Rectifier Reactive Power Control for Wider Electrolyzer DC Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electrolyzers require a DC voltage range that is limited by the amplitude of the alternating voltage, leading to high conversion losses when high DC voltages are needed, and existing methods for adjusting DC voltage do not efficiently extend the range or minimize losses.
Innovation Solution
A method involving the exchange of reactive power between an AC/DC converter and the AC grid, using an inductance to adjust the AC voltage amplitude, allowing for DC voltages to be set below the critical value and higher voltages with minimal conversion losses, achieved by controlling semiconductor switches to manage the reactive power flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the amplitude of the alternating voltage on the AC input is adjusted to a correspondingly low value to generate DC voltage below the critical voltage Ucr, then the DC voltage can be set below Ucr, but high conversion losses occur when high DC voltages are required
Solution Approach 1:
The patent applies dynamics by making the rectifier system adjustable and operable over the entire operating range for DC voltage, from slightly below the critical voltage Ucr up to the maximum permissible DC voltage UDC,max. The rectifier can adapt its operation mode dynamically: using reactive power exchange when DC voltage needs to be below Ucr, and standard rectification when high DC voltages are required, thus avoiding high conversion losses.
Solution Approach 2:
The patent changes the operating parameters of the rectifier by introducing reactive power exchange capability. By controlling the exchange of reactive power Q(t) with the AC grid, the system can effectively adjust the AC voltage amplitude seen by the converter circuit, enabling DC voltage output below the critical voltage Ucr without physically adjusting the transformer amplitude, thereby maintaining high efficiency across the entire voltage range.
2Ease of operation
If an actively-controlled single-stage rectifier is employed, then the rectifier can be steplessly adjustable, but the minimum DC voltage is limited to the value of the amplitude of the alternating voltage applied to the input side
Solution Approach 1:
The patent introduces reactive power exchange as an intermediary mechanism between the AC grid and the DC load. By controlling the exchange of reactive power Q(t) with the AC grid, the system can effectively decouple the minimum DC voltage from the AC voltage amplitude. The inductance L acts as a mediator that allows reactive power flow to influence the voltage relationship, enabling DC voltages below the AC amplitude while maintaining stepless adjustability.
Solution Approach 2:
The patent changes the operational parameters by allowing the rectifier to operate with variable reactive power exchange. This enables the minimum DC voltage to extend below the critical voltage Ucr by controlling the reactive power Q(t), thus expanding the adaptable voltage range while preserving continuous adjustability through control of the semiconductor switches.
3Adaptability or versatility
If reactive power is exchanged with the AC grid to adjust AC voltage amplitude, then DC voltage range is extended, but additional control complexity is introduced
Solution Approach 1:
The patent applies universality by making the AC/DC converter perform multiple functions: it not only converts AC to DC but also exchanges reactive power with the AC grid. The same semiconductor switches and control circuitry that regulate DC voltage output are used to control reactive power exchange, eliminating the need for separate control systems and reducing overall complexity despite the expanded functionality.
Solution Approach 2:
The patent merges the voltage regulation function and reactive power compensation function into a single control system. By combining these functions in the actively-controlled rectifier, the control complexity is managed through unified control of semiconductor switches, allowing DC voltage range extension without proportionally increasing system complexity.
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
Enables a wider DC voltage range for electrolyzers with reduced conversion losses, facilitating efficient operation and safe connection/isolation of DC loads like electrolyzers with minimal impact on the AC grid.
Implementation Method 1
A method involving the exchange of reactive power between an AC/DC converter and the AC grid, using an inductance to adjust the AC voltage amplitude
Data Source
AI summary
A method and related apparatus for extending a DC voltage range of a rectifier circuit for the supply, from an AC grid, of a DC load which is connected to a DC rectifier output of the rectifier circuit, wherein an AC rectifier input of the rectifier circuit is connected via a grid connection point to the AC grid, wherein the rectifier circuit includes an AC/DC converter having an AC input and a DC output, wherein the AC/DC converter includes a converter circuit having semiconductor switches and freewheeling diodes connected in an antiparallel arrangement thereto, wherein an inductance is connected between the AC input of the AC/DC converter and the grid connection point. The method includes setting a desired DC operating voltage UDOC,soll on the DC output of the AC/DC converter or on the DC rectifier output, or both, by an actuation of semiconductor switches of the AC/DC converter, wherein, when the desired DC operating voltage UDC,soll lies below a value of an amplitude Û4 of an alternating voltage on the AC input of the AC/DC converter, the semiconductor switches of the AC/DC converter are actuated for an exchange of reactive power Q1(t) with the AC grid, which has a voltage-lowering effect upon the amplitude Û4 of the AC voltage at the AC input of the AC/DC converter, such that the amplitude Û4 approaches the desired DC operating voltage UDC,soll, and wherein the exchange of the reactive power Q1(t) with the AC grid is executed during or shortly before an electrical connection or an electrical isolation of the DC load to or from the rectifier circuit.