Grid-Connected Inverter Starter With Pre-Charging Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Grid-connected inverters face challenges with excessive inrush current during startup, which can damage power components and compromise system safety and reliability, especially when active power filters are incorporated into AC electric grids without a soft start process.
Innovation Solution
A starter system for grid-connected inverters is introduced, featuring a controller that sends control signals to manage the switching of a first switch and a precharge branch circuit, delaying the transition to chopping mode to prevent excessive inrush current, thereby protecting power components and ensuring a stable soft start process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the grid-connected inverter is directly connected to the AC electric grid without a soft start process, then the startup speed is fast, but a large inrush current is generated which threatens the safety of power components and may cause failure of the APF grid connection
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC-side capacitor through a pre-charging switch and resistor before connecting to the AC grid. This preliminary charging action ensures that when the main switch closes, the voltage difference is minimized, preventing large inrush current while maintaining fast startup. The controller activates the pre-charging circuit first, then closes the main switch after the capacitor is sufficiently charged.
Solution Approach 2:
The patent uses an intermediary approach by introducing a pre-charging resistor and switch as intermediate components between the DC source and the AC grid connection. These intermediary elements control the charging process, allowing the system to transition smoothly from uncharged to connected state without direct abrupt connection that would cause inrush current.
2Device complexity
If the inductance at the AC side is small and only a filter capacitor is arranged at the DC side in the APF, then the device complexity is reduced, but a large start-up inrush current is generated which greatly threatens the safety of the power components
Solution Approach 1:
The patent applies preliminary action by implementing a pre-charging circuit that activates before the main power connection. The controller first closes the pre-charging switch to charge the DC capacitor through the pre-charging resistor, ensuring the capacitor is sufficiently charged before the main switch closes. This preliminary charging action prevents large inrush current while maintaining simple device structure.
Solution Approach 2:
The patent introduces intermediary components (pre-charging switch and pre-charging resistor) that mediate between the DC source and the main power circuit. These intermediaries provide a controlled path for initial charging, protecting the power components from inrush current without significantly increasing overall device complexity.
3Reliability
If a delay period is introduced between turning on the first switch and entering chopping mode, then the inrush current is minimized and power components are protected, but the startup time is increased
Solution Approach 1:
The patent applies preliminary action by performing the capacitor charging operation before the main power connection. The controller activates the pre-charging circuit first, which quickly charges the capacitor to the required voltage level, then closes the main switch. This preliminary charging action minimizes the delay needed after connection, reducing overall startup time while ensuring component protection.
Data Source
AI summary
A starter of the grid-connected inverter and a control method thereof are disclosed. The starter comprises a controller, and a first switch and a first resistor connected in parallel. The controller includes an input end, and first and second output ends. The input end inspects the DC voltage signal from the inverter. When the DC voltage exceeds a predetermined voltage threshold, the first output end sends a first control signal to turn on the first switch, and the second output end sends a second control signal to make the grid-connected inverter enter into a chopping mode. There is a delay period between the send time of the first control signal and that of the second control signal.