DC-to-DC Converter Fault Tolerance via Switch Synchronization
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Solution Overview
Problem
Conventional DC-to-DC converters with flying capacitors face instability and switch burnout due to open-circuit or short-circuit failures, which prevent voltage control and lead to excessive voltage application.
Innovation Solution
A DC-to-DC converter design that includes a controller performing pulse width modulation (PWM) control to synchronize the states of specific switches, reducing the step-up ratio and increasing switching frequency, allowing stable operation even when the flying capacitor's voltage cannot be controlled, effectively converting the converter to a two-level operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PWM control is performed to synchronize switch states (first and second switches same state, third and fourth switches same state), then the DC-to-DC converter can operate stably even when the second capacitor fails, but the step-up ratio is reduced
Solution Approach 1:
The controller dynamically adjusts the switching states of the four switches based on the operational condition of the second capacitor. When the second capacitor is detected to have failed (open-circuit or short-circuit), the controller transitions to a degraded mode where the first and second switches are controlled to enter the same state, and the third and fourth switches are controlled to enter the same state. This dynamic adaptation allows the converter to maintain stable operation under faulty conditions while accepting a reduced step-up ratio as a trade-off for reliability.
2Strength
If the voltage of the flying capacitor cannot be controlled due to open-circuit or short-circuit failure, then the converter structure remains intact, but excessively high voltage is applied to switches causing switch burnout
Solution Approach 1:
The controller implements preliminary protective action by continuously monitoring the voltage across the second capacitor (flying capacitor). When an abnormal condition is detected (voltage exceeding predetermined thresholds indicating open-circuit or short-circuit failure), the controller proactively changes the switching strategy before excessive voltage can damage the switches. The controller forces the first and second switches to the same state and the third and fourth switches to the same state, which prevents voltage spikes and protects the switches from burnout even though the second capacitor has failed.
3Weight of stationary object
If switching frequency is increased to reduce inductor size and weight, then the converter becomes more compact, but control difficulty increases due to flying capacitor voltage maintenance requirements
Solution Approach 1:
The controller changes the operational parameters of the switching circuit based on the health status of the second capacitor. In normal operation, the controller manages the flying capacitor voltage to enable high-frequency switching with reduced inductor size. When the second capacitor fails, the controller adjusts the switching patterns (forcing synchronized states) and operating frequency to maintain stability. This parameter adaptation allows the system to achieve compact dimensions while managing the increased control complexity through automated fault detection and response.
Data Source
AI summary
A DC-to-DC converter includes a first capacitor, first to fourth switches connected in series between first and second electrodes of the first capacitor, a second capacitor connected to a connection node of the first switch and the second switch and a connection node of the third switch and the fourth switch, an inductor connected to a connection node of the second switch and the third switch, and a controller that performs PWM control. In a case where a failure occurs in the second capacitor, the DC-to-DC converter performs PWM control such that the first switch and the second switch enter the same state and the third switch and the fourth switch enter the same state on the basis of a result of comparison between a first detection voltage that is a measured output voltage and a target output voltage of the DC-to-DC converter.