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AC motor drive query

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abhishek.2138

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I am working on Single phase AC motor control project.

I have generated SPWM using opamps. Sine wave of 50 Hz & Triangular wave of 15 KHz modulated by TLC3702 Comparator.

Time delay between upper & lower MOSFET pair is of 200 nS created by NOT gates. MOSFET used are 15N60C3.

When I slowly given the input AC supply to bridge rectifier-filter capacitor, my input fuse blows??

What could be the reason???

Can we start motor(150 watt washing machine motor used) in open loop (without feedback) by just switching the MOSFET H-Bridge by SPWM signals????

H-bridge circuit attached....

Please help...
 

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  • IGBT Bridge.pdf
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  • HCPL-3140.pdf
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  • 15N60C3.pdf
    684.1 KB · Views: 43
Last edited:

Your gate driver circuit is flawed and can't work this way. Isolated or bootstrap supply for both high side drivers required.

I guess, the MOSFETs have been destroyed and are shorting the DC bus.

"open loop" drive of an AC motor is basically possible. Correct V/f curve has to be applied.

It's however difficult to achieve sufficient torque at lower frequency with a single phase motor. What's the exact motor type?
 
Most single phase induction motors have a centrifugal switch which cuts-off either an auxiliary start winding or an auxiliary starting capacitor.

At lower RPM, the centrifugal switch will engage again, reconnecting the start winding and/or capacitor.
Neither are designed to operate continuously, and will eventually be damaged.

Now, even with a permanent split capacitor (PSC) motor, your torque curve will be abnormal if the speed range is large. The capacitor's reactance will vary with frequency, and the resulting field vector will deviate.
 
In the present circuit, power ground & opto-coupler grounds were separate. Later I made both grounds common, then I got upto 15 AC output at motor terminal with AC input of around 50 VAC (through variac).

But then as you said MOSFETs get shorted (only high side).
The motor type is single phase capacitor start & run motor with capacitor permanently connected.(Washing machine motor).

I decided to use MOSFET driver L6385E or L6384E. Can you name some popular MOSFET driver ICs?

- - - Updated - - -

Gate Resistor calculation ----

Turn on time for 15N60C3 = Turn-on delay time + Rise time = 10+5 = 15 nS
Turn off time for 15N60C3 = Turn-off delay time + Fall Time = 80+10= 90 nS (max.)

Minimum Current source & sink capacity of above MOSFET Driver is 300 mA & 450 mA respectively.

So to switch MOSFET for 300 mA current, turn-on time (Ton) = total gate charge (Q) / current (I) = 63 nC / 300 mA = 210 nS
Rg-on = Driver Voltage (V) / Driver Current (I) = 15 / 0.3 = 50 Ω.

similarly for turn-off, turn-off time = 63 nC / 0.45 = 140 nS
Rg-off = 15 / 0.45 = 33 Ω.

Is this correct calculation or we need to consider Gate plateu voltage, 5V for 15N60C3 such that Gate resistor = (driver output voltage - gate plateu voltage) / driver current capacity

Rg-on = (15-5) / 0.3 = 33 Ω &
Rg-off = (15-5) / 0.45 = 22 Ω

Which calculation is correct??

OR is there any other calculation involved???

Please help...
 

Attachments

  • L6384E.pdf
    331.5 KB · Views: 39
  • L6385E.pdf
    204.7 KB · Views: 36

When you are debugging a power circuit, it is always useful to test at reduced power levels.

The first thing to do, is don't attempt to drive a motor. Replace the load with a power resistor of -let's say- 10 or 15 watts.

Then you limit the supply current. The time-honored method is to place an incandescent lamp bulb in series between the DC supply and the bridge. About 40 or 60 watts.
During normal operation, the lamp will glow dimly and still allow enough voltage for your circuit to operate. In case of a short in the bridge, the lamp will glow brightly and limit the current to 60/230 = 0.26 amp. Which should be safe for the Mosfets.

The lamp trick is so useful that I've kept several incandescent lamps for that purpose. Incandescent lamps are no longer available where I live.
 

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