Simplest way of converting 240Vrms mains into 450VDC?

1. 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.

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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?

2. 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.

Klaus

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3. 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.

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

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4. 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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5. 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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6. 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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7. Re: Simplest way of converting 240Vrms mains into 450VDC?

Originally Posted by David_
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.

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

SPWM sinewave this what a electronic lights dimmer produce, and motors does not like that at all, and they produce strange noises.
I did try once to use a electronic lights dimmer to slow down a regular cooling fan (220V) and the motor coils turned in to a speaker

Only reliable solution this is using Variac to boost voltage, but it is a costly solution for this small project.

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

SPWM sinewave this what a electronic lights dimmer produce
No. Light dimmers implement phase angle control and cut part of the sinusoidal mains waveform without changing the frequency. Variable frequency drives with sine PWM generate true sine waves by means of a high frequency carrier, with small VFD at the upper audible range or even above.

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

Originally Posted by FvM
No. Light dimmers implement phase angle control and cut part of the sinusoidal mains waveform without changing the frequency. Variable frequency drives with sine PWM generate true sine waves by means of a high frequency carrier, with small VFD at the upper audible range or even above.
I have one from the ones controlled by foot switch, I will use my GDS2102A to check it waveform.

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

This is for a single-phase motor(fan).

I have been thinking about voltage doubler directly at the mains but I don't know math good enough to be able to actually calculate the current that such a circuit could be made to supply, but from what I have read the current are very low.

I don't consider isolation to be a criteria since the original circuit isn't isolated, but still I wouldn't mind winding a SMPS transformer and I must say that I got very intrigued by the smijesh linked to an article about, the LT3751.
It appears to be very suitable, except for one thing which might be a problem of sorts.

This fan isn't used all day, it gets turned on in intervals determined by temperature and other factors so it spends much of a day off, I'm not sure but when reading about AC-DC converters and in regards to efficiency it is clear that converters generally have lower efficiency the lower the current you draw from the output... Now I can't recall what I thought might be a problem but it had to do with the fact that the circuit will often be in a state with no output load at all.

I have made a circuit layout of a high-voltage H-bridge and I will begin by simply rectifying the output from an isolation transformer that converts 230Vrms into 250Vrms, and see what kind of amplitude that will allow me to create. Then I can asses how high of an output in DC voltage I actually need.

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I have decided that I will make it an priority to actually calculate what a mains voltage doubler would be capable of in terms of delivering output current, I know that the equations for the energy stored in a capacitor or coil are really simple equations but I have some problems with how it fits together and what different equations actually imply apart from the numbers actually calculated(I can get numbers and I know they represent for example a value in Henry's that a coil need to be but I can't see deeper into the equation to understand more than the amount of the output value) but this is not the place to go through this but I will for sure need to open a thread about this when I have made the most I can my self.

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In any case, the LT3751 might be called as a "High Voltage Capacitor Charger Controller with Regulation", the regulation it refers to is that the IC can function as an ordinary voltage regulator and there are configurations supplied in the datasheet for using it as a offline high-voltage input, high-voltage output flyback converter which I will look into more also.

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The fact that the LT3751 is a capacitor charger seams suitable since that is an application which is only intermittently operating, or it can be.

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

Two last tips to add as Industrial Maintenance Electrician, what ever root you plan to follow.
The fan will have increased consumption in humid days, and inrush current will be also increased at that conditions.
Therefore how frequently the fan will be used this is not a judgement factor.

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

By chance we can obtain your desired 450VDC by starting with 230VAC mains, then run it through a voltage half-doubler (that is, add 50 percent).

My experimental schematic has 4 capacitors and 8 diodes. It can work because your Ampere draw is low. Capacitors C1 & C2 charge in series during one half of the cycle, then discharge in parallel during the other half. C3 & C4 perform in a similar manner.

The severe ripple can be cured with a smoothing capacitor.

If you disconnect the load, output voltage rises to +-500V (peaks). It drops quickly when you turn on the load.

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