Synchronizing Rectifier and Inverter Switching to Reduce Common-Mode Current
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Solution Overview
Problem
Conventional methods for reducing common mode voltage and current in power converters are insufficient, as they either fail to adequately decrease the common mode current or voltage, leading to inefficiencies and increased costs due to larger filter sizes.
Innovation Solution
A control method that synchronizes the switching operations of the rectifier stage and inverter stage in a power converter, ensuring that potential variations applied to input phases correspond to potential variations of the same sign on output phases, thereby compensating for common mode voltage generated by one stage with the other, using pulse width modulation to achieve this synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the chopping frequency applied to the inverter stage is increased, then the power conversion efficiency is improved, but the common mode current increases due to increased dv/dt variations
Solution Approach 1:
The patent merges the control of the rectifier stage and inverter stage by synchronizing their switching operations. The switching commands are generated based on a common reference signal, ensuring that switching events in both stages are coordinated to reduce common mode voltage variations while maintaining high chopping frequency for efficient power conversion.
Solution Approach 2:
The patent changes the timing parameters of switching operations in both stages. By adjusting the switching instants and durations based on synchronized control signals, the dv/dt variations are reduced without compromising the chopping frequency, thereby maintaining power conversion efficiency while reducing common mode current.
2Device complexity
If conventional synchronization methods are used to reduce common mode current, then the filter size can be reduced, but the common mode current is not sufficiently reduced
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing the switching operations before the common mode current problem manifests. The control system proactively coordinates the switching instants of both stages based on predicted voltage variations, preventing excessive common mode current generation at its source rather than merely filtering it afterward.
Solution Approach 2:
The patent converts the potentially harmful effect of switching operations into a beneficial synchronized pattern. By coordinating the switching events of the rectifier and inverter stages, the individual harmful dv/dt variations are transformed into a unified switching pattern that minimizes overall common mode voltage fluctuations, turning the switching action itself into a solution rather than just a problem source.
Data Source
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AI summary
The invention relates to a method and control system for reducing the common-mode current in a power converter comprising a rectifier stage (1, 1') connected to several input phases (R, S, T) and an inverter stage (2, 2') connected to several output phases (U, V, W). During each switching period, the rectifier stage (1, 1') and the inverter stage (2, 2') are controlled synchronously such that a potential variation applied to an input phase (R, S, T) always corresponds to a potential variation of the same sign applied to an output phase (U, V, W).