Problem with reaching appropriate voltage in a 3 phase PWM system

There is a 380V star connected ac motor. I apply 3 phase sinusoidal pwm to this motor. My dc bus is 310V. I get ~190V rms voltage when i measure the voltage on the terminals X-Y through a low pass filter (Vxy). This is the fundamental voltage, i think. But when i measure the voltage between one terminal and negative of the dc bus, say Vxn, i get the same value. Is this normal? Since this motor is 380V, my voltage is too low. According to this my dcbus must be ~622V. But in a 380V(l-l) 3 phase system, i can get ~530VDC for dcbus. So what must i do to achieve the rated voltage of the motor? I think one way is, to implement space vector pwm. In this case we can at least reach near the rated voltage. In this case, can't i use 230VAC one phase system to obtain my dcbus to use with this motor? So do the commercial motors, with one phase inputs, use delta connected motors?

Re: 3 phase pwm systems

Hello, i'm not an expert in this matters, i'm just a student but i think i know what your mistake is.

you have a low dc bus voltage for two reasons:

1) you actually need 2*310V because the average value of the switching voltage will be equivalent to the neutral voltage (duty-cycle=50%) so you can have a swing up and down of 310V at each fase (220*SQRT(2), right)

2) you really need to have more than 2*310V because you need to take into account the conduction losses and that you can't have 0% or 100% duty-cycles, if it was me designing that i would try to be between 5%-95% duty-cycle, because from my limited experience i've learned that too low or too high duty-cycles are difficult to realize

then you just need 3 inverters and supply to them with the correct control (3 fase) voltages

i hope this helps.

Re: 3 phase pwm systems

Hi there,

If you need to drive 380V motor with DC power line from AC 220V, you need the BOOST the DC line with the SPM supply to reach the desire DC bus voltage for 380V system.

TR2000

Re: 3 phase pwm systems

I have required a circuit diagram that operate a 24v dc relay from 310v dc supply using transistor.