What phenomena does core saturation in an Inverter Transformer cause?

Phenomena caused by core saturation in an Inverter Transformer

Core saturation refers to the phenomenon where the magnetic flux density of the core material reaches its limit, and the flux can no longer be increased linearly. For Inverter Transformers, core saturation can lead to a series of serious electrical faults and performance degradation:

Voltage waveform distortion and jitter

Voltage jitter: Core saturation causes a sharp decrease in the impedance of the core to the external magnetic field, resulting in significant distortion of the primary voltage. The output voltage waveform will change from an ideal sine wave or square wave to a distorted waveform with "broken lines" or "spiks." This phenomenon is commonly referred to as "voltage jitter" or "voltage bounce." In severe cases, it may cause the inverter output voltage to exceed the safe range.

Increased Current Peaks and Noise

Current spikes and surges in magnetic saturation current: After the core enters the saturation region, the induced electromotive force cannot effectively limit the increase in current, resulting in spikes in the excitation current waveform. This current distortion not only increases the system's electromagnetic interference (EMI) but can also damage switching devices due to excessive current.

Magnetism Bias and Efficiency Decrease

Magnetic flux asymmetry caused by magnetism bias: In a full-bridge converter structure, core saturation is often accompanied by magnetism bias (magnetism bias refers to the offset of the center point of the core's working hysteresis loop). Magnetism bias leads to inconsistent positive and negative pulse voltage widths, further exacerbating the nonlinear distortion of the core. Without effective anti-magnetism measures (such as a primary-side series capacitor), the core will not be able to recover to its initial flux state in each cycle, resulting in a sharp drop in efficiency.

 Equipment Failure and Overvoltage Risk

Overvoltage risk: When the core is saturated, the induced electromotive force on the primary side decreases significantly, while the secondary-side inductance remains relatively constant, potentially causing extremely high voltage spikes at the moment of turn-off. Such overvoltage surges can penetrate the insulation layer, damage the transformer itself, and even lead to catastrophic failures of the entire inverter system.