Calibrating Medium-Voltage Grid Connection Using Low-Voltage Detectors
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Solution Overview
Problem
Current methods for connecting a photovoltaic system to a medium-voltage network require multiple expensive switches and voltage measurement devices, leading to high costs and heat losses, while also facing challenges in achieving accurate voltage measurements for grid connection and synchronization.
Innovation Solution
A method that calibrates voltage values from a capacitive voltage divider on the medium-voltage side using measurements from a voltage detector on the low-voltage side, allowing the controller to connect the system to the grid using a motor-driven isolating switch, with optional amplification for interference-free transmission, thereby reducing the number of expensive switches and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement is provided on both medium-voltage side and low-voltage side with capacitive voltage divider, then safety is improved, but measurement precision deteriorates and device complexity increases
Solution Approach 1:
The patent divides the voltage measurement function into two segments: a capacitive voltage divider on the medium-voltage side for safety monitoring and an isolating transformer on the low-voltage side for precise measurement. Each segment performs its specific function optimally, with the capacitive divider providing safety monitoring and the isolating transformer providing accurate measurement for grid connection verification.
Solution Approach 2:
The patent introduces an isolating transformer as an intermediary device on the low-voltage side that mediates between the medium-voltage network and the measurement system. This intermediary provides both galvanic isolation for safety and high-precision voltage measurement for grid connection verification, resolving the contradiction between safety and measurement accuracy.
2Reliability
If multiple switches are used for connection (one on medium-voltage side and one on low-voltage side), then safety and control are improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the precise voltage measurement function from the switch control system and places it on the low-voltage side with the isolating transformer. This allows the medium-voltage side switch to be controlled remotely based on accurate voltage information, reducing the need for additional switches on the medium-voltage side and simplifying the overall switching architecture.
Solution Approach 2:
The patent enables the low-voltage side measurement system to serve itself by providing accurate voltage measurements that automatically enable or disable connection based on grid conditions. This self-service mechanism reduces the need for complex control systems and multiple switches, as the system can autonomously determine when connection is safe and appropriate.
3Extent of automation
If motor-driven switch is used on low-voltage side for connection, then automation is improved, but cost and heat losses increase
Solution Approach 1:
The patent replaces the mechanical motor-driven switch system with a electronically controlled switching mechanism. The accurate voltage measurements from the isolating transformer enable precise electronic control of the switching operation, reducing mechanical wear and heat losses associated with traditional motor-driven switches while maintaining full automation capability.
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
This approach minimizes the number of expensive switches and voltage measurement devices, ensures accurate grid connection and synchronization, and reduces costs while maintaining high accuracy in voltage measurements, allowing for efficient and reliable connection to the medium-voltage grid.
Implementation Method 1
a capacitive voltage divider (8), arranged on a medium-voltage side of the medium-voltage transformer, for detecting first voltage values
Implementation Method 2
a voltage detector (6), arranged on a low-voltage side of the medium-voltage transformer, for detecting second voltage values
Implementation Method 3
an amplifier (9) for amplifying the first voltage values
Data Source
Figure 1
AI summary
The invention relates to a method for connecting an energy generation installation (3) to a medium voltage network (4), wherein a calibration factor is first determined by a control (10) of the energy generation installation (3), via which first voltage values are matched to second voltage values, wherein, during an idle state of a medium voltage transformer (5), the first voltage values are captured on a capacitive voltage divider (8), arranged on the medium voltage side of the medium voltage transformer (5), and the second voltage values are captured on a voltage detector (6), arranged on the low voltage side of the medium voltage transformer (5). A a circuit breaker (13), arranged on the medium voltage side of the medium voltage transformer (5), is closed by the control (10) of the energy generation installation when voltage values determined on the capacitive voltage divider (8) exceed a first threshold after application of the calibration factor. The invention further relates to a photovoltaic installation suitable for carrying out the method.