Importance

Loading Importance Indicators...

Abstract

A control system is provided for positioning between a power source, such as a distributed generator, and a utility or utility grid to control the injection of dc current and even harmonics into the utility or utility grid. In one embodiment, the control system is particularly suited for grid-tied operation and includes a power converter for acting as an ac current source by converting power received from the power source to ac current for transmittal to the utility. The control system further includes a voltage transformer between the power converter and the utility connection to block dc current and isolate the power source from the utility. A feedback control loop is included in the control system to measure, with a pair of current transformers, dc current and even harmonics in the current flowing into (power converter side) and out (utility side) of the voltage transformer. A signal combiner is used to combine the outputs of the two current transformers such that its output to a harmonic analyzer of the feedback control loop represents the load current of the voltage transformer. The harmonic analyzer determines the magnitude and phase of the second harmonic of this load current and transmits this as output to a controller of the feedback control loop. The controller creates a control signal that it transmits to a reference device connected to, or integrated with, the power converter which creates a reference signal having a dc offset that functions to substantially zero out the linearized second harmonic magnitude. The reference signal is used to control the operation and output of the power converter to substantially eliminate dc current injection into the voltage transformer which in turn effectively limits the amplitude of even harmonics in the current supplied to the utility.

Loading the Abstract Image...

First Claim