Check Thyristor Holding Current in Simscape model

I am using a thyristor in a Simulink Simscape electrical model. I have copied over all of the applicable parameters from the manufacturer's spec sheet into the model. There was a lot of 1:1 correspondence, but not 100%.

One thing the spec sheet specifies is the holding current, I_H. This parameter is only available if I select "Lookup Table" for "I-V characteristics defined by". However, I do not have the vector data for the voltages and currents. I have much more data to fit the nonlinear equations version.

Looking at the help on mathworks: https://www.mathworks.com/help/sps/ref/thyristor.html

It states: "You do not specify the holding current directly because its value is primarily determined by other block parameters. However, the holding current can be influenced by the Product of NPN and PNP forward current gains parameter on the Advanced tab. Reducing the gain increases the holding current."

Under "Product of NPN and PNP forward current gains" it then states: "This is the product of the NPN forward gain BFNPN and the PNP forward gain BFPNP. The value must be greater than one for latching to occur. The smaller the value, the larger the latching current becomes. However, latching current is primarily set by other block parameters, and the total gain has only a small effect."

But what are the "other block parameters" that determine the holding current? What is the formula? I would like to check that these other parameters make the same holding current as the spec sheet. If they're all parameters I took directly from the spec sheet and they calculate to the same value, great. If not, then I know I need to adjust gain. If there's parameters I don't have, this could give me a clue to the values these parameters need to be.

Thank You.

Answer 1

[Rick Hyde]

The holding current will depend on the NPN and PNP transistor I-V characteristics which, in-turn, depend on forward gain, forward emission coefficient, and ohmic resistances. The thyristor model also has an internal gate-cathode resistor which can have an effect if the external circuit resistor is higher than this integral value. Defining equations in our thyristor library block are the NPN and PNP bipolar transitor equations as defined in the reference pages:

https://www.mathworks.com/help/releases/R2023a/sps/ref/npnbipolartransistor.html

https://www.mathworks.com/help/releases/R2023a/sps/ref/pnpbipolartransistor.html

plus equivalent circuit here:

https://www.mathworks.com/help/releases/R2023a/sps/ref/thyristor.html

However, finding holding current requires either simulation or writing an iterative equation solver given these defining equations as a starting point. You can explore impact of block parameters on holding current by opening our basic thyristor test harness model:

>> ee_thyristor

Click on the "Latch Current" hyperlink to enable hold current testing. You can then experiment with changing block parameters and how it impacts latching current. For example, try modifying V_GT as well as the overall gain.

You might find the system-level thyristor model in our library useful too: "Thyristor (Piecewise Linear)" - here you specify holding current directly plus on-state I-V characteristics.

I hope that helps

Best regards

Rick Hyde