How to increase or decrease the frequency of AC current linearly? Suggest me some ideas
Frequency multiplier circuits are conventional technology.
Welcome to the PF.
If you say more about your application, we will be able to make better suggestions. For example, for some applications, a Frequency Synthesizer is a good choice:
I want to switch the poles of an electromagnet using a AC power supply... In Order to control the switching speed I would like to control the frequency of the AC current.
still not too much info forthcoming from you
Tell us about the electromagnet ...
its voltage and current rating ?.
Is it a commercial or home made electromagnet ?
what sort of AC power supply are you using?
why do you want to vary the switching speed ?
what do you think it will achieve .... ie ... what are your goals ?
Would a circuit that continuously reverses the polarity of a DC supply do what you want? It would have a control that varies the rate at which polarity reverses. How often do you want the polarity to reverse? Maximum rate, minimum rate?
Essentially you need to build a variable frequency signal generator that outputs the appropriate waveform for your application. That can drive an appropriate circuit to deal with the voltages and currents you require.
Depending on the frequency range and precision you desire there are many ways to do this, from microprocessor controlled PWM to digitally controlled numerical methods, to counter based DAC's to analog oscillators or multivibrators.
Look at application circuits for the 555 timer. (google 555 variable multivibratorand look at images)
We need more system requirements in order to pin down what is best for your level of expertise.
You need a cyclo converter or an AC source from Ametek or Chroma. Easier to buy it than to build it yourself if you have little experience in power electronics.
Start with rectifying the source AC. And use it as the power source.
A. Power a variable-speed motor driving an AC generator
B. Use analog sine oscillator with a variable frequency to drive a power amplifier
C. Use a variable frequency digital sine generator to create a sine wave to drive a power amplifier
D. Use a variable frequency digital generator to drive a set of switching elements to approximate a sine wave
I can go on like this for a long time. As noted above, I need more information to narrow the idea stream down
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