Parallel Power Converter Switching Delay for Circulating Current Control
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Solution Overview
Problem
In power converters with parallel units, mismatched switching actions create circulating currents and short circuits, leading to poor system performance, and adding AC filter inductors increases weight and bulkiness, which is undesirable for weight-critical applications.
Innovation Solution
A method to reduce circulating currents by adjusting the switching delay of semiconductor switches in parallel power converter units, using a single controller to synchronize switching actions and detect short-circuits by analyzing phase currents for characteristic frequencies, and implementing a delay compensating circuit to minimize overlapping times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If AC filter inductors are added to reduce circulating current, then circulating current is reduced, but weight and bulkiness increase
Solution Approach 1:
The patent changes the timing parameter (switching delay) of the power converter units to synchronize their switching actions. By adjusting the delay time of switching signals, the patent eliminates the root cause of circulating current (mismatched switching) without adding physical components like inductors, thus reducing weight while solving the harmful current issue.
Solution Approach 2:
The patent applies preliminary synchronization actions by pre-adjusting the switching delays before the power converter units operate in parallel. The controller pre-calculates and applies the appropriate delay values to ensure that switching actions are synchronized from the start, preventing circulating current formation rather than correcting it after occurrence.
2Object-generated harmful factors
If AC filter inductors are added to reduce circulating current, then circulating current is reduced, but device size increases
Solution Approach 1:
The patent changes the timing parameter (switching delay) of the power converter units to synchronize their switching actions. By adjusting the delay time of switching signals, the patent eliminates the root cause of circulating current (mismatched switching) without adding physical components like inductors, thus reducing volume while solving the harmful current issue.
Solution Approach 2:
The patent replaces the mechanical/electrical solution (AC filter inductors) with a control-based solution (switching delay adjustment). Instead of using physical passive components to filter and block circulating currents, the patent uses active control of switching timing to prevent their generation, achieving the same goal with reduced size.
3Object-generated harmful factors
If switching delay is adjusted to synchronize switching actions, then circulating current is reduced, but control complexity increases
Solution Approach 1:
The patent employs feedback mechanisms where the controller monitors the operation status of parallel power converter units and automatically adjusts switching delays accordingly. This closed-loop control ensures synchronization while minimizing circulating current, and the complexity is managed through automated algorithms rather than manual configuration.
Solution Approach 2:
The controller performs multiple functions: it generates switching signals, monitors operational status, detects short circuits, and adjusts switching delays for synchronization. By consolidating these functions into a single multi-functional controller, the patent reduces overall system complexity compared to having separate dedicated circuits for each function.
Data Source
AI summary
A method for reducing a circulating current in a power converter includes: for each phase current provided by the power converter: determining a characteristic frequency in the respective phase current, wherein the characteristic frequency is a switching frequency of the switching units of commutation cells of the power converter or related to the switching frequency. The method further includes: determining a magnitude of the characteristic frequency; comparing the magnitude of the characteristic frequency with a predetermined magnitude; and, when the magnitude is larger than the predetermined magnitude, adding or reducing in steps a switching delay to a top or bottom switching unit of a commutation cell of a first power converter unit of the power converter until the magnitude of the characteristic frequency is equal to or below the predetermined magnitude.