Ideal DC Transformer in LTSpice

Thread Starter

Jarvis_

Joined Jan 20, 2019
3
I am conducting some simulation work where I would like to incorporate the LTC3588-1 component model in LTSpice.

I have an electrical model of a physical system that requires the use of an ideal DC transformer. While I have used the model successfully in Simulink and SIMetrix, such a transformer is not available in LTSpice.

Could anyone please offer some advice about how an ideal DC transformer may be constructed in LTSpice?
 

Thread Starter

Jarvis_

Joined Jan 20, 2019
3
That is a good, relevant link - however I don't believe I can achieve what I am looking for using coupled inductors. The typical way of making a transformer in LTSpice doesn't give me the result I need as the inductors inevitably load the circuit.

What I would like is a power conserving transformer that satisfies V1=NxV2 and I2=NxI1, with no inductance terms or saturation. I believe this can be achieved using a combination of current and voltage sources, but I am not sure how to go about it.

This post summarises my problem, unfortunately the images are no longer available so I cannot replicate the circuit.
 

Papabravo

Joined Feb 24, 2006
18,096
... however I don't believe I can achieve what I am looking for using coupled inductors. The typical way of making a transformer in LTSpice doesn't give me the result I need as the inductors inevitably load the circuit.

What I would like is a power conserving transformer that satisfies V1=NxV2 and I2=NxI1, with no inductance terms or saturation. I believe this can be achieved using a combination of current and voltage sources...
Nonsense! Reread post #4 carefully.
There is no such thing as an ideal DC transformer.
 

Bordodynov

Joined May 20, 2015
2,982
I will give an explanation. The upper circuit uses a galvanically isolated transformer and there is no drain current to ground. LTspice (and other Spice) in this case, swear for the presence of a floating node in the scheme. Applying the option solves this problem. In fact, I connected two resistors to the pins of the transformer primary winding. The voltages on the pins of the primary winding depend on the values of these resistors. But for work it does not matter. Important differential voltage on the primary winding. By the way, my transformer is bidirectional. The operation of such a transformer depends on the ratio of turns. I applied 10: 100. Nothing would change at 1:10.
 

Bordodynov

Joined May 20, 2015
2,982
My one winding with N = 1 actually represents the two dependent sources described. I just added series resistance and parallel capacitance. There are two windings in my transformer. My winding has 3 pins. Through the third pin energy is transmitted. The windings are connected through this pin. The diagram is not visible but it is. In ordinary (not ideal) transformers, a core joins this pin. Winding can be a lot. See my page on the Internet. It shows how to design transformers.
 

Papabravo

Joined Feb 24, 2006
18,096
I will give an explanation. The upper circuit uses a galvanically isolated transformer and there is no drain current to ground. LTspice (and other Spice) in this case, swear for the presence of a floating node in the scheme. Applying the option solves this problem. In fact, I connected two resistors to the pins of the transformer primary winding. The voltages on the pins of the primary winding depend on the values of these resistors. But for work it does not matter. Important differential voltage on the primary winding. By the way, my transformer is bidirectional. The operation of such a transformer depends on the ratio of turns. I applied 10: 100. Nothing would change at 1:10.
I partially understand what you are doing, but where is the shunt capacitor Gshunt. Is it between the windings? Is it the initial charge on this capacitor that allows the .op solution to exist?
 

Bordodynov

Joined May 20, 2015
2,982
This is the conductivity connected between each node of the circuit and the ground. Or is it a resistor (Rshunt=1/Gshunt) connected between each circuit node and ground.
The use of this parameter solves the problem of floating nodes of the circuit. For example, different parts of the (real) scheme may be isolated from each other and do not have a common ground. Then, in order to solve the problem, a high-resistance resistor is added to the circuit for modeling. In this case, I also added a small capacitor besides the resistor. Moreover, it is justified because optocoupler and transformer have a parasitic capacitance.
 

Papabravo

Joined Feb 24, 2006
18,096
This is the conductivity connected between each node of the circuit and the ground. Or is it a resistor (Rshunt=1/Gshunt) connected between each circuit node and ground.
The use of this parameter solves the problem of floating nodes of the circuit. For example, different parts of the (real) scheme may be isolated from each other and do not have a common ground. Then, in order to solve the problem, a high-resistance resistor is added to the circuit for modeling. In this case, I also added a small capacitor besides the resistor. Moreover, it is justified because optocoupler and transformer have a parasitic capacitance.
Got it.
 
Top