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This paper presents a solution for bulk ac power transmission over extra long distance based on an unconventional transmission line that is little longer than a half wavelength (\lambda / 2^+). This solution is very convenient to be applied in countries where the generation sites are very distant from the consumption centers. However, it has some restrictions regarding feeding loads at intermediate points. To overcome this drawback, an HVAC tap based on power-electronics converters is proposed. This tap allows feeding local loads as well as integrating power plants to the main circuit without changing the transmission system's electrical characteristic. This paper also presents an application example of a \lambda / 2^+ line with an HVAC tap draining and injecting energy from the line. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis between results from applications of the p-q and the p-q-r theories in shunt active power filters for three-phase four-wire systems, discussing aspects related to the influence of the system voltage in the control methods that calculate the compensating currents. It is shown that in some cases, a preprocessing of the system voltage is required if the goal is to achieve sinusoidal compensated currents. On the other hand, when the goal is to compensate zero-sequence current, the need of energy storage elements in the active filter is discussed. In this case, if zero-sequence components are present simultaneously in the system voltage and load current, they produce zero-sequence power flow, and the control methods based on both theories must contain additional calculations to allow the elimination of energy storage elements in the active filter. A control strategy based on the p-q theory is proposed to eliminate the neutral current without the need of energy storage elements, with the advantage of avoiding the extra transformation from αβ0 to pqr coordinates that is needed in the p-q-r theory. Simulation results are presented for the purpose of comparing the performance of both control methods. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and software implementation of a robust synchronizing circuit, i.e., phase-locked loop (PLL) circuit, designed for use in the controller of active power line conditioners. The basic problem consists of designing a PLL circuit that can track accurately and continuously the positive-sequence component at the fundamental frequency and its phase angle even when the system voltage of the bus, to which the active power line conditioner is connected, is distorted and/or unbalanced. The fundamentals of the PLL circuit are discussed. It is shown that the PLL can fail in tracking the system voltage during startup under some adverse conditions. Moreover, it is shown that oscillations caused by the presence of subharmonics can be very critical and can pull the stable point of operation synchronized to that subharmonic frequency. Oscillations at the reference input are also discussed, and the solution of this problem is presented. Finally, experimental and simulation results are shown and compared. [ABSTRACT FROM AUTHOR]