Multi-Carrier Modulation for Switch-Mode Power Circuit EMI Reduction
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Solution Overview
Problem
Switch-mode power circuits generate broad band spectral components that disturb other electronic equipment, leading to the need for bulky, expensive, and dissipative filter components and challenging shielding implementations due to high voltage and current levels, resulting in design trade-offs between thermal and electrical isolation.
Innovation Solution
The use of multi-carrier modulation (MCM) with at least two carriers of different frequencies, combined using OR or AND operations, to create a control signal for switch-mode power circuits, which reduces high frequency signal content and allows for the utilization of out-of-band intermodulation frequencies, thereby minimizing interference with communication systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional single-carrier PWM is used, then switching control is simple, but high frequency spectral components cause electromagnetic interference requiring bulky filters and shielding
Solution Approach 1:
The single carrier signal is segmented into multiple carrier signals with different frequencies. Each carrier signal processes the input signal independently through separate signal processing units, and the results are combined. This segmentation distributes the spectral energy across multiple frequency bands, reducing peak spectral components and electromagnetic interference.
Solution Approach 2:
Multiple processed signal streams from different carrier frequencies are merged together in the combiner unit to form the final control signal. This merging combines the benefits of multiple frequency distributions while maintaining the switching control functionality, effectively reducing electromagnetic interference without sacrificing control performance.
2Object-affected harmful factors
If filter components are added to reduce high frequency content, then electromagnetic interference decreases, but the circuit becomes bulky, expensive and dissipative
Solution Approach 1:
Instead of using filters to remove high frequency content, the invention converts the harmful high frequency spectral concentration into beneficial distributed spectral content across multiple carrier frequencies. The multi-carrier modulation inherently spreads the energy spectrum, transforming the potential harm of high frequency content into a beneficial distribution that reduces peak spectral components without requiring energy-dissipative filter components.
3Object-affected harmful factors
If shielding is implemented to block electromagnetic interference, then interference with communication systems reduces, but mechanical complexity and thermal management become difficult
Solution Approach 1:
Instead of blocking electromagnetic interference with shielding after it is generated, the invention inverts the approach by preventing the generation of harmful spectral components in the first place. Through multi-carrier modulation, the spectral energy is distributed across multiple frequency bands, avoiding concentration at frequencies that would interfere with communication systems, thus eliminating the need for complex shielding structures.
4Object-affected harmful factors
If multi-carrier modulation is used, then high frequency peaks and spectral components are reduced, but signal processing complexity increases
Solution Approach 1:
The signal processing is segmented into multiple independent parallel units, each handling one carrier frequency. This segmentation allows each processing unit to be relatively simple while the collective system achieves spectral distribution. The parallel architecture maintains simplicity at the component level while achieving the overall goal of reducing spectral components.
Data Source
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AI summary
A switch-mode power circuit is disclosed herein that comprises a controllable element that controls a current in response to a control signal supplied to the controllable element; and a control unit connected to the controllable element and providing the control signal. The control unit comprises: a first signal processing unit having an output and being supplied with a first carrier signal and an input signal; a second signal processing unit having an output and being supplied with a second carrier signal and the input signal; and a combiner unit connected to the first and second signal processing units combining the outputs of the first and second signal processing units to form a signal representative of the control signal.