In recent, large penetration of photovoltaic power generation and wind power generation is promoted for a development of sustainable power supply system. Since most of those power generation system do not have inertia, replacement of synchronous generators with renewable energy resources causes reduction of inertia and deteriorate stability of power system such as transient stability and frequency stability. To solve the problem, the authors have studied Virtual Synchronous Generator (VSG) control by PMSG wind generator without battery energy storage. Since the system does not have a battery, kinetic energy of PMSG is used to absorb impact of system fault and rotating speed of PMSG is changed from optimal point. This paper proposes a novel VSG control including a function that recovers rotating speed of PMSG to optimal point. Simulation studies clarify the effectiveness of the proposed control system.

In recent years, the smart inverter that is an advanced inverter has been investigated as a solution to voltage problem in the distribution network in which a lot of photovoltaic(PV)s are introduced Among multiple functions of the smart inverter, voltage-reactive power control (Volt-Var) and voltage-active power control (Volt-Watt) have been attracted attention because of their effectiveness. However, the problem is how to determine optimal curves setting of Volt-Var and Volt-Watt. In this paper, we suggest the determination method of optimal Volt-Var and Volt-Watt curves, and verify the effectiveness of the optimal curves on distribution network.

The prospective transient recovery voltage (TRV) at current interruption for circuit breakers should be measured by using an ideal circuit breaker. But it is very difficult to measure the prospective TRV because there is no ideal circuit breaker. Instead of this method, it is often used diodes in low voltage measurements. In this case, it is difficult to decide the current zero by the forward voltage drop of the diode. Furthermore, the maximum value of the TRV becomes small by the forward voltage drop of the diode. Reverse current injection principle is well known to measure the TRV. The prospective TRV for the short circuit testing circuit will be measured by using this reverse current injection principle. But, there was not the reverse current injection circuit until now. In this paper, reverse current injection circuit is constructed. The prospective TRV for breaker terminal fault was measured by the reverse current injection circuit.

This letter proposes an optimization approach to suppress the fluctuation of wind farm (WF) output by using the kinetic energy of variable speed wind generators (VSWGs). A trade-off between the output smoothing and the generator efficiency cannot be directly considered in conventional methods using the kinetic energy of VSWG. We address the issue how to realize the output smoothing with little generator efficiency degradation considering the trade-off.