Half power point

Abstract: This article analyzes the impact of forced power system oscillations on mode damping estimation. Parametric (Yule-Walker) and non-parametric (Welch) methods for mode estimation are tested in the presence of forced power system oscillations. For mode damping estimation based on non-parametric methods, an application of Half Power Point method is proposed. Performances of the mode estimators are evaluated using both simulated and real synchrophasor data from the Nordic Grid. The presence of forced oscillations poses difficulties to mode damping estimators, these difficulties are identified, illustrated and explained herein.

Abstract: The large current flowing through transformer windings during external short-circuit events causes strong vibration, and the tank emits multi-frequency sound. This paper investigates the transient acoustic signal theoretically and experimentally and proposes to monitor the winding condition with the spectrum of the acoustic signal. A two-wire model is first built as a basic unit of winding structure. The dynamic equation of the model is constructed based on the principle of least action. The coupling action between the electromagnetic force and the motion of the wires is described as the second-order term of the wire spacing in the equation. The solution shows that the spectrum of the winding vibration contains half power frequency and its multiples in some cases. If the winding is loosened and deformed, the motion space and vibration amplitude would be enlarged, and the natural frequency of winding would decrease. As a result, the vibration spectrum would contain half frequency and its odd multiples. Then, the acoustic signal of a 110-kV transformer is measured on a multiple short-circuit test platform. The acoustic time-frequency spectrums are consistent with the theoretical analysis. The half frequency ratio (HFR) of the acoustic spectrum raises along with the increase of short-circuit times. After 21 short-circuits, the HFR raises obviously, indicating serious deformation of the winding, while no obvious change is found in the short-circuit reactance (SCR). The results prove that the HFR of acoustic signal is a more sensitive indicator than SCR, which can characterize the cumulative process of short-circuit on the winding.

Abstract: This paper details the development of our millimeter- wave wideband power amplifier design. By treating the power combiner as an impedance transformer which allows different loading impedance to be taken into account, a compact wideband power-combining network can be constructed. With small transmission-line attenuation being sustained and maximum output power easily extracted from the transistors over the 77- 110 GHz frequency range, a power amplifier can then be designed using 65-nm CMOS process to cover the whole W-band. In the on-wafer measurement, the gain is around 18 dB, the output reflection coefficients is below -10 dB, and the output-referred 1 dB compression point can reach 12 dBm at 1.2 V bias condition; when the bias is increased to 2.5 V, a 18 dBm output power is recorded. To our knowledge, this is the first CMOS power amplifier that covers the whole W-band.

Abstract: The present invention relates to power supplies, and more particularly, to a power supply having a maximum power point tracking function that can reduce manufacturing costs and circuit size by using a maximum power point tracking section with a simplified circuit in a solar photovoltaic power generator supplying power using sunlight instead of using a micro controller, the maximum power point tracking section that controls power switching according to a result of integration of a value obtained by dividing a power variation by a voltage variation to track a maximum power value. A power supply having a maximum power point tracking function according to an aspect of the invention may include: a converter section switching input power, and converting the switched input power into predetermined DC power; and a maximum power point tracking section detecting a voltage and a power value of the input power, dividing a variation of the detected power by a variation of the detected voltage, integrating a result of the division, and controlling the switching operation of the converter section according to a value of the integration.