Multi-Level Converter Switch Stress Reduction via Averaging Sequence
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Solution Overview
Problem
Multi-level DC-DC converters experience undesirable voltage spikes across switches at critical operating points, leading to potential damage and inefficiencies due to transient voltage stress, which existing control methods fail to adequately address.
Innovation Solution
A system and method that employs an averaging sequence to control multi-level converters, avoiding operation at critical duty ratio values by generating pulse-width modulated signals based on error values between measured and reference output voltages, and using dead-band regions to reduce shoot-through paths and voltage spikes, while maintaining output voltage regulation and inductor current symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional control methods are used at critical duty ratio values, then output voltage regulation is achieved, but voltage spikes and transient stress occur across switches
Solution Approach 1:
The control system proactively detects when the duty ratio approaches critical values and preemptively applies dead-band regions or modifies the switching sequence to prevent voltage spikes before they occur. This preliminary anti-action avoids the harmful transient effects while maintaining voltage regulation through alternative control mechanisms.
Solution Approach 2:
The system dynamically adjusts the switching sequence and duty ratio application based on real-time operating conditions. When critical duty ratio values are detected, the control method transitions to an alternative sequence that avoids simultaneous switch transitions, thereby dynamically preventing voltage spikes while maintaining output regulation.
2Object-affected harmful factors
If averaging sequence is used to avoid critical duty ratio values, then voltage spikes are reduced, but control complexity increases
Solution Approach 1:
The control method pre-defines multiple switching sequences and their associated duty ratio applications. The controller is programmed with knowledge of critical duty ratio values and pre-planned alternative sequences, eliminating the need for complex real-time calculations and reducing control implementation complexity.
Solution Approach 2:
The system changes the parameter of duty ratio application by using fractional or averaged duty ratios over multiple switching cycles instead of direct critical values. This parameter transformation allows the system to achieve the desired average duty cycle while avoiding instantaneous critical values that cause voltage spikes.
3Reliability
If dead-band regions are applied to reduce shoot-through paths, then switch stress is reduced, but switching frequency and ripple increase
Solution Approach 1:
The system applies dead-band regions periodically or selectively only when approaching critical duty ratio values, rather than continuously. This periodic application reduces switch stress at critical moments while minimizing the overall impact on switching frequency and ripple, maintaining productivity during non-critical operation.
Data Source
Figure 1
Figure 2A~2C
Figure 2D
AI summary
In various embodiments described in the present disclosure, various methods and systems are introduced, that may reduce and/or eliminate the voltage spikes on the power switches by avoiding operation at zero-ripple duty ratios. In a first aspect, a method for reducing voltage spikes across switches in a multi-level converter is provided, the method comprising: receiving an error value associated with a difference between a measured output voltage and a reference output voltage; determining a target duty cycle value based at least on a control feedback loop adapted to minimize the error value; if the target duty cycle value is equal or approximately equal to one or more critical duty ratio values, controlling the operation of the multi-level converter to operate the multi-level converter with an averaging sequence, the averaging sequence adapted to, on average, result in, or sufficiently approximate, the one or more critical duty ratio values, but not operate at the one or more critical duty ratio values; and generating one or more pulse-width modulated signals to control the operation of the multi-level converter based on at least one of the target duty cycle and the averaging sequence.