How can I avoid singularity error in fixed step simulation of synchronous generator?

Dear all,

In the attached "test3bus_syncgen.mdl" model, I'm trying to use a droop-controlled synchronous generator model to represent the V-f reference of a three bus microgrid model. The generator model represents a battery whose power has been already calculated according to power balance and battery constraints and is stored in "Powerdata.mat" along with the input power for the other devices. All the other devices are current-controlled models with active power as their inputs.

The problem I'm facing with this model is that it shows singularity errors for fixed step simulation with step size of 1 second. When I reduce the step size to 1 microsecond, it works fine but is of course, extremely slow. This is not ideal as I want to run the simulation for 1 hour. The inbuilt machine model has an integrator block which may also be the source of the problem. But can anyone tell me how to change the absolute tolerance value of the block to avoid the error? Or is there any other workaround?

When I use a three phase voltage source instead of the droop-controlled synchronous machine, the model works fine for the fixed step size of 1 second.

Answer 1

[Sabin]

This error happens when very large or infinite values are fed to integrator blocks, e.g., due to a division by zero (1/0 = inf). Solvers have problems integrating such values. Also, models that are unstable or on the edge can quickly accumulate. To debug this, might be useful to use Port Value Displays and Step Through a Simulation to understand what is happening. Solver Profiler can also give good indications about what is going on in terms of zero crossings, resets, stiffness, etc. For this model it is possible to run it at 1 second rate by using Discrete Phasor with 1 second sample time in the powergui block (and 1 second sample time in the global solver configuration).