Design of a cascaded H-bridge converter for insulation testing

This paper describes a design of a cascaded H-bridge converter for insulation testing of the crosslinked polyethylene (XLPE) cable. This high voltage generator produces a sinusoidal waveform at a very low frequency (VLF) of 0.1 Hz. The design of the cascaded H-bridge converter consists of two main parts, a modulation unit and a switching unit. The modulation unit compares the 0.1 Hz reference sinusoidal waveform with the 10 kHz of carrier waveform. The switching unit consists of 6 H-bridge modules using phase disposition (PD) multicarrier modulation scheme to generate 13 levels of PWM signals. The cascaded H-bridge converter can covert the high voltage direct current (HVDC) to multilevel step-pulse signals and change to the sinusoidal waveform at 0.1 Hz by the low-pass filter. The use of multilevel H-bridge converter helps reduce the total harmonic distortion (THD) from single level H-bridge converters. The experimental results show that the THD value is less than 5% complied to the IEEE 400.2 standards.