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This paper describes ramp rate control of a photovoltaic (PV) generator with an electric double-layer capacitor. The capacitor absorbs rapid fluctuations of PV generation, and allows the generator to change its output at a limited ramp rate. The output is mainly determined by a moving average of the PV generation, but the capacitor voltage is also counted to keep the voltage at a specified value, and accordingly, to make the capacitor small. An expression for the capacitor size is derived. The feedback gain of the capacitor voltage is also examined to maintain enough energy storage in the capacitor. Some experiments are executed to demonstrate and validate the proposed method. Index Terms--Capacitor, control, energy storage, photovoltaic (PV) power system, power system dynamics.

There is a low-frequency interarea oscillation mode in middle and western 60-Hz areas of Japan. Its stability determines available transfer capacity of a tie-line. We propose a method of monitoring its stability by phasor measurements synchronized using the global positioning system. The phase angle between two places deviates randomly. However, its Fourier spectrum shows a clear peak corresponding to the interarea mode. We estimate its frequency and damping from the spectrum. The estimation results agree well with those obtained by curve fitting for large disturbances. It is also possible to estimate the eigenvector. We examine how the eigenvalue varies with the total generation and power flow in the areas. Index Terms--Global positioning system (GPS), interarea oscillation mode, monitoring, power system stability, synchronized phasor measurement.

There is a low-frequency interarea oscillation mode in middle and western 60-Hz areas of Japan. The mode is damped, i.e., stable for small disturbances, but diverges in an oscillatory manner for large disturbances. It restricts power transmission in the areas. This paper shows that the instability is caused by nonlinear interactions between a few modes. The areas are represented with West30-machine system model prepared by the IEE of Japan. Numerical simulations are executed to obtain a critical case in which generator swings last without diverging or damping. Natural oscillation modes contained in the swings, are then calculated. Two modes have strong interactions with the interarea mode, and act so as to deteriorate its damping. Last, we examine how their influence changes with load level of the system. Index Terms--Autoparametric resonance, interarea oscillation mode, power system stability.

A combined cycle power plant, which combines a gas turbine and a steam turbine, can achieve high energy efficiency. Many combined cycle plants have been installed in the world. However, a large-scale blackout occurred in Malaysia in 1996. Combined cycle and gas turbine plants sequentially tripped out. The cause of this chain trip was thought to be a system frequency drop. Considering these backgrounds, it is important to study dynamic behavior of combined cycle plants. Several dynamic models of the combined cycle plant have been proposed. In our analysis, we use some of them and build a model for a single-shaft combined cycle plant. We execute numerical simulations to see how the combined cycle behaves when the system frequency drops. Index Terms--Combined cycle, dynamic models, gas turbine, plant trip-out, under frequency.

A thyristor-controlled series capacitor (TCSC) substantially improves transmission capacity. It also mitigates subsynchronous resonance (SSR) accompanying conventional series capacitors. With an appropriate angle of thyristor firing, electrical damping becomes almost zero, which is called SSR neutral. This quality comes from TCSC itself. However, negative damping still remains, and is large for firing angle 170~180[degrees] where little current flows through thyristors. This paper deals with control of firing angle. First, we oscillate the firing angle at a given frequency, and present an analytical method of calculating electrical damping. Next, we show that the damping improves at all frequencies if the firing angle oscillation is in phase with that of rotor angle. Synchronizing torque decreases, however, so a limit must be put on the control gain. Lastly, we execute numerical simulations to verify our analytical results. Index Terms--Damping control, SSR, TCSC.