PCS Frequency Control for Off-Grid PV Inverter Curtailment
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Solution Overview
Problem
Existing power conversion systems struggle to efficiently manage power flow and energy distribution during grid disconnection, particularly when the battery charge is high or power output is low, leading to potential energy interruption and inefficiencies.
Innovation Solution
A power conversion system with a microcontroller unit that adjusts AC frequency based on battery charge ratio and power output, ensuring seamless transition and efficient energy distribution by controlling photovoltaic inverters to prevent islanding and maintain power supply to loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power conversion system maintains standard AC frequency during grid disconnection, then photovoltaic inverters can continue outputting power, but the rechargeable battery may become overcharged and energy management becomes inefficient
Solution Approach 1:
The system dynamically adjusts the AC output frequency based on the charged ratio of the rechargeable battery. When the battery charged ratio exceeds a predetermined threshold during grid disconnection, the microcontroller unit increases the AC frequency above standard levels, which automatically causes photovoltaic inverters to stop outputting power, thereby preventing overcharge and optimizing energy management.
Solution Approach 2:
The invention changes the AC frequency parameter from a fixed standard value to a variable parameter that can be adjusted based on battery charge state. By modifying the frequency parameter, the system controls the operation state of connected photovoltaic inverters, transforming a static parameter into a dynamic control variable for energy management.
2Reliability
If the power conversion system increases AC frequency to stop photovoltaic inverter output, then battery overcharge is prevented, but power flow management complexity increases
Solution Approach 1:
The microcontroller unit continuously monitors the charged ratio of the rechargeable battery and uses this feedback to automatically adjust the AC output frequency. This closed-loop feedback mechanism simplifies the control logic by using frequency adjustment as an automatic response to battery charge state, reducing the need for complex manual power flow management while maintaining reliable battery charge control.
3Ease of operation
If the power conversion system uses fixed frequency output, then system operation is simple, but energy distribution efficiency decreases during grid disconnection
Solution Approach 1:
The system transitions from fixed frequency operation to dynamic frequency adjustment based on real-time battery charge conditions. During grid disconnection, when battery charge exceeds thresholds, the frequency is automatically increased to control photovoltaic inverter output, optimizing energy distribution efficiency while maintaining simple automated operation through microcontroller-based control.
Data Source
AI summary
A power conversion system (PCS) is provided. A micro-control unit of the PCS obtains a current charged ratio of a rechargeable battery according to a state-of-charge (SOC) signal received from the rechargeable battery, and obtains an output power of the PCS according to the voltage and current detected by a voltmeter-and-current meter of the PCS. When the micro-control unit detects that the mains off-grid occurs, the following steps are performed: judging whether a current charged ratio of the rechargeable battery is greater than the first ratio; when it is determined that the current charged ratio is greater than the first ratio, judging whether the output power is less than a first power; and when it is judged that the output power is less than the first power, increasing a frequency of an alternating current output from an alternating current (AC) power port of the PCS, so that a photovoltaic (PV) inverter coupled to the AC power port stops outputting power.