What Are Grid-Forming Inverters?

A grid-forming inverter is a power electronic device that plays a crucial role in the operation and stability of electrical power grids. The increasing penetration of renewable energy sources, such as solar and wind, has brought about significant changes in power generation and distribution. However, the lack of rotational inertia in inverter-based resources poses challenges to the stability and reliability of the power grid. To address this issue, grid-forming inverters that continuously monitor grid voltage and frequency and adjust their output accordingly to maintain stability and synchronization with the power grid are required.

Traditionally, inverters in power systems have been designed to operate in grid-following mode, meaning they follow grid voltage and frequency and regulate active and reactive power. In a grid-forming inverter, voltage and frequency are actively controlled, and this capability is particularly important in microgrids and in situations where there is limited or unreliable access to the main power grid.

Developing grid-forming inverters presents several challenges that need to be addressed to ensure their effective implementation and integration into power systems. To overcome these challenges, grid-forming inverters can be designed and simulated with MATLAB^®, Simulink^®, and Simscape Electrical™ to perform comprehensive system modeling, develop efficient control algorithms, and perform rigorous testing and validation.

The control algorithms within grid-forming inverters are designed to regulate the output voltage and frequency, ensuring stable power generation and grid synchronization. By actively controlling these parameters, grid-forming inverters contribute to grid stability, power quality, and the integration of renewable energy sources. Some of the key control techniques used in grid-forming inverters are:

1. Voltage and frequency droop control: Droop control is a standard control technique for regulating voltage and frequency in the presence of multiple generating units.
2. Virtual inertia and frequency support: Virtual inertia provides a synthetic inertia response by controlling the rate of change of the inverter’s output power, mimicking the behavior of rotating masses in traditional power plants. Frequency support involves adjusting the inverter’s output frequency to help regulate the grid frequency within acceptable limits.
3. Phase-locked loop (PLL): By accurately detecting the grid frequency and phase, phase-locked loops enable the inverter to establish and maintain synchronization with the grid.
4. Fault ride-through: Fault ride-through capability of inverters helps them to remain connected to the grid and maintain operation even in the presence of grid faults, ensuring uninterrupted power supply and system reliability.

Modeling and simulation using Simulink and Simscape Electrical enables engineers to evaluate the inverter’s performance under various scenarios, including grid disturbances, fault conditions, and renewable energy integration. This helps to identify potential issues and optimize the design. Simulated system response can also be evaluated against applicable industrial standards.

Using Embedded Coder^®, production code for grid-forming inverter controllers can be generated and hardware-in-the-loop (HIL) testing can be performed to assess the inverter’s performance under various operating conditions.