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    Simplest way of converting 240Vrms mains into 450VDC?

    Hello.

    I am building a SPWM Variable Frequency Drive that should be able to output at least 240Vrms @ 50Hz to drive a fan that may consume at most 30W, as far as I know for that I need a DC rail of 450Vdc.

    What is the simplest/easiest way to achieve a 450Vdc rail?

    My first idea was a PFC circuit which I used a online design tool to generate the BOM for but the component required is making me question this idea, the design tool says I need a 11454µH inductor with a peak current of 0,57A. Which is expensive.

    Since I know that the maximum current the fan will draw at 240Vrms is 0,125A I put in some margin and used that current for the 450Vdc rail which equates to around 60W, but thinking about the whole situation where the 450Vdc rail supplies what becomes 240Vrms is making me unsure of how much current that 450Vdc rail needs to be able to supply.

    Should I just go with a offline flyback-converter? But that creates a lot of reflected voltage on the primary requiring a MOSFET with a very high VDS rating, I think it was the flyback topology that had that characteristic at least.

    Regards.

    - - - Updated - - -

    I am new to the whole VFD thing and changing the speed of a AC motor, but I just realized that I should be able to rectify 230Vrms, chop that into a SPWM sinewave and just adjust the frequency down to a frequency with the correct ratio to whatever the highest sinewave SPWM voltage that would be produced, no?

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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Hi,

    the design tool says I need a 11454µH inductor
    I don't think the value is correct.
    Please review your input and calculations.

    Klaus
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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Perhaps a voltage doubler based on capacitors? With a Villard type it is easy to select a value for the charge-pump capacitor, in order to obtain a desired output voltage at the load.

    Click image for larger version. 

Name:	230VAC Villard doubler small chg pump cap load 30W 450VDC.png 
Views:	3 
Size:	27.0 KB 
ID:	151110

    This schematic shows the raw concept. You may wish to add components that smooth the spikey waveforms. Etc.



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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Hi,

    I am building a SPWM Variable Frequency Drive that should be able to output at least 240Vrms @ 50Hz to drive a fan that may consume at most 30W, as far as I know for that I need a DC rail of 450Vdc.
    Single phase or 3 phase?
    You know that there are optimized waveforms for 3 phase to lower the necessary bus voltage?

    Klaus
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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Keep researching boost converters there are simple 8 pin chips to do the control and give unity power factor - sine wave input current - which is very useful ...



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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Hope you need to convert 240V @ 50Hz to 450VDC @133mA (60W/450)
    Here the output voltage is almost double to the input voltage, so I am suggesting isolated DC DC converter
    Try this IC
    https://www.analog.com/en/technical-...v-to-400v.html



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    Re: Simplest way of converting 240Vrms mains into 450VDC?

    Quote Originally Posted by David_ View Post
    I should be able to rectify 230Vrms, chop that into a SPWM sinewave and just adjust the frequency down to a frequency with the correct ratio to whatever the highest sinewave SPWM voltage that would be produced, no?
    Yes, perhaps it is sufficient to start with a 330VDC supply. A fan is the kind of load that tolerates variations in voltage. Furthermore an inductive load can overheat if we slow down the frequency while leaving the AC voltage unchanged.

    I tried dropping 120VAC mains through a 2:1 step-down autotransformer, to reduce speed of my window fan. The frequency remains at 60 Hz. It works and the fan runs about 50 percent speed, with less noise.

    I suppose I could have fed it 120VAC @ 30 Hz, but advice says we should reduce voltage if our load is all or partially inductive (such as a fan which contains coils). The slower frequency automatically creates increased Ampere draw unless we reduce voltage.

    design tool says I need a 11454µH inductor with a peak current of 0,57A. Which is expensive.
    You can get by with a smaller Henry value if you choose a faster switching frequency. Besides which if you operate in CCM (rather than DCM) then current peaks are smaller.



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