Transformer coupled modular multilevel converter as rectifier for hydrogen electrolyser
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Solution Overview
Problem
Existing AC-DC conversion systems for hydrogen electrolyzers, such as 12-pulse thyristor rectifiers, suffer from harmonic issues and reactive power variations, necessitating the use of harmonic filters and STATCOMs, which are inefficient and costly.
Innovation Solution
A system utilizing a transformer and a modular multilevel converter with converter branches and inductors to convert AC current to DC current, controlled by a control unit to stabilize the grid and reduce harmonic pollution, allowing for flexible power management and reactive power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a 12-pulse thyristor rectifier is used for AC-DC conversion, then the conversion function is achieved, but harmonic pollution increases and reactive power varies with load
Solution Approach 1:
The converter is divided into multiple independent converter branches (at least two branches per AC line), where each branch can be independently controlled. This segmentation allows the system to synthesize the output current waveform through coordinated control of multiple branches, reducing harmonic content while maintaining the required power conversion capability.
Solution Approach 2:
The invention employs dynamic control of the converter branches where the switching states and current distribution among branches are continuously adjusted based on the load conditions. This dynamic operation enables the system to maintain low harmonic distortion across varying load levels and to regulate reactive power output according to grid requirements.
2Power
If a 12-pulse thyristor rectifier is used, then power conversion is achieved, but reactive power compensation is required
Solution Approach 1:
The converter branches are designed to perform multiple functions simultaneously: they provide the primary AC-DC power conversion while also enabling reactive power compensation and harmonic mitigation. By coordinating the operation of multiple converter branches, the system can regulate both active and reactive power output without requiring separate compensation devices.
3Object-generated harmful factors
If harmonic filters and STATCOM are added to the thyristor rectifier system, then harmonic and reactive power issues are addressed, but system complexity and cost increase
Solution Approach 1:
The invention combines the functions of power conversion, harmonic mitigation, and reactive power compensation into a single integrated converter system. The multiple converter branches work together to simultaneously achieve low harmonic distortion and flexible reactive power control, eliminating the need for separate harmonic filters and STATCOM devices that would otherwise be required.
4Object-generated harmful factors
If modular multilevel converter is used, then harmonic pollution is reduced and grid stability is enhanced, but converter structure becomes more complex
Solution Approach 1:
The modular multilevel converter is constructed by dividing the overall conversion function into multiple identical or standardized converter branches. Each branch contains similar power electronic components and control logic, which simplifies the design and manufacturing process despite the increased overall system capacity. The modular structure also facilitates easier maintenance and scalability.
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
The system effectively reduces harmonic pollution, eliminates the need for harmonic filters and STATCOMs, and enhances grid stability, particularly in renewable energy environments, supporting high-current electrolyzers with modular scalability.
Implementation Method 1
at least one transformer connectable to an electrical power grid. The at least one transformer is configured for galvanically isolating the system from the electrical power grid and for adapting an input voltage level associated with an alternating current received from the electrical power grid
Implementation Method 2
a converter unit connected to the at least one transformer. The converter unit is configured to convert the received alternating current into a direct current output between a positive pole and a negative pole of the converter unit. The converter unit comprises at least one modular multilevel converter
Implementation Method 3
Each converter branch comprises at least one converter cell and at least one inductor
Data Source
AI summary
A system comprises at least one transformer for galvanically isolating the system from an electrical power grid and adapting an input voltage level associated with an alternating current received from the electrical power grid. A converter unit connected to the transformer is configured to convert the alternating current into a direct current output between a positive pole and a negative pole. The converter unit comprises at least one modular multilevel converter comprising at least two converter branches. Each branch comprises a converter cell and an inductor. One branch is connected from an AC line of the transformer to the positive pole and another branch is connected from the AC line to the negative pole. An electrolyser unit may be arranged between the positive and negative poles, and a control unit may be configured to control the direct current output based on a reference value.