Power Converter Grid Impedance Estimation With Benign Current Injection
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Solution Overview
Problem
Existing power converter controllers face challenges in accurately estimating grid impedance during online operation without disrupting active power profiles and ensuring robust, adaptive control performance, especially under uncertain and time-variant grid conditions.
Innovation Solution
A system and method for estimating grid impedance using a processor-based power converter controller that injects benign current injections to measure symmetrical components of current and voltage at the point of common coupling, allowing for accurate impedance calculation without interfering with the active power profile, using a current controller, voltage controller, and impedance module to determine parameters such as injection interval, duration, and frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active current injection methods are used to estimate grid impedance, then measurement precision is improved, but the active power profile is disrupted and grid compliance may be violated
Solution Approach 1:
The patent applies partial action by injecting only the minimum necessary current signal required for impedance estimation. The injection current is designed as a small perturbation that provides sufficient measurement data while causing negligible disruption to the active power profile, thus resolving the contradiction between measurement precision and power profile stability
Solution Approach 2:
The patent changes the parameter of injection current magnitude to be sufficiently small that it does not significantly alter the operating point or disrupt the active power profile. By adjusting this parameter, the system achieves impedance estimation without violating grid compliance requirements
2Measurement precision
If systematic perturbation is injected for impedance estimation, then measurement precision is improved, but operation of power converter set points is interfered with
Solution Approach 1:
The patent uses minimal perturbation signals that provide adequate measurement precision without significantly affecting the operation of power converter set points. The injection is designed to be just sufficient for estimation purposes while maintaining normal converter operation
3Speed
If fast reaction to small operation point changes is required, then response speed is improved, but accurate grid impedance estimation becomes more difficult
Solution Approach 1:
The patent performs preliminary impedance estimation continuously or at frequent intervals, so that when small operation point changes occur, accurate impedance data is already available for immediate control adjustment. This eliminates the delay between impedance measurement and control response
Solution Approach 2:
The patent implements continuous or near-continuous impedance estimation, ensuring that the impedance data remains current and accurate even as operating conditions change rapidly. This continuous monitoring enables fast response to operation point changes without sacrificing measurement accuracy
Data Source
AI summary
A system and method for estimation of grid impedance in a power converter controller is disclosed in which a current controller is provided to inject an injection current while operating online and coupled to a power grid at a point of common coupling (PCC), the injection current being benign to an operating current of the power converter. A voltage controller is provided to regulate input voltage of the power converter. An impedance module is provided to determine parameters for the injection current, including injection interval and duration, current magnitude, current frequency, and symmetrical components. The impedance module may extract measurements of current and voltage at the PCC at an operating point shifted from a previous operating point in response to the injection current. The impedance module may extract symmetrical components of current and voltage measurements, and compute estimated grid impedance based on the extracted symmetrical components.