Abstract
M.Ing.
This study investigates the limits to which distortion can be compensated in electrical
distribution networks. Many factors hinder the "ideal" compensation of the line current
to a perfect sinusoidal, in phase, scaled replica of the supply voltage.
The different power theories that can be used to derive the reference compensation current,
is one of the fundamental limits. The differences and correspondences between the FBD
and Czarnecki theories are investigated in detail. Furthermore, it is shown by simulation
and practical results, that the effectivity of compensation by the instantaneous power
theory is load dependent.
The compensation strategy and topology also impose limits on the effectivity of compensation.
The position and strategy of a compensator determine whether the consumer is
able to isolate his distortion from the rest of the network, or isolate himself from the
distortion of other consumers. Distortion frequencies and system impedances are chosen
specifically to visually show the effect of the different topologies and strategies, by means
of simulation.
One of the most important limits brought about by new technology, is the lagging of
the reference compensation current, due to the use of signal processing in determining
the reference signals. The effect of this lagging reference is clearly shown by means of
simulation and practical compensation systems. An effectivity index for this phenomenon
is defined for steady state systems.
The dynamic limitations of this lagging reference compensation current is investigated
thoroughly. A method is derived by which the maximum fault, due to the sampling time
and signal processing time, can be calculated when a high f-region occurs in the line
current.
The dynamic response of the compensation system is also limited by the ' di-ability of the
converter. Therefore, a method is developed to calculate the individual fault contribution
of the lagging reference as well as the converter. This method enables designers to determine
the parameters of the signal processing system and the converter in the planning
phase. The use of a maximum sampling frequency is stressed.
In the experimental work, a 10kVA, PWM-switched IGBT inverter is used as a parallel
voltage fed compensator. It compensates for two non-linear loads : a three phase diode
rectifier with an inductive load, and a three phase diode rectifier with a capacitive load.
The practical compensation according to the instantaneous power theory of these two
loads, confirms that the result of this compensation is load dependent. The effect of the
lagging reference compensation current in a practical system is also shown.