Search

Grid-forming (GFM) inverters are promising solutions for future power systems with high penetration of renewables. The successful design of GFM inverters is crucial for achieving current limiting, enabling them to withstand disturbances such as voltage sags and phase jumps in grid voltages. However, when the parameters are not properly tuned, a cascaded voltage and current controller can compromise grid stabilization performance due to issues like controller windup, post-fault recovery failure, and harmonic instability. To address this challenge, this paper proposes a dual control scheme consisting of GFM and current control that work in parallel. The dual control scheme incorporates emulation signal generators integrated with the dual controllers. This integration allows for adjusting their internal states during standby mode to track to references, enabling a seamless transition between the running and standby modes. Numerical simulations and experiments demonstrate that the proposed controller exhibits promising performance under both normal and faulted conditions. • The proposed controller eliminates the issues caused by the cascaded controller. • The proposed controller avoids transient instability during the current limitation. • The proposed emulation signal generator enables smooth switching between GFM and current control. [ABSTRACT FROM AUTHOR]

If a blackout occurs, self-starting units, like grid-forming inverters, are needed for a black start and a restoration in a low voltage grid. Reliable power supply of the grid by grid-forming inverters can be achieved by storage systems connected to the grid-forming inverters. The use of storage systems as a power source for the grid-forming inverters requires that the storage systems must not be completely discharged or charged, otherwise the functionality of balancing the power of the grid-forming inverters is not guaranteed and a restoration failure would result. This paper presents a concept for grid restoration and maintaining a reliable island operation using a secondary control structure in combination with the implementation of a state machine in smart meters to handle such critical cases of the storage systems. The secondary control can also restore the nominal frequency after load changes without any communication between grid elements. RMS simulations are carried out in DIgSILENT PowerFactory showing the restoration process and island operation in different scenarios. • Approach is based on the secondary control with grid-forming inverters and state machines. • Enabling a nominal frequency, ensuring a nominal operation of the island low voltage grid. • An approach to keep the state of charge of batteries in a range of normal operation. [ABSTRACT FROM AUTHOR]

• Analysis of the interactions between existing synchronous units and grid-forming type converters during short-circuits. • An optimal grid-forming control parameter tuning procedure considering different disturbances is presented, aiming to reduce the associated battery energy storage system power regulating effort following the disturbances. • Identification of a novel rule-based adaptive control solution to switch between different sets of control parameters used in grid-forming type converters depending on the network status following a fault-type disturbance. Operating isolated power systems with increasing shares of renewable energy sources requires the integration of battery energy storage systems in order to assure enhanced frequency regulation capabilities. The control mode of power converters interfacing battery energy storage systems to the grid can be based on grid-forming type structures given its superior performance with respect to the mitigation of network frequency disturbances. Nevertheless, in case of network faults, the interactions between existing synchronous units and the grid-forming type converters may adversely affect the global system behavior. Therefore, this paper addresses the study-case of a MW-scale isolated power system with large shares of converter-interfaced renewable generation, operating with both synchronous machines and a grid-forming type power converter. An optimal grid-forming control parameter tuning procedure considering different disturbances is presented, aiming to reduce the associated battery energy storage system power regulating effort following the disturbances. Moreover, it is proposed and discussed the need of a novel rule-based adaptive control solution to switch between different sets of control parameters used in grid-forming type converters depending on the network status following a fault-type disturbance. Extensive numerical simulations performed over different operating scenarios illustrate the performance of the proposed solution. [ABSTRACT FROM AUTHOR]