HF Transformer VS Reg Transformer

Jerry
Jerry Registered Users Posts: 19 ✭
in General Solar Power Topics #1
Hi All :D,

I am doing a research about inverter's Topology.

SMA released new series inverter, HF topology series.

Regarding SMA's HF series, there are some questions came through my mind, what is difference becuase i hadn't seem any other factory switch to HF topology yet.
Worth to use?


1. I am wondering what is different bettween this product lines with their existing products line since different Topology used

2. Can HF Topology used on a design more than 10kws?
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Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: HF Transformer VS Reg Transformer

    There can be several interpretations of HF inverters. In this case I believe it refers to transformerless design. This is popular in Europe but not in U.S.

    They do a buck-boost SEPIC DC-DC converter to establish the high voltage D.C. that exceeds the peak of sinewave output plus some switching and filter losses. (about 380vdc) then a standard H-bridge PWM chopper followed by filter to create the sinewave. There is no pure inductive isolated transformer between panel and grid so conceivably a component failure could subject lines to PV panels with direct grid voltage.

    A HF inverter design could have a HF transformer isolated design with opto isolator similar to the switching power supply in your computer. Many GT-only inverters use this method.

    Outback and Xantrex XW hybrid battery-grid tie inverters use a LF transformer to provide isolation between grid and PV/battery side connections. There are some cost saving tricks to using the LF transformer to perform the sinewave filtering of the high freq PWM inputs waveform. Conventional torroid chokes for HF PWM filter have to have a large cores capable of not saturating during the peak 60 Hz 'low freq high magnetic bias' current so it maintains its high frequency filtering inductance. There are no critical semiconductors (MOSFET's, rectifiers) on secondary side and the LF transformer provides better surge protection to nasties from the grid.

    DC to AC sinewave inverters have full wave rectified sinewave shaped D.C. supply current pulses due to 60 Hz output load. PV panels need to have a smooth D.C. current load to operate at maximum efficiency and run an MPPT algorythm. There always has to be some LF electrical storage element capable of smoothing out the 120 Hz current pulses so the PV panels don't see them.
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: HF Transformer VS Reg Transformer

    Hi,

    First post :D Excellent and informative forum greatly enjoy.

    I believe HF stands for high frequency. High frequency designs are physically more compact because transformers are smaller. High frequency transformer designs can provide isolation. Military and aircraft use 400 Hz because transformers and inductors are smaller and weigh less. Higher frequency designs require faster switching devices increasing production costs.
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  • Jerry
    Jerry Registered Users Posts: 19 ✭
    #4
    Re: HF Transformer VS Reg Transformer

    Thanks to both, RC and Steve

    SMA had also released transofmerless series inverter while HF series released at the same time


    Have any one install theses new prodcuts in any case?

    Becuase I would like to know which might be great option to go with

    HF Inverter or TL Inverter?

    However, I know TL inverters is still not popular in US, I dunno why.....
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: HF Transformer VS Reg Transformer

    As I understand, transformer inverters[less--fixed -BB.] are a bit more efficient but have no isolation between PV input and AC output.

    Normally, the NEC and UL type codes require a barrier between AC power and local power (double insulated or other type) with a minimum of 1,800 VAC of AC Grid input to output power isolation isolation. The intent is to protect against line surges, lightning, etc.).

    Now, normally the output of a power supply is low voltage DC--and it is obvious why you don't want 600-1,800 VAC running around the inside of a laptop computer.

    But, when your "Output Power" is a 600 Volt Rated Solar panel + wiring + breakers/fuses + connectors + etc.--Since the Vsolar and Vac-power are both rated for 600 VAC maximum (and hypot tested to 1,800 VAC)--Then what is the need for an 1,800 volt barrier between Vsolar and Vac-mains?

    The AC Mains barrier of 1,800 volts is not really that much against lightning or even a 12,000 volt line cross (local distribution to 120/240 VAC house wiring).

    Add that the Solar DC Side should be designed to use 10kA AIC (amps interrupt current) for the breakers and fuses (i.e., meet all of the requirements for a 600 VAC rated circuit design)--I would be hard pressed to make a case against using a Tranformerless design.

    Might make a bit of difference in the design of the solar array for a transformerless design--Normally no combiner fuses/breakers are required for two or one parallel connected solar panel arrays... Perhaps with TL designs, there is a backfeed potential to to the solar panels and array wiring. Therefore X Amp rated fuses/breakers would be required... A small issue to be sure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
    Re: HF Transformer VS Reg Transformer
    Jerry wrote: »
    Thanks to both, RC and Steve

    However, I know TL inverters is still not popular in US, I dunno why.....

    They weren't allowed until the release of the UL1741-2008 rules, before that a design was required to have isolation in the US/CA.

    You can get into the 97% efficiency's with non-isolated, ~96% with isolated, from the end user it would make no difference what the internal technology is, is a box that converts PV power to mains power.

    There are many manufactures selling the non-isolated designs now, its not really anything special, just another option.
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  • Jerry
    Jerry Registered Users Posts: 19 ✭
    #7
    Re: HF Transformer VS Reg Transformer
    Solar Guppy wrote: »
    They weren't allowed until the release of the UL1741-2008 rules, before that a design was required to have isolation in the US/CA.

    You can get into the 97% efficiency's with non-isolated, ~96% with isolated, from the end user it would make no difference what the internal technology is, is a box that converts PV power to mains power.

    There are many manufactures selling the non-isolated designs now, its not really anything special, just another option.


    Thanks for sharing, Guppy.

    Regarding UL1741-2008, is a Non-isolated design still required to install own's isolated equitments for isolated less Inverter (TL)? (I will check for it online)

    My friend tell me that design of transfomer inverter has better protection degree then TL inverters to against failure in US regional at the moments, which is I am not really sure!
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  • SoleTrain
    SoleTrain Registered Users Posts: 3
    #8
    Re: HF Transformer VS Reg Transformer

    Just wanted to comment a few things in this thread-

    The SMA HF inverter is not on the US market yet. It does have a transformer (high frequency) and is not a hybrid transformer inverter. The transformer is very small and therefore the HF inverter will weigh much less than the current Sunny Boy inverter of comparable size.

    BB - The HF inverter does have the galvanic isolation to keep the DC and AC from crossing over; The TL inverters separate the two sides electronically. The TL inverters measure through a common point and if there ever was a case where the DC tried to cross over into the grid the inverter would disconnect. They ahve been using TL inverters in Germany for years and they are very safe.

    Jerry:
    2. Can HF Topology used on a design more than 10kws?

    The HF inverters do not have a limitation on their use with respect to capacity requirements. They can even be used in 3-phase applications.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: HF Transformer VS Reg Transformer

    SoleTrain,

    Sorry, I had a typo in my first paragraph--I intended to type about transformless GT inverters...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Jerry
    Jerry Registered Users Posts: 19 ✭
    #10
    Re: HF Transformer VS Reg Transformer

    Thanks to All

    I doubt,

    1. HF is still more pupular design for a small power inverter market in US

    2. TL Inverters is going accpetable on the market due to higher effiency (?!) althought it required to purchase additional surge protector
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #11
    Re: HF Transformer VS Reg Transformer

    The downside to HF type power converters in my opinion is that is takes correspondingly less energy in a voltage surge to make it through the transformer and cause havoc with the circuit on the other side. It takes a big spike to get through a big ol transformer.
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