Inverter Ground Fault Detection and Substring Segmentation
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Solution Overview
Problem
Existing power generation systems with PV modules connected in series face limitations due to high DC voltages exceeding safety limits, requiring grounding that restricts flexibility, especially with transformerless inverters, and existing methods for ground fault detection and decoupling are not comprehensive enough to ensure safe operation.
Innovation Solution
An improved inverter system that continuously monitors and regulates the potential of series-connected substrings using a ground fault detector and insulation resistance tester, allowing for safe decoupling and division into potential-free substrings, ensuring all points remain within the allowed potential range during operation and fault conditions, and integrates a controller for safe state management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PV modules are connected in series to generate high DC voltage, then power generation efficiency is improved, but DC voltage exceeds safety limits
Solution Approach 1:
The string is divided into multiple substrings with switching devices (DC switches) that can decouple individual substrings. This allows the system to maintain high voltage during operation by keeping all substrings connected, but can quickly segment the string into safe-voltage substrings when a ground fault occurs, ensuring voltage at any point does not exceed safety limits.
Solution Approach 2:
The system dynamically adjusts the configuration of the string based on operational needs and fault conditions. During normal operation, the entire string remains connected for maximum power generation. Upon detecting a ground fault, the controller dynamically reconfigures the string by opening DC switches to create potential-free substrings, transitioning from a static high-voltage configuration to a dynamic safe-state configuration.
2Object-affected harmful factors
If grounding is implemented at string midpoint to distribute potential, then DC voltage safety is improved, but system configuration flexibility is reduced
Solution Approach 1:
The system uses the inverter's own bridge circuit and DC switches to create artificial grounding points and manage potential distribution without requiring external physical grounding at the string midpoint. The controller intelligently controls the switching devices to maintain potential within safe ranges, allowing the system to adapt its configuration dynamically rather than being constrained by fixed grounding requirements.
3Reliability
If decoupling and division into substrings is performed to ensure safety, then compliance with potential limits is improved, but system complexity increases
Solution Approach 1:
The DC switches serve multiple functions: they act as normal operational switches for power generation, serve as protection devices for creating potential-free substrings during ground faults, and enable flexible reconfiguration of the string. This multi-functionality reduces the need for separate dedicated protection components, thereby limiting the increase in system complexity while achieving reliable compliance with potential limits.
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
The system ensures compliance with maximum generator potential limits both during operation and fault conditions, maintaining safety and flexibility by continuously monitoring and managing substring potentials, allowing for reliable power generation and grid compatibility without immediate decoupling.
Implementation Method 1
a ground fault detector configured to detect a ground fault in conductors of a DC side
Implementation Method 2
an insulation resistance tester configured to monitor an insulation resistance
Implementation Method 3
This DC voltage is transformed in an inverter into a grid-compatible AC voltage
Data Source
AI summary
The invention relates an inverter that may be set up as part of a power generation system for the connection of a number of substrings, which, using DC switches, can be connected to each other in series into a string and with the inverter. The inverter includes a bridge circuit to transform the power generated by the string comprising series-connected substrings into a grid-compatible AC voltage and to feed the power into a grid. The inverter also includes a ground fault detector arranged on the AC side of the bridge circuit for ground fault monitoring of the string. A controller connected to the ground fault detector controls the DC switches so that in case of a ground fault, a complete decoupling of the connection of the string from the bridge circuit and a separation of the string into potential-free substrings is performed. A method of operating such a power generation system is also described.