Inverter Control Loop Harmonic Injection for Phase Loss Detection
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Solution Overview
Problem
Current methods for detecting single-phase phase losses in an energy supply grid connected to a PV installation via a transformer are inefficient, particularly with Ynd transformers, as they require complex measurement equipment on the high-voltage side and do not provide effective grounding, making it difficult to detect faults on the low-voltage side.
Innovation Solution
An operating method for an inverter connected to an energy supply grid via a transformer that uses a control loop with positive feedback to amplify harmonic components, allowing detection of single-phase phase losses on the low-voltage side, and includes a shutdown mechanism if output current amplitudes exceed a threshold, ensuring effective detection and disconnection from the transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ynd transformer is used for galvanic separation and effective grounding, then grounding requirements are met and fault current paths are blocked, but single-phase phase losses cannot be detected on the low-voltage side
Solution Approach 1:
The patent applies partial action by intentionally introducing a controlled harmonic component (excessive action relative to normal operation) into the control loop. This harmonic injection creates a measurable effect only under fault conditions, allowing phase loss detection without compromising the transformer's grounding function. The harmonic component acts as a detection signal that amplifies itself only when a phase loss occurs.
Solution Approach 2:
The patent implements feedback by creating a control loop with positive feedback for the harmonic component. When a single-phase phase loss occurs, the harmonic component is amplified through this feedback mechanism, producing a measurable response that indicates the fault condition. This feedback-based detection method enables reliable fault detection while maintaining the transformer's galvanic separation and grounding effectiveness.
2Difficulty of detecting and measuring
If measurement equipment is placed on the high-voltage side to detect phase losses, then detection is possible, but device complexity and cost increase significantly
Solution Approach 1:
The patent uses an intermediary approach by introducing a harmonic component as a mediator between the control system and the fault detection function. This harmonic intermediary enables detection on the low-voltage side without requiring complex high-voltage measurement equipment. The harmonic component translates the fault condition into a measurable signal within the inverter's existing control loop.
Solution Approach 2:
The patent replaces complex mechanical/electrical measurement equipment on the high-voltage side with a software-based control algorithm implementing harmonic injection and feedback. This substitution eliminates the need for additional physical measurement devices while achieving the same detection capability through signal processing and control theory.
3Difficulty of detecting and measuring
If other transformer types like YNy are used to project phase losses onto the low-voltage side, then detection becomes possible, but effective grounding is lost
Solution Approach 1:
The patent segments the detection function from the transformer selection criteria. Instead of requiring a specific transformer type that compromises grounding, the detection function is separated and implemented through harmonic injection in the control loop. This allows the use of Ynd transformers that provide both galvanic separation and effective grounding while adding an independent detection mechanism through control signal manipulation.
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 reliable and fast detection of single-phase phase losses on the low-voltage side of the transformer, maintaining operational stability and compliance with grounding requirements without interfering with dynamic fault-ride through regulations.
Implementation Method 1
the actuation signals are generated as a function of a harmonic component of the output voltages of the inverter at a multiple of the fundamental frequency using a control loop with positive feedback
Data Source
AI summary
A method for operating an inverter which is connected to an energy supply grid via a transformer for feeding in electrical energy into the energy supply grid, includes measuring output currents and output voltages of the inverter, and actuating power switches of the inverter using actuation signals that are generated as a function of the measured output currents and the measured output voltages at a fundamental frequency of the energy supply grid. The actuation signals are further generated as a function of a harmonic component of the measured output voltages of the inverter at a multiple of the fundamental frequency using a control loop with positive feedback.