Inverter Grid Synchronization Without PLL or Inrush Current
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Solution Overview
Problem
Inverter-based resources (IBRs) face challenges in startup and synchronization with the grid due to inertia-free characteristics and the limitations of phase-locked loop (PLL) bandwidth, leading to prolonged synchronization processes and potential inrush currents.
Innovation Solution
The implementation of direct current (DC) control throughout each switching cycle allows for a transient-free inverter startup and grid synchronization by regulating the inverter current to zero and estimating the grid phase angle based on current samples and switching functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PLL-based synchronization is used, then grid synchronization can be achieved, but the synchronization process is prolonged and inrush currents occur
Solution Approach 1:
The patent extracts and removes the PLL component from the synchronization system. By directly calculating the grid phase angle from voltage samples without using PLL, the system eliminates the bandwidth limitations and delay inherent in PLL-based methods, achieving instant synchronization without prolonged transient processes
Solution Approach 2:
The patent performs preliminary action by pre-calculating the initial grid phase angle and voltage magnitude before closing the circuit breaker. The control system calculates θ_g(0) and V_g(0) from voltage samples taken during the pre-charge phase, enabling the inverter to be ready for immediate synchronization without waiting for PLL convergence
2Ease of operation
If conventional startup procedures are used, then inverter can be started, but inrush current is generated affecting grid stability
Solution Approach 1:
The patent implements a pre-charge phase where the inverter is started in an open-circuit state before connecting to the grid. During this phase, the DC control algorithm calculates the initial operating point (V_g(0), θ_g(0)) without drawing current from the grid, eliminating inrush current while still enabling the inverter to be ready for immediate synchronization
Solution Approach 2:
The patent changes the control parameters dynamically during startup. By using DC control with switching-cycle-based feedback, the system maintains current at zero during the pre-charge phase, then transitions to regular control strategy after synchronization, achieving both ease of operation and elimination of harmful inrush current
Data Source
AI summary
Systems and methods for starting inverter-based resources (IBRs) and synchronizing them with their tied grid are provided. The startup can utilize direct current (DC) control throughout each switching cycle, enabling a process without any inrush current. This can mitigate the inrush current instantly or essentially instantly, thereby giving a transient-free inverter startup and grid synchronization.