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DC 2 AC inverter with synus output in UPS systems

Discussion in 'Electronic Design' started by RealInfo, Feb 11, 2013.

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  1. RealInfo

    RealInfo Guest

    Hi all

    How exactly synus output voltage is generated in UPS systems ?
    I understand how rectangular or PCM voltage is generated but in case when pure synus voltage is needed , how this is done ?

  2. Jamie

    Jamie Guest

    Cheap designs use a transformer. The output side (appliance side) will
    have the line voltage on it, passing through the output side as it goes
    to the receptacles. As this is taking place, the other side of the
    transformer (low side) is generating a low voltage, a voltage that
    matches your battery. THe battery is connected to the center tap of the
    low side (+) and will be a push pull type of inverter.

    When commercial power is present on the high side of the transformer
    it will also be present on the low side. This voltage should match the
    battery voltage or actually be a little higher. Because when it is a
    little higher it is also used to charge the battery! Of course there is
    some more intelligence behind it to control the charge rate. This also
    may explain why some UPS systems will not charge a battery that is to
    low, because the active circuit is not operating due to insufficient
    battery voltage.

    When line voltage goes away or even dips in the middle of a wave the
    low side will see an absence of voltage or I should say the unloaded
    inverter will now detect a load present to it's inverter transistors and
    thus create current in the primary at that moment.

    Just think of an inverter operating at all times into a push pull
    primary (low side) but the secondary has voltage is back feeding it. The
    primary side will not generate any current because it is being
    canceled out however, when the back feed takes a lunch break at any time
    on the sine wave, there will be no canceling of currents and thus at
    that point, the inverter will contribute current to the needed high side

    That is the best I can explain it.

    You can do this with high frequency toroidal transformers too, the
    difference being you need to monitor the line voltage directly
    from your low side inverter circuit to know when and at what phase
    angle to come in on.

  3. RealInfo

    RealInfo Guest

  4. josephkk

    josephkk Guest

    Simple answer, pwm and huge inductors to smooth it out. Big bux. Lesser
    approximations vary considerably.

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