"Solver was unable to reduce the step size without violating the minimum step size value" in Simscape simulation

The physical model I built in Simscape is the height adjustment of the air spring.

The working principle of the system is: input the control command, the flow of the controlled object air pump, the opening and closing status of the air spring valve and the air tank valve are controlled in real time, the air spring is fed in and exhausted, and finally the spring height is adjusted. There are 3 height modes: high, medium and low.

When I performed simulation analysis, the following error message appeared:

Solver is encountering difficulty in simulating model 'Height_Passive_New' at time 0.00058062527253207891. Simulink will continue to simulate with warnings. Please check the model for errors.

Caused by:

Solver was unable to reduce the step size without violating the minimum step size value of 2.0628E-18 for 1 consecutive times at time 0.000580625. This usually may be caused by violating algebraic constraints in the differential-algebraic system or by the high stiffness of the system. Try tightening the error tolerances, and/or the tolerances for computing consistent conditions. If the problem persists, please check the system or increase the solver Number of consecutive min steps violation parameter.

Suggested Actions

Open Solver Profiler to explore such issues

After many attempts, I still cannot solve the problem. I sincerely ask friends who see this question to help me solve it. Thank you very much!

Answer 1

[Ashok]

Hi David,

The warning "Solver was unable to reduce the step size without violating the minimum step size value" could arise due to various reasons. A few reasons are high model stiffness, presence of algebraic loops or exceptions related to Differential Algebraic Equations (DAEs). You can read more in the link below.

https://www.mathworks.com/matlabcentral/answers/1598074

I ran the model in open-loop with the “Flag” variable given as a constant input and I found that,

• When “Flag” is set to 1, the simulation runs successfully.
• When “Flag” is set to 0, the warning, "Solver was unable to reduce the step size without violating the minimum step size value" appears and the simulation is frozen.
• When “Flag” is set to -1, the assertion error, “Gas volume must be greater than minimum physical volume” occurs. This error arises from the “Translational Mechanical Converter (G)” block named “Air Spring”.

A “Stiffness Impact Analysis” using the “Solver Profiler”, indicates that the warning as well as the error mentioned above arises from the state, “Time derivative of Pipe_G.T_I (Temperature of gas volume)”. This state points to the “Translational Mechanical Converter (G)” block. Hence, check the values and units and values of the block parameters. Also, examine the upstream blocks to identify potential modelling improvements.

The procedure to perform “Solver Impact Analysis” is described in the following documentation page.

https://www.mathworks.com/help/simscape/ug/simscape-stiffness-analysis.html

The open-loop model used is attached for your reference.

I believe this will assist you.