Adding a current sensor to my Simscape Electrical model results in large current oscillations

I have a Simscape electrical model in release R2017b, where a step input is connected to a controlled voltage source. The voltage source is connected in series to a "DC Motor" block and a "Current Limiter" block.

With no "Current Sensor" block in series with the circuit, I see my expected simulation results in the "Simscape Results Explorer". However, when I add in a Current Sensor block in series with the rest of my circuit, I see unexpected transient behavior in the form of large current oscillations that do not match what the Simscape Results Explorer shows for the exact same model with no current sensor.

Why is adding a current sensor affecting the dynamics of my circuit?

Answer 1

[MathWorks Support Team]

A step change in voltage implies an infinite impulse current. The current sensor dynamics cannot handle this, which is why you see incorrect simulation results.

Add an "Inductor" block with a very minor inductance in series with the circuit. This will force a continuous change in current that the sensor dynamics can handle.

https://www.mathworks.com/help/simscape/ref/inductor.html

[NDUKWE]

Hello.

Thank you for your answer. Unfortunately, I am having this same issue with attaching a current sensor to my table based battery. I am simulating discharging the battery with a negave constant via a controlled current source while measuring the voltage, SOc and current in the battery.

I noticed that once i remove the current sensor, the scope values become normal but once i attach the current sensor, i keep getting arbitrary values.

I have also used an inductor in series as you adviced and tired it with different high and low values but it seems not to be working for me.

please, what are my options or perhaprs the exact inductance values to use?

Thanks

[Andres Adam]

Hi @NDUKWE, the idea behind adding an inductor is that it limits rapid changes in current. It should act as long as it is non-zero compared to the rest of your model. Try making it 1% of your circuit impedance.

Other than that, the issue is hard to pinpoint from that information. Email [e-mail] to see if we can help you with that!

[NDUKWE]

Thanks. The answer is quite helpful.

Please, what SOC estimation algorithm is used for the simulink specialised power system battery block? (my apologies if I am asking lots of questions already) Thanks

[Andres Adam]

That I do not know exactly at the moment. I could some good information about the battery model at its documentation page:

https://www.mathworks.com/help/sps/powersys/ref/battery.html

It is based on a paper from 2009:

Tremblay, O.; Dessaint, L.-A. Experimental Validation of a Battery Dynamic Model for EV Applications. World Electr. Veh. J. 2009, 3, 289-298.

You can consider posting it as a question in MATLAB Central or emailing support :)