MLPE Shutdown Control Using Converter Coding and Current Thresholds
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Solution Overview
Problem
Conventional photovoltaic systems face safety risks due to high voltages and high costs associated with communication circuits for controlling shutdown circuits, and voltage fluctuations can lead to failed chopped wave coding, causing the system to power down and lock.
Innovation Solution
A method for controlling module level power electronics (MLPE) devices that detects current thresholds and coding information, adjusting output voltage or power to prevent power exceeding inverter capabilities, thereby avoiding shutdown failures and reducing system costs by eliminating the need for communication circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a communication host and communication circuit are arranged to control shutdown circuits, then safety of maintenance personnel is ensured, but the cost of the photovoltaic system becomes high
Solution Approach 1:
The patent extracts the communication host and communication circuit from the system, eliminating the need for complex communication infrastructure. Instead, it uses the existing converter chopped wave to encode control signals directly into the power transmission线路, achieving shutdown control without additional communication hardware.
Solution Approach 2:
The patent makes the power transmission线路 serve dual functions: both power transmission and signal transmission. The converter chopped wave, originally only for power conversion, is utilized to encode control signals, eliminating the need for separate communication circuits and reducing system complexity.
2Device complexity
If voltage coding signal or current coding signal is formed based on converter chopped wave, then communication circuit cost is reduced, but voltage fluctuation causes chopped wave coding failure and system lockout
Solution Approach 1:
The patent introduces feedback mechanisms where the MLPE device detects the coding signal status and the converter monitors the voltage/current status. This closed-loop feedback allows the system to adjust and re-transmit coding signals when detection fails, preventing permanent lockout and ensuring reliable shutdown control despite voltage fluctuations.
Solution Approach 2:
The patent implements preliminary detection of current and coding signal reception status before attempting shutdown control. By detecting whether the coding signal is properly received and whether current is within threshold, the system can take preliminary corrective actions (re-transmission, parameter adjustment) before the shutdown sequence is initiated, preventing coding failures.
3Reliability
If the shutdown circuit operates at right side of maximum power point with high open-circuit voltage, then shutdown control can be achieved, but even small voltage fluctuation generates excessive power that exceeds inverter capacity
Solution Approach 1:
The patent dynamically adjusts the operating point of the photovoltaic module during shutdown control. Instead of operating at the fixed right side of maximum power point, the system dynamically moves the operating point to the left side where power is lower, ensuring that even with voltage fluctuations, the generated power remains within inverter capacity while maintaining shutdown control capability.
Data Source
AI summary
Provided are a method for controlling operation of a module level power electronics (MLPE) device, a method for controlling MLPE devices and a photovoltaic system. In the method for controlling operation of a MLPE device, if it is determined that a current of a photovoltaic string where the MLPE device is located is less than a current threshold and coding information sent by a converter in the photovoltaic system is not received for a first preset time period, an output voltage or an output power of the MLPE device is controlled to be less than a corresponding threshold.