In recent years, the increasing use of MOSFETs and IGBTs, along with soft switching technologies, has significantly raised the switching frequencies in power electronic circuits. This advancement has led to more compact designs, but it also introduces new challenges such as the effects of parasitic components and increased electromagnetic interference (EMI). As a result, EMI has become one of the most critical concerns in the power electronics industry.
Conducted interference is a primary method through which noise propagates in power electronics. Among the different types, differential mode and common mode interference are the most prevalent. In most cases, the conducted interference in power converters is dominated by common mode noise. This paper presents a passive common mode interference suppression technique based on the compensation principle and successfully applies it to various power converter topologies. Both theoretical analysis and experimental results confirm that this approach effectively reduces high-frequency common mode conducted interference. The advantage of this method lies in its simplicity—no additional control circuits or auxiliary power supplies are required, and it does not rely on other parts of the power converter. Its compact structure makes it highly suitable for practical applications.
The compensation principle relies on the fact that common mode noise arises from the interaction between the high dV/dt of the switching device and parasitic capacitances. As shown in Figure 1, the common mode current includes a displacement current that flows into the ground plane. The dV/dt at the switching device’s terminal is particularly high, causing a common mode current to flow through the parasitic capacitance between the device and the heat sink. The proposed suppression circuit detects this dV/dt, inverts it, and feeds it into a compensation capacitor, generating a current that cancels out the original noise current. These two currents are equal in magnitude but 180 degrees out of phase, resulting in their cancellation at the ground point according to Kirchhoff’s current law. This leads to a significant reduction in the common mode voltage measured on the LISN resistor.
This technique was applied to a single-ended flyback converter as a case study. A new common-mode noise suppression circuit was added to the existing transformer structure. An additional winding, NC, was introduced, allowing the compensation capacitor to generate an inverted current that counteracts the parasitic noise. The size of the compensation capacitor depends on the parasitic capacitance and the turns ratio of the windings. If the ratio is 1:1, the capacitance value matches the parasitic capacitance; otherwise, it is adjusted accordingly.
The experiment used a 5kW/50Hz marine inverter’s auxiliary power supply as a test platform. The AC input passed through a LISN, then into a rectifier bridge, and finally into the flyback circuit. Measurements showed that the compensation circuit effectively reduced the common mode current. However, some high-frequency components remained due to the influence of distributed parameters at higher frequencies. Adjusting the compensation capacitor to better match the parasitic capacitance could further improve performance.
Despite its advantages, this technology has limitations. For example, if the input capacitor has a large equivalent series inductance, it can limit the effectiveness of the compensation circuit. Similarly, increased leakage inductance in the transformer can cause waveform distortion, reducing the suppression capability. To address these issues, reducing the input capacitor's inductance and improving the winding design can help minimize leakage inductance.
In conclusion, the passive common mode noise suppression technique based on the compensation principle demonstrates promising results in reducing EMI in power converters. It offers a simple, cost-effective solution that can be easily integrated into existing designs. With proper optimization, it can significantly enhance the performance and reliability of power electronic systems.
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