The introduction highlights the growing use of MOSFETs and IGBTs in power electronics, along with soft switching technologies, which have led to higher switching frequencies and more compact designs. However, this advancement has also introduced challenges such as parasitic components and increased electromagnetic interference (EMI). As a result, EMI has become a major concern for the industry.
Conducted interference is a key way that noise propagates in power electronics. It mainly occurs in two forms: differential mode and common mode interference. In most cases, common mode interference dominates. This paper presents a passive common mode suppression technique based on the compensation principle, successfully applied across various power converter topologies. Both theoretical analysis and experimental results confirm its effectiveness in reducing high-frequency conducted common mode interference. The advantage of this method is that it does not require additional control circuits or auxiliary power supplies, making it simple and compact.
The compensation principle works by detecting the dV/dt of the switching device and generating an inverted current through a compensation capacitor. This current cancels out the original noise current, effectively reducing the common mode voltage seen at the LISN resistor. The application of this technique in a single-ended flyback circuit demonstrates its practicality. An additional winding is added to the transformer core to generate the necessary compensation current, which is carefully sized based on the parasitic capacitance and winding turns ratio.
Experiments were conducted using a 5kW/50Hz marine inverter’s auxiliary power supply. The setup included a LISN, rectifier bridge, and flyback circuit. A 100pF ceramic capacitor was used as the compensation capacitor. Measurements showed a significant reduction in common mode current, with a peak suppression of about 14 mA. While some high-frequency noise remained, the overall performance was promising.
However, there are limitations. High input inductance and transformer leakage inductance can reduce the effectiveness of the compensation circuit. To address these issues, input capacitors should be optimized, and winding techniques can help minimize leakage inductance.
In conclusion, the proposed passive common mode noise suppression technique offers a practical and cost-effective solution for reducing EMI in power converters. Its simplicity and compatibility with existing structures make it a viable option for future applications.
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