Voltage Source Converter Harmonic Cancellation via Magnetic Coupling
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Solution Overview
Problem
Existing voltage source converters face challenges in maintaining a stable and reliable connection between AC and DC networks while effectively canceling harmonic voltage components, leading to inefficiencies and increased size, weight, and cost.
Innovation Solution
A voltage source converter design featuring a plurality of limbs with phase elements, DC side sub-converters, and AC side sub-converters that operate as waveform synthesizers, coordinated by a controller to present a constant DC voltage and cancel selected harmonic components, with additional windings in a daisy chain arrangement providing filtering capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage source converters use conventional converter designs with primary and secondary converters, then power conversion between AC and DC networks is achieved, but the size, weight, and cost of the converter increase due to the need for multiple converters and complex coordination
Solution Approach 1:
The patent combines the functions of primary and secondary converters into a single integrated converter structure. The converter includes a primary converter portion with switching elements connected between DC and AC terminals, and a secondary converter portion with chain-link converters connected in parallel, all sharing common magnetic coupling windings. This merging eliminates the need for separate physical converter units while maintaining the ability to perform both power conversion and harmonic cancellation functions, thereby reducing overall size and weight.
Solution Approach 2:
The integrated converter design allows the same converter structure to perform multiple functions: power conversion between AC and DC networks, harmonic voltage component cancellation, and reactive power compensation. The primary and secondary converter portions work together within a single converter unit to achieve these diverse functions, eliminating the need for additional dedicated equipment and reducing the overall footprint.
2Power
If voltage source converters use multiple primary switching elements per phase element, then power conversion capability is improved, but the complexity of control and coordination increases
Solution Approach 1:
The converter is segmented into distinct functional portions: a primary converter portion with switching elements for power conversion, and a secondary converter portion with chain-link converters for harmonic cancellation. Each portion has dedicated switching elements and control logic, allowing independent optimization and simplifying the overall control architecture. The magnetic coupling windings provide natural decoupling between the portions while enabling coordinated operation.
Solution Approach 2:
The magnetic coupling windings act as an intermediary between the primary and secondary converter portions. These windings magnetically couple the two portions, allowing power and control signals to be transferred between them without direct electrical connection. This intermediary mechanism simplifies coordination by providing a natural interface that automatically balances the operation of both converter portions.
3Reliability
If voltage source converters present constant DC voltage to the DC network, then power quality is improved, but additional filtering components and control mechanisms are required
Solution Approach 1:
The converter uses its own secondary converter portion with chain-link converters to generate compensating voltage waveforms that cancel harmonic components in the DC voltage. This self-service approach eliminates the need for external filtering components by using the converter's internal resources to purify its own output, thereby maintaining DC voltage stability without adding external complexity.
Solution Approach 2:
The converter incorporates feedback control mechanisms that monitor the DC voltage output and automatically adjust the switching of the secondary converter portion to cancel detected harmonic components. This closed-loop feedback system maintains constant DC voltage by continuously correcting deviations, eliminating the need for large passive filtering components while ensuring voltage stability.
4Reliability
If voltage source converters cancel harmonic voltage components from AC side voltage, then power quality is improved, but the rating and size of AC side sub-converters must be increased
Solution Approach 1:
The converter uses the magnetic coupling windings to transform the harmful harmonic voltage components into useful canceling signals. The secondary converter portion detects harmonic components in the AC voltage and generates opposing harmonic signals through the magnetic coupling, which automatically cancel the harmful harmonics. This converts the problem of harmonic distortion into a beneficial self-correcting mechanism, improving power quality without requiring oversized AC side sub-converters.
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 configuration ensures a stable and reliable power transfer between AC and DC networks, optimizes sub-converter performance, reduces the rating of AC side sub-converters, and provides additional functionality, resulting in cost and size savings while maintaining high-quality power transfer.
Implementation Method 1
each winding magnetically coupled to a respective one of a plurality of additional windings, and the plurality of additional windings are electrically interconnected in a daisy chain arrangement
Data Source
Figure 1~2a
Figure 2b~2c
Figure 3a
AI summary
A voltage source converter (30) comprises first and second DC terminals (32,34) for connection to a DC network (58). The voltage source converter (30) includes at least one limbs connected between the first and second DC terminals (32,34). The or each limb includes: a phase element (36) including a plurality of switching elements (40) switchable to selectively interconnect a DC side voltage at a DC side of the phase element (36) and an AC side voltage at an AC side of the phase element (36); a DC side sub-converter (38) connected to the DC side of the phase element (36), the DC side sub-converter (38) configured to be operable as a waveform synthesizer to control the DC side voltage so as to form a DC voltage for presentation to the DC network (58); and an AC side sub-converter (39) connected to the AC side of the phase element (36), the AC side sub-converter (39) configured to be operable as a waveform synthesizer to control the AC side voltage so as to form a or a respective AC phase voltage for presentation to a or a respective AC phase of an AC network (50). The voltage source converter (30) includes a controller (60) programmed to selectively coordinate the operation of the DC and AC side sub-converters (38,39) as the respective waveform synthesizers to simultaneously: synthesize one or more selected harmonic voltage components to control the or each DC side voltage so as to present a constant or substantially constant DC voltage to the DC network (58); and cancel the or each selected harmonic voltage component from the or each AC side voltage so as to present a or a respective AC phase voltage free of the or each selected harmonic voltage component to the corresponding AC phase of the AC network (30).