Novel complex waveform generator for evaluation of HVDC station class surge arresters

High-voltage and high-frequency stresses comprising of AC and DC components are encountered across the surge arresters at various nodes in HVDC stations. There is a need to generate these stresses to evaluate surge arresters employed at different locations in the HVDC networks. In the present work, an attempt is made to develop complex waveforms using a novel single-stage DC-AC converter. The presented switched-mode converter is based on a coupled inductor which gives an extra degree of freedom to obtain a higher gain with the modulation in the duty ratio. Fixing the turns ratio of the coupled inductor, the duty ratio is appropriately modulated to generate the complex waveform of high frequency and high amplitude. The proposed converter offers a single-stage solution for DC-AC inversion using pulse width modulation, with fewer components, higher power density, and the ability to generate a frequency of 600 Hz. The detailed converter and controller design analysis is discussed in the present investigation. The breakdown operation of the surge arrester demands a massive short-circuit current from the source side, which may be difficult to obtain if a high-gain amplifier is used without proper protection. The presented switched-mode converter-based approach rectifies the issue of the short-circuit current during the insulator breakdown. A simulation study is performed to validate the circuit for both positive and negative buck-boost regions. Further, a hardware setup is developed to verify the generation of high-frequency and high-voltage complex waveforms. The developed converter could be widely used for insulation evaluation and condition monitoring of various high-voltage equipment.