Low Voltage Ripple Technology for Electron Beam Additive Power Supply

1. Introduction
In the electron beam additive manufacturing process, the energy stability of the electron beam directly determines the molten pool temperature, cladding layer uniformity, and mechanical properties of the printed part. The electron beam energy is controlled by the output voltage of the high-voltage power supply. Voltage ripple will cause fluctuations in the electron beam energy, which in turn leads to defects such as unstable molten pool shape, cracks, or pores in the printed part. Due to the imperfect design of the filtering link and weak load disturbance suppression capability, the output voltage ripple coefficient of the traditional electron beam additive power supply is usually between 1% and 2%, which is difficult to meet the strict requirement of a ripple coefficient ≤0.5% for high-precision additive manufacturing (such as aerospace precision parts). Therefore, the development of low voltage ripple technology to reduce the output ripple of the electron beam additive power supply has important engineering significance for improving the quality of additive manufacturing.
2. Generation Mechanism and Suppression Difficulties of Voltage Ripple
(1) Ripple Generation Mechanism
The voltage ripple of the electron beam additive power supply mainly comes from three aspects:
1.Input-side ripple: The power supply input is usually AC mains power. After rectification and filtering, there is still low-frequency ripple (frequency 100Hz, corresponding to twice the 50Hz mains frequency). If the filtering is not thorough, it will be transmitted to the high-voltage output terminal;
1.Switching link ripple: The main circuit of the power supply adopts a high-frequency switching topology (such as phase-shifted full-bridge, LLC resonant topology). High-frequency ripple (frequency consistent with the switching frequency, usually 20kHz~100kHz) is generated during the turn-on and turn-off of the switching tube;
1.Load disturbance ripple: During the electron beam additive process, the load (molten pool) impedance changes dynamically with the printing material, layer thickness, and scanning speed, leading to fluctuations in the output current and thus causing voltage ripple (frequency is not fixed, usually 1Hz~10kHz).
(2) Suppression Difficulties
1.Multi-frequency ripple superposition: Low-frequency ripple (100Hz), high-frequency ripple (20kHz~100kHz), and load disturbance ripple (1Hz~10kHz) are superimposed. Traditional single filtering methods (such as capacitor filtering, inductor filtering) are difficult to suppress multi-frequency ripple at the same time;
1.High-voltage scenario limitations: The output voltage of the electron beam additive power supply is high (usually 30kV~80kV). High-voltage filter capacitors have small capacity and inductors have large volume, so the filtering effect is limited;
1.Balance between dynamic response and ripple suppression: To suppress load disturbance ripple, it is necessary to improve the dynamic response speed of the power supply, but fast response may increase the switching ripple, and there is a contradiction between the two.
3. Key Technologies for Low Voltage Ripple
(1) Multi-Level Composite Filtering Technology
Aiming at the problem of multi-frequency ripple superposition, a multi-level composite filtering structure of "input-side low-frequency filtering + middle-side high-frequency filtering + output-side high-voltage filtering" is adopted to realize full-frequency ripple suppression.
1.Input-side low-frequency filtering: An LC filter circuit is used. The inductor is a low-frequency ferrite inductor (inductance 10mH), and the capacitor is a large-capacity aluminum electrolytic capacitor (capacity 2200μF) to suppress 100Hz low-frequency ripple, reducing the input-side ripple coefficient to below 0.5%;
1.Middle-side high-frequency filtering: An LLC resonant filter circuit is set between the main power circuit and the high-voltage conversion link. Using the frequency selection characteristics of the LLC resonant topology, the ripple at the switching frequency (such as 50kHz) is resonantly absorbed. At the same time, through the synergistic effect of the resonant in