Cascaded Solid-State Transformer Bus Voltage Equalization
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Solution Overview
Problem
Conventional power transformers are large in size, unstable in output voltage, and cannot improve electric energy quality, while existing solid-state transformers face bus voltage imbalances due to module parameter differences, leading to abnormal operation and high costs.
Innovation Solution
A solid-state transformer with cascaded modules and a bus voltage equalization module that consumes energy from bus capacitors to equalize voltages across modules, using a load and/or switching device to stabilize bus voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a plurality of modules are cascaded to achieve required voltage level, then voltage level requirement is met, but bus voltage imbalance occurs due to module parameter differences
Solution Approach 1:
The patent introduces a bus voltage equalization module as an intermediary component between 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 voltage imbalances by providing a controlled discharge path for excess voltage in high-voltage modules, thereby balancing voltages across all cascaded modules without affecting their primary power conversion function.
Solution Approach 2:
The patent dynamically changes the discharge resistance parameter by selecting different discharge resistors (R1, R2, R3, etc.) based on the detected bus voltage level. When voltage imbalance is detected, the system adjusts the discharge resistance value to optimize the equalization process, allowing faster or slower discharge depending on the severity of voltage imbalance and system requirements.
2Reliability
If direct current/direct current topology is used to equalize bus voltages, then bus voltage equalization is achieved, but cost increases and applicability decreases
Solution Approach 1:
The patent extracts the voltage equalization function from the main power conversion modules and implements it through a separate, dedicated bus voltage equalization module. This extracted approach allows each cascaded module to focus on its primary power conversion task while the equalization module handles voltage balancing independently, simplifying the overall system architecture and reducing complexity compared to integrated DC/DC topologies.
Solution Approach 2:
The patent employs simple, inexpensive components for voltage equalization: a coupling capacitor, discharge switches (which can be simple MOSFETs or even diodes), and discharge resistors. These components are much simpler and cheaper than full DC/DC converter topologies. The discharge resistors are intentionally designed as power-dissipating elements that only need to function temporarily during voltage equalization events rather than continuously.
3Ease of manufacture
If modules differ in device parameters, then module manufacturing flexibility is improved, but bus voltage imbalance occurs
Solution Approach 1:
The patent creates equipotential conditions across all cascaded modules by introducing the bus voltage equalization module. The coupling capacitor in the equalization module is connected to the bus of each module, and through controlled discharge, ensures that all modules operate at consistent voltage levels despite having different device parameters such as different capacitor values, drive parameters, or load sizes.
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 approach reduces costs and enhances the applicability of solid-state transformers by ensuring consistent bus voltages, allowing normal operation and improved efficiency.
Implementation Method 1
The bus voltage equalization module is configured to consume a part of energy in the bus capacitor in each cascaded module, to equalize bus voltages of all the cascaded modules
Data Source
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.