Power Converter Frequency Droop Control for Grid Switchover
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Solution Overview
Problem
Existing control methods for power converters in AC systems, such as microgrids, face complexity and cost issues due to the need to switch between active front-end control and voltage control, especially during transitions between connected and disconnected states with the utility grid, requiring rapid switchover and precise timing, which is challenging and resource-intensive.
Innovation Solution
A control device and method that uses a frequency droop mechanism to adjust the frequency control value based on power flow direction, forming a power control value to target electric power, and delivering these values to the power converter to control alternating voltage frequency, enabling smooth transitions and adaptation to frequency variations in the AC system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active front-end control is used to control phase currents, then current control precision is improved, but device complexity increases due to needing to switch between AFE control and voltage control
Solution Approach 1:
The power converter is designed to perform both current control (AFE mode) and voltage control (islanded mode) functions using the same hardware architecture. The control device dynamically selects between AFE control and voltage control based on grid connection status, eliminating the need for separate control systems and reducing overall device complexity.
Solution Approach 2:
The control system dynamically switches between AFE control and voltage control modes based on real-time grid connection status. During grid-connected operation, AFE control is applied for precise current control. During islanded operation, the system transitions to voltage control for autonomous operation, optimizing performance for each operational state without increasing hardware complexity.
2Adaptability or versatility
If switchover between AFE control and voltage control is implemented, then adaptability to grid connection status is improved, but reliability decreases due to potential black out situations during switchover
Solution Approach 1:
The control device monitors grid connection status in advance and initiates the switchover process before complete grid disconnection occurs. By detecting grid status changes early and pre-positioning control parameters, the system ensures seamless transition between AFE and voltage control modes without interrupting power supply to the microgrid.
Solution Approach 2:
The control system maintains continuous voltage output during the switchover process by ensuring that the voltage control mode is already prepared and can immediately take over when AFE control disengages. This continuous action prevents any interruption in power supply, maintaining reliability during mode transitions.
3Reliability
If rapid switchover is implemented to prevent black out, then reliability is improved, but device complexity increases due to stringent timing requirements
Solution Approach 1:
The control device continuously monitors grid connection status and provides real-time feedback to the control algorithm. This feedback mechanism enables the system to detect grid disconnection events and initiate switchover to voltage control mode within approximately 100 microseconds, achieving rapid response without requiring overly complex control logic or additional hardware.
4Measurement precision
If AFE control is used when utility grid is connected, then current control precision is improved, but ease of operation worsens due to manual switching requirements
Solution Approach 1:
The control device automatically detects grid connection status and autonomously selects the appropriate control mode without requiring manual intervention. When the utility grid is connected, AFE control is automatically applied for precise current control. When the grid is disconnected, the system automatically switches to voltage control, making the system self-sufficient and easy to operate.
Data Source
AI summary
A control device (101) for controlling a power converter (109) is configured to form a frequency droop value based on electric power supplied by the power converter to an alternating current system, decrease a frequency control value by the frequency droop value, form a power control value based on a target value of the electric power, increase the frequency control value by the power control value, and supply the frequency control value to the power converter to control alternating voltage frequency of the power converter. The electric power is driven to a value at which a combined effect of the frequency droop value and the power control value makes the alternating voltage frequency of the power converter to be the same as operating frequency of the alternating current system. Thus, the electric power can be controlled by changing the power control value.