Multi-State Deadtime for Multi-Level Power Converter Voltage Overshoot
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Solution Overview
Problem
Multi-level power converters in wind turbines experience voltage overshoots due to parasitic inductance, leading to device damage, increased losses, and reduced efficiency, which existing solutions like soft switching and snubber circuits attempt to mitigate but at the cost of slower switching speeds and higher costs.
Innovation Solution
Implementing a double transition deadtime in a multi-level power converter, where inner and outer switching devices operate differently during state transitions, with inner devices turning off while maintaining an alternate current path through outer devices, and both turning on simultaneously during midpoint to positive/negative voltage transitions, to reduce voltage overshoots and ensure safe commutation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft switching and snubber circuits are used to reduce voltage overshoots, then device reliability is improved, but switching speed decreases and system cost increases
Solution Approach 1:
The patent applies dynamics by making the deadtime duration variable rather than fixed. The control system dynamically adjusts the deadtime based on the instantaneous current direction and magnitude, selecting from multiple predefined deadtime values. This dynamic adaptation allows the system to maintain fast switching when possible while providing extended protection only when necessary, thus improving reliability without permanently sacrificing switching speed.
Solution Approach 2:
The patent changes the parameter of deadtime duration from a constant value to a variable parameter with multiple discrete states. By implementing a multi-level deadtime mechanism where the duration is selected based on operating conditions (current direction and magnitude), the system can optimize between protection and performance, avoiding the need for slow soft-switching circuits or expensive snubbers.
2Reliability
If deadtime is extended to reduce voltage overshoots, then device reliability is improved, but productivity decreases due to longer transition times
Solution Approach 1:
The system dynamically selects deadtime duration based on real-time operating conditions. When current magnitude is low or direction favors safe commutation, a shorter deadtime is applied, minimizing impact on productivity. When current magnitude is high or conditions require extended protection, a longer deadtime is selectively applied, ensuring reliability without unnecessarily sacrificing productivity during normal operation.
Solution Approach 2:
The patent applies partial action by providing extended deadtime protection only when and where needed, rather than applying maximum protection continuously. The multi-level deadtime mechanism applies extended durations selectively based on instantaneous conditions, achieving sufficient reliability protection without the continuous productivity penalty that would result from always using the maximum deadtime value.
3Device complexity
If uniform deadtime is applied to all switching devices, then control simplicity is maintained, but voltage overshoots on inner devices increase
Solution Approach 1:
The patent applies local quality by differentiating the deadtime treatment for inner versus outer switching devices. Inner devices, which are more susceptible to voltage overshoots due to their position in the circuit topology, receive extended deadtime protection when needed. Outer devices follow standard commutation timing. This localized differentiation protects vulnerable inner devices without unnecessarily complicating the control of the entire system or affecting outer device performance.
Solution Approach 2:
The system changes the deadtime parameter from a uniform value applied to all devices to a differentiated set of values based on device position (inner vs. outer) and instantaneous operating conditions. This parameter differentiation allows the control system to maintain relative simplicity while effectively addressing the specific vulnerability of inner devices to voltage overshoots.
Data Source
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AI summary
A method for operating a multi-level bridge power converter of an electrical power system connected to a power grid includes providing a plurality of switching devices of the power converter in one of a neutral point clamped topology or an active neutral point clamped topology, the plurality of switching devices including a first group and a second group of switching devices. The method also includes providing a multi-state deadtime for the first and second groups of switching devices that changes based on different state transitions of the power converter. Further, the method includes operating the first and second groups of switching devices according to the multi-state deadtime to allow the first group to switch differently than the second group during the different state transitions, thereby decreasing voltage overshoots on the first group during one or more of the different state transitions and providing safe transition between commutation states of the power converter.