The DC high-voltage generator achieves the conversion from low voltage to high voltage through high-frequency power electronics technology, and its core principle and topology can be summarized as follows:
1、 Working principle
Rectification and inversion
Input AC power (such as 220V/380V) is rectified and filtered to convert it into DC power, and then converted into high-frequency AC power (usually 30-100kHz) through a full bridge or half bridge inverter circuit composed of IGBT (Insulated Gate Bipolar Transistor). High frequency conversion can significantly reduce the volume of transformers and improve power density.
High voltage boosting and rectification
High frequency AC power is stepped up to several thousand to several hundred kilovolts through an intermediate frequency transformer, and then converted into high DC voltage through a multi-stage silicon stack voltage doubling rectifier circuit (such as the Cockcroft Walton circuit). The voltage doubling circuit achieves voltage multiplication through the principle of capacitor series charging and parallel discharging, while utilizing the unidirectional conductivity of the silicon stack to complete rectification.
Voltage Stability and Feedback Control
Adopting closed-loop feedback control technology, the output voltage is monitored in real time through a voltage sensor and compared with the set value. The error signal is controlled by a PWM (Pulse Width Modulation) controller to adjust the conduction duty cycle of the IGBT, dynamically adjust the output voltage, and ensure stability better than 0.1%. Some devices also introduce a 0.75 times voltage locking function to facilitate the testing of zinc oxide lightning arresters.
2、 Topological structure
Half bridge isolated converter
Composed of two IGBTs, two capacitors, and a transformer. By alternately conducting IGBTs, an alternating voltage is generated on the primary side of the transformer, and the secondary side is rectified by voltage doubling to output high voltage. This structure has low cost and strong resistance to imbalance, but its output power is limited (usually ≤ 700W), making it suitable for small and medium power scenarios.
Full bridge conversion circuit
Using four IGBTs to form an H-bridge, the primary voltage of the transformer is the input DC voltage, and the output power can reach over 2000W. The drive of the full bridge structure is complex, but the voltage resistance requirements of the switch tube are low, which is suitable for high-power requirements (such as power cable voltage resistance tests).
Cascaded voltage doubling circuit
By connecting multiple voltage doubling rectifier units in series, the no-load output voltage can reach 2nUm (where n is the number of stages and Um is the peak AC voltage). Due to voltage drop and fluctuation coefficient limitations, the number of stages usually does not exceed 5, with a maximum output voltage of about 2MV, suitable for ultra-high voltage testing.
3、 Technical advantages
High frequency: increase power density and reduce equipment size.
Modular design: Supports segmented structure, compatible with high and low voltage levels (such as single section 100kV/4mA, two sections 200kV/2mA).
Multiple protection: Integrated overvoltage, overcurrent, zero position closing, disconnection protection, and poor grounding alarm functions to ensure operational safety.
Intelligent control: using microcontrollers or DSPs to achieve parameter display, fault diagnosis, and remote communication, enhancing user experience.