Current-Source Converter for Low-Impedance Wind Turbine Generators
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Solution Overview
Problem
Low-impedance electric machines, such as those with superconducting field windings, face challenges in current regulation due to high ripple and fault currents, which are difficult to manage with conventional voltage source converters, leading to operational inefficiencies and control issues.
Innovation Solution
Implementing a current source converter system with a current source rectifier, current source inverter, and capacitors across single-phase coils to minimize current ripple and include a crowbar circuit for fault protection, along with a controller for managing the converter assembly and power distribution among multiple converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a voltage source converter is used to excite low-impedance machines, then the converter structure is simple and conventional, but high current ripple and fault currents occur leading to control difficulties
Solution Approach 1:
The patent inverts the conventional voltage-source converter approach by using a current-source converter. Instead of applying switched voltages and relying on machine impedance to limit current, the invention directly controls phase currents through the converter switches, effectively reversing the traditional control paradigm to suit low-impedance superconducting machines
Solution Approach 2:
The patent changes the fundamental operating parameters of the converter by switching between current modes rather than voltage modes. The current-source converter operates with a stiff DC link current and switches current directly to the armature, fundamentally altering the converter's electrical characteristics to match the low-impedance nature of superconducting machines
2Stability of the object's composition
If low-pass filter is inserted to reduce current ripple, then current ripple is reduced, but system loss increases and control challenges arise
Solution Approach 1:
The patent extracts and removes the low-pass filter component from the system by directly controlling the converter switches to produce smooth sinusoidal phase currents. The current-source converter topology inherently provides current continuity through the stiff DC link, eliminating the need for additional filtering components and their associated losses
3Ease of operation
If voltage source converter is used, then conventional control methods apply, but very high fault currents result due to low impedance
Solution Approach 1:
The patent prepares for fault conditions in advance by using a current-source converter with a stiff DC link that inherently limits fault currents. The converter topology and control strategy are designed beforehand to prevent excessive current buildup, providing built-in protection against the low-impedance fault current problem without requiring additional protective equipment
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 current source converter system effectively reduces current ripple and manages fault currents, ensuring stable operation and high-fidelity current delivery to low-impedance machines like superconducting generators, enhancing their efficiency and reliability.
Implementation Method 1
at least one capacitor across the plurality of single-phase armature coils. The capacitor(s) of the current source converter assembly is configured to absorb high frequency components of current pulses
Implementation Method 2
superconducting machines, such as superconducting generators, include at least one superconducting coil which generates a static or rotating magnetic field
Implementation Method 3
at least one armature coil which also generates a static or rotating magnetic field that interacts with the field from the superconducting coil
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An energy conversion system includes a low-impedance generator having at least one armature winding set. The armature winding set includes a plurality of single-phase coils. The system also includes a current source converter assembly electrically coupled to an armature of the generator. The current source converter assembly includes at least one current source converter that includes a current source rectifier coupled to a current source inverter via a DC link and at least one capacitor across the plurality of single-phase armature coils. The capacitor(s) of the current source converter(s) is configured to absorb high frequency components of current pulses generated by the current source converter so as to minimize current ripple in a current applied to the plurality of single-phase coils.