited to 100% of the Inverter power, if the load has a large inertia then increasing the ramp times may not help and a larger Inverter will have to be installed so the regenerative power can be increase.

NOTE Use the following formula to calculate the maximum over speed hysteresis setting:

P0322 * 1.02 - P1082 = P2162

Example:

P0322 = 1700 rpm. P1082 = 1500 rpm.

1700 * 1.02 - 1500 = 234

So the maximum over speed set in P2162 is 234 rpm.

NOTE High torque settings can increase ramp times but still result in limitations of ramp times due to field weakening and the fundamental properties of the motor. Over fluxing and motor saturation can also have a negative effect with regards to speed control.

2 Resolution of issues

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Figure 3. Screenshot of trace showing the effect of high regenerative energy in the motor

2.6 Key parameters for ramp timings

P0304 = rated motor voltage P0305 = rated motor current P0308 = rated motor power factor P0311 = rated motor speed P0322 = maximum motor speed P1900 = 1 followed by run command to perform a motor ID P1960 = 1 followed by run command to perform a speed optimization if using SLVC. P0341 = motor inertia may need reducing for shorter ramp times. P0640 = motor current limit. P1520 = upper torque limit. P1521 = lower torque limit. P1530 = power limit. P1531 = regenerative limit. P1470 = P gain for speed controller. P1472 = Integration time for speed controller. P1496 = acceleration pre controller percentage.

Actual speed and setpoint moving away from each other

Power limit P1531