Schneider XW Pro and Modified Sine Wave Generators
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RCinFLA
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Do not use a modified sinewave input to a hybrid sinewave inverter.
Hybrid inverters synchronize to AC input before closing connect relay and inverter runs in parallel with AC input.
Paralleling a hybrid sinewave inverter from a modified sinewave source input will cause high current spikes in both inverter and MSW source.
Hybrid inverters synchronize to AC input before closing connect relay and inverter runs in parallel with AC input.
Paralleling a hybrid sinewave inverter from a modified sinewave source input will cause high current spikes in both inverter and MSW source.
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Thanks for the reply.
You mention the hybrid inverter runs in ‘parallel’ with the AC input. I need to understand more about what you’re saying and make sure we are thinking about the same configuration.
I can see the XW Pro syncing to the AC source. If the voltage, frequency and THD purity of a genset is indistinguishable from grid quality, the XW Pro should be happy with that for its input.
Clearly any quality deviations of freq/THD in that input power are a negative for the XW Pro just like when the ERCOT grid freq sagged badly in their winter debacle.
The situation I am thinking of is a grid down circumstance and a back up generator is available to substitute AC input (replacing the grid power) to the inv/charger (XW Pro) to charge the ESS batteries and give it input energy to continue driving the regular loads. (This config would not be driving loads downstream of the XW Pro in ‘parallel’ with the generator.)
I am missing what is in paralleled in your comment.
Maybe I could have stated the question better as … does the XW Pro actually monitor incoming power for voltage, frequency and THD and then take itself offline below some quality level?
If not, any outboard generator design must assure electrical quality above some minimum level. (Like a big diesel prime and a 500# Marathon head).
If so, what are the specific cutoff points where the Schneider box shuts down?
Best regards,
B
You mention the hybrid inverter runs in ‘parallel’ with the AC input. I need to understand more about what you’re saying and make sure we are thinking about the same configuration.
I can see the XW Pro syncing to the AC source. If the voltage, frequency and THD purity of a genset is indistinguishable from grid quality, the XW Pro should be happy with that for its input.
Clearly any quality deviations of freq/THD in that input power are a negative for the XW Pro just like when the ERCOT grid freq sagged badly in their winter debacle.
The situation I am thinking of is a grid down circumstance and a back up generator is available to substitute AC input (replacing the grid power) to the inv/charger (XW Pro) to charge the ESS batteries and give it input energy to continue driving the regular loads. (This config would not be driving loads downstream of the XW Pro in ‘parallel’ with the generator.)
I am missing what is in paralleled in your comment.
Maybe I could have stated the question better as … does the XW Pro actually monitor incoming power for voltage, frequency and THD and then take itself offline below some quality level?
If not, any outboard generator design must assure electrical quality above some minimum level. (Like a big diesel prime and a 500# Marathon head).
If so, what are the specific cutoff points where the Schneider box shuts down?
Best regards,
B
dougbert
Solar Addict
the Pro does qualify incoming AC before syncing to it. If it does not pass vetting, it won't sync. As to actually vetting mechanics, IDK
RCinFLA
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Inverter is operating in parallel with AC input once sync'd and pass-through relay closes. XW has two sets of ACin relays and two separate AC inputs, typically for grid input and generator input, but only one is used at a time, with AC1 (grid input) taking priority if both AC inputs are present.
'qualify' is a pretty general term.
The LF inverter really only synchronizes zero crossing and rms voltage, before it closes pass-through relay. It may not connect if the rms voltage, or frequency, of the input source is out of range of inverter tracking limits.
Other common reason for not connecting is with a synchronous conventional generator which output frequency is dependent on engine rpm. Inverter phase tracking is slow, purposely, to avoid sudden phase shifting on inverter AC output. When a synchronous generator engine rpm governor control is unstable causing engine rpm to vary the inverter will be unable to track and lock to it.
Once it does connect, if AC input waveform is so different from inverter's sinewave, it will cause overload current spikes on inverter that will be detected and cause it to open the pass-through relay releasing from the AC input connect.
Same thing happens when grid goes down or glitches. It overloads inverter causing it to disconnect pass through relay.
It will then start the sync, connect, overload, and release process all over again.
Flashing ACin green LED mean AC voltage detected, and inverter synchronizing in process. Farther away AC input frequency is from inverter span range center frequency, the longer this sync'g time will be.
Solid ACin green LED (along with 'clunk' of relay) happens when pass-through relay connects.
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BentleyJ
Solar Wizard
Based on experience with the older XW+ model, the Schneider does not shut down it just does not qualify the Gen input on AC2, the relay does not close so power comes from only from batteries (and solar if you are DC coupled and have charge controllers) until the batteries reach the LBCO setting. On the XW+ there are user settings in the AC Settings menu for high & low voltage limits as well as high & low frequency limits.
If you wish to use a generator with high THD or a square wave perhaps a stand alone AC battery charger that plugs directly into the generator is an alternate way to go.
RCinFLA
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I would take the money you would spend on a separate charger and buy a sinewave generator.
One of the advantages of XW inverter is it has good efficiency and AC input power factor when charging from AC input source.
Most lower cost chargers have just rectifier-filter capacitor AC to DC input conversion. They have very poor AC input power factor and not too great input to output conversion efficiency.
One of the advantages of XW inverter is it has good efficiency and AC input power factor when charging from AC input source.
Most lower cost chargers have just rectifier-filter capacitor AC to DC input conversion. They have very poor AC input power factor and not too great input to output conversion efficiency.
Bentley,
An external charger alternative was in the back of my mind when I started down this road. I like the Schneider inv performance, but it carries some system complexity as well.
On one hand, I hate to pay twice for charging and the potential issues of two chargers driving the ESS … but on the other hand, redundant equipment after a hardware fail during SHTF would be a plus.
1800 rpm gens are def not cheap/available compared to even 3-4 five Kw internet specials. Also, I’ve never studied running serious ‘dual’ DC charging current to a batt bank.
Grid uncertainty is driving more learning ops and trade offs ahead.
An external charger alternative was in the back of my mind when I started down this road. I like the Schneider inv performance, but it carries some system complexity as well.
On one hand, I hate to pay twice for charging and the potential issues of two chargers driving the ESS … but on the other hand, redundant equipment after a hardware fail during SHTF would be a plus.
1800 rpm gens are def not cheap/available compared to even 3-4 five Kw internet specials. Also, I’ve never studied running serious ‘dual’ DC charging current to a batt bank.
Grid uncertainty is driving more learning ops and trade offs ahead.
Being old school, MSW doesn’t have a lot of appeal to me and a lot of the genjunk I see still appears to be on a race to the bottom.
I have a Honda GX with a 2pole MeccAlte 7.5k head that I converted to tri-fuel about 15 yr ago and it still carries the day, but besides being decades legacy old, it’s noisy enough to hear a 1/4 mile away. Now the idea of it running four hr into a 20KwH ESS and letting the Schneider silently invert us all night long for about 20 hr of quiet is something that I can build to. (But they are getting harder to find as the new inv/gens sweep the market … crappy MSW and all).
A big sine inv/ESS is especially attractive since we rarely burn more than a KwH in any one hour of the day (excluding summer).
Yes! Back in the 80s I worked for a pipeline where we built batt rooms w sixty 2v C&D 1000ah cells and those old chargers were lucky to make 0.6pf and they buzzed you crazy. Techs hated tending all of it but they worked rock solid. ?
I haven’t looked at what you can buy today, I just remember having to size up the Onan Kva’s because of the pbm you mentioned.
Good point! ??
Ah, perfect. Excellent diagram!
This raises two possibly obvious questions:
1. If there is no grid and no gen on the XW Pro’s two AC inputs, I presume there is a mode where the relays get locked out and the inverter can operate in off grid mode … correct?
2. With grid or gen pwr qualified, relays pulled in and the inverter actually synchronized/paralleled directly with the source, what keeps inverter current from flowing back to the grid or genset?
(This also seems particularly important in the situation where there would be a relay driver failure (or stuck software bit), putting 220 back on the pwrco transformer, heating up the primary voltage back where a lineman is clearing a tree break.)
Schneider Engineers have to have a fail safe mode in here somewhere. Presuming something like the software looks for current sense indication of energy flowing back into to inputs and shutting down the inverter entirely. I’d like to hear
a Schneider XW Engineer explain how their software/hardware design here fills the safety bill.
I appreciate your assist!!!
B
RCinFLA
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There are even more things involved. Here is a short course on XW hybrid inverters.
1) If no AC input detected, the input relays remain open, and inverter just operates as stand alone at its calibrated freq and voltage. The purpose of the input relays is to allow inverter to sync to AC input before tying the two together in parallel. Basically, same thing utility power distribution does with multiple power plants connected to grid.
2) The LF inverter is true continuous bidirectional converter with just minor continuous adjustments to PWM control on battery side MOSFET's. When running in parallel, just a slight adjustment in PWM control on inverter raises or lowers its output voltage relative to AC node. If inverter raises its output AC voltage slightly it pushes current to AC node from battery. If inverter lowers its AC output relative to grid it sucks power from AC node to charge battery.
The current sensors tell the controller what to do based on firmware features. Raise the inverter output AC slightly and the inverter supplies more of output load from battery and AC input current is reduced. Keep raising inverter output AC voltage even more and it will take over all AC output load and drive AC input power to zero. Raise it a little further and it will supply all AC output loads and push power backwards into grid. All this contingent on max power capability of inverter and state of charge of battery. The current and voltage sensors measure AC voltage and AC current phase and can tell the AC flow direction from this information.
You can set maximum allowed AC input current, like based on generator capability, and inverter will manage the inverter supplement of AC output and battery charging to stay under the set max AC input. AC output has priority over charging so as AC output loads get closer to AC max input setting the amount of battery charging is reduced. If AC output load exceeds the max set AC input limit, then inverter will supply the short fall from battery power. All this happens in a smooth continuous flow. The AC output load can be greater than either the inverter or generator can supply individually by combining generator and inverter power together.
Normally the inverter runs all the time but there is a standby mode that shuts off inverter and only the AC input to AC output pass-through is active. If grid input drops the inverter will wake up but this is a bit longer process to get inverter fired up and results in greater AC output drop out time. In standby mode the controller keeps tabs on AC input phase and voltage, so it knows how to start up inverter in proper phase and voltage.
There are a lot of other safety things that are checked. One of the more difficult things for inverter to do is recognize when AC input goes open circuit, like if you flip AC input breaker off. You could have a legit zero AC input current that should not disconnect relays but that cannot be distinguished from an open circuit input until a current is pulled by inverter through AC input. Meanwhile there is AC voltage on AC input even if supplied by inverter. As part of the anti-islanding safety requirement, the inverter will attempt to wobble its phasing slightly, periodically, to check if AC input is still there. The slight wobbling phase will create some AC input current draw that tells the inverter the AC input is still present and valid.
All hybrid inverters detect grid collapse or grid glitch by momentary current overload on inverter and they release pass-through relay connecting inverter from AC input. Inverter continues to operate, picking up AC output loads, assuming the AC output load is not exceeding inverter's capability, which would then result in inverter shutting down with overload alarm.
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RCinFLA - from pix & comments you’re obviously knowledgeable...
Are you familiar w/ Schneider XW Pro AC2 issue of not qualifying? I have a small off-grid sys w/ 2 XW Pro inverters. I haven’t connected charge controllers. Too late in season.
My master-slave config works. My batter bank is working. I can pull power from battery bank factory pre-charge through inverters to power house but I can’t get inverter to qualify AC2 generator as source to charge batteries. Some say to switch generator to AC1 but that doesn’t make sense given Schneider was supposedly designed off-grid. Any ideas on settings?
Are you familiar w/ Schneider XW Pro AC2 issue of not qualifying? I have a small off-grid sys w/ 2 XW Pro inverters. I haven’t connected charge controllers. Too late in season.
My master-slave config works. My batter bank is working. I can pull power from battery bank factory pre-charge through inverters to power house but I can’t get inverter to qualify AC2 generator as source to charge batteries. Some say to switch generator to AC1 but that doesn’t make sense given Schneider was supposedly designed off-grid. Any ideas on settings?
acdoctor
Solar Enthusiast
I have the XW+ the book says it will take any generator you through at it. Under size, under voltage and the like. I have a 11 kw Siemens non inverter. If I let it warm up good I can charge at 100 amps while running water heater 4500 watts.
RCinFLA
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1) Generator must be within XW frequency limits setting. You can check generator output frequency with a DVM that has frequency counter function.
2) Generator (fixed rpm synchronous type) must have stable rpm governor control. It cannot wobble in rpm too much or its output frequency will wobble and inverter will not be able to phase lock to it. (remains with blinking green LED). DVM will not detect a frequency wobble that will cause inverter not to phase lock. Best to just listen for smooth even sound from generator with no 'wha-wha' pitch variance sound.
3) Need to make sure you do not initially overload generator when inverter connects. This will cause inverter to connect but immediately release from generator when it bogs down from overload. Reduce AC input maximum allowed current by reducing 'input breaker size amperage' setting.
Voltage and distortion from generator are rarely a reason for not connecting to generator. Some old synchronous generator's AC output voltage will be a function of rpm speed and usually if frequency is within range the AC voltage will also be within range. Inverter does not pre-qualify generator waveform distortion. This is effectively done after inverter connects to generator where there will be inverter current spikes if generator distortion is too great, but inverter can take a lot of AC input distortion. If there is too great inverter current spikes the inverter will just release from generator.
2) Generator (fixed rpm synchronous type) must have stable rpm governor control. It cannot wobble in rpm too much or its output frequency will wobble and inverter will not be able to phase lock to it. (remains with blinking green LED). DVM will not detect a frequency wobble that will cause inverter not to phase lock. Best to just listen for smooth even sound from generator with no 'wha-wha' pitch variance sound.
3) Need to make sure you do not initially overload generator when inverter connects. This will cause inverter to connect but immediately release from generator when it bogs down from overload. Reduce AC input maximum allowed current by reducing 'input breaker size amperage' setting.
Voltage and distortion from generator are rarely a reason for not connecting to generator. Some old synchronous generator's AC output voltage will be a function of rpm speed and usually if frequency is within range the AC voltage will also be within range. Inverter does not pre-qualify generator waveform distortion. This is effectively done after inverter connects to generator where there will be inverter current spikes if generator distortion is too great, but inverter can take a lot of AC input distortion. If there is too great inverter current spikes the inverter will just release from generator.
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acdoctor
Solar Enthusiast
Have you went to AC settings and looked at AC2 there you can adjust high and low voltage and frequency. Seems like you also have to set the breaker size for generator. Hope this helps.
acdoctor
Solar Enthusiast
Do you have generator power to both AC2 connections? Have those phases terminated to the correct input. They can’t be reversed. AC1 on both has no power. You have verified the settings for assignment of AC1 and AC2 in both inverters. Generator is running smooth, no surge. Try a different generator.
That’s all I have.
That’s all I have.
