UPS phase lock Loop for input and output

[stanleystan]

Why does UPS systems have a phase lock loop?
What is the phase lock loop circuit it used for?

Is it to sync and phase the AC generator with the output?

 

[Venkadesh_M]

you are talking about which UPS.

PLL can be used to sync one wave with another, but I don think that can be used in UPS to sync the output with AC.
Because if a small out of phase occurs that can make a great damage.

 

[stanleystan]

Yes UPS systems have PLL to sync the input with the output so they are in sync

When the AC input gets disconnected , an AC generator turns on with has a "slew rate" from the AC generators motor

The PLL with sync the AC generators AC voltage input with the UPS systems output AC waveform

I'm confused how to measure the Slew rate time duration of the AC generators motor and also how long it takes the the PLL circuit to sync the input and output

The PLL circuit syncs the AC input with the Output AC waveform

 

[Venkadesh_M]

Hi, I am having lot of questions.

What do you mean slew rate of generator, Do you mean time taken to start from zero speed to rated speed ?

Is the ultimate aim of the system is to provide a totally "un"interrupted power supply ?

What is the purpose of the inverter after starting the generator? will they run parallely ?

what is the status of sync when the generator is starting ?

 

[chuckey]

I think you are getting confused. Generators have to be run for at least 10 seconds before they can take load, this is simply to allow their control circuits to operate and the output voltage to stabilise.
In a full supported system, the battery UPS generates mains that was synchronised with the now missing mains and the diesel starts. Once the mains has "gone" (< 80%?) the UPS takes the load. After the diesel has stabilised (10 seconds?), it would be very sophisticated if the UPS changed its frequency to that of the diesel generator, but in the systems I have used, the Diesel alternator just takes the load from the mains via a contactor. The side effect is that the diesel alternator now supplies the UPS. With certain UPSs, if the frequency of the alternator is out by 1 HZ from its nominal, they will not use that generated mains, which gives you 10 minutes to sort the diesel or get the mains back.
Frank

 

[stanleystan]

What do you mean slew rate of generator, Do you mean time taken to start from zero speed to rated speed ?

Yes, how do u measure the Time duration of how long it takes the AC generator/alternator to start from zero speed to supply the UPS?

I put the Oscilloscope Probes where at or DVM fluke meter probles where?

Is the ultimate aim of the system is to provide a totally "un"interrupted power supply ?

Yes UPS is an Uninterrupted power supply

When the Mains disconnect, the AC generator will start and supply the UPS with an AC voltage at 115VAC at 60hz

What is the purpose of the inverter after starting the generator? will they run parallely ?

The inverter section, inverts the AC generators 120VAC at 60hz into DC and Back to a clean conditioned AC waveform at 120VAC at 60hz

what is the status of sync when the generator is starting ?

It's free running, no sync at that time when the mains are turned off

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the battery UPS generates mains that was synchronised

Why are UPS synchronized? for what reasons

How does your UPS system synchronize, if they don't use PLL circuits?

With certain UPSs, if the frequency of the alternator is out by 1 HZ from its nominal, they will not use that generated mains, which gives you 10 minutes to sort the diesel or get the mains back.

Yes the AC generators more drifts up and down, not constant at 60hz

The AC generator should output 120VAC at 60hz steady right?

 

[Venkadesh_M]

Did you mean this ?

This kind of systems has no need to use PLL.

I put the Oscilloscope Probes where at or DVM fluke meter probles where?

You have to put the DVM probes in AC output of generator and wait to reach its rated voltage in output.

Why are UPS synchronized? for what reasons

To share the AC load, when the existing system is not enough to handle the whole load. but not the case, they will make some different wiring for the load, they will not make it parallel.

Now a days the paralleling mechanism is working in feeding the excess UPS power to grid. in place of solar inverters.

How does your UPS system synchronize, if they don't use PLL circuits?

PLL can be used here, because it is correcting its output from the phase error, which is not allowed here. and also it is depend on waveforms, we cant make a exact sine wave using a inverter.

They will synthesize the AC waveform by taking lot of samples from the AC with DSP processors.

The AC generator should output 120VAC at 60hz steady right?

for load sharing with synchronous sources, they cant be ~0.001HZ diff, simply they shd be in-phase.

 

[stanleystan]

for load sharing with synchronous sources, they cant be ~0.001HZ diff, simply they shd be in-phase.

So the load slows down the AC motor frequency? so it's not at 60hz 115VAC

PLL can be used here, because it is correcting its output from the phase error, which is not allowed here.

Why don't u want the output to have a phase error?

When the mains are not connected , the AC generator motor and the UPS output is free running? or in sync no phase error?

You have to put the DVM probes in AC output of generator and wait to reach its rated voltage in output.

To measure the Time it takes the AC generator to reach the rated voltage

Oscope channel#1 on the output of the AC generator
Oscope Channel#2 on the output of the UPS ?

Measure the time difference between the output of the Ac generator and the output of the UPS?

 

[Venkadesh_M]

So the load slows down the AC motor frequency? so it's not at 60hz 115VAC

I said the difference in frequency not the supply frequency, there should not be any diff frequency before doing synchronization. But in your case no need for synchronization.

Why don't u want the output to have a phase error?

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Their terminal voltages must be equal. If the voltages of the two AC generators are not equal, one of the AC generators could be picked up as a reactive load to the other AC generator. This causes high currents to be exchanged between the two machines, possibly causing generator or distribution system damage.

Their frequencies must be equal. A mismatch in frequencies of the two AC generators will cause the generator with the lower frequency to be picked up as a load on the other generator (a condition referred to as "motoring"). This can cause an overload in the generators and the distribution system

Their output voltages must be in phase. A mismatch in the phases will cause large opposing voltages to be developed. The worst case mismatch would be 180° out of phase, resulting in an opposing voltage between the two generators of twice the output voltage. This high voltage can cause damage to the generators and distribution system due to high currents.

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When the mains are not connected , the AC generator motor and the UPS output is free running? or in sync no phase error?

PLL cant be used here, because it is correcting its output from the phase error, which is not allowed here.
a t has been missed.

Oscope channel#1 on the output of the AC generator
Oscope Channel#2 on the output of the UPS ?

Measure the time difference between the output of the Ac generator and the output of the UPS?

But who will take care of your oscilloscope ? You can use this method only if your oscilloscope is rated for terminal voltage or you have to use potential dividers. and also you have to use Earthed neutral as common.

The frequency of a AC synchronous generator (alternator) will be totally depend on speed also the voltage.
So voltage and frequency will increase with the driving speed, you can see it in the oscilloscope, but it will take about only 2 sec max.

 

[stanleystan]

Well the UPS power factor means the input and output voltage ratio loss?

Most UPS get overloaded on their outputs be applying to much load to it

UPS systems don't like to much load when it's in the battery mode inverter mode, which causes the UPS to get damaged

When the UPS system is running on batteries and inverters DC to AC output, when overloading it or to much load will damage a UPS system very fast, why is that?

It's more sensitive in battery mode to put a load on it

Loads can be inductive loads and capacitive loads, in battery mode it blows the UPS very easy

Maybe because the batterys can't handle inductive loads or capacitive loads because of the Voltage current transfer curve

Inductive loads and capacitance loads draw more current and in rush current

 

[Venkadesh_M]

Well the UPS power factor means the input and output voltage ratio loss?

No. power factor is the ratio of actual power and apparent power.
In electrical formula for power is V * I. but all the loads can use the whole apparent power due to inductivity and capacitivity there comes PF.
actual power cant be more than apparent power so PF cant be more than 1.

Most UPS get overloaded on their outputs be applying to much load to it

All UPS.

UPS systems don't like to much load when it's in the battery mode inverter mode, which causes the UPS to get damaged
When the UPS system is running on batteries and inverters DC to AC output, when overloading it or to much load will damage a UPS system very fast, why is that?
It's more sensitive in battery mode to put a load on it

Mainly there is two types of UPS, ON line and OFF line.

In ON line mode, every time load will be power through inverter and battery.
In OFF line mode, If the main power is not available then only battery will be used through inverter.

The inverters generally cant bear much impact more than specified. so the answer is depend on inverter.

Loads can be inductive loads and capacitive loads, in battery mode it blows the UPS very easy
Maybe because the batterys can't handle inductive loads or capacitive loads because of the Voltage current transfer curve
Inductive loads and capacitance loads draw more current and in rush current

The inductance and capactance make PF worse. That means the load needs more apparent power for taking the actual power.

If the apparent power increases then the current increases(Its V * I but voltage cant increase). so if you put more reactive load that will reduce the life time of inverter.