Low-voltage Ride-through Curve Research Articles

A Study on Energy Management and Cooperative Control Considering LVRT in a Hybrid Microgrid

Recently, the establishment of technical standards for grid connection has gained interest in academia and industry. These standards have focused on the reactive power control function of the grid-connected inverter and maintenance of grid operation, and include detailed information about the grid support function. However, remote control communication and control devices for grid support functions, and other distributed sources, such as wind power and energy storage systems, other than inverters have not been addressed. In this paper, the control of the interlinking converter (ILC) in a hybrid microgrid considering low voltage ride-through (LVRT) among grid support functions is investigated. The proposed method consists of an energy management system considering LVRT and a cooperative control scheme. In the energy management system, an algorithm capable of mode selection was constructed by applying the LVRT curve. Then, considering the LVRT situation, the allowable reactive power range of the ILC was mathematically analyzed through the cooperative control of the energy storage device and the ILC. The proposed method enables us to perform active and reactive power control of the ILC in a hybrid distribution network, considering the power factor under various conditions. This functionality, such as supplying reactive power, significantly contributes to the enhanced grid resilience with distributed power sources, including renewable energy. The proposed strategies were verified through experiments after configuring an experimental set of distributed power sources.

Autonomous Operation of Grid Synchronizing Breakers with Low Voltage Ride Through (LVRT) Capabilities

With rapidly increasing penetration level of renewable energy sources (RES) in electric grids, it is noteworthy that stable and reliable operation of electric power systems is urgently needed, given the inverter interfaced RES has less inertia compared to conventional rotational generation units. Meanwhile, it should be also noted that grid operation can be categorized as normal and abnormal conditions. For each type of grid operation condition, the inverter interfaces should produce reliable power generation into the grid. Especially during fault operation, low-voltage ride through (LVRT) is a critical operation condition that needs to be achieved in each interface inverter. Furthermore, when the system is operated in severe conditions, the faulty areas should be effectively isolated from the rest of the system. Considering the operation requirements in electric grids, in this paper, an autonomous operation of grid synchronizing breakers is designed and implemented. Particularly, the developed grid synchronizing breakers can autonomously detect grid operation condition by measuring the grid-connected current and grid side voltage. An extended LVRT curve is designed to support the original LVRT curve so that enhanced fault mitigation and isolation can be achieved. In the meantime, the designed circuit breaker can automatically synchronize with the external grid voltage. Therefore, transient process when breaker is turned on or off can be successfully controlled without violating the existing standards. A simulation model is implemented in MATLAB/Simulink to verify the effectiveness of the proposed method.

Transient Stability of Power Systems Under High Penetrations of Wind Power Generation

This paper investigates the impact of high levels of penetration of wind power generation in the problem of transient stability of power systems. The investigation takes into account the stability issues related to the disconnection of wind power plants due to violation of voltage limits defined by the low-voltage ride-through curve. Different levels of penetration are investigated, starting at 10.59% for wind power plants based on types 1, 2, 3 and 4 wind turbine generators, until 75.24% for those based on type 3. Simulation results show that the secure power system operation can be maintained in most of the situations, from the point of view of transient stability, for the crescent penetration of wind power plants.

Implementation of the Low-Voltage Ride-Through Curve after Considering Offshore Wind Farms Integrated into the Isolated Taiwan Power System

In response to the power impact effect resulting from merging large-scale offshore wind farms (OWFs) into the Taiwan Power (Taipower) Company (TPC) system in the future, this study aims to discuss the situation where the offshore wind power is merged into the power grids of the Changbin and Changlin areas, and study a Low-Voltage Ride-Through (LVRT) curve fit for the Taiwan power grid through varying fault scenarios and fault times to reduce the effect of the tripping of OWFs on the TPC system. The Power System Simulator for Engineering (PSS/E) program was used to analyze the Taipower off-peak system in 2018. The proposed LVRT curve is compared to the current LVRT curve of Taipower. The research findings show that if the offshore wind turbine (OWT) set uses the proposed LVRT curve, when a fault occurs, the wind turbines can be prevented from becoming disconnected from the power grid, and the voltage sag amplitude of the connection point during the fault and the disturbances after the fault is cleared are relatively small. In addition, according to the transient stability analysis results, the system can return to stability after fault clearance, thereby meeting the Taipower transmission system planning criteria and technical key points of renewable energy power generation system parallel connection technique.

Multiobjective optimization in combinatorial wind farms system integration and resistive SFCL using analytical hierarchy process

This paper presents a positive approach for low voltage ride-through (LVRT) improvement of the permanent magnet synchronous generator (PMSG) based on a large wind power plant (WPP) of 50 MW. The proposed method utilizes the conventional current control strategy to provide a reactive power requirement and retain the active power production during and after the fault for the grid codes compliance. Besides that, a resistive superconducting fault current limiter (RSFCL) as an additional self-healing support is applied outside the WPP to further increase the rated active power of the installation, thereby enhance the dc-link voltage smoothness, as well as the LVRT capability of the 50 MW WPP. This is achieved by limiting the exceed fault current and diminishing the voltage dip level, leading to increase the voltage safety margin of the LVRT curve. Furthermore, the effect of the installed RSFCL on the extreme load reduction is effectively demonstrated. A large WPP has a complicated structure using several components, and the inclusion of RSFCL composes this layout more problematic for optimal performance of the system. Hence, the most-widely decision-making technique based on the analytic hierarchy process (AHP) is proposed for the optimal design of the combinatorial RSFCL and 50 MW WPP to compute the three-dimensional alignment in Pareto front at the end of the optimization run. The numerical simulations verify effectiveness of the proposed approach, using the Pareto optimality concept.

Comparison of New LVRT Compatible MV Network Short-Circuit Protection Schemes

Traditionally short-circuit protection operation time delays in medium-voltage (MV) networks have been dependent on magnitude of fault-current or impedance with fixed time delays or inverse time curves without consideration of protection selectivity issues with distributed generation (DG) units’ low-voltage-ride-through (LVRT) curves and possibility of intended island operation. In the future, these issues need to be considered increasingly in MV network protection specifications. In this paper two new future-proof directional short-circuit protection schemes are compared and evaluated. Both schemes enable, without use of high-speed communication, the definition of grid code LVRT curve compatible voltage dependent protection operation time delays during grid connected operation for intelligent electronic devices (IEDs) in MV distribution network which consists of multiple protection zones.

Future-Proof MV Distribution Network Short-Circuit Protection Scheme

Short-circuit protection operation time delays in medium-voltage (MV) networks have traditionally been dependent on fault-current magnitude or measured impedance with fixed time delays or inverse time curves. However, MV feeder protection selectivity issues with low-voltage-ride-through (LVRT) curves of distributed generation (DG) units and possibility of intended island operation must be considered increasingly in the future as a part of the protection scheme. Therefore, this paper proposes a future-proof, directional short-circuit protection scheme for Smart Grids. The proposed scheme enables the definition of LVRT curve compatible protection operation time delays during normal, grid connected operation for protection relays in MV distribution network having multiple protection zones without use of high-speed communication based interlockings/blockings between relays.