Grid access of non-synchronous generation: Review of the Spanish regulation

The development of wind and solar photovoltaic generation depends critically on the access to the grid. In contrast to synchronous generation, the access to the grid of converter based generation (also called non-synchronous generation) is affected by a number of technical constraints. The Spanish regulation of the grid access of non-synchronous generation has been recently reformulated. This contribution will review the new regulation. The past regulation will be also discussed.

A Digital Displacement Hydrostatic Wind-turbine Transmission

In 1984 a hydrostatic wind-turbine transmission with ‘secondary control’ was proposed by Stephen Salter using the, then only conceptual, Digital Displacement® (DD) principle for controlling the flow of the primary, rotor-driven, ring-cam pump. This transmission ‘could achieve the correct ratio of tip-speed to wind-speed in conjunction with true synchronous generation’. In the following years DD machines were progressively developed. To start with they were relatively small in capacity but the power ratings were systematically increased, until it seemed that a high-power hydrostatic wind-turbine transmission might indeed be feasible. In 2006, Artemis Intelligent Power (Artemis), a company that had been formed from Salter's original university team, began working on a megawatt-scale, hydrostatic, wind-turbine transmission based on new pump and motor designs. In 2011 Artemis completed a 1.5 MW transmission and dynamometer test-rig. This was one of the largest hydraulic transmissions ever made and, with a shaft-to-shaft efficiency of 93%, one of the most efficient. Using secondary control to respond rapidly to gusting wind and to instantaneous grid faults, it was also the most controllable. This paper discusses the design of the transmission and test-rig and presents the results of steady-state efficiency tests. Subsequent papers will describe systematic experimental work to account for the various energy losses and to develop a comprehensive simulation model of the DD wind-transmission.

Simulation of Low Inertia Power Systems Based on Shifted Frequency Analysis

New types of power system transients with lower time constants are emerging due to the replacement of synchronous generation with converter interfaced generation and are challenging the modeling approaches conventionally applied in power system simulation. Quasi-stationary simulations are based on classical phasor models, whereas EMT simulations calculate the instantaneous values of models in the time domain. In addition to these conventional modeling approaches, this paper investigates simulation based on dynamic phasor models, as has been proposed by the Shifted Frequency Analysis. The simulation accuracy of the three modeling approaches was analyzed for characteristic transients from the electromagnetic to the electromechanical phenomena range, including converter control as well as low inertia transients. The analysis was carried out for systems with converter interfaced and synchronous generation whilst considering the simulation step size as a crucial influence parameter. The results show that simulations based on dynamic phasors allow for larger step sizes than simulations that calculate the instantaneous values in the time domain. This can facilitate the simulation of more complex component models and larger grid sizes. In addition, with dynamic phasors, more accurate simulation results were obtained than with classical phasors, in particular—but not exclusively—in a low inertia case. Overall, the presented work demonstrates that dynamic phasors can enable fast and accurate simulations during the transition to low inertia power systems.