In bulk power systems, synchronous generators (SGs) regulate the grid frequency and voltages. The per-unit kinetic energy (defined as inertia) of SGs plays a vital role on the regulation of frequency. Driven by the desire for clean electricity, modern grids witness an energy transition from fossil fuels to renewable energies. However, renewable energy sources require power electronics, e.g. photovoltaic (PV) inverters, to feed into the grid. Therefore, inverters gradually replace SGs. However, unlike SGs, PV inverters only track maximum power points and feature no massive rotational parts, and hence no inertia. In consequence, a phase-out of fossil fuels inevitably poses an inertia shortage and grid formation challenge. As a result, remaining SGs are vulnerable to frequency disturbances, leading to cascading failures and/or even blackouts. Increasing spinning generation reserve suffers from high operating costs and low efficiency.
Existing grid-tied inverters possess the potential for grid support and challenge mitigation. To deliver inertia, a well-proven approach (as mandated in Ontario and Hydro-Quebec) delicately regulates the speed of wind turbines through power converters. However, inertia from rotating wind turbines is inferior to synchronous inertia. This inferiority is caused by a target conflict between inertia emulation and maximum power point tracking or turbine speed regulation. Instead of using wind turbines, existing capacitors in grid-tied converters also allow inertia emulation. More techniques (such as energy reserve) enable inertia delivery from solar PV inverters are ongoing. Another promising research direction aims to duplicate the functions of SGs through grid-tied inverters, known as virtual synchronous machines (VSMs). Similar to SGs, VSMs are expected to form grids and contribute inertia and grid formation among other services. Energy storage in VSMs is essentially for the implementation of power management. On top of typical SG functionalities, stand-alone energy storage systems benefit from control flexibility, thereby having the potential of power quality conditioning (such as reactive power compensation and harmonic filtering), which provides add-on benefits.
This Research Topic aims to address the design and control challenges of smart PV inverters that support modern power systems, laying the foundation for future power systems with 100% renewable energies. Topics of interest include, but are not limited to:
• Design of grid-tied solar PV inverters with grid-forming capabilities
• Modeling of grid-forming and grid-following solar PV inverters
• Fault-ride-through and current-limitation techniques of grid-forming inverters
• Design of solar PV inverters with virtual inertia
• Energy storage techniques for ancillary services
• Energy policy and market design of grid-supportive services
• Virtual synchronous machine (VSM) control of solar PV inverters
• Advanced digital control of solar PV inverters
• Converter-level and system-level stability analysis
• Synchronization among multiple solar PV inverters
In bulk power systems, synchronous generators (SGs) regulate the grid frequency and voltages. The per-unit kinetic energy (defined as inertia) of SGs plays a vital role on the regulation of frequency. Driven by the desire for clean electricity, modern grids witness an energy transition from fossil fuels to renewable energies. However, renewable energy sources require power electronics, e.g. photovoltaic (PV) inverters, to feed into the grid. Therefore, inverters gradually replace SGs. However, unlike SGs, PV inverters only track maximum power points and feature no massive rotational parts, and hence no inertia. In consequence, a phase-out of fossil fuels inevitably poses an inertia shortage and grid formation challenge. As a result, remaining SGs are vulnerable to frequency disturbances, leading to cascading failures and/or even blackouts. Increasing spinning generation reserve suffers from high operating costs and low efficiency.
Existing grid-tied inverters possess the potential for grid support and challenge mitigation. To deliver inertia, a well-proven approach (as mandated in Ontario and Hydro-Quebec) delicately regulates the speed of wind turbines through power converters. However, inertia from rotating wind turbines is inferior to synchronous inertia. This inferiority is caused by a target conflict between inertia emulation and maximum power point tracking or turbine speed regulation. Instead of using wind turbines, existing capacitors in grid-tied converters also allow inertia emulation. More techniques (such as energy reserve) enable inertia delivery from solar PV inverters are ongoing. Another promising research direction aims to duplicate the functions of SGs through grid-tied inverters, known as virtual synchronous machines (VSMs). Similar to SGs, VSMs are expected to form grids and contribute inertia and grid formation among other services. Energy storage in VSMs is essentially for the implementation of power management. On top of typical SG functionalities, stand-alone energy storage systems benefit from control flexibility, thereby having the potential of power quality conditioning (such as reactive power compensation and harmonic filtering), which provides add-on benefits.
This Research Topic aims to address the design and control challenges of smart PV inverters that support modern power systems, laying the foundation for future power systems with 100% renewable energies. Topics of interest include, but are not limited to:
• Design of grid-tied solar PV inverters with grid-forming capabilities
• Modeling of grid-forming and grid-following solar PV inverters
• Fault-ride-through and current-limitation techniques of grid-forming inverters
• Design of solar PV inverters with virtual inertia
• Energy storage techniques for ancillary services
• Energy policy and market design of grid-supportive services
• Virtual synchronous machine (VSM) control of solar PV inverters
• Advanced digital control of solar PV inverters
• Converter-level and system-level stability analysis
• Synchronization among multiple solar PV inverters
