Voltage support experimental analysis of a low-voltage ride-through strategy applied to grid-connected distributed inverters

In recent decades, different control strategies have been designed for the increasing integration of distributed generation systems. These systems, most of them based on renewable energies, use electronic converters to exchange power with the grid. Capabilities such as low-voltage ride-through and reactive current injection have been experimentally explored and reported in many research papers with a single inverter; however, these capabilities have not been examined in depth in a scenario with multiple inverters connected to the grid. Only few simulation works that include certain methods of reactive power control to solve overvoltage issues in low voltage grids can be found in the literature. Therefore, the overall objective of the work presented in this paper is to provide an experimental analysis of a low-voltage ride-through strategy applied to distributed power generation systems to help support the grid during voltage sags. The amount of reactive power will depend on the capability of each inverter and the amount of generated active power. The obtained experimental results demonstrate that, depending on the configuration of distributed generation, diverse inverters could have different control strategies. In the same way, the discussion of these results shows that the present object of study is of great interest for future research.Peer ReviewedPostprint (published version

Optimal voltage-support control for distributed generation inverters in RL grid-faulty networks

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.During grid faults, the stability and reliability of the network are compromised, and the risk of a widespread disconnection of distributed generation power facilities is increased. Distributed generation inverters must support the power system to prevent this issue. Voltage support depends substantially on the currents injected into the grid and the equivalent grid impedance. This paper considers these two aspects and proposes an optimal voltage-support strategy in RL grids. The control algorithm guarantees a safe operation of the inverter during voltage sags by calculating the appropriate reference currents according to the equivalent impedance and the voltage sag characteristics, avoiding active power oscillations, and limiting the injected current to the maximum allowed by the inverter. Consequently, the grid can be better supported since the voltage at the point of common coupling is improved and the voltage support objectives are achieved. The proposed control strategy is validated through experimental tests in different grid scenarios. Throughout the work, it is assumed that the grid impedance is known, but the proposed solution requires calculating the grid impedance angle.Peer ReviewedPostprint (author's final draft

Control strategy for distribution generation inverters to maximize the voltage support in the lowest phase during voltage sags

IEEE Voltage sags are considered one of the worst perturbations in power systems. Distributed generation power facilities are allowed to disconnect from the grid during grid faults whenever the voltage is below a certain threshold. During these severe contingencies, a cascade disconnection could start, yielding to a blackout. To minimize the risk of a power outage, inverter-based distributed generation systems can help to support the grid by appropriately selecting the control objective. Which control strategy performs better when supporting the grid voltage is a complex decision that depends on many variables. This paper presents a control scheme that implements a smart and simple strategy to support the fault: the maximum voltage support for the lowest phase voltage. Therefore, the faulted phase that is more affected by the sag can be better supported since this phase voltage increases as much as possible, reducing the risk of under-voltage disconnection. The proposed controller has the following features: a) maximizes the voltage in the lowest phase, b) injects the maximum rated current of the inverter, and c) balances the active and reactive power references to deal with resistive and inductive grids. The control proposal is validated by means of experimental results in a laboratory prototype.Postprint (author's final draft

Modelo simplificado de generador basado en inversores para estudios de protecciones y estabilidad de corto plazo en resolución de transitorios electromagnéticos

The new dynamics of inverter-based generation (IBG) and the lack of accurate models jeopardize the safety of power systems. Additionally, most of the detailed models for electromagnetic transients (EMT) from manufacturers are black boxes. For this reason, the objective of this work was to propose a generic IBG model in EMT resolution suitable for short-circuit, protections, and short-term voltage stability studies. For this purpose, the model considered different functionalities, such as synchronization in case of unbalanced voltage sags, flexible negative sequence current injection, peak current limitation, dynamic reactive power control, and fault ride-through (FRT). This model allowed grid operators to meet the challenge of performing accurate simulations with high integration of renewable resources in their energy matrix. The model was also based on a voltage-controlled current source in the ATP/EMTP software. The short-circuit response was evaluated in a simulation scenario for different fault events presenting a reliable behavior due to the consideration of technical and regulatory requirements and constraints of IBGs. Finally, the proposed model has a fast initialization and is suitable for simulations with large time steps, making it valuable for EMT simulations in large grids.Las nuevas dinámicas de la generación basada en inversores (IBG) y la falta de modelos precisos ponen en peligro la seguridad de los sistemas de potencia. Adicionalmente, la mayoría de los modelos detallados para transitorios electromagnéticos (EMT) de los fabricantes son cajas negras. Por esta razón, el objetivo de este trabajo fue proponer un modelo de IBG genérico en resolución EMT apropiado para estudios de cortocircuito, protecciones y estabilidad de tensión de corto plazo. Para ello, el modelo consideró diferentes funcionalidades, como sincronización ante huecos de tensión desbalanceados, inyección flexible de corriente de secuencia negativa, limitación de corriente pico, control dinámico de potencia reactiva y soportabilidad ante fallas (FRT). Este modelo permitió a los operadores de red enfrentar el reto de realizar simulaciones precisas con gran integración de recursos renovables en su matriz energética. El modelo, además, se basó en una fuente de corriente controlada por tensión en el software ATP/EMTP. La respuesta de cortocircuito se evaluó en un escenario de simulación para diferentes eventos de falla presentando un comportamiento confiable debido a que se consideran los requerimientos y limitantes técnicas y regulatorias de los IBG. Finalmente, el modelo propuesto tiene una rápida inicialización y es apropiado para simulaciones con grandes pasos de tiempo, haciendo que sea valioso para simulaciones EMT en grandes redes