On Jul 4, 8:08*pm, Keith Dysart wrote:
The system I have in mind has ports through which energy can flow in
or out of the system and components inside the system which can
store energy. For such a system, the energy flowing in to ports
of the system minus the energy flowing out of ports *must
equal the increase in energy being stored in the system.

This must be true at all times, or energy is being created or
destroyed; a bit of a no-no.

But you are not tracking energy - you are tracking power. As Roy has
said, there is no requirement that instantaneous power must balance.
Where are the stored energy terms in any of your instantaneous power
equations? How do you handle the difference in dimensions between
energy and power? The only condition for which NET power must balance
is during a time interval in which there is zero NET stored power,
e.g. during one cycle.

I have rev'ed my zero interference article to include the following
statement:

"Over a time period of many cycles, e.g. one second at MHz
frequencies, the net average energy and the net average power are
related by joules/second. Thus, if certain conditions are met, net
average power can be used to track the net average energy flow based
on the conservation of energy principle. However, at time intervals of
less than one cycle, as exists for instantaneous power, power cannot
be used to track energy because energy is often stored in a reactance,
is not moving at that instant, and is therefore technically not power.
In fact, unlike energy, power often appears and disappears. There are
special cases where average power in joules/second can be used to
track average energy in joules but instantaneous power is not one of
those special cases."
--
73, Cecil, w5dxp.com