High frequency vs low frequency inverters

AGB · December 2018

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.

BB. · December 2018

Here is an article:

https://www.homepower.com/articles/solar-electricity/equipment-products/how-inverters-work

-Bill

clockmanfran · December 2018

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Freitas' https://www.homepower.com/articles/solar-electricity/equipment-products/how-inverters-work is a little out of date with what is happening.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.

AGB · December 2018

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. · December 2018

Look for devices that are FCC Class A (commercial) or FCC Class B (residential--lower emissions standards--I.e., electrically quieter/generate less radio frequency noise).

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

-Bill

Vic · December 2018

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

Cosuper_Energy · December 2018

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.

AGB · December 2018

It looks like high frequency development is getting better with the weight advantage.

bill von novak · December 2018

clockmanfran said:

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.

Abenr · April 2019

In general low frequency inverters are far superior for starting difficult loads.. ie. motors.

They are usually more expensive as the transformers/ coils are much larger,so a lot more copper. Usually also a more industrial design.

In simple terms a low frequency inverter has an output impedance close to what you get from grid mains..(low)

Here is a poor but easy to understand explanation..1 gas engine 1l puts out 100hp at 6000 rpm and 100ft lb torque engine 2 is 6l and puts out 100 hp at 2000 rpm and 400ftlb torque.given identical gearboxes the #2 engine will give far better acceleration from standing start under heavy load.... its the torque that is the difference.. torque is comparable to impedance...

Tecnodave · April 2019

@bill von novak.
Technically clockmanfran's inverter is a high/low frequency design.....that is it uses high frequency electronics to drive a low frequency transformer. True low frequency inverters are obsolete, they did the switching at 60 hz.....very inefficient. Most if not all "low frequency" inverters are really "high/low" frequency designs. It all traces back to Milt Rice and the Dynamote Brutus inverter, the first operational high/low frequency design and the roots of both MagnaSine and Outback designs. I have two of the Brutus inverters , still operational and still in use! Will start a much larger water pump than my MagnaSine with a whopping 11,900 watt surge capability from a 3200 watt inverter!

aaron3333 · June 2020

My name is Aaron. I use a submersible pump of 1.5 HP. This 2800wats. I have a Must PV1800 3kva inverter I have 8 pieces of 100ah Solar batteries connected. Yet the entire system shuts down when I turn on the submersible pump. Inverter displays ⚠ 72 or ⚠4 which is translated as low battery or battery bus error.

We've worked on the batteries by tightening all terminals. Yet problem still persist. And when the sun is so high and the pump stands on for about 10 seconds, the life wire from breaker to inverter gets hotter and begin to melt.

Please help me fix

mike95490 · June 2020

What is the voltage of your battery system ? 3,000w is about 125A at 24V, so you will need some beefy #00 cables to handle it,
( thats 2 ought wire 2/00 Conductor Diameter 9.26 mm )
48V battery system is better, only needing 65A That's going to need #4 wire if it's a short run, more that a foot or so, you need #2 wire
#2 ( Conductor Diameter 6.54 mm, 0.36inch )
#4 ( Conductor Diameter 5.18 mm 0.25inch)

https://www.powerstream.com/Wire_Size.htm

Don't even think of this at 12V, the cable size is huge, and the risk of fire is nearly certain.

High frequency vs low frequency inverters

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