DC Bus Voltage Control Circuit for Wind Turbines
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Solution Overview
Problem
Wind turbines face challenges in effectively dissipating regenerative energy and controlling DC bus voltages during grid faults, which can lead to voltage overshoot and imbalance, requiring efficient mechanisms to manage energy flow and maintain voltage balance.
Innovation Solution
A circuit comprising switches, discharge resistors, and capacitors connected to positive and negative DC buses, allowing independent operation to discharge excess voltage and balance bus voltages, with additional switches and resistors for enhanced power dissipation and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a 3-level bridge converter is used in medium voltage systems, then the converter can operate at medium voltage levels, but the DC bus voltages may become unbalanced and exceed maximum operating voltage during grid faults
Solution Approach 1:
The patent divides the single DC bus system into two separate DC buses (positive DC bus and negative DC bus) with independent voltage control. This segmentation allows each bus to be managed independently through dedicated switches and discharge resistors, preventing voltage imbalance and overvoltage conditions during grid faults while maintaining medium voltage operation capability.
2Object-affected harmful factors
If grid fault protection is implemented, then safety during faults is improved, but regenerative energy dissipation control becomes more complex
Solution Approach 1:
The patent introduces independent discharge resistors (first discharge resistor and second discharge resistor) as intermediary components for each DC bus. These resistors act as mediators that safely dissipate regenerative energy during grid faults without requiring complex active control systems, thereby protecting the converter while maintaining relatively simple control architecture.
3Reliability
If DC bus voltage control is implemented, then voltage balance is maintained, but the system response time during faults is reduced
Solution Approach 1:
The patent implements preliminary action by having discharge switches and discharge resistors pre-configured and ready to operate independently on each DC bus. During normal operation, the system maintains readiness to activate these components, enabling immediate response during grid faults without requiring complex real-time control decisions, thus maintaining voltage balance while minimizing response time.
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
The solution effectively dissipates regenerative energy and controls DC bus voltages during grid faults, preventing voltage overshoot and imbalance, ensuring reliable operation of 3-level bridge converters in wind turbines and other renewable energy systems.
Implementation Method 1
a capacitor bank for storing a positive DC voltage and a negative DC voltage, the capacitor bank including a first capacitor in parallel with the first switch and the first discharge resistor, and a second capacitor in parallel with the second switch and the second discharge resistor
Implementation Method 2
the first switch operates independently from the second switch to discharge the positive DC voltage through the first discharge resistor and the second switch operates independently from the first switch to discharge the negative DC voltage through the second discharge resistor
Data Source
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AI summary
In an embodiment, a circuit 100 includes: a first switch 120,220 serially connected to a first discharge resistor 130,230, the first switch and the first discharge resistor connected to a positive DC bus 170,270; a second switch serially connected to a second discharge resistor 132,232, the second switch and the second discharge resistor connected to a negative DC bus 180,280; and a capacitor bank 140 for storing a positive and a negative DC voltage, the capacitor bank including a first capacitor in parallel with the first switch and the first discharge resistor, and a second capacitor in parallel with the second switch and the second discharge resistor, wherein the first switch 120,220 operates independently from the second switch 122,222 to discharge the positive DC voltage through the first discharge resistor 130,230 and the second switch operates independently from the first switch to discharge the negative DC voltage through the second discharge resistor 132,232.