Grid-Forming Vector Current Control for Stable Weak-Grid Support
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Solution Overview
Problem
Conventional grid supporting control methods for converter-interfaced renewable energy resources face challenges such as high complexity, difficult tuning, stability issues, and loss of synchronism during faults, making them unsuitable for both strong and weak grids, and requiring significant commissioning effort.
Innovation Solution
A simplified grid forming vector current control system emulating a virtual synchronous machine (VSM) with a droop control unit, current control unit, virtual admittance unit, and phase locked loop (PLL) unit, which reduces complexity and enables flexible grid support by emulating inertia and synchronism, using a virtual current source connected in parallel to the VSM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional grid supporting control methods are used, then grid support capability is provided, but system complexity increases and tuning becomes difficult
Solution Approach 1:
The control system is segmented into distinct functional modules: a virtual synchronous machine module that emulates generator behavior, a droop control module for power-frequency regulation, and a phase-locked loop module for synchronization. This modular segmentation allows each component to be independently designed, tuned, and optimized, reducing overall system complexity while maintaining comprehensive grid support capability.
Solution Approach 2:
The patent introduces a virtual synchronous machine as an intermediary layer between the power converter and the grid. This virtual machine emulates the inertial and damping characteristics of physical synchronous generators through software-based control, providing grid support benefits without requiring actual synchronous generators. The intermediary absorbs the complexity of emulating generator behavior while presenting a simplified interface to the rest of the system.
2Reliability
If virtual synchronous machine control is implemented, then inertia emulation is achieved, but commissioning effort increases
Solution Approach 1:
The system employs parameter-based configuration where inertia and damping characteristics are defined through adjustable parameters rather than fixed hardware characteristics. The virtual synchronous machine controller accepts parameter inputs (such as inertia constant H and damping coefficient D) that can be modified through software configuration. This allows grid operators to adapt the system behavior to different grid conditions without physical reconfiguration, significantly reducing commissioning time and effort.
3Reliability
If sophisticated converter control methods are used, then full grid support is provided, but stability issues and loss of synchronism occur during faults
Solution Approach 1:
The control system implements multiple feedback mechanisms: the phase-locked loop continuously monitors grid voltage phase and frequency to maintain synchronization, the droop control provides feedback between power injection and frequency deviation, and the virtual synchronous machine uses feedback from grid conditions to adjust its emulated behavior. These feedback loops enable the system to automatically adapt to grid disturbances and maintain stability during faults by continuously correcting deviations from desired operating conditions.
4Adaptability or versatility
If converter-interfaced renewable energy resources are used, then renewable energy integration is achieved, but grid instability risk increases
Solution Approach 1:
The patent uses the virtual synchronous machine to create a software-based copy of synchronous generator behavior. This copy replicates the inertial response, damping characteristics, and synchronization behavior of physical generators through mathematical models and control algorithms. By copying the stabilizing effects of synchronous generators into the control software, renewable energy resources can provide grid support and stability services previously only available from conventional generators, enabling stable integration of renewable energy at high penetration levels.
Data Source
AI summary
The present disclosure provides a grid forming vector current control system configured to emulate a virtual synchronous machine (VSM). The disclosed system comprises a droop control unit, a current control unit, a virtual admittance unit and a phase locked loop (PLL) unit. The virtual admittance unit and the PLL unit are configured to emulate an inertia of the VSM. A virtual current source is connected in parallel to the VSM.