Date of Award
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
An electronic compensator is described that is capable of compensating the reactive current drawn by arc furnaces and other nonlinear, time-varying loads. Consisting of three independent single-phase pulse-width modulated (PWM) inverters, along with appropriate controller and detector stages, the proposed compensator responds quickly to sudden load changes and compensates the reactive current drawn by the load. Unlike conventional static var compensators, the electronic compensator can also supply the active current demanded by the load if an energy source independent of the utility is available. Simulations are conducted, including the modelling of the furnace current and voltage waveforms during the early stage of scrap melting, in order to determine the effectiveness of several suggested detection methods that can be used to separate the active and reactive components of the furnace current. Actual waveforms observed on an arc furnace are included that corroborate the computer modelling. Comparisons are made between a voltage source inverter that uses a fast SCR as the main switching device and one that uses a GTO. Various characteristics of the two inverters are discussed, such as the switching device losses and the snubber circuit losses. The design of the GTO gate drive circuit is described. Test results from two constructed inverters are given. A low-pass filter is required to attenuate the high frequency harmonic currents generated by the PWM inverter. The design of the filter is discussed and an example of a minimum-size filter is illustrated. In addition, the use of the modified unipolar control strategy, which is novel in the design of the compensator, doubles the effective switching frequency and thereby further reduces the size of the low-pass filter. The design ideas presented in this research are applied in the construction of a small-scale electronic compensator. Experimental results indicate that the electronic compensator can accurately compensate an arc furnace.
Cox, Mickey Dale, "An Electronic Load Compensator for Arc Furnaces (Reactive Current, Static Var Compensator)." (1986). LSU Historical Dissertations and Theses. 4229.