Fastloop control
When using the 6 channel output module together with a 6 or 10 channel input module, you can make use of the fastloop control on one output channel. When a fast control loop is required (for example with a pressure regulator), this mechanism can be used.
The architecture of the GOcontroll Moduline controllers introduce a certain latency between input and output. This latency is caused by a communication from the input module to the application processor and from the application processor to the output module. In optimized configuration, this latency can be reduced to ~15ms. For most control loops this is not a problem at all but when a fast response is required, this latency can be to much.
Fastloop on Moduline controllers bypasses the application processor. The output module retrieves its reference directly from the input module. Only the setpoint is communicated from the application processor to the output module.
NOTE: There will be no failure check on the pressure sensor. A failure of the pressure sensor can introduce a faulty reference voltage which can lead (for this example) to an excessive increase of pressure ultimately leading to damaged components. As a solution: on application level, the sensor signal can be checked and, depending on failure, the setpoint can be set to 0.
LIMITATIONS: Since fastloop uses a dedicated communication bus, only one output module can be used for this mechanism.
Setup:
In this example we demonstrate a pressure controller for a fuel cell system using Matlab Simulink. The setpoint can be dynamically changed by the application processor but for this example we target a pressure of 1 bar.
The pressure sensor that is used has a range from 0 to 2 bar on a voltage scale of 0.5V to 4.5V and is connected to channel 1 on the 6 channel input module on slot 1.
Channel 1 from the 6 channel input module is configured as Analog input – mV (1mV resolution) on a voltage range of 0 tot 5V. This means that the output module will retrieve a value between 0 and 5000 from the input module. 1 bar (Our target setpoint) corresponds with 2500 mV.
The proportional valve is controlled by channel 6 of the 6 channel output module on slot 2. Channel 6 function is set as Fast loop half bridge control.
- Reference signal module points to slot 1
- Reference signal channel points to channel 1
- Fast loop gain is the P factor. For example if P needs to be 0.95 , a value of 95 needs to be added.
- Fast loop basic duty is the duty-cycle that is added. This enables the possibility to pre-energize the coil.
When we sent a setpoint of 2500 to the output modules configured in fastloop mode, the output will calculate the error between measured voltage and setpoint. Multiply this value with the gain and add the basic duty-cycle. The outcome will be the duty-cycle on the output pin of the controller.
