Polyphase Transformer MMC Power Converter Current Suppression
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Solution Overview
Problem
Existing power converters with modular multilevel converter (MMC) circuits are complex and expensive to manufacture, particularly due to the need for multiple MMC modules and inductances to suppress internal alternating currents, and they suffer from stray fields and ohmic losses, especially in high-voltage direct current applications.
Innovation Solution
A power converter design incorporating an n-phase transformer and n MMC modules, each with two submodules in series, featuring sub-module half-bridges with semiconductor switches and decoupling capacitors, where MMC modules are connected in series with electrical taps and controlled to generate phase-shifted voltages, eliminating the need for inductances to suppress circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductances are added to suppress MMC-internal alternating currents, then current suppression is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts and removes the inductance components from the converter circuit. By using a polyphase transformer with series-connected windings and electrical taps, the circuit achieves current suppression without requiring separate inductance elements, thus reducing device complexity while maintaining reliability
Solution Approach 2:
The polyphase transformer serves multiple functions: it transforms voltages between different levels, provides electrical isolation, and suppresses circulating currents through its series-connected winding configuration. This multi-functionality eliminates the need for separate inductance components that would otherwise be required for current suppression
2Strength
If multiple MMC modules are implemented to ensure adequate dielectric strength, then voltage handling capability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines multiple transformer windings into a single polyphase transformer structure with series-connected windings. This merging approach achieves the required voltage handling capability and dielectric strength through the transformer's inherent series configuration, eliminating the need for multiple separate MMC modules and reducing overall device complexity
Solution Approach 2:
The patent changes the circuit configuration by introducing electrical taps between series-connected transformer windings and connecting these to decoupling capacitors. This parameter change in the circuit topology enables voltage handling with reduced component count and lower device complexity
3Reliability
If inductances are added to suppress circulating currents, then current control is improved, but ohmic losses and manufacturing cost increase
Solution Approach 1:
The patent removes inductance components from the circuit and replaces them with a transformer-based solution. The series-connected transformer windings with electrical taps provide current control functionality without the ohmic losses associated with separate inductance elements, reducing energy loss while maintaining current control capability
4Adaptability or versatility
If a complex converter circuit with multiple MMC modules is used, then voltage conversion capability is improved, but manufacturing cost increases
Solution Approach 1:
The patent merges multiple functional requirements into a single polyphase transformer structure. The series-connected windings with electrical taps provide voltage conversion capability for multiple voltage levels, eliminating the need for multiple separate converter modules and significantly reducing manufacturing cost
Solution Approach 2:
The polyphase transformer with series-connected windings serves multiple voltage conversion functions simultaneously. It can handle different voltage levels and provide isolation, making the converter circuit more versatile while reducing the number of components needed, thereby lowering manufacturing cost
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 stray fields and ohmic losses by allowing currents from adjacent series circuits to compensate each other, minimizing the cross-section of common supply lines and eliminating the need for inductances, thereby simplifying the converter structure and reducing manufacturing costs.
Implementation Method 1
an n-phase transformer and a power converter circuit with n MMC modules... phase-shifted driving of the MMC modules to generate and provide a plurality of phase-shifted voltages at terminals of the MMC modules; and applying the phase-shifted voltages to windings of a first side of a polyphase transformer
Implementation Method 2
The power converter includes decoupling capacitors for supplying electrical energy to the transformer and/or for removing electrical energy from the transformer. Each winding of a first side of the transformer forms a series circuit with one of the decoupling capacitors
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
In order to transmit electrical energy between a DC voltage system and an at least n-phase AC voltage system, a power converter (10) is provided and comprises an n-phase transformer (20) and a power converter circuit (12) with n MMC modules (30), wherein the number n is at least three. The MMC modules (30) are connected in series. The power converter (10) comprises decoupling capacitors (16) for supplying electrical energy to the transformer (20) and/or for removing electrical energy from the transformer (20). Each winding (21) of a first side (21s) of the transformer (20) forms a series circuit (17) with each of the decoupling capacitors (16), wherein each of the series circuits (17) is connected in parallel with each of the MMC modules (30). Operating methods (100, 200) for converting a DC voltage (UDC) into an at least three-phase AC voltage (U22, U22', U22'') and for converting an at least three-phase AC voltage (U22, U22', U22'') into a DC voltage (UDC) are also provided.