Controllable Commutation Inductor for HVDC Inverter Failure Recovery
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Solution Overview
Problem
Existing commutation technologies for inverter systems, particularly in large size wind farm HVDC transmission, face commutation failure issues that complicate the converter valve structure, increase costs, and pose technical challenges due to the need for complex modifications and additional components.
Innovation Solution
A commutation device utilizing a controllable commutation inductor with a three-phase semi-bridge structure, where a switch-controlled inductor is integrated with the converter transformer and inverter, allowing for reduced leakage inductance and increased turn-off angle during commutation failure, without altering the thyristor valve structure, and is coordinated with a control and protection system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If forced commutation technology is used with charge and discharge circuit and auxiliary bridge arm, then commutation failure can be addressed, but converter valve structure becomes greatly changed and complicated
Solution Approach 1:
The invention extracts and removes the complex charge and discharge circuit and auxiliary bridge arm from the converter valve structure, retaining only the essential commutation inductor element. This simplifies the overall structure while maintaining commutation failure prevention capability through the controllable commutation inductor alone.
Solution Approach 2:
The invention introduces a controllable switch (IGBT) in parallel with the commutation inductor, enabling dynamic control of the inductor's effectiveness. During normal operation, the switch is off and the inductor is active; during commutation failure, the switch turns on to short the inductor, dynamically adjusting the system response without requiring complex structural changes.
2Reliability
If forced commutation technology with auxiliary components is implemented, then commutation reliability improves, but implementation cost increases
Solution Approach 1:
The invention removes the expensive auxiliary components (charge and discharge circuits, auxiliary bridge arms) from the system, retaining only the essential commutation inductor and a controllable switch. This extraction of unnecessary components significantly reduces implementation cost while maintaining commutation reliability through the simplified controllable commutation inductor approach.
3Device complexity
If traditional commutation device is used, then structure is simple, but commutation angle is large and turn-off angle is reduced during commutation failure
Solution Approach 1:
The invention makes the commutation inductor controllable through a parallel IGBT switch, enabling dynamic adjustment of its effect. During commutation failure, the switch turns on to short the inductor, rapidly reducing the commutation angle and increasing the turn-off angle to restore reliable operation, all while maintaining a relatively simple overall device structure.
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 enhances commutation properties, reduces costs, and simplifies engineering implementation by maintaining the original valve structure, while providing flexible control and minimizing direct current system disruptions.
Implementation Method 1
the leakage inductance value of the commutation inductor can be reduced, the commutation angle is reduced, and the turn-off angle is increased
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A commutation apparatus based on a controllable commutation inductor (3), and an implementation method therefor. The commutation apparatus uses a three-phase half-bridge structure. The three-phase half-bridge structure consists of serially connected commutation units. Each of the commutation units comprises a converter transformer and a converter inverter (2). A commutation inductor is serially connected between the valve side of the converter transformer and the converter inverter. A controllable inductor in the commutation inductor is used together with a control protection system in a converter station. When the converter station normally operates, a switch is turned off, and the controllable inductor is comprised in the commutation inductor; when the control protection system in the converter station detects a commutation failure, the switch is turned on, so that a leakage inductance value of the commutation inductor is lowered, the commutation angle is reduced, and the turn-off angle is increased. The commutation apparatus improves a commutation feature of a converter valve on an inverter side when a commutation failure occurs, and the commutation apparatus has the advantages of requiring less elements, is easy to implement, and requiring low cost.