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LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 07:35pm 04 Mar 2019
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Synchronizing our inverters to noisy generators
I have been thinking about this and I am severly discouraged from doing so when I look at the output waveforms of cheap noisy generators.
It is very hard and slmost useless to get a phase lock.
To me, it makes more sense to convert all my inputs to (rectified) DC.
Then the only thing I need to worry about is matching their voltage to assure proper load sharing without wasting any energy.
For example, assume I am at a camp site that charges me $1/kWh for shore power. I also have the following sources of power:
1. 150V, 150Ah battery 2. 1.5 kWh PV Panels 3. A few $99 cheap gasoline and propane generators that turn cheap gasoline and propane fuel into something that looks like a CardiB soundtrack on an oscilloscope.
My objective is to load share between all these power sources according to priority (cheap to expensive power). So I want to dip into "shore power" only when the above 3 does not provide enough power.
Please note that I want to blend the power sources: so at no point in time am I exclusively drawing "shore power" (unless all the above 3 are completely depleted)
What is your solution?
LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 07:43pm 04 Mar 2019
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My solution is to convert all these inputs to (rectified) DC.
A diode OR configuration is used to source power from all these sources.
To ensure that shore power draw is minimum, I need to figure out a way to either reduce the voltage of shore power compared all these sources, or, slightly increase, say by a volt, enough to reverse bias the shore power rectifier, the voltage of all these sources.
Since I control all these other sources except the shore power, this should not be a theoretical challenge.
The Warpverter takes the diode OR configuration output as input and inverts it back to AC.
When the Warpverter fails to maintain load regulation from these low cost sources, the line regulation module brings the voltage of these 3 sources near the shore power voltage.
If the voltages from all these 3 sources are matched with the voltage from shore power, then the diode OR configuration should allow seamless load sharing.
LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 07:47pm 04 Mar 2019
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The reality of this seamless load sharing is to be tested in the field though.
High power diodes are far from perfect diodes and their Vf change depend on ambient conditions and Id (current through the diode). Ensuring the voltages from all these 3 sources are matched with the voltage from shore power itself could be a losing battle.
If that FAILS spectacularlly, another idea could be to use an active switch to connect each source in sequence with a duty cycle to reflect the load sharing amount that's targeted.
Nothing beats the simplicity of a diode OR configuration, so that will be my first approach.
davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499
Posted: 11:37pm 04 Mar 2019
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Have a look at hi-side FET switching to reduce loss.
But then you will need a means of controlling them. You are probably sensing your voltage sources so this is probably not difficult.Edited by davef 2019-03-06
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 01:24am 05 Mar 2019
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the solution I have fooled around with is to use a inverter generator that can share an output. the one I used has a separate set of connections for paralleling.
these little gennies can sync to the inverter and backfeed a H bridge.
however I have only tried it with a honda and one inverter, LFP batteries and I didn't try and fully charge the cells. I used the battery voltage as a trigger to cut the motor.
I fired it up once and tried it, found out it worked. Only get a bit over 5 kwh on a tank of juice but that seems to be plenty. From memory the honda generator was quite expensive, like A$1800-$1900. so we made a decision to spend the money on extra panels and hire a generator if the system needed a top up.
the reality of traveling is that it is often difficult to get sun onto panels and shore power is very cheap and sometimes its free. I'm confused, no wait... maybe I'm not...
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:20am 05 Mar 2019
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Has been working fine here for a couple of years, still working fine right at this moment.
But you are right, load sharing is dead simple for dc sources, and a huge can of worms trying to synchronize to a gasoline generator that changes speed when the load changes, and trying to synchronize anything to that is just not going to work.
Its like trying to find the soap in the bath. It keeps running away from you every time you think you have it cornered.Edited by Warpspeed 2019-03-06Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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