In accordance with European plans, dynamic controls are developed to allow for system-wide integration of 100 % renewable energy sources (RESs) interfaced through power electronic converters while maintaining security. At the heart of the development is the concept of the grid-forming resource (GFR) which brings together both the technologies of renewable energy resource and grid-forming converter. Extending on an extensive review, a grid-forming converter control and protection scheme is presented to ensure operation under small-and large-signal transients as needed for overall system security. The scheme is shown to be practical in offering inertial response emulation and frequency control based on droop characteristics to maintain power balances rapidly, to control voltages, as well as to support transient stability enhancement under grid faults. The integration with the control of wind energy conversion systems (WECSs) creates a grid-forming wind park as the prototype of the GFR. Feedforward signals exchanged between grid and resource-side controls enhance fast overall controllability. The principal claims are substantiated based on a scenario developed in the European project initiative MIGRATE with a focus on the Irish power transmission system. The model comprises more than 2000 individual WECSs grouped into wind parks, where ten wind parks are GFRs. The transient behavior of this scenario comprising 100 % converter-interfaced generation is shown to be superior compared with a counterpart case comprising synchronous machinery. The results validate the fact that GFRs with their proposed controls are expected to be key elements in creating a renewable and secure electric power system.

This paper investigates the effect of using phase-locked loop (PLL) on the performance of a grid-forming controlled converter. Usually, a grid-forming controlled converter operates without dedicated PLL. It is shown that in this case, the active power dominant dynamics are highly dependent to the grid short circuit ratio (SCR). In case of using PLL, the obtained results illustrate that the SCR has a negligible effect on the dynamic behavior of the system. Moreover, the power converter will not participate to the frequency regulation anymore; therefore, the converter response time can be adjusted independently to the choice of the droop control gain, which is not possible without PLL. A simple equivalent model is presented which gives a physical explanation of these features.

This paper presents a control system implementation in dqz-coordinates for equalizing the average energies stored in each arm of a Modular Multilevel Converter (MMC); a control objective that is typically referred to as horizontal and vertical energy balancing. The proposed control scheme is obtained from analysis and simplification of a detailed time-invariant dqz-frame state-space representation of the MMC. The state variables of the model are the equivalent arm capacitor energies and the current components, and it will be shown that this representation is very suitable for designing outer-loop energy controllers in dqz coordinates that rely on linear inner current control loops. Moreover, a series of justified assumptions on the energy dynamics will be presented, providing significant insight that simplifies the control design. Finally, by proving that the unbalances of the average values of the converter equivalent arm capacitor energies in abc coordinates appear as undesired oscillations in dqz coordinates, active filtering is proposed as a mean to dissipate them and, therefore, achieve the desired balanced operation. Operation of the proposed control strategy is demonstrated by time-domain simulation of a 1 GW MMC-based HVDC converter terminal.

In this paper, the application of a new methodology for the parametric modal analysis is presented. A new matrix is proposed, in which, the elements describe the first order sensitivities of all the eigenvalues with respect to parameters of the system. For the sake of clarity the system analyzed is a reduced equivalent model of a high voltage direct current (HVDC) point to point connection based on voltage sourced converter (VSC). This simplification is based on some hypothesis on the operation point of the system. The new methodology is compared to a widely used tool called participation factors.

This paper deals with the nonlinear control approach of Voltage Source Converter (VSC) based on MTDC (multi-terminal direct current) transmission systems. A nonlinear control approach based on Backstepping method is proposed for two different control methods: active power and DC voltage. The proposed control approach, based on Lyapunov theory, is capable of analytically obtaining a control laws in order to regulate the active power and dc bus voltage in an MTDC system. Furthermore, the dynamic interactions between the active power nonlinear control design and the DC voltage droop control are examined. Finally, the validity of the proposed control design approach is verified by time-domain simulations under the Matlab/ Simulink environment.

Recently, Modular Multilevel Converters (MMCs) have received an increasing attention since this topology of converters is a viable solution for high-voltage and high-power applications. However, many research results concerning the control problems of modular multilevel converters have been proposed in the literature which the main control problems are to control the grid and differential currents as energy stored in each sub-modules. This paper deals with the modeling and the control of modular multilevel converters. Since the voltage fluctuations between the arms of each phase introduce circulating currents containing a second harmonic component, which distorts the arm currents and may increase the ripple on capacitor voltages, a control approach based on resonant controller is proposed to eliminate the circulating currents. The effectiveness of the proposed control method is illustrated by numerical simulations and compared with a classical approach commonly used in the literature.

This paper deals with a novel rotor-flux Kalman observer of a Dual Three-Phase Induction Machine. It will be shown analytically how this observer is built. This rotor-flux estimator can be used for the Direct Rotor Field-Oriented Control. A closed-loop control of this flux is therefore added. Simulation results shows the efficiency of this Kalman filter.

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