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single phase induction motor speed control by H Bridge

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abc_de

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hello
i am trying to run my single phase induction motor capacitor start with h-bridge by unipolar spwm modulation. output of bridge is 230Vac stable.
i have start motor in linear fashion 5HZ>10hz>15hz>20hz>25hz>30hz>35hz>40hz>45hz>50hz by V/F method.

i have connect output of h bridge direct to L-N terminal of motor.

my problem is motor start is delayed, when it start it vibrates and produce sound after reach 50hz motor vibrates too much.
during motor run time i check the output of h bridge output get distorted very badly. :-( without load output is fine

then i check 230 vac fan motor (which do not have capacitor) it runs fine.

any suggestion what is cause of malfunction :thinker: and how to overcome the problem
 

Seeing distortion with reactive load suggests a wrong modulation scheme like free-wheeling switches in PWM off state.

A single phase motor capacitor might achieve insufficient torque below 50 Hz. Better to run the motor with a three-phase inverter, omitting the capacitor.
 
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    abc_de

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fvm may be possible
u mean to say should i remove capacitor and run motor with 3 phase inverter by phase offset 90 degree.

one more doubt in single phase motor both winding have different resistance start winding =20ohm main winding =11ohm
means each leg of igbt carry different amps. is it distory igbt ?
 

Voltage ratio of main and auxiliary winding of capacitor run motors can be different. For optimal variable speed drive of single phase motors, you'll need a specialized inverter.
 

you would be special in inverter ?
should i give different voltage to main and start winding for same current?
 

My electrical machines textbook assumes Vh (auxiliary winding voltage) > Va (main winding voltage) and respectively Ih < Ia. But I'm not sure if all PSC (permanent split capacitor) motors are designed so.

I would measure windings currents in 50 Hz operation and try to achieve the same currents with inverter operation, particularly take care that rated current isn't exceeded.
 

abc_de said:
hello
i am trying to run my single phase induction motor capacitor start with h-bridge by unipolar spwm modulation. output of bridge is 230Vac stable.
i have start motor in linear fashion 5HZ>10hz>15hz>20hz>25hz>30hz>35hz>40hz>45hz>50hz by V/F method.


then i check 230 vac fan motor (which do not have capacitor) it runs fine.
Click to expand...

Ask yourself: what is the capacitor's reactance at 5Hz as compared to 50 Hz? Simple answer, 10 times as much.
Do you understand haw capacitor-start motors are started? The auxiliary winding, thanks to the capacitor receives a phase-shifted current which causes a magnetic vector in quadrature with the main magnetic vector, creating a starting torque.
With 10 times as much reactance at 5 Hz as its original design intent, the resultant vector will be insufficient to properly start the motor. The motor will mostly vibrate, as you have noticed, and you will have completely eliminated the main advantage of a capacitor-start motor: its high starting torque.
 
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Now understand more
Then how i can spin my motor by 3 phase inverter by 90degree phase shift. Even both coils have different resistance resultant different current from each leg ??
 

I've never seen a VFD for a single-phase motor. For the reasons outlined above.

There are VFDs with a single phase power input, but their output is always for a three-phase motor.

I could be wrong, but it would be a special type of equipment.
 
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Thanks, FvM for the app note.

What the app note indicates that the motor must be modified. Both the capacitor and the centrifugal switch must be removed on a capacitor start motor. Like the OP wishes to control.

Also for the reasons outlined in the app note, I like better the circuit in figure 5, where the two phases are connected as a three-phase open-delta configuration.
 

presently I am following microchip app notes AN1660 and AN967. in app note they suggest for three phase configuration without start cap. but still I am confused about difference in winding of motor.
 

A previously mentioned, winding ratios can be different. AN967 is describing it with parameter alpha. It must be determined for a specific motor. PSC motors designed for direction reversal can be expected to have 1:1 winding ratio, so that mains and auxiliary winding can be exchanged.
 

Fvm i have check my my motor it have different winding.
Start winding have 90 degree Phase shift from main winding. For motor direction change usually switch or relay is placed to phase the shift by lead or leg.
 

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