PV Battery Charging Control for Grid-Disconnect Overvoltage
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Solution Overview
Problem
When trouble occurs in a grid interconnection system, the power conversion device on the photovoltaic cell panel side may be disconnected from the electric power grid, causing an overvoltage and a large burden on the photovoltaic cell panel due to the loss of the generated power flow path.
Innovation Solution
The power system executes a disconnection charging control mode when the DC voltage exceeds a predetermined threshold, causing the second power conversion device to charge the storage battery, thereby absorbing the generated power from the photovoltaic cell panel and suppressing overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power conversion device is disconnected from the electric power grid during grid trouble, then the safety and protection of the photovoltaic cell panel is improved, but the generated power loses its flow path causing overvoltage and burden on the panel
Solution Approach 1:
The patent introduces a storage battery as an intermediary component between the photovoltaic cell panel and the grid disconnect point. When grid trouble occurs and the power conversion device is disconnected, the storage battery serves as a mediator to absorb the generated power, preventing overvoltage on the photovoltaic panel while maintaining system safety.
Solution Approach 2:
The patent extracts the power absorption function from the grid-connected power conversion device and places it in a standalone storage battery system. This allows the photovoltaic panel to be disconnected from the grid while the storage battery independently handles the generated power, resolving the contradiction between safety disconnect and power flow continuity.
2Reliability
If a DC-side switch device is opened to disconnect the photovoltaic cell panel from the power conversion device during grid trouble, then the protection of the power conversion device is improved, but the generated power loses its flow path causing overvoltage and large burden on the photovoltaic cell panel
Solution Approach 1:
The storage battery acts as an intermediary power absorption device that remains connected to the photovoltaic panel even when the DC-side switch opens. This mediator ensures continuous power flow path for the generated power, preventing overvoltage while allowing the switch to open for device protection.
Solution Approach 2:
The system performs preliminary action by having the storage battery ready to absorb power before the grid disconnect occurs. The control device detects grid trouble and immediately directs the storage battery to charge, establishing an alternative power path before the DC-side switch opens, thus preventing overvoltage from the outset.
3Object-affected harmful factors
If the storage battery charges during grid disconnection to absorb generated power, then the overvoltage suppression is improved, but the control system complexity increases due to voltage detection and mode switching
Solution Approach 1:
The second power conversion device performs self-service by detecting the DC voltage at its own input terminal and autonomously switching to charging mode when overvoltage is detected. This eliminates the need for complex external communication systems, as the device monitors and responds to voltage conditions independently, reducing overall control system complexity.
Solution Approach 2:
The control device implements feedback by continuously monitoring the DC voltage at the input terminal of the second power conversion device. When the voltage exceeds a predetermined threshold, the feedback loop triggers automatic mode switching to charging, creating a simple yet effective closed-loop control system that suppresses overvoltage without complex external intervention.
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 solution effectively absorbs the generated power into the storage battery, preventing overvoltage on the photovoltaic cell panel during grid trouble by providing an alternative current path, allowing quick detection and response to voltage rises without relying on external communication, thus ensuring the system's reliability and efficiency.
Implementation Method 1
the second power conversion device charges the storage battery
Data Source
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AI summary
The power system includes a photovoltaic cell panel, a first power conversion device converting the DC power from the photovoltaic cell panel into AC power, and outputting the AC power to an electric power grid, a DC-side switch device provided between the photovoltaic cell panel and the first power conversion device and opening upon a trouble, a storage battery, and a second power conversion device connected to a connection point between the photovoltaic cell panel and the DC-side switch device and controlling charging and discharging of the storage battery. The second power conversion device includes a normal charging control mode for charging the storage battery based on a command signal from the system host monitor. Disconnection charging control mode is preferably executed when the DC voltage of the connection point exceeds a predetermined threshold value even if the command signal does not instructs the normal charging control mode.