PV Inverter Droop Control for Grid-Forming Synchronization
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Solution Overview
Problem
Conventional PV systems rely on phase-locked loops for grid connection, lacking independent grid-forming capability and stability under renewable energy fluctuations, and model-based control methods are complex and require recalibration.
Innovation Solution
A model-free control scheme with an active power-frequency droop controller and proportional integral controller for inverter synchronization, enabling grid-forming capacity in both islanded and grid-connected modes, using a multi-mode switch for smooth transitions and independent frequency regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional phase-locked loop control is used for grid connection, then the PV system can synchronize with the grid, but it lacks independent grid-forming capability and stability under renewable energy fluctuations
Solution Approach 1:
The patent changes the control parameters from phase-locked loop frequency locking to active power-frequency droop characteristics. The inverter controller is configured to output active power according to active power-frequency droop characteristics, allowing the PV system to independently determine grid frequency rather than merely synchronizing to it. This parameter transformation enables grid-forming capability while maintaining control simplicity.
2Measurement precision
If model-based control methods are used for real-time maximum power point estimation, then the control accuracy is improved, but the computation process becomes complex and time-consuming
Solution Approach 1:
The patent extracts the maximum power point tracking function from complex model-based computation and implements it through simple active power-frequency droop characteristics. By removing the need for real-time model estimation and replacing it with predetermined droop curves, the system achieves adequate power point control without complex computation, significantly reducing processing complexity while maintaining operational effectiveness.
Solution Approach 2:
The patent replaces expensive and complex model-based estimation algorithms with simple, computationally inexpensive droop control characteristics. The droop control uses basic measurements and predetermined parameters rather than requiring continuous complex model calculations, effectively using a simpler control mechanism to achieve the necessary control accuracy without the overhead of sophisticated computation.
3Ease of operation
If PV systems operate as current sources connected to the grid, then the control is simple, but the system cannot support black-start operations independently
Solution Approach 1:
The patent inverts the conventional control approach by making the inverter output voltage the controlled variable rather than the current. The inverter controller outputs voltage according to reactive power-voltage droop characteristics and active power-frequency droop characteristics, enabling the PV system to establish grid voltage and frequency independently. This inversion transforms the system from grid-following current source to grid-forming voltage source while maintaining operational simplicity through droop characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables PV systems to stabilize grid frequency and voltage independently, supporting black-start operations and efficient power delivery across varying solar conditions without reliance on external grids.
Implementation Method 1
An inverter converts PV array voltage to a voltage usable as a power source to a power system load
Implementation Method 2
Proportional integral controller generates a frequency shift value that adjusts output of the active power-frequency droop controller to yield a phase angle control for modulation of the inverter drive signals
Implementation Method 3
solar panels to absorb and convert sunlight into electricity
Data Source
AI summary
A grid-forming photovoltaic (PV) system and method for both islanded connection and grid-connected mode is provided. An inverter converts PV array voltage to a voltage usable as a power source to an electric power system load. Active power-frequency droop controller regulates a modulator that generates drive signals to drive the inverter. Proportional integral controller generates a frequency shift value that adjusts output of the active power-frequency droop controller to yield a phase angle control for modulation of the inverter drive signals. A control mode switch selects among a plurality of control modes for operation of the proportional integral controller. A model-free control algorithm controls the control mode switch, including a control mode (221b) for synchronizing the PV system with the grid in which proportional integral controller (a) detects offset between inverter output voltage and grid output voltage and (b) generates the frequency shift value.