Full-bridge modular multilevel sub-module based high-voltage bipolar pulse generator with low voltage DC input for pulsed electric field applications

High voltage (HV) pulse generators (PGs) are the core of pulsed electric field applications. Applying HV pulses produces electrical pores in a biological cell membrane, in which if the size of the pores increases beyond a critical size, the cell will not survive. This paper proposes a new HV-PG, based on the modular multilevel converter with full-bridge sub-modules (FB-SMs). In order to alleviate the need of complicated sensorless or sensor based voltage balancing techniques for the FB-SM capacitors, a dedicated self-regulating charging circuit is connected across each FB-SM capacitor. The individual capacitor charging voltage-level is obtained from three successive stages namely: convert the low-voltage DC input voltage to a high-frequency square AC voltage; increase the AC voltage-level via a nano-crystalline step-up transformer; and rectify the secondary transformer AC voltage via a diode full-bridge rectifier. The HV bipolar pulses are formed across the load in a fourth stage through series connected FB-SMs. The flexibility of inserting and bypassing the FB-SM capacitors, allows the proposed topology to generate different pulse-waveform shapes, including rectangular waveforms with specifically reduced dv/dt and ramp pulses. The practical results, from a scaled down experimental rig with five FB-SMs and a 1kV peak to peak pulse output, validate the proposed topology.