The power capacity of distributed generators such as photovoltaic and wind turbine is growing, many of distributed generators are connected to a grid by inverters. The inverters are controlled by a PLL (Phase Locked Loop) in order to be synchronized with power system frequency. Power system will become unstable, if the capacity of inverter-connected-type distributed generators becomes larger and larger, because inverter frequency is controlled to follow the grid frequency. The concept of "Virtual Synchronous Generator" (VSG), which is to control inverters to behave like a synchronous generator, has been proposed. VSG has virtual inertia which is realized by an energy storage device to pretend rotor's inertia. In this paper, the control scheme of VSG is investigated which is based on the swing equation of a synchronous generator. Numerical simulation results show both ride-through capability of voltage dip and enhancement ability of grid stability.

The electron swarm behaviour in SF6 gas is studied for E/N values from 141 to 707 Td by a three-term Boltzmann equation method, in which the effect of generation and loss of electrons due to ionisation and attachment is considered properly. A consistent set of electron collision cross sections, which gives the swarm parameter values in agreement with previous measurements, is determined considering the latest cross section data. The calculation is performed mainly for the steady-state Townsend condition. The validity of the results obtained has been confirmed by a Monte Carlo simulation carried out parallel to the analysis. The present results are also compared with those of the usual two-term Boltzmann analysis. It is found that the two-term approximation is fully valid for deduction of the swarm parameters for E/N values as considered despite the fact that SF6 is a strongly electronegative gas.

The world's largest pulsed superconducting coil was successfully tested by charging up to 13 T and 46 kA with a stored energy of 640 MJ. The ITER central solenoid (CS) model coil and CS insert coil were developed and fabricated through an international collaboration, and their cooldown and charging tests were successfully carried out by international test and operation teams. In pulsed charging tests, where the original goal was 0.4 T/s up to 13 T, the CS model coil and the CS insert coil achieved ramp rates to 13 T of 0.6 T/s and 1.2 T/s, respectively. In addition, the CS insert coil was charged and discharged 10 003 times in the 13 T background field of the CS model coil and no degradation of the operational temperature margin directly coming from this cyclic operation was observed. These test results fulfilled all the goals of CS model coil development by confirming the validity of the engineering design and demonstrating that the ITER coils can now be constructed with confidence.

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The electron swarm behaviour in SF6 is calculated and analysed for a wide range of E/N values from 71 to 5656 Td by both a Boltzmann equation method and a Monte Carlo simulation, using a set of electron collision cross sections determined by the authors. The Monte Carlo result shows clearly that the difficulty in deducing the electron energy distribution increases as the E/N values decrease due to a large electron attachment probability, while the result of the Boltzmann equation analysis shows that the set of cross sections determined by the authors is again fully valid for E/N>707 Td, since the effective ionisation coefficient agrees with measurements at very high E/N. The swarm parameters for important experimental conditions are deduced and the validity of the usual two-term method is discussed in detail.