Solid-State Transformer Bus Voltage Equalization in Cascaded Modules
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Solution Overview
Problem
Conventional power transformers are large in size, unstable in output voltage, and unable to improve electric energy quality, while existing power electronics devices for solid-state transformers face challenges in voltage level requirements and bus voltage imbalances due to differing module parameters, leading to abnormal operation and overvoltage failures.
Innovation Solution
A solid-state transformer with cascaded modules and a bus voltage equalization module that consumes part of the energy in each module's bus capacitor to equalize voltages, using a load and switching device to ensure consistent bus voltages across all modules, thereby improving applicability and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a plurality of modules are cascaded to achieve high voltage level, then the voltage level requirement is met, but bus voltage imbalance occurs due to differing module parameters
Solution Approach 1:
The patent introduces a bus voltage equalization module as an intermediary component between the cascaded modules. This module includes a coupling capacitor connected to the bus and a discharge circuit with a discharge switch and discharge resistor. The equalization module mediates the voltage imbalance by providing a controlled discharge path for the coupling capacitor, thereby stabilizing the bus voltage across all cascaded modules during startup and operation.
2Reliability
If a DC/DC topology is used to equalize bus voltages, then voltage equalization is achieved, but the cost increases and applicability decreases
Solution Approach 1:
The patent replaces the expensive and complex DC/DC equalization topology with a simple, low-cost voltage equalization module. This module uses basic components (coupling capacitor, discharge switch, discharge resistor) that are inexpensive and easy to implement. The equalization function is achieved through a simple discharge mechanism rather than complex bidirectional energy flow control, significantly reducing cost and improving applicability.
3Adaptability or versatility
If modules with differing parameters are used, then design flexibility is improved, but bus voltage imbalance occurs during startup
Solution Approach 1:
The patent implements preliminary voltage equalization action during the startup phase. The control unit detects the startup state and activates the discharge switch in the voltage equalization module, which discharge the coupling capacitor through the discharge resistor. This preliminary action equalizes the bus voltage across all modules before normal operation begins, ensuring stable startup even when modules have different parameters such as capacitor values, drive parameters, or load sizes.
Data Source
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AI summary
This application provides a solid-state transformer and a bus voltage equalization method for a solid-state transformer. The solid-state transformer may include a plurality of cascaded modules and a bus voltage equalization module. Input terminals of all the cascaded modules are connected in series, and output terminals of all the cascaded modules are connected in parallel, and are used as a parallel output terminal of the solid-state transformer. The bus voltage equalization module is connected in parallel to the parallel output terminal of the solid-state transformer. Each cascaded module may include a bus capacitor (for example, all capacitors connected in series to each other on a direct current bus). The bus voltage equalization module may equalize bus voltages of all the cascaded modules by consuming a part of energy in the bus capacitor in each cascaded module. Based on this application, the bus voltages of all the cascaded modules may be equalized by using the bus voltage equalization module. In this way, there are lower costs and higher applicability.