HVDC Converter Auxiliary Waveform Synthesizer for DC Ripple Reduction
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Solution Overview
Problem
High voltage direct current (HVDC) power transmission systems face challenges due to DC voltage ripple caused by sinusoidal AC waveforms, leading to increased installation costs, interference with telephone lines, and the need for large passive filtering equipment, which is undesirable in limited space environments like offshore wind farms.
Innovation Solution
A voltage source converter with auxiliary converters that act as waveform synthesizers to minimize DC ripple by generating a range of waveforms, reducing the need for passive filtering equipment and allowing the use of low-cost cables, while also enabling soft-switching of semiconductor devices and minimizing harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sinusoidal AC waveforms are used for power transmission, then power transmission efficiency is improved, but DC voltage ripple increases causing cable damage and interference with telephone lines
Solution Approach 1:
The patent introduces an intermediary device (DC voltage regulator or filter) between the voltage source converter and the DC network to eliminate the harmful DC voltage ripple while maintaining the benefits of sinusoidal AC waveforms. This intermediary component absorbs or filters out the ripple without affecting the main power transmission function.
2Reliability
If passive inductive and capacitive filtering equipment is used to minimize DC ripple, then DC voltage stability is improved, but device size, weight and cost increase significantly
Solution Approach 1:
The patent replaces the traditional mechanical/passive filtering system (large inductors and capacitors) with an active control system using power electronic devices. This substitution maintains DC voltage stability while dramatically reducing the size and weight of the filtering equipment by using semiconductor-based active filters instead of bulky passive components.
3Reliability
If large passive inductive and capacitive elements are employed for filtering, then DC ripple reduction is improved, but installation space requirements increase which is problematic for offshore wind farms
Solution Approach 1:
The patent changes the operating parameters and control strategies of the voltage source converter to minimize DC ripple generation at the source. By optimizing switching frequencies, pulse width modulation techniques, and control algorithms, the system achieves effective ripple reduction without requiring large physical filtering components, thereby reducing installation space requirements for offshore applications.
4Reliability
If conventional DC filtering equipment is used, then DC voltage quality is improved, but system complexity and cost increase
Solution Approach 1:
The patent integrates multiple functions into the voltage source converter itself, allowing it to perform both power conversion and DC ripple filtering simultaneously. The converter is designed with built-in control capabilities that enable it to regulate DC voltage and minimize ripple without requiring separate dedicated filtering equipment, thereby reducing overall system complexity while maintaining DC voltage quality.
Data Source
AI summary
A voltage source converter is used in high voltage direct current power transmission and reactive power compensation. The voltage source converter includes first and second DC terminals for connection in use to a DC network, three phase elements and at least one auxiliary converter connected between the first and second DC terminals, each phase element including a plurality of primary switching elements and at least one AC terminal for connection in use to a respective phase of a multi-phase AC network, the plurality of primary switching elements being controllable in use to facilitate power conversion between the AC and DC networks, the or each auxiliary converter being operable in use to act as a waveform synthesizer to modify a first DC voltage presented to the DC network so as to minimize ripple in the DC voltage.