Reactive Power Converter with Magnetically Coupled Choke Pair
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Solution Overview
Problem
Existing converters for reactive power compensation are prone to damage from short-circuit currents, either due to direct connections with low inductance or the cost disadvantage of using multiple coupling inductances, which can lead to high current surges and increased costs.
Innovation Solution
A converter with a triangular connection configuration using magnetically coupled choke pairs instead of individual coupling inductances, which limits short-circuit currents and reduces the risk of damage by ensuring currents are limited by multiple inductances, and includes a control method to regulate phase module currents and voltages effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If phase branches are directly connected to AC power grid without coupling inductance, then device complexity is reduced, but short-circuit currents can cause damage to inverter components
Solution Approach 1:
The patent merges the coupling inductance functions into a single shared inductor that serves all three phase branches simultaneously. This shared inductor is connected to the neutral point of the delta configuration, providing current limiting protection for all phases while reducing the total number of inductors from three (one per phase) to one, thereby resolving the contradiction between device complexity and reliability.
2Reliability
If multiple coupling inductors are used in each phase branch, then protection against short-circuit currents is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple coupling inductors into a single shared inductor that provides protection for all phase branches. Instead of having separate inductors L1, L2, and L3 for each phase, a single inductor L is placed at the neutral point, reducing component count and complexity while maintaining the current-limiting function for all phases during short-circuit conditions.
3Device complexity
If a single coupling inductor is used for all phase branches, then device complexity is reduced, but current surges can still occur during faults
Solution Approach 1:
The patent introduces a neutral point as an intermediary connection that links all three phase branches through a shared inductor. This neutral point acts as a mediator that enables the single inductor to effectively limit currents in all phases during fault conditions, preventing direct short-circuit paths while maintaining system simplicity.
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 reduces the risk of damage from short-circuit currents and lowers the overall cost of the converter by using a compact, magnetically coupled choke pair design that accounts for magnetic coupling when regulating phase module currents, ensuring controlled reactive power compensation.
Implementation Method 1
the first and second phase branches are electrically connected to each other via a magnetically coupled first choke pair, having a first and a second lateral connection and a central connection
Data Source
Figure 1
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AI summary
The invention relates to a converter (10, 101, 102) for outputting reactive power. The converter (10, 101, 102) comprises three phase branches (1, 2, 3) which can each be connected to an associated phase of an alternating voltage supply system and are connected to one another in delta. Each of the phase branches (1, 2, 3) has a phase module (7, 9, 11) with a series circuit comprising two-pole submodules (8), wherein a voltage which is dropped across each phase module corresponds to the sum of the voltages which are dropped across the submodules of said phase module. The first and the third phase branch are electrically connected to one another by means of a magnetically coupled first throttle pair (22) in this case. Furthermore, a control device (31) for controlling phase module currents is provided, said control device comprising current controllers which are associated with the phase modules, a decoupling unit (600), which is arranged upstream of the current controllers, for decoupling control differences by computer during control of the phase module currents in respect of the mutual dependence of the phase module currents on account of the magnetic coupling in the first throttle pair (22) in such a way that decoupled computer actuating variables can be derived from the decoupled control differences by means of the current controller, a coupling unit (800), which is arranged downstream of the current controllers, for correcting the decoupled computer actuating variables in accordance with the magnetic coupling of the first throttle pair so as to obtain corrected actuating voltages, and also a control unit for driving the submodules, so that the voltages which are dropped across the phase modules can be adjusted in such a way that they correspond to the corrected actuating voltages. The invention further relates to a control method for a converter of this kind.