Voltage Source Converter With Chain-Link Cells For HVDC
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Solution Overview
Problem
Existing voltage source converters for high voltage direct current (HVDC) power transmission and reactive power compensation face challenges such as high losses, electromagnetic interference, and complex designs due to the need for high-power insulated gate bipolar transistors (IGBTs) and large passive snubber components, as well as the expense and difficulty of transporting and assembling multilevel converter arrangements.
Innovation Solution
A voltage source converter design featuring chain-link converters with series-connected switching elements and energy storage devices, allowing for reduced voltage across switching elements, minimized component count, and the use of semiconductor devices with low power dissipation, enabling operation at higher voltage levels and independent module operation to generate stepped variable voltage sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If series connected IGBTs are used to achieve high power ratings, then power rating is improved, but device complexity and losses increase due to complex IGBT drive and large passive snubber components
Solution Approach 1:
The converter is divided into multiple independent converter cells connected in series, where each cell operates autonomously with its own switching elements. This segmentation eliminates the need for complex active IGBT drive circuits and large passive snubber components, as each cell switches independently at lower voltages while collectively achieving the required high power rating through series connection.
Solution Approach 2:
The problematic complex IGBT drive circuitry and large passive snubber components are extracted and eliminated from the design. Instead, the patent uses simpler switching elements with minimal external components, reducing device complexity and losses while maintaining high power capability through the series-connected cell architecture.
2Manufacturing precision
If IGBTs switch on and off several times at high voltage to control harmonic currents, then harmonic control is improved, but losses and electromagnetic interference increase
Solution Approach 1:
The high voltage switching operation is segmented across multiple converter cells, each switching at lower voltage levels. This reduces the energy loss and electromagnetic interference associated with each switching event while maintaining the ability to control harmonic currents through coordinated switching of the series-connected cells.
Solution Approach 2:
The switching voltage parameter is changed from high voltage (in conventional IGBT designs) to lower voltage for each individual cell switching event. By distributing the voltage stress across multiple cells and switching each at a fraction of the total voltage, the patent reduces switching losses and electromagnetic interference while preserving harmonic control capability.
3Stability of the object's composition
If multilevel converter arrangement with large capacitors and DC side reactors is used, then voltage variation is constrained, but equipment becomes expensive, large and heavy making pre-assembly and transportation difficult
Solution Approach 1:
The energy storage function is segmented and distributed across multiple converter cells, each with its own smaller capacitor. This eliminates the need for one or two large capacitors and heavy DC side reactors, reducing overall equipment weight and size while maintaining voltage stability through the distributed energy storage architecture.
Solution Approach 2:
The patent transitions from a centralized energy storage approach (large capacitors and reactors) to a distributed energy storage approach across multiple cells. This dimensional change in the energy storage architecture reduces the physical footprint and weight of the equipment while maintaining the required voltage variation constraints through coordinated cell operation.
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 design reduces switching losses, minimizes the need for cooling equipment, and allows for a greater operating range independent of switching element ratings, resulting in a more cost-effective, compact, and efficient converter system capable of handling faults by opposing fault currents.
Implementation Method 1
each limb portion including at least one switching element connected in series with a chain-link converter... the switching elements of the first and second limb portions being operable to switch the respective chain-link converters in and out of circuit
Implementation Method 2
the chain-link converters being operable to generate a voltage waveform at the AC terminal. The series combination of one or more switching elements connected in series with a chain-link converter... reduces the voltage range that each chain-link converter would be required to generate
Implementation Method 3
Each chain-link converter is preferably operable when the respective limb portion is switched out of circuit to generate a voltage to offset the voltage across the limb portion and thereby minimize the voltage across the respective switching element
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
A voltage source converter (37) for use in high voltage DC power transmission and reactive power compensation. The voltage source converter (37) comprises at least one converter limb (34) including first and second DC terminals (36, 38) for connection in use to a DC network (22) and an AC terminal (44) for connection in use to an AC network (20). The or each converter limb (34) defines first and second limb portions (34a, 34b), each limb portion (34a, 34b) including at least one switching element (40) connected in series with a chain-link converter (42) between a respective one of the first and second DC terminals (36, 38) and the AC terminal (44). The switching elements (40) of the first and second limb portions (34q, 34b) is operable to switch the respective chain-link converters (42) in and out of circuit between the respective DC terminal (36, 38) and the AC terminal (44). The chain-link converters (42) are operable to generate a voltage waveform at the AC terminal (44).