Three phase Inverter only works with ideal switch not with MOSFET model.

[Alshammari]

Hi everyone,

I am conducting a three-phase inverter with R-load, and it is only working with ideal switch not with a MOSFET model. I attached the ideal switch circuit with its Vphase result, and the real MOSFET model with its Vphase result. Please I need help to make the MOSEFT mode circuit works normally, and any hints to avoid this problem later?
*******************
ideal:

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Mosfet model: GS66504B

 

[KlausST]

Hi,

a MOSFET is controlled with V_GS. While V_GS means: "Voltage of Gate with respect to Source" ...

Your simulation is like a MOSFET is controlled by V_G. (the missing "S") In such a case the voltage is usually referenced to GND.
Your Gate drive voltage is referenced to GND. This does not work.

I wonder why in your first schematic you put extra effort to drive the ideal switch unnecessarily with a floating voltage ..
But then at the MOSFET circuit you missed this - here essential - circuit.
In simplest case just do waht V_GS says: Connect the gate control signals B1..B6 to the according MOSFET_SOURCEs.

****
A simple look at any MOSFET half bridge circuit ... would also show what is missing at your circuit.

Klaus

 

[austinmariam]

Hi,

a MOSFET is controlled with V_GS. While V_GS means: "Voltage of Gate with respect to Source" ...

Your simulation is like a MOSFET is controlled by V_G. (the missing "S") In such a case the voltage is usually referenced to GND.
Your Gate drive voltage is referenced to GND. This does not work.

I wonder why in your first schematic you put extra effort to drive the ideal switch unnecessarily with a floating voltage ..
But then at the MOSFET circuit you missed this - here essential - circuit.
In simplest case just do waht V_GS says: Connect the gate control signals B1..B6 to the according MOSFET_SOURCEs.

****
A simple look at any MOSFET half bridge circuit ... would also show what is missing at your circuit.

Klaus

Hey,

Klaus is right. Your gate drive needs to be referenced to the MOSFET source, not GND. V_GS means 'Gate-to-Source Voltage,' and if you don't reference it properly, the MOSFET won't switch correctly. Check out a standard half-bridge circuit to see how it's usually done. Just connect B1..B6 to the respective MOSFET sources, and it should work.
Cheers!

 

[Alshammari]

Hi,

a MOSFET is controlled with V_GS. While V_GS means: "Voltage of Gate with respect to Source" ...

Your simulation is like a MOSFET is controlled by V_G. (the missing "S") In such a case the voltage is usually referenced to GND.
Your Gate drive voltage is referenced to GND. This does not work.

I wonder why in your first schematic you put extra effort to drive the ideal switch unnecessarily with a floating voltage ..
But then at the MOSFET circuit you missed this - here essential - circuit.
In simplest case just do waht V_GS says: Connect the gate control signals B1..B6 to the according MOSFET_SOURCEs.

****
A simple look at any MOSFET half bridge circuit ... would also show what is missing at your circuit.

Klaus

Thanks Klaus, It worked. That was a silly mistake from me, thanks again.

 

[ededopipo]

Make sure that the gate drive of the MOSFETs is sufficient to activate them properly. MOSFETs require a gate drive signal with a suitable voltage and pulse duration (often 10 to 15 V for typical MOSFETs).

 

[gavinray]

Hi ,
Based on your description, the issue likely stems from differences between ideal switches and MOSFETs in practical implementations. Below are key troubleshooting steps and solutions to resolve the MOSFET-based inverter issues:

1. Critical Differences: Ideal Switches vs. MOSFETs
Ideal switches assume instantaneous switching and zero losses, while MOSFETs introduce:

Parasitic capacitances (Cgd, Cgs, Cds) causing switching delays/ringing.
Gate drive requirements (sufficient Vgs to fully turn on/off).
Body diode reverse recovery (inductive spikes in R-load commutation).


2. Common Issues & Fixes
Issue 1: Gate Drive Problems

Symptoms: MOSFETs not turning on/off fully, distorted Vphase.
Solutions:

Ensure gate drive voltage exceeds MOSFET threshold voltage (e.g., 10–15V for logic-level MOSFETs).
Use a dedicated gate driver IC (e.g., IR2110) for fast rise/fall times.
Add a pull-down resistor (4.7–10 kΩ) to prevent floating gates.



Issue 2: Missing Dead Time

Symptoms: Shoot-through current (cross-conduction) in phase legs.
Solutions:

Insert dead time (100–500 ns) between high-side and low-side PWM signals.
Use hardware dead-time generators or configure it in your PWM controller (e.g., Arduino, STM32).



Issue 3: Parasitic Oscillations

Symptoms: High-frequency ringing in Vphase waveforms.
Solutions:

Add snubber circuits (RC networks) across MOSFETs to dampen ringing.
Use ferrite beads or small gate resistors (10–100Ω) to suppress gate-loop oscillations.



Issue 4: Body Diode Limitations

Symptoms: Voltage spikes during R-load commutation.
Solutions:

Add external fast-recovery diodes (e.g., UF4007) in parallel with MOSFETs if the body diode is too slow.




3. Simulation-Specific Tips

Model Accuracy:

Use SPICE models from the MOSFET manufacturer (e.g., Infineon, STM) instead of generic models.
Verify parameters like Rds(on), Coss, and Qgd match the datasheet.


Solver Settings:

Reduce simulation time steps (e.g., 1 ns) to capture fast switching transitions.
Enable “Skip initial operating point solution” (e.g., in LTspice) if the solver fails to converge.




4. Prototyping Checklist

Measure gate-source voltage with an oscilloscope to confirm proper turn-on/off.
Check for shoot-through by monitoring current spikes during switching.
Verify dead time using a 4-channel scope (compare high/low PWM signals).
Test with lower voltages (e.g., 12V DC bus) before scaling up.


5. Example Fix (LTspice/Simulink)
If your MOSFET-based simulation fails:

Replace MOSFETs with ideal switches + series resistance (Rds(on)) to isolate gate drive issues.
Gradually reintroduce MOSFET parasitics (Cgd, Cgs) to identify instability sources.


Debugging Workflow:

Start with ideal switches + Rds(on). If Vphase matches the ideal case, focus on gate drive/dead time.
Add parasitic capacitances incrementally to pinpoint oscillation causes.
Finally, test with full MOSFET models.


Share your schematic and scope/probe setup details if the issue persists. Community members can help diagnose further!
Tags: #InverterDesign #MOSFET #GateDrive #PowerElectronics #Simulation

Hi everyone,

I am conducting a three-phase inverter with R-load, and it is only working with ideal switch not with a MOSFET model. I attached the ideal switch circuit with its Vphase result, and the real MOSFET model with its Vphase result. Please I need help to make the MOSEFT mode circuit works normally, and any hints to avoid this problem later?
*******************
ideal: