syncronization of two single phase alternators (driving by a 12V dc motor) at 100Hz.

[jawadali19252]

i am doing my FYP on synchronization of two single phase alternators at 100Hz. i have complete one set(speed control module>12 V dc motor>alternator 150W) and put that on a board. this gives a pure sine wave. now i put another DC motor and alternator on board. now to synchronize the second alternator with first alternator, infact i have to control the speed of dc motor.for this i decide to take feedback(voltage) from alternator and give to zero crossing detection circuit, which will convert the sine to square wave and by using micro controller i will find the time period of that wave so hence i will find freq(1/T) and also RPM(120*f/p).

(1)but the issue is to design the circuit of zero crossing detection cct with accurate values of components. i have seen many cct of this. but they are for 50 or 60 Hz.
(2) how can i make the both output voltages of alternators same?

kindly help

 

[BradtheRad]

Power stations need to do the same thing with their generators/ alternators.

It's a question how to get them to match speed, and also match phase.

I picture that you would have two frequency-to-voltage converters. These would get the speeds reasonable close.

But it would need something more to achieve phase sync.

Someone will no doubt suggest a microcontroller. Did you consider this already?

how can i make the both output voltages of alternators same?

This is a different adjustment than speed or phase. The easy way is to adjust field voltage to one unit.

If you want both units to perform identically, then you'll need to add or remove turns from one generator, so it matches the other's output. This is extremely tedious and painstaking. It can result in an unbalanced armature.

Another easy method is to place an impedance inline with the stronger generator. The impedance might be resistive or inductive. You lose some efficiency however.

 

[D.A.(Tony)Stewart]

There will be 2 speed control loops and 2 field control loops with a reference voltage for each to match the outputs with no load.

When combining 2 voltage sources with and without a load, there be stability problems to resolve with no load and mismatched source impedance ; winding , cable resistance and field regulation impedance.

Current sensing in each source is essential for stability on current sharing which will depend on phase error for lag/lead and field voltage.
Since both outputs are ganged the voltage and current mismatch will affect stability. A flywheel may be needed for each to improve phase stability in each unless you can calculate precisely the cross generator load effects from mismatched current sharing to prevent oscillation.

This may be complex at first try but is a solvable problem if you can determine make each loop critically damped under worst case no load and full load conditions.

The loop compensation for speed must come from a common time base, with better performance using a shaft encoder rather than a zero crossing detector on voltage as inductive load transients may introduce stability errors. Several PID loops will be necessary for perfect synchronization for step load.

position is phase, velocity is the rate of phase change and acceleration is 2nd derivative of phase which is proportion to DC motor current and excess torque ( noload-load).

Begin by characterizing the phase gain block & frequency response from inertia in each component (from step response tests) and analyze like a PLL control system.

Since loading affects the closed loop response and gain, the current sense may also be used to control feedback gain and maintain a minimum of 10 dB gain margin.