Voltage and Frequency Converter - Page 1
Forum section: electronics / projects

author: Dinheaven
author_rank: Contributor
timestamp: September 16, 2014, 01:35:15 am
content: Greetings,Firstly, I'm truly sorry if my post here is off topic as it is my second post in the forum.So, For my Final Project, I'm required to design and develop a power supply module that converts 230Vac/50Hz to 115Vac/400Hz for Aircraft Equipments.As My Course is specialised in Avionics electronics, I'm required to convert the 'normal' AC power supply of 230Vac/50Hz from my lab wall socket to 115Vac/400Hz to be used for aircraft equipments.After doing some research, I perceive that to convert the voltage supply, i need to use the step-down transformer and to convert the Frequency supply, I need to use the Frequency Converter but, The information i received on the internet about the Frequency Converter is vague.So my questions are,Firstly, Can anybody explain to me on the Circuit operation of the Frequency Converter?, and if possible, provide me a link to its circuit diagram.Second, As Both the Voltage and Frequency has to be converted, Shall I convert the Frequency first or Voltage first?If you guys need any info on this project, just mention it. Thanks for viewing

author: moffy
author_rank: Super Contributor
timestamp: September 16, 2014, 01:52:56 am
content: https://www.pes.ee.ethz.ch/uploads/tx_ethpublications/cavalcante_COBEP01.pdf.Have a read.

author: Jebnor
author_rank: Regular Contributor
timestamp: September 16, 2014, 02:04:39 am
content: How about AC->DC-> AC? Like the architecture of an online UPS, but 120V/400Hz output.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 16, 2014, 02:06:53 am
content: Quote from: moffy on September 16, 2014, 01:52:56 amYour link doesn't work. Gotta remove that period at the end.https://www.pes.ee.ethz.ch/uploads/tx_ethpublications/cavalcante_COBEP01.pdf

author: DanielS
author_rank: Frequent Contributor
timestamp: September 16, 2014, 02:07:07 am
content: Unless your exercise requires that you do frequency and voltage conversions separately, it would be much simpler to do a straight AC(-DC)-AC converter.As far as schematics go, I recommend Google Image search - on the first result page for "frequency converter," I see 50+ images that look like something you might want to take a look at.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 16, 2014, 05:45:29 am
content: The arguably simplest method is a motor-alternator pair. Slightly less simple, but more compact, would be a motor with special secondary windings so it generates harmonics (50Hz * 8).Wound-rotor motors can be used for frequency conversion because the rotating frequency can be the sum or difference in winding frequencies, assuming the shaft can be controlled to some other speed (say with a synchronous induction motor and gearing). This mainly only helps for generating oddball frequencies, and isn't much different from the MG set.The harmonic conversion process can also be done statically with nonlinear components (saturable reactors, diodes), though it will probably end up larger for the same output (it will take more than a few stages to reach the 8th harmonic, and a lot of extra filter components to keep the input and output clean).By far, the most compact and efficient solution is an electronic inverter (AC-DC-AC) or VFD (voltage-frequency drive). This amounts to a large class D audio amplifier, with a hard-wired output signal.Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 16, 2014, 12:12:53 pm
content: Quote from: T3sl4co1l on September 16, 2014, 05:45:29 amHaving wired up a few, I thought VFD stood for variable frequency drive.

author: Dinheaven
author_rank: Contributor
timestamp: September 17, 2014, 03:48:07 am
content: Quote from: moffy on September 16, 2014, 01:52:56 amThanks alot!. But I still cant determine whether the 90kVA / 400Hz Inverter has the 400Hz Frequency at the input, or only at the output. Is the input 90kV already at 400Hz or only at the output voltage of 115KV is the frequency 400Hz?

author: Dinheaven
author_rank: Contributor
timestamp: September 17, 2014, 03:55:00 am
content: Quote from: Jebnor on September 16, 2014, 02:04:39 amQuote from: Alex Eisenhut on September 16, 2014, 02:06:53 am@Jebnor,Thanks for the video!! I learn alot about AC->DC->AC conversion in the video.. So for my project, I only need to 'modify' the system to not include the battery and the charger and also to use the step-down transformer at the end since i need to decrease my output voltage. I'm still confused on which part of the system should I include the Frequency Conversion.@ Alex EisenhutHAHAHA nice one bro!!Nice of you to chase that period away

author: Dinheaven
author_rank: Contributor
timestamp: September 17, 2014, 04:04:37 am
content: Quote from: DanielS on September 16, 2014, 02:07:07 amQuote from: T3sl4co1l on September 16, 2014, 05:45:29 am@DanielSNope I do not need to do both separately but im still Confused on where do the frequency conversion happens in the straight AC(-DC)-AC converter. I goggled the Frequency Converter and already studying it right now. Thanks for the info! Will update soon enough.@T3sl4co1lThanks Tim!!I'm yet to try researching the motor-alternator pair or the wound-rotor motor you mentioned as I'm still finding information on the AC(-DC)-AC converter and the Frequency conversion operation. The VFD do make me curious though on how it operates. Will do research and update you here soon. Thanks for the info again!

author: Dinheaven
author_rank: Contributor
timestamp: September 17, 2014, 04:15:12 am
content: Quote from: evb149 on September 16, 2014, 06:11:05 amQuote from: Alex Eisenhut on September 16, 2014, 12:12:53 pm@evb149Unfortunately i cant use the PFC module(I think) as i have to design the hardware on a PCB which maybe means that i cant use a PFC module in between. Although, if i were to use the PFC module, doesnt the output power is too high at 370DC? I only need 115Vac.@Alex EisenhutIs there any difference between the Voltage-Frequency Drive and the Variable-Frequency Drive? Sorry for my ignorance by the way.@T3sl4co1lTim, I forgot to mention that my project must be a cost efficient. So..... does that narrow it much or is the other methods of conversion still available?

author: poorchava
author_rank: Super Contributor
timestamp: September 17, 2014, 06:09:11 am
content: My first try would be a PFC stage followed by a sine wave inverter of some sort. For PFC you can get complete application schematics, calculators, BOMs reference designs etc, from companies who manufacture PFC controllers (typical suspects: NXP, PowerIntegrations, TI, LT, ST, OnSemi, Infineon).For sine wave inverters you can get a lot of reference designs, papers etc from google.

author: David Hess
author_rank: Super Contributor
timestamp: September 17, 2014, 08:02:27 am
content: What kind of power level is involved?If you are just powering a few 400 Hz aircraft gyros then a 400 Hz oscillator and push-pull linear amplifier driving a step-up transformer can produce 400 Hz 115 volts from any convenient DC voltage. Higher power levels are going to require a real inverter.The AC to DC to AC design is pretty straightforward. The hardest part is the DC to AC inverter if you want a sine wave output at high power.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 17, 2014, 08:12:23 am
content: Quote from: Alex Eisenhut on September 16, 2014, 12:12:53 pmYes, this is most common.. I think I've seen "voltage frequency drive" before, since that's what it does (both are varied in proportion, not just frequency). So, I wrote the more descriptive one, but that may be misleading. So, this ^ too.Tim

author: DanielS
author_rank: Frequent Contributor
timestamp: September 17, 2014, 04:52:44 pm
content: Quote from: Dinheaven on September 17, 2014, 04:04:37 amIf you glanced at some of the many schematics, you should have noticed that the bulk of them are simply an AC-DC rectifier, sometimes with SCRs to adjust the DC voltage, and a set of output bridges to drive the output.The output frequency is determined by the output stage driver IC. Since 400Hz is a relatively low frequency, you could generate the output drive sequence from a microcontroller and use MOSFET driver ICs to drive output devices.

author: Seekonk
author_rank: Super Contributor
timestamp: September 17, 2014, 10:06:18 pm
content: "230Vac/50Hz from my lab wall socket to 115Vac/400Hz to be used for aircraft equipments. "I have four of them. Found them on ebay. Can't imagine I paid more than $50 for any of them. Some had the 400hz oscillator, others had a wide range oscillator and another I drive with an audio oscillator. In 50Hz land they probably aren't that cheap. Just use a good size audio amplifier and a 12-24V power transformer to boost up the voltage.

author: dannyf
author_rank: Super Contributor
timestamp: September 17, 2014, 10:14:03 pm
content: Assuming that square wave works equally well. Just rectify the ac, and run it through two switches -> a H-bridge for example, driven by a 400Hz oscillator.

author: Dinheaven
author_rank: Contributor
timestamp: September 18, 2014, 07:00:13 am
content: Quote from: poorchava on September 17, 2014, 06:09:11 amQuote from: David Hess on September 17, 2014, 08:02:27 am@poorchavaUmm whats a PFC stage? I've been studying aircraft electronics for close to 4 years now but i just cannot believe how shallow my knowledge is in electronics.Is the PFC stage similar to the AC-(DC)-Ac converter?@David HessMy product rating is 50W. I understand the 400 Hz oscillator is used to increase the 50Hz freq to 400Hz but why do i need the push-pull linear amplifier driving a step-up transformer? Im trying to decrease the voltage from 230Vac to 115Vac. Sorry if im being dumb or something but i am really clueless.

author: Dinheaven
author_rank: Contributor
timestamp: September 18, 2014, 07:09:02 am
content: Quote from: DanielS on September 17, 2014, 04:52:44 pm@DanielSSo I sees the similarity between the AC-(DC)-AC converter and the frequency converter is that both has a rectifier and an inverter right? So i only need to combine both systems with the inclusion of the 400HZ oscillator to increase the input frequency. Do i need a step-up or Step-down transformwer for my circuit operation?

author: Dinheaven
author_rank: Contributor
timestamp: September 18, 2014, 07:22:43 am
content: Quote from: Seekonk on September 17, 2014, 10:06:18 pmQuote from: dannyf on September 17, 2014, 10:14:03 pm@SeekonkSo i need to include an audio amplifier and a power transformer in my circuit but yet why do i alot of people ask me to step up my voltage? I'm trying to decrease the input voltage of 230Vac to output voltage of 115Vac. I understand about the addition of the 400hz oscillator which is to increase my input frequency to the 8th harmonics(Correct me if I'm wrong). Can you explain the 'Increase Voltage part please'?@dannyfThe H-bridge switches enables a voltage to be applied across a load in either direction. Is it used to drive the 400hz oscillator or a Dc motor. Why do i need a DC motor in my circuit?Guys if I post dumb questions in my replies please forgive my ignorance as i am totally clueless here

author: David Hess
author_rank: Super Contributor
timestamp: September 19, 2014, 09:23:41 pm
content: Quote from: Dinheaven on September 18, 2014, 07:00:13 amPFC stands for power factor correction. Older AC input switching power supplies used a diode rectifier and capacitor filter to produce about 340 volts DC but this simple design has the disadvantage of drawing power only at the peaks in the AC line voltage which results in poor power factor. Power factor correction solves this by drawing power continuously in a way that makes the input look like a resistive load. 50 watts is too low to require power factor correction in most cases.QuoteI was just suggesting a push-pull linear amplifier driving a step-up transformer as the simplest solution if your power requirements are not great. 50 watts is certainly feasible this way.

author: Seekonk
author_rank: Super Contributor
timestamp: September 20, 2014, 04:12:23 pm
content: Most all of my variable frequency power supplies are just oscillators and audio amplifiers that output about 30V AC. They take that and put it into a reverse transformer that boosts it up to 150V AC. This would be for low power applications generally under 100W. Higher power ones are generally digital because an analog solution wastes more than half the power in heat. I don't know about your neck of the woods, but I have purchased 300W PA amplifiers for under $20. You will be driving an inductive load so it could easily blow up if driven too hard. That is called education. Diodes from the output of the amplifier to the power supply rails should help prevent that.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 20, 2014, 04:57:12 pm
content: Just get a surplus industrial VFD. Then add a LC filter on the output if needed.

author: Dinheaven
author_rank: Contributor
timestamp: September 22, 2014, 06:24:16 am
content: So after viewing and researching the mentioned equipment above, I did manage to narrow down into these equipments that are suitable for my Project. I'm looking towards the Electronic Inverter AC->DC->AC, Variable Frequency Drive (VFD) & the solid state AC-AC converter.Some question though, Once the 230Vac is rectified to become DC voltage, Does it stay the same at 230V or to a new voltage? &,To increase output to 400Hz, i'll need a oscillator circiuit right? Doesnt the inverter include an oscillator circuit?