Modular Low-Voltage Cells for High-Voltage dv/dt and Loss Control
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Solution Overview
Problem
High voltage devices face challenges such as low yield ratio, significant conduction loss, thermal dissipation issues, and harmonic generation due to structural limitations, making them costly and difficult to scale for medium voltage applications.
Innovation Solution
A high voltage device is constructed from modular low voltage cells, each comprising low voltage semiconductor devices and passive components, with a control algorithm to balance voltage and reduce switching loss by controlling the on and off time of cells, allowing for scalable and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If high voltage devices are used to simplify conversion system architecture, then device count is reduced, but device yield ratio becomes very low and cost increases
Solution Approach 1:
The patent divides a high voltage device into multiple lower voltage devices connected in a cascaded configuration. Each lower voltage device operates at a reduced voltage level (e.g., 1.7 kV devices for a 6.5 kV total voltage), which improves individual device yield ratio and reduces cost while maintaining the overall high voltage functionality through series connection of multiple segments.
2Device complexity
If high voltage single device is used, then architecture is simplified, but conduction loss becomes significant due to 1D barrier limitation
Solution Approach 1:
The patent segments the high voltage blocking function across multiple lower voltage devices in series. This segmentation allows each device to operate within its optimal conduction region, reducing the specific conduction loss per device compared to a single high voltage device with a thick 1D barrier that suffers from high on-resistance.
3Device complexity
If high voltage single device is used, then architecture is simplified, but thermal dissipation becomes difficult
Solution Approach 1:
The patent distributes the power dissipation and heat generation across multiple separate lower voltage devices rather than concentrating it in a single high voltage device. This segmentation enables better thermal management as each device has its own thermal path and can be independently cooled, avoiding the thermal bottleneck of a single high voltage device.
4Stress or pressure
If high voltage devices are used, then voltage handling is improved, but strong dv/dt creates harmonics and challenges for system integration
Solution Approach 1:
The patent segments the voltage transition across multiple devices in series, which distributes the dv/dt stress and reduces the equivalent dv/dt seen by each individual device and the overall system. This segmentation effectively lowers the harmonic generation and electromagnetic interference compared to a single high voltage device switching at the same frequency.
5Reliability
If passive RC network is used for voltage sharing, then dynamic voltage sharing is improved, but switching loss increases due to energy dissipation in capacitors
Solution Approach 1:
The patent employs active feedback control through intelligent gate drivers that monitor and adjust the switching timing of each device in the cascaded configuration. This feedback mechanism dynamically balances the voltage sharing across devices during transient conditions without relying on passive RC networks, thereby eliminating the additional switching loss caused by capacitor discharge while maintaining proper voltage distribution.
6Reliability
If passive components are used for voltage balancing, then voltage sharing is achieved, but device scalability becomes difficult
Solution Approach 1:
The patent uses active feedback control in gate drivers that can adapt to different numbers of series-connected devices. The control system automatically adjusts the voltage sharing strategy based on the actual configuration, enabling easy scalability from a few devices to many devices in series without requiring redesign of passive balancing networks or recalibration of fixed component values.
Data Source
AI summary
The present disclosure provides a high voltage device built from modular low voltage cells. Each low voltage cell includes a plurality of low voltage semiconductor devices and one or more low voltage passive components. Each cell can be a current-bidirectional two-quadrant switch or a four-quadrant switch. All the cells may be identical and controlled with a delay time in between. Therefore, the total on and off time of the high voltage device can be controlled to reduce the output equivalent dv/dt. The cell's voltage balancing can be achieved through a control algorithm disclosed herein.