Sunday, January 9, 2011

Manual Control and Automatic Control for Frequency Inverter

Manual Control for frequency control
It is to implement the manual drive for the frequency inverter. The manual operating mode for the motor assumes the following:
• Start the motor at frequency 10, 25 and 50 Hz.
• Stop the motor.

These three phase induction motor is controlled by the inverter. The motor starter will switch and protect any three phase loads. The ensemble formed by ET200S Direct Starter, inverter and motor have to be programmed. Telegrams will be sent to it for programming the inverter. The standard telegram was selected in the hardware configuration for SINAMICS G120. Ladder Logic LAD is used for programming the manual drive control.

Automatic for frequency control
This scope is the implementation of automatic control of the frequency inverter used for controlling the induction motor. The automatic control contains in a sequence steps executed in a defined order. A sequencer contains of a series of steps and transitions that are activated in a fixed order depending on the step enabling conditions.

Below are presented a few usual sequencer types in S7 Graph: linear sequencer, alternative and simultaneous sequencer and parallel sequencer. The following sequence will be designed:
Step 1 – Run at 10Hz.
Step 2 – Run for 10s 10Hz.
Step 3 – Run at 25Hz.
Step 4 – Hold for 10s 25Hz.
Step 5 – Slow down to 10Hz.
Step 6 – Hold for 10s 10HZ.
Step 7 – Ramp up to 50HZ.
Step 8 – Hold 50Hz for 10s.
Step 9 – Reverse rotation sense to -50Hz.
Step 10 – Hold 10s -50Hz
Step 11 – Slow down to 0Hz.
Step 12 – Stop.

Integration of manual and automatic control modes for frequency inverter
In this case there are a series of conditions to consider:
• The switching between two subsystems (operating modes of the inverter) is possible at any time.
• A force stop is available in each subsystem, when the inverter brings the motor in its initial state.

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