The first idea of MIGRATE is to provide solutions to such problems, by identifying and ranking power system stability issues, and then assessing the capabilities of existing PE so as to appraise the extent of potential improvement of current system control practices. The outputs of such assessments should be a review of measures, modelling and simulation methods for security assessment and system control when dealing with stability problems under high PE penetration. In order to understand the listed problems (1 to 4), a rigorous modelling approach is proposed: first, for each identified stability phenomena, a model problem allowing an understanding of the dynamics of the considered system is proposed (with the necessary numerical simulations tools, i.e. e.g. EMT and HIL analyses). When the sources of instabilities are understood, adequate indicators (KPIs) which measure, for each model problem, the distance to instability (maximum penetration of PE before encountering possible stability issues), are put forward. The modelling work includes the loads (mainly DSO loads at substation level) with a proposal to calibrate models with on-line measurements. In a second step, generic cases (combining several of the single phenomena studied in the model problems) are suggested. It is assumed that the numerical simulations of the proposed generic test cases will account for the possible couplings of the most critical stability phenomena and therefore will be representative of situations encountered in the real power system. The generic test cases together with validations based on real system behaviour will allow addressing system issues when combining the locations of PE connections into the system and the different types of PE technologies. From the numerical simulations of the generic test cases, a set of manageable generic KPIs (combining the KPIs of the model problems), will be given so as to understand the distance to instability with the existing control strategies. These set of KPIs will be tested in a laboratory test system using an RTDS equipment and co-simulation platforms available at TU Delft.

As a result, recommendations for the network connection code implementation (on the basis of the three most impacted European connection codes, i.e. RfG, HVDC and DCC) will be proposed, i.e. a methodology to assess the conditions under which higher levels of PE penetration can be implemented without harming the system operational security. The recommendations will be supported by network simulations of the EirGrid and National Grid control zones, using different PE configurations (penetration level, technologies, and localization) which could represent the set of the possible evolutions foreseen in the next decade.

Electro-magnetic transient (EMT) and Hardware in the Loop (HiL) analyses.

To complement the above mentioned recommendations, additional work shall be carried to exploit emerging monitoring, computing and communication technologies to properly equip European TSOs to operate the power system as it moves toward high penetrations of PE. To this end, the MIGRATE consortium will define requirements, develop and pilot test new real-time monitoring and forecasting solutions of the proposed KPIs including area inertia, wide band oscillation characteristics and short-circuit capacity. In the pilot tests, the monitored and forecasted KPIs will be used to propose and test control solutions based on existing WAMS/PMU infrastructure. It is essential that these solutions are validated through pilot testing to confirm their interoperability in a live environment at the EU transmission network level to safeguard the direct impact and effectiveness of the new functions developed. The field tests will be designed to make full use of sensors (e.g. WAMS/PMUs) already deployed by various TSOs to maximise the value of existing infrastructure.

To complement the work related to the modified dynamic behaviour of the power system and the interactions between the controllers of PE will be addressed (weakening of existing protection system) since the massive connection of power electronics is going to change the short circuit dynamics dramatically, and as a consequence, the existing protection systems (developed for short-circuit currents generated by synchronous machines) will no longer respond to these short-circuit dynamics. In this work, the ability of existing protection devices to properly operate under system disturbances generated by PE will be studied as well as technical and technological requirements for future protection systems in order to keep actual levels of reliability. Firstly, accurate models for desktop protection studies and HiL tests will be provided and the existing protection functions/solutions under high PE penetration will be assessed. Secondly, new protection solutions allowing 100% PE penetration to be reached will be developed and tested by performing HiL tests with real protection equipment supplied by Schneider Electric in order to check the feasibility (both technical and economic) of the proposed solutions. The outputs of this work will be a set of recommendations for the design of protection schemes for power systems with high penetration of PE, completing the set of recommendations for the network connection code implementation mentioned above.

The increasing penetration of PE interfaced renewables has already resulted in power quality (PQ) challenges as evidenced by harmonic distortions, voltage sags and other disturbances (problem 2), e.g. recent outages and even a fire of an offshore power component. The increasing penetration of PE in power networks changes for instance the levels of harmonics in the network. PE devices are one of the major sources of PQ disturbances but they are in turn also affected by PQ disturbances. In the MIGRATE project, appropriate models and methodologies will be developed to evaluate the influence of PE based devices on PQ in future power systems. Cost effective mitigation options will be investigated and compared in order to reach the extent at which PE-based devices could also become part of the solution for attaining and maintaining required PQ levels in the network while continuing to fulfil their primary design goals and functionalities.

The major challenge, opening new concepts, addressed by the MIGRATE consortium is the operation of transmission networks with no synchronous machines (i.e. 100% PE penetration) with HVDC links and FACTS. System operation for very high penetrations of PE have been addressed for UPS, radial topologies and micro grids, but the transposition of this research work to transmission system is not possible due to the specific characteristics of transmission networks (cf. section 1.4.1.3). To this end, a model problem will be defined and studied so as to propose new control strategies and management rules when operating at 100% PE penetration. An example of such a model problem (cf. figure on the right) will be studied for the following situations:

It will be assumed that at least one of the inverters has an infinite primary energy source in order to balance the system, without an a priori knowledge of which one during the design phase. These simulations should allow the simulation of representative cases of possible disturbances when operating at 100% PE penetration. In the work to be carried out, novel control and management rules will be proposed and developed while keeping the costs under control. The viability of such new control and management rules within transmission grids to which some synchronous machines are connected will be checked so as to enable operation with existing equipment. A set of requirement guidelines for converter-based generating units will be provided, as technology-agnostic as possible, to ease the implementation of the above control and management rules.

In all modelling and simulation work to be carried out, the MIGRATE partners will make sure that there are no overlaps, i.e. the models problems, the generic cases and the scenarios developed in WP1 will be used  in WP4 and WP5 whenever relevant. All WPs will resort to HiL techniques as a complementary approach to take into account phenomena that may not be included in models but that could impact the dynamic behaviour of the components (inverters for instance). The links between the different work packages is further described in section 3.1.1 Moreover, special attention has been paid by the universities, especially TU Delft, UNIMAN and ENSAM so as to minimize duplication of dedicated equipment taking into account the existing facilities in the different laboratories. For example, RTE will use a laboratory facility where most of the equipment has been purchased mainly by funding from the TWENTIES project. In addition, the ambition of the three laboratories is to build a partnership based on complementarities so as to be able to anticipate complex R&D problems when joining resources.