High frequency vs low frequency inverters

AGBAGB Registered Users Posts: 24 ✭✭
Can anyone help me understand the advantages of using low frequency inverters over high frequency invereters?
I know the low frequency inverters are bulky and heavy.
Any article on this topic will be helpful.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,608 admin
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • clockmanfranclockmanfran Registered Users Posts: 41 ✭✭
    edited December 2018 #3

    I think that  the writer of that article 'Christopher Freitas' https://www.homepower.com/articles/solar-electricity/equipment-products/how-inverters-work  is a little out of date with what is happening.

    From 2015, We operate our Low Frequency OzInverter at 23.4kHz Modulation frequency, and is a H bridge configuration.  

    Its called a Low frequency as we operate with a specially wound toroid transformer that matches the core material and therefore gives us parameters for the back charging. ie it can operate backwards and take a GTI output thats above the Ozinverter set AC voltage output and feed it backwards into DC to charge the batteries. 

    With our toroid transformer losses are kept minimal, normally for a 6kW, and I mean a real 6kW, the OzInverter will tick over using about 30 watts, while a standard laminated transformer as shown in Mr 'Freitas' article is very lossy, say about 200 watts.  However a toroid has horrendous surges and these need to be controlled. 

    I do know of some research going on with HF (ie without a substantial weight transformer) that is very fast to match input to output without sag, but is does need good capacitors, so far its has limits of around 1.8kW, but things are moving fast with new open source code writing.

    interestingly I think that 'Midnite' are developing a modular form of HF inverter, they started talking about it in 2014, and it looks like they are paralleling up to get a good Wattage. 

    Lots of fun things happening in the Inverter world.  




    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (9 years running).  ... 5kW PV on 3 Trackers, (5 years) .... 9kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • AGBAGB Registered Users Posts: 24 ✭✭
    Thank you both. This is very helpful.
    I was wondering if any of them produce interference to electrical equipments but it looks like, it all depends on the implementation and the controls built in. Also as things keep improving, the difference would most likely be how manufacturers decide to implement their choice. 
  • BB.BB. Super Moderators, Administrators Posts: 28,608 admin
    Look for devices that are FCC Class A (commercial) or FCC Class B (residential--lower emissions standards).

    Many AC inverters (and other solar power devices) never bothered to get FCC testing done (not cheap to do). And generally they were noiser that those folks that went to the expense and trouble to do the work.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,958 ✭✭✭✭

    clockmanfran said,   "    ...   normally for a 6kW, and I mean a real 6kW, the OzInverter will tick over using about 30 watts, while a standard laminated transformer as shown in Mr 'Freitas' article is very lossy, say about 200 watts   ...".

    High quality Low Frequency inverters can have low Tare (idle) losses  --  The Xantrex SW+ 5548 in use here have a Tare of "less than 20 Watts at full voltage".   To be fair,   these inverter/chargers output 120 VAC (NA models)  and need a second 5548 if 240 VAC (for NA)  is needed.   These are REAL inverter/chargers with true 5500 Watt output,  continuous,   and weigh about 135 Lbs (about 61 KG)  each.   The LF transformer has an EI transformer with steel laminations,  and weighs about 50 Lbs for each inverter.

    If one is concerned about Emissions,   agree with BB Bill,   look for FCC Class b,  or the similar EU specs.

    Good inverter/chargers are not inexpensive  --  quality comes at a price  but is usually worth it,  IMO.

    FWIW,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cosuper_EnergyCosuper_Energy Registered Users Posts: 6 ✭✭
    depend on your loads, and the place you install the inverter.
    the efficiency, high frequency is higher than the low frequency inverter.
    peak power, high frequency inverter is 2 time of rated power. but the low frequency inverter is 3 times of rated power.
  • AGBAGB Registered Users Posts: 24 ✭✭
    It looks like high frequency development is getting better with the weight advantage. 
  • bill von novakbill von novak Solar Expert Posts: 828 ✭✭✭✭

    I think that  the writer of that article 'Christopher Freitas' https://www.homepower.com/articles/solar-electricity/equipment-products/how-inverters-work  is a little out of date with what is happening.

    From 2015, We operate our Low Frequency OzInverter at 23.4kHz Modulation frequency, and is a H bridge configuration.  


    I'd consider that a high frequency design.  You can use a transformer with a high or low frequency design.

    Generally low frequency designs switch at 120Hz (like the old Trace SW series.)  The transformer then provides the voltage transformation needed to hit the right voltages at the output.  High frequency designs operate at much higher frequencies than 120Hz.  They can either use a transformer (like the old Fronius inverters that I use for my solar system) or go transformerless (like most of SMA's inverters today.)  Both transformer based designs and transformerless have pluses and minuses.
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