Common-Bus Converter Switching Phase Control for Harmonic Reduction
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Solution Overview
Problem
In vehicle propulsion systems, multiple inverters or converters connected to a common bus experience inefficiencies due to common switching frequencies leading to increased root mean square (RMS) current and ripple current, which results in harmonic distortion and requires larger, more costly DC link filter capacitors.
Innovation Solution
A controller circuit adjusts the switching frequency and phase of individual converters connected to a common bus, applying frequency shifts and phase shifts to reduce the RMS and ripple current components, thereby minimizing harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If multiple converters are driven with a common switching frequency, then the system operation is simplified, but the ripple current and harmonic distortion increase
Solution Approach 1:
The patent applies parameter changes by varying the switching frequencies of multiple converters instead of using a common frequency. Each converter is assigned a slightly different switching frequency, which causes the ripple current components to be distributed across different frequencies rather than adding constructively at a single frequency. This reduces the peak ripple current magnitude and harmonic distortion while maintaining simplified system operation.
2Device complexity
If a common switching frequency is used for all converters, then the control system is simpler, but the RMS current and ripple current increase requiring larger filter capacitors
Solution Approach 1:
The patent changes the frequency parameter of each converter to be slightly different from the others. This frequency diversification causes the ripple current spectral components to spread across a broader frequency range rather than concentrating at a single frequency. As a result, the RMS current is reduced and the required filter capacitor size is minimized, while the control system remains relatively simple through centralized frequency management.
3Stability of the object's composition
If converters operate at the same switching frequency, then synchronization is easier, but the ripple current components add constructively increasing harmonic distortion
Solution Approach 1:
The patent introduces slight variations in the switching frequency parameter among converters while maintaining their overall synchronization. This frequency diversification prevents the ripple current components from adding constructively at the same frequency, thereby reducing harmonic distortion. The converters remain synchronized in their operational rhythm but operate at slightly different frequencies, achieving a balance between synchronization ease and harmonic reduction.
Data Source
AI summary
A system is provided that may include plural converters that are connected to a common bus. Each of the converters may be configured to convert an alternating current (AC) through the common bus to a direct current (DC) by alternating switches of each of the plural converters between open and closed states in a switching cycle. The system may also include a controller circuit that may be configured to adjust the AC conducted onto the common bus to the plural converters so that a root mean square of a ripple current component of the AC meets one or more designated criteria.