What is the impact of specific grid code requirements regarding fault ride-through capability on wind turbine converter design?

Grid code requirements for fault ride-through (FRT) capability significantly impact wind turbine converter design by necessitating over-sizing of components, advanced control strategies, and the implementation of protective measures to ensure the turbine remains connected to the grid during voltage dips. Fault ride-through capability refers to the ability of a wind turbine to remain connected to the grid during a voltage dip caused by a fault, such as a short circuit. Grid codes specify the minimum voltage level and duration for which a wind turbine must remain connected. Wind turbine converters are power electronic devices that convert the variable frequency AC power generated by the turbine into grid-frequency AC power. These converters are crucial for controlling the active and reactive power injected into the grid. The requirement to ride through faults forces several design changes: Over-sizing of converter components is needed. During a voltage dip, the converter must be able to handle increased currents and voltages. This requires the use of components with higher current and voltage ratings, increasing the cost and size of the converter. Advanced control strategies are implemented to manage the flow of reactive power during the fault. The converter must be able to rapidly inject reactive power into the grid to support the voltage and prevent a voltage collapse. This requires sophisticated control algorithms that can quickly respond to changes in grid voltage. Protection measures are integrated to protect the converter from damage during a fault. This includes overcurrent protection, overvoltage protection, and short-circuit protection. These protection measures must be carefully designed to prevent the converter from tripping offline during a fault. Additionally, harmonic filtering is often required. During a fault, the converter can generate harmonics that can distort the grid voltage. Harmonic filters are used to reduce the amplitude of these harmonics and improve power quality. The DC-link capacitor, which stores energy within the converter, is also a critical design consideration. The DC-link capacitor must be sized appropriately to provide a stable voltage during the fault. If the capacitor is too small, the DC-link voltage can fluctuate excessively, leading to converter instability or shutdown. For example, some grid codes require wind turbines to remain connected during voltage dips as low as 15% of the nominal voltage for several hundred milliseconds. To meet this requirement, wind turbine converters must be designed with robust components, advanced control systems, and effective protection measures. In summary, grid code requirements for fault ride-through capability have a significant impact on wind turbine converter design, necessitating over-sizing of components, advanced control strategies, and the implementation of protective measures.