Using the BERTA algorithm to control the servomotors allows you to test several proportional, integral or derivative gains and droops by bypassing the actual speed governor control chain.
To test the full speed governor control chain, a 10 volt peak signal modulated on to the frequency error simulated by BERTA is injected directly into the speed governor’s frequency transductor. In other words, the 115 volts RMS voltage signal from the power transformer is replaced by a signal from DA converter No. 7.
To control the servomotors directly using the BERTA controller, the output signal from the selected AD converter is injected into the input port of the actuated servomotor control chain.
NOTE: In a real test, the actual speed governor controller must be disabled and all the required connections and calibrations must be made. In a test simulation using the BERTA Training application, going from one configuration to the next one is done automatically using the GO BERTA switch (as shown in Modern PID Speed Governor Setup).
The procedure to test a modern PID speed governor is as follows:
First, define properly the PID settings to ensure that they are as close as possible to the real speed governor values.
Adjust the following parameters in the Settings panel:
Integrator set point only; slow uptake - PID set point, fast uptake: - Type of permanent droop:
For servomotor set point - For servomotor position - For power:
Frequency meter time constant in seconds
Derived gain and its time constant
Proportional and its time constant
Ensure that the servomotor displacement is stable
Click Mean P S values to adjust the PID BERTA initial condition
Wait the required computing time (5 seconds if this value has not been changed)
Use the GO BERTA switch to switch to the PID controller. The icon changes from red to green
Check that the switch has not caused a perceptible servomotor movement. Otherwise, return to GO BERTA Off mode, wait until it is fully stabilized and repeat the previous three steps
Perform the first test following the procedures described in the preceding paragraphs
Once the disturbance is stopped, the reset is done and acquisition ended, change the BERTA PID settings and perform another test.
NOTE: Never launch a mean value calculation in GO BERTA mode as this may corrupt the BERTA controller settings.
The frequency sinus disturbance lets you insert into the speed governor a signal frequency error whose amplitude is frequency modulated, This type of test analyzes the turbine and speed governor frequency behavior.
The procedure is the following:
Select the Frequency sinus disturbance type
Define the frequency error amplitude dF0 (p.u.) by peak size: The preset value is 0.01 p.u.
Define the amplitude frequency modulation Fr_sin (Hz). The preset value is 0.075 Hz.
Select the servomotor command mode using the GO BERTA switch.
Click on GO Acquis to start recording acquisition group 2 signals to the data file and increment the test counter.
Click on GO Disturbance to insert the disturbance into the simulator.
Examine the following graphs:
Simulated mechanical power
Simulated electrical power, s in the following example:
Frequency error peak amplitude dF0 (p.u.) = 0.02 p.u.,
Amplitude modulation frequency Fr_sin (Hz) = 0.5 Hz
Click GO Disturbance to stop the disturbance, stop the frequency error and return the servomotors to the initial position.
Click Go Acquis to stop recording signals.
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