DIY Frequency Changer 60Hz to 400Hz?

Thread Starter

frank51

Joined Dec 17, 2012
10
Will someone please provide a schematic for a "do-it-yourself" project on building an inverter that will change 115V AC 60Hz to 115V AC 400Hz?

I understand that the 115V AC 60Hz (from a wall outlet) will have to be rectified to DC, and then inverted to 115V AC 400Hz. The load will be approximately 300 Watts--nothing too elaborate. This is for an aviation project.

Your help is greatly appreciated. Thank you!
 

thatoneguy

Joined Feb 19, 2009
6,359
Such things exist, but aren't common, 400Hz is pretty much military and aircraft use only.

You are essentially looking at a Variable Frequency Drive, which is used with induction motors for speed control.

What amount of power (voltage/current@400Hz) did you need to convert? What type of efficiency is required?
 

studiot

Joined Nov 9, 2007
4,998
Hello Frank, on piece of information missing from your specification.

Waveshape.

Do you need a sinudoidal wave, or will a square wave do?
 

Thread Starter

frank51

Joined Dec 17, 2012
10
Hi Studiot -- First, thank you for helping! The wave required is sinudoidal. Additionally, the load is a small motor requiring 115V AC, 400 Hz. Under load, it draws approximately 1 Ampere. Thanks again for your interest/help.
 

strantor

Joined Oct 3, 2010
5,369
for $99, this will do what you want. I highly doubt you could design something for less, especially when you factor in what your time is worth.

Is your motor 3 phase or single phase?
 

Thread Starter

frank51

Joined Dec 17, 2012
10
Hi Stantor -- The motor I have is single phase--it's small. The VFD that you suggested has an output of 230V AC, and a wave that is not sinusoidal. I need a 115V AC output with a sinusoidal wave. I really appreciate you taking the time to help. Thank you!
 

strantor

Joined Oct 3, 2010
5,369
The wave output of any inverter is not going to be sinusoidal. They work by switching semiconductors. I don't think you need an absolutely sinusoidal wave. No motor explicitly requires that, that I'm aware of. The motor windings "average out" the PWM for a sinusoidal current waveform. If you actually do require a pure wave, you're probably going to need a 400hz generator coupled to another motor.
 

Thread Starter

frank51

Joined Dec 17, 2012
10
Hi Strantor -- You are right; I probably do not need a pure sinusoidal wave. Are there single-phase, 115V AC, 400 Hz output drives available?
 

strantor

Joined Oct 3, 2010
5,369
Hi Strantor -- You are right; I probably do not need a pure sinusoidal wave. Are there single-phase, 115V AC, 400 Hz output drives available?
There are, actually. I only recently became aware of them. However they can't be used with every type of single phase motor, and they cost more.

the Optidrive E2 Single Phase is for use with PSC (Permanent Split Capacitor) or Shaded- Pole Single-Phase induction motors.
Do you know what type of motor you have?
 

strantor

Joined Oct 3, 2010
5,369
I believe it's an induction motor. Thanks.
Ok, there are different types of induction motors. Capacitor start, capacitor run, capacitor start/capacitor run, permanent split phase, etc.

How man capacitors do you see? Is there a huge capacitor?
 

timescope

Joined Dec 14, 2011
298
The wave output of any inverter is not going to be sinusoidal.
This is not correct as there are numerous pure sine wave inverters available. I use a Latronics pure sine wave inverter model 48-BKZ-24 (24v dc, 800w @240v 50Hz). The total harmonic distortion is specified at less than 4%.

The Xantrex XW 6048 inverter/charger (6000 watts) is specified at less than 5% THD at rated output.

Motors do not like square waves due to the high harmonic content, discussed here some time ago :
Square wave on AC motor

Timescope
 

Thread Starter

frank51

Joined Dec 17, 2012
10
Hi Strantor -- In reference to your question regarding the capacitor: There is one capacitor that's 1.5 uf ±10%, at 208 VAC. Thanks.
 

strantor

Joined Oct 3, 2010
5,369
This is not correct as there are numerous pure sine wave inverters available. I use a Latronics pure sine wave inverter model 48-BKZ-24 (24v dc, 800w @240v 50Hz). The total harmonic distortion is specified at less than 4%.

The Xantrex XW 6048 inverter/charger (6000 watts) is specified at less than 5% THD at rated output.
The term "inverter" is broad. It can refer to a VFD (AKA VSD, ASD, drive, et. al.) which is a dedicated inverter for a motor which is what I was talking about, or it can refer to the appliance/utility type that you're talking about. Indeed, some devices do need a pure sine wave and thus need one of these "pure sine wave inverters." Motors are not one of these devices. Motors will accept quite a nasty input and not fuss much about it.
Motors do not like square waves due to the high harmonic content, discussed here some time ago :
Square wave on AC motor

Timescope
An inverter, or what we should refer to as a VFD from now on, does not feed a "square wave" per se, to the motor. It feeds a bipolar PWM "sine" wave to the motor. It's a bunch of nasty chopped up DC, pulsed at several KHz, that the motor interprets as an ordinary line frequency. The inductance of the motor's coils "average out" the PWM pulses, so an oscope reading of the voltage across the motor's terminals would look ghastly, but a simultaneuos oscope reading of the current through those same coils would reveal a pretty sine wave. see the illustrations below:



and this real life picture of the comparison of PWM voltage Vs. coil current as measured on an oscope:


These VFDs only get away with this because of the motor's inductance. Your xantrex or whatever needs a pure sine wave output because the laptop charger that you plug into it has no high inductance coils to sort out the nastiness.

Now, you were onto something though with the "square wave" bit. All this switching in the KHz range causes voltage spikes that are higher than what a motor would ordinarily experience if connected directly to line voltage. This can cause the insulation in the motor to break down prematurely. For this reason, "Inverter Duty" motors are sold, with better insulation and better cooling (for running <full speed).
 

timescope

Joined Dec 14, 2011
298
strantor,

Thanks for the nice pics. They also illustrate how pure sine wave inverters work as they also use pwm techniques. The output transformer removes most of the harmonics.

Timescope
 
Last edited:

timescope

Joined Dec 14, 2011
298
Hi Everyone,

The thread title is DIY Frequency changer.... and the op asked for a schematic. The input and output voltages are the same so we just need to rectify the input and use an H bridge output driven by pwm to obtain the 400Hz sine wave. The pwm can be obtained by comparing a 400Hz sine wave with a high frequency triangular wave.

Timescope
 
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