I am aware of the droop control but i cannot figure out how to implement this in MATLAB. I find papers about the droop control in case of distributed generation units which are connected to the grid by means of an inverter. Here, you can decouple the active and reactive power, generate the reference voltage accordingly and control the power sharing according to the droop control principle. This is no possible in case of synchronous generators where you can change the input power (governor control) and field excitation (excitation control).
In the following book you will find the main models to do the required control actions. In addition, you will find demonstrations using the simulink.
https://www.researchgate.net/publication/307926879_Dynamic_Security_of_Interconnected_Electric_Power_Systems_-_Volume_2_Dynamics_and_stability_of_conventional_and_renewable_energy_systems?_sg=lbOXwPS5p1eTW3Kge5uRNhWcZtdflZc8BXOTLnXUfh7P1e9n7iyZEq1ku7qgQvggN_Za8XuXtDOgR4__weZfOgb0HDe4qiaFjnBodXjK.TWe_wmcOhus0Otrc-zGbY12hHW7vuPosF0o1dSKJVkwnjH_Bq1bpfWYChy-itZoqOA2bgzXZxowVt1Dun4xYrw
Synchronous machines which are tied to grid have the same frequency and voltage, changing the load demand on one machine is achieved by varying the power output. if its a steam turbine means adding more steam to the unit, if its the hydro machine, allowing more water to pass through the turbines by opening the wickets gates (guide vanes) using the speed governor. since the units are at synchronous speeds, even varying excitation also plays a key role in voltage control. A dynamic model of the PID controller is at play
I know this but the problem is in simulation. If we change the input power of the generator, its speed varies and hence output frequency varies and hence the synchronization with the grid or the other machine fails. How to solve this?
Can you share a reference to the model used in the simulation? So that we will try to guide you.
More detail condition is required.
But from your query, I expect that the system is isolated from utility grid and just two generators are in charge of whole electrical load. Then, one of them shall move into isochronous mode (as a swing machine) while another MW mode (load limit mode) or you have control system called as PMS (power management system) or EMS (energy management system) which calculate the power flow and issue the load demand to each generator in real time simulation basis.
When load changes then generators' voltage and frequency change automatically. They may be small deviations from nominal values. You can't prevent that. By using secondary controllers you can make that transition period very small.
For the steady state simulations, you can initialize the generators such that they generate the specified power. In this way, frequency and voltage will be at the desired value in steady state operation. But, if you want that after a disturbance (for example an increase in load power), the disturbance power is distributed between generators with a specific proportion, their governor settings (primary frequency control) and secondary controllers should be set appropriately.
for simulation purpose
1) You should have to remove MW control mode (If you are using) then put both generators in droop control or frequency control mode whatever is available.
and
2) you also need to configure proper governor model in close loop which is sensitive to the terminal/ Grid frequency.
after these configuration if you can check by using raise/lower command of fuel stoke reference(FSR for GE turbine) or the parameter which controls the speed.
By doing this another generator's governor will also come in action to maintain grid frequency and ultimately MW sharing will change according to increase and decrease in speed reference of one generator.
you can refer droop control of GE make turbine on wikipedia
https://en.wikipedia.org/wiki/Droop_speed_control
You have to control the power angle of one of the machines; for that the frequency has to change temporarily, either increase or decrease for the power angle to change. Once reached the desired power the frequency goes back to its nominal value. So, the controlled variable is the power angle.
In short, it is controlled by power angle. If the load angle is larger it will produce more load-units, if it is less it will produce less load-units but both will remain same in synchronism.
If power demand is greater than power production, than frequency will fall. And frequency should be controlled by varying the generator input in that way to keep the required frequency maintain. (It is controlled by speed droop method)
I did not see your matlab model, dont use built-in model of generation, make your own then you will have a fully control on both, "terminal voltage" (by varying the excitation current) and "frequency" (by varying the input generation)
Do not waste your time go back read book power system analysis by SADAT chapter 11 ,12 will answer your questions beetroot than short discussion will not give you the answer you want
As long as the units are synchronised, voltage and frequency remains constant. This means that excitation and governor loop control is monitored for two units at the same time. Two modes of control exists, either joint mode and individual control. In joint mode the power sharing becomes equal as this is an automatic control by a setpoint. In individual mode, u can change the set point of each machine and wat matters most is the Load. For hydro turbines, u need to control how much water goes to the turbine by either opening of upstream gates or regulating the guide vanes on the turbine. This is done by the speed governor
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