28 Apr
2005
28 Apr
'05
6:46 a.m.
>>>> "Simon" == Simon Fryer
<fryers at gmail.com> writes:
Simon> All, On 4/27/05, Kevin Handy <kth at srv.net> wrote:
Simon> [chomp]
> Note that you can now buy solid state phase
converters.
>
> I have a brother that switched to one in his wood-shop, and it has
> many advantages: More efficient (cheaper to run); more motors work
> with it; more power is available on created phases; quieter; etc.
>
> It works much better than the rotery ones he used to use; which
> were designed as phase converters, not just some large three pase
> motors; and his equipment is much happier, too.
Simon> All the solid state phase converters I have come across use a
Simon> three phase H bridge to generate three phases from a common
Simon> intermediate DC rail. The incoming voltage is converted to DC,
Simon> switched, PWM synthesising a sinusoidal at the required
Simon> frequency.
Simon> The PWM works pretty well for induction motors. I would expect
Simon> big iron to have some issues.
Why? I would expect power supplies to be every bit as tolerand of
distorted waveforms as motors are, even assuming that these converters
produce major distortion.
Simon> Depending on how the three phases are used for the big iron,
Simon> it may be possible for all three phases to be wired the
Simon> same. That is electrically connect all three phases together,
Simon> to a single phase supply. This can only be done if each phase
Simon> is used independently of the others (separate
Simon> transformers/SMPS). If there is anything in the machine that
Simon> wants all three phases - find a nice clean sinusoidal source.
Motors will -- disk drives for example. The larger disk drives (DEC
RP04 class, for example) use three phase motors. They also are picky
about the phase order being right, otherwise they spin on the wrong
direction which is not a Good Thing.
paul