Virtual Generator Inverter Control for Off-Grid Frequency Stability
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Solution Overview
Problem
In power supply systems with AC and DC power generators operating autonomously, fluctuations in load cause bus voltage frequency to fluctuate, leading to potential disconnection of the DC power supply device.
Innovation Solution
A control device for the inverter that simulates a virtual power generator using rotor, governor, and automatic voltage regulator models to match synchronization and droop characteristics with the AC power generator, controlling pulse width modulation to stabilize voltage frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the AC power generator performs rotation speed control by droop characteristics during autonomous operation, then the system can operate independently without grid connection, but the bus voltage frequency fluctuates due to load variations
Solution Approach 1:
The control device continuously monitors the bus voltage frequency and adjusts the inverter's output power in real-time based on frequency deviations. This closed-loop feedback mechanism counteracts load fluctuations and stabilizes the bus voltage frequency while maintaining autonomous operation.
Solution Approach 2:
The system dynamically changes the inverter's output power parameters in response to frequency deviations. By adjusting the active and reactive power output of the inverter based on real-time frequency measurements, the system maintains stable bus voltage frequency during autonomous operation.
2Productivity
If the bus voltage frequency fluctuates due to load variations, then the system responds to changing power demands, but the inverter is likely to be disconnected from the linked state
Solution Approach 1:
The control device uses frequency feedback to detect when bus voltage frequency deviates from the acceptable range for inverter operation. When frequency fluctuations approach disconnection thresholds, the system automatically adjusts inverter output to bring frequency back within acceptable limits, preventing disconnection.
Solution Approach 2:
The system takes preliminary action by adjusting the inverter's output power before frequency deviations become severe enough to cause disconnection. This preventive control strategy counteracts load fluctuations early, maintaining frequency within the operational range and preventing inverter disconnection.
3Adaptability or versatility
If a DC power supply device is connected to the same bus as the AC power generator, then the system provides combined power generation, but the DC power supply device experiences disconnection due to frequency fluctuations
Solution Approach 1:
The control device monitors bus voltage frequency and uses this feedback to adjust the inverter's output power. This active frequency regulation prevents the frequency fluctuations that would otherwise cause the DC power supply device to disconnect, ensuring stable operation of the combined power generation system.
Solution Approach 2:
The system dynamically changes the inverter's active and reactive power output parameters in response to frequency measurements. By adjusting these parameters to maintain frequency within acceptable ranges, the system prevents disconnection of the DC power supply device while enabling combined power generation.
Data Source
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AI summary
A combined electric power generations' supply system includes an AC power generator that supplies power by off grid independent operation, a DC power supply device, an inverter that converts DC power output by the DC power supply device into AC power. The rotation calculation unit calculates a value relating to a rotation of a rotor when driving the virtual power generator according to an active power command based on a rotor model calculates a value relating to the rotation of the rotor of the virtual power generator and the active power command. The output determination unit determines values relating to an active power and a reactive power to be output to the inverter based on the calculated value relating to the rotation. The modulation control unit performs control of a pulse width modulation of the inverter based on the determined value relating to the active power and reactive power. A time constant relating to synchronization power of the rotor model matches a time constant relating to synchronization power with the AC power generator.