Full-Bridge Modular Multilevel Submodule-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.