Although it is well known that an adequate dynamic load model in power system is indispensable for stability analyses especially when renewable energies highly penetrate nearby loads, researches on dynamic load model are quite poor even in the beginning of a low-carbon era. The authors have represented an actual dynamic load as parallel of an induction motor (IM), a resistor and a capacitor behind fixed impedance, and identified parameters of the dynamic load model using measured data during and after voltage sags. The results were already reported. Since some improvements on the identification were made, the newest results are reported here. The most important three parameters are identified ; IM ratio is 50%, IM inertia is 0.5 sec., and IM loading is 50% at peak demand when power system stability becomes the worst.
With increasing penetration of renewable energies, especially, photovoltaic energy, more and more concern about power stability will be required because most distributed generators like solar inverters don't have fault ride-through (FRT) capability and reactive power supply capability which is called as dynamic voltage support (DVS). These capabilities haven't been required for a grid code in Japan. Penetration of large amount of PV into power system would deteriorate power system stability in the future. This paper first presents an effect of a distributed generator with FRT and DVS on voltage stability of power system by a simple simulation. Next this paper describes how to perform those capabilities of solar inverter and notes a relation between FRT/DVS and islanding. Then, we examined the methods in a factory test and manufactured a 20-kW prototype of a solar inverter with FRT/DVS capabilities. Finally we performed a field test in real power system, resulting in a good performance.
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