Power Converter Switching Delays for Common-Mode Current Reduction
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Solution Overview
Problem
Contemporary power converters generate excessive common-mode (CM) currents and voltages, leading to electromagnetic interference (EMI) and challenges in meeting electromagnetic compatibility (EMC) requirements, particularly in heavy-duty vehicles with multiple sources and loads connected to a traction voltage system.
Innovation Solution
Introduce an inter-phase delay in the switching of AC phases within the power converter to avoid simultaneous switching between DC rails, using a space vector modulation (SVM)-type control scheme, which allows for the synthesis of a zero output AC voltage vector while spreading switching transients in time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filters (pole-chassis capacitances, Y-capacitances, filter capacitances) are used to reduce CM currents, then electromagnetic compatibility (EMC) requirements are improved, but cost, weight and volume increase
Solution Approach 1:
The patent extracts and eliminates the need for additional filter components (pole-chassis capacitances, Y-capacitances, filter capacitances) by implementing a control strategy that inherently reduces CM currents through modified switching sequences, thereby removing the source of EMI without adding filtering hardware
Solution Approach 2:
The patent changes the switching parameters and sequences of the power converter by introducing inter-phase delays and modifying the timing of switching events, which transforms the spectral characteristics of CM currents to reduce their magnitude without requiring additional filtering components
2Object-affected harmful factors
If filters (pole-chassis capacitances, Y-capacitances, filter capacitances) are used to reduce CM currents, then electromagnetic compatibility (EMC) requirements are improved, but device complexity increases
Solution Approach 1:
The patent removes the need for complex filtering hardware (multiple capacitor types and configurations) by implementing a simpler control-based solution that modifies switching sequences to inherently reduce CM currents
Solution Approach 2:
The patent replaces the mechanical/hardware-based filtering approach (physical filters with capacitors and inductors) with a control-theory-based approach that uses modified switching sequences and inter-phase delays to achieve the same EMI reduction effect
3Productivity
If simultaneous switching of all AC phases is performed, then productivity is improved, but common-mode currents increase causing electromagnetic interference
Solution Approach 1:
The patent segments the simultaneous switching event into sequential switching events with inter-phase delays, dividing the switching process across different time intervals to prevent the constructive addition of CM currents while maintaining overall switching productivity
Solution Approach 2:
The patent introduces periodic inter-phase delays in the switching sequence, creating a rhythmic pattern where phases are switched at staggered intervals, which transforms the CM current spectrum to reduce peak magnitudes while maintaining the periodic nature of power conversion operation
Data Source
Figure 1~2A
Figure 2B~3
Figure 4~5
AI summary
A computer system is provided, including processing circuitry configured to control a switching (800) of a plurality of switching elements of an electric power converter to synthesize an output alternating current (AC) voltage vector. For each AC phase of a plurality of AC phases (u, v, w), the converter is configured to switch the AC phase between being either connected to a first or to a second DC rail. In response to a demand for synthesizing a zero output AC voltage vector, an inter-phase delay (d1-4) is introduced between switching of each AC phase to avoid simultaneous switching of all AC phases from the first DC rail to the second DC rail or vice versa during a same switching period, in order to reduce common mode (CM) voltage and current. A corresponding electric power converter, electric vehicle, computer-implemented method, computer program/storage medium are also provided.