Star-Connected DC-DC Converter Bridge Arms
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Solution Overview
Problem
Existing DC-DC conversion systems for high-voltage high-capacity DC power transmission face challenges such as low utilization rate, high losses, and manufacturing difficulties in transformer-based systems, as well as limitations in power transmission and efficiency due to the requirement of high inductance inductors in voltage division type topologies.
Innovation Solution
A DC-DC conversion system with a phase element comprising multiple bridge arms in star connection, where each bridge arm includes a variable voltage source, and a controller to manage these sources, allowing for energy balance through AC circular current paths, reducing the need for inductive devices and enhancing efficiency by controlling DC and AC voltage components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transformer-based isolated DC/DC converter topology is used, then voltage conversion and isolation are achieved, but the system suffers from low utilization rate, high losses, and manufacturing difficulties
Solution Approach 1:
The patent extracts and eliminates the transformer component from the DC-DC conversion system. By using a voltage source converter with multiple bridge arms connected in star configuration, the system achieves voltage conversion without requiring a transformer, thereby eliminating transformer losses and manufacturing difficulties while maintaining voltage conversion capability
Solution Approach 2:
The patent replaces the electromagnetic transformation mechanism (transformer) with an electronic conversion mechanism (voltage source converter with controllable bridge arms). The controller adjusts the voltage of each bridge arm to achieve the desired DC voltage conversion ratio, substituting mechanical/electromagnetic transformation with electronic control
2Power
If an auto-transformer based DC-MMC topology is used, then voltage bearing capability is improved, but the isolated transformer limits frequencies and active power of AC voltages
Solution Approach 1:
The patent implements dynamic voltage control by making each bridge arm's voltage controllable through a controller. This allows the system to dynamically adjust the output voltage and frequency characteristics, eliminating the fixed limitations imposed by transformer-based systems while maintaining high voltage bearing capability
Solution Approach 2:
The voltage source converter with multiple controllable bridge arms serves multiple functions: voltage conversion, frequency conversion, and active power control. This universal structure can handle various frequencies and power levels without being constrained by transformer characteristics
3Ease of operation
If a voltage division type DC-MMC topology is used, then DC conversion is achieved through internal control, but high inductance inductors are required which limit transmitted power and running efficiency
Solution Approach 1:
The patent extracts and removes the high inductance inductor from the system. By using a voltage source converter with controllable voltage sources in each bridge arm, the system achieves DC conversion through voltage control rather than relying on high inductance filtering, thereby eliminating the power and efficiency limitations imposed by large inductors
Solution Approach 2:
The patent changes the control parameter from current-based control (requiring high inductance) to voltage-based control. By directly controlling the voltage of each bridge arm, the system achieves efficient DC conversion without requiring high inductance components, thus improving transmitted power capability and running efficiency
4Reliability
If multiple power electronic devices and filters are used, then conversion functionality is achieved, but the device count and system complexity increase
Solution Approach 1:
The patent merges multiple functions into a single integrated voltage source converter structure. The multiple bridge arms perform both voltage conversion and filtering functions simultaneously, eliminating the need for separate filter components and reducing the overall device count while maintaining conversion functionality
Solution Approach 2:
Each bridge arm in the voltage source converter serves multiple purposes: voltage generation, voltage regulation, and harmonic filtering. This multi-functional design reduces the total number of components needed compared to traditional systems that require separate devices for each function
Data Source
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AI summary
A Direct Current (DC)-DC conversion system and a control method thereof are provided. The system includes a phase element and a controller. The phase element includes multiple bridge arms. The multiple bridge arms are in star connection and form a common terminal and multiple output terminals. Each of the bridge arms includes a variable voltage source. The controller is connected to each of the variable voltage sources, and is configured to control a voltage of each of the variable voltage sources. Compared with the conventional art, the DC-DC conversion system and control method thereof provided by the invention have the advantages that each of the bridge arms in the phase element forms star connection, so that a circulation current for energy balance only circulates in the system, rather than flowing into a DC system. In addition, the system adopts relatively smaller numbers of power electronic devices and filters, so that the system may be applied to the field of high-voltage high-capacity DC power transmission and may reduce limits of inductive devices to DC power transmission of the DC-DC conversion system.