This paper analyses different design trade-offs for a Modular Multilevel Converter (MMC)-based Arbitrary Wave shape Generator (AWG) used for High Voltage (HV) testing and certification of grid assets such as transformers, switchgear, and cables. Modulation techniques, number of submodules, output voltage levels, arm inductance, and series damping resistance play an essential role in obtaining different waveforms with good quality. Phase-Shift Carrier (PSC) modulation technique proves to be a superior modulation technique for different periodic waveforms over Nearest Level Control (NLC), even when a large number of submodules is considered. With the traditional second-order filter design strategy, proper values of the arm inductance and series resistance can be selected, guaranteeing a good quality of the generated voltage waveforms to verify different dielectric properties of grid-assets. The design of such an AWG is demonstrated with the simulations in MATLAB-Simulink.

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This paper presents a comparison in Partial Discharge (PD) behaviour when an air corona setup is subjected to different waveforms, namely an idealized 50 Hz sinusoidal and staircase-based sinusoidal waveforms near inception voltage and at a higher voltage. In this study, it has been observed that the PD repetition rate and the Phase-Resolved PD (PRPD) pattern with the staircase waveform better resemble that of a pure sinusoidal waveform if the number of voltage levels of the staircase waveform is sufficiently increased. When observed more closely at the PRPD pattern near inception voltage, PDs tend to occur near the slope of the staircase waveform, even when the step voltage is small.

SiC MOSFETs have become more and more popular in recent years. Apart from its superior performance, attentions should be paid to its driving method. In this paper, an improved transformer driving circuit is proposed which can provide an almost constant negative turn-off voltage within a wide dutycycle range. Both simulation and experimental results are given to verify the effectiveness of this method.

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