Hybrid Converter Harmonic Suppression via Modular Submodules
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Solution Overview
Problem
Existing hybrid converters for high-voltage direct current transmission require complex structures and high costs due to the need for two self-commutated converters on both AC and DC voltage sides to effectively suppress harmonics, leading to increased complexity and expense.
Innovation Solution
A hybrid converter design featuring a modular multi-level self-commutated converter with phase module branches having series-connected submodules, each with an energy store and power semiconductor switches that can be switched on and off, allowing for zero or inverse voltage generation, eliminating the need for central energy storage and additional active filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If two self-commutated converters are used on both AC and DC voltage sides to suppress harmonics, then harmonic suppression is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the functions of two separate self-commutated converters into a single hybrid converter by connecting a line-commutated converter and a self-commutated converter in series. This unified structure achieves harmonic suppression on both AC and DC sides without requiring two independent converters, thereby reducing device complexity while maintaining effective harmonic mitigation.
Solution Approach 2:
The hybrid converter performs multiple functions simultaneously: it acts as a power converter, a harmonic filter, and a reactive power compensator. The self-commutated converter portion generates voltage components that suppress harmonics on both AC and DC sides, while the line-commutated converter handles main power conversion, creating a multi-functional device that eliminates the need for separate harmonic suppression systems.
2Object-generated harmful factors
If two self-commutated converters are used on both AC and DC voltage sides to suppress harmonics, then harmonic suppression is improved, but cost increases
Solution Approach 1:
The patent combines power conversion and harmonic suppression functions into a single hybrid converter structure, eliminating the need for two separate self-commutated converters. This merging reduces component count, material requirements, and manufacturing costs while maintaining effective harmonic suppression performance on both AC and DC voltage sides.
Solution Approach 2:
The hybrid converter serves multiple purposes: main power conversion, AC-side harmonic suppression, and DC-side harmonic suppression. This multi-functionality eliminates the need for additional dedicated harmonic filters or active filters, significantly reducing overall system cost while achieving comprehensive harmonic mitigation.
3Power
If a line-commutated converter is used, then power transmission capability is improved, but harmonic generation increases
Solution Approach 1:
The self-commutated converter acts as an intermediary between the line-commutated converter and the AC/DC networks. It generates voltage components with frequencies that are integer multiples of the fundamental AC voltage frequency, which counteract and suppress the harmonics generated by the line-commutated converter, thereby enabling high power transmission with reduced harmonic pollution.
Solution Approach 2:
The patent converts the harmful harmonics generated by the line-commutated converter into beneficial effects by using the self-commutated converter to generate opposing voltage components. These voltage components are specifically designed to cancel out the harmonic currents, transforming the harmonic problem into an opportunity for active harmonic compensation and purification of the AC and DC voltage networks.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a hybrid converter (18) for transmitting electrical power between an alternating voltage network (2) carrying alternating voltage and a direct voltage network (3), comprising a network-clocked converter (4), the power semiconductor switches (9) of which are designed to switch on once in a period of the alternating voltage and which is connected to a connection unit (10) for connecting the alternating voltage network (2), and a self-commutated converter (19), which likewise can be connected to said alternating voltage network (2) and which comprises phase module branches (20) having power semiconductor switches (27, 28, 34, 35) that can be switched both on and off and which is connected in series with the network-commutated converter (4). The aim of the invention is to effectively damp overtones of the fundamental oscillation both on the direct voltage side and on the alternating voltage side of the hybrid converter and to provide a converter having a simple construction and thus being cost-effective at the same time. In order to achieve said aim, the phase module branches (20) have a series circuit of sub-modules (24), wherein each sub-module (24) has two connection terminals (31, 32), an energy store (25), and a power semiconductor circuit of power semiconductor switches (27, 28, 34, 35) that can be switched on and off, said power semiconductor switches being controllable in such a way that the voltage that drops at the energy store or a zero voltage at the two connection terminals (31, 32) of the respective sub-module (25) drops.