I'm trying to simulate a 3-phase inverter for BLDC(PMSM) in LTSpice. The problem is that drain current is way too high and also phase voltage isn't right.

enter image description here enter image description here **New image enter image description here *One leg

If I put one source(48V) I get spikes as drain current(green) instead of rectangle signal, blue signal is drain-source voltage: Blue line is drain-source voltage Here are phase currents: enter image description here If I put two sources then I get rectangle but is way too high(3.5kA): enter image description here Here are phase currents: enter image description here Here are phase to phase voltage(blue) and voltage on one phase(green): enter image description here

To get SPWM I compare sine wave and triangle wave, for other two phases I change Phi to 120 and 240. Also I have dead time circuit and that works fine.

It works the same even with or without back-EMF. I tried changing Rm and Lm parameters but nothing changes.Rm=1 Ohm, Lm=0.5 mH. I tried adding ground but it doesnt work either.

UPDATE1: Thanks to everyone. I realized that I need to bootstrap MOSFETs. Now I'm trying to make driver with bootstrap capacitor and pnp and npn as seen in some datasheets/forums but it doesn't work for 3 phases(uploaded new pictures). I don't know what's wrong. Tried with/without ground but it doesn't help. Is it better to just include gate driver model? I just need it for simulation to measure currents, voltages etc.

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  • \$\begingroup\$ What’s your gate drive for the high side MOSFETs? \$\endgroup\$ – winny Aug 15 '18 at 21:03
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    \$\begingroup\$ Welcome to EE.SE. Can you redo the screengrabs without the grid (which makes text difficult to read) and crop them properly? \$\endgroup\$ – Transistor Aug 15 '18 at 21:04
  • \$\begingroup\$ You don't need external diodes, the transistors have them builtin. Gate drives should be referenced to the source of each transistor, if they are to be of the same amplitude. Also, see this for an example on how to model this behaviourally. \$\endgroup\$ – a concerned citizen Aug 16 '18 at 8:03

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