# Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation
## 3 Solid-State Marx PGs
### Modular PGs
need for an HV source, another enhancement was presented in [102; 103]; the circuit is shown in Figure 20. This converter is supplied by an LV source, and the capacitors are charged sequentially through a current-limiting inductor to reduce power losses. The generator is configured as an H-bridge shape; one leg comprises two arms of cascaded HB submodules and the other leg comprises two arms, each built using a switch in series with series-connected reverse blocking diodes that prevent reverse voltage during the pulse generation state. The arms are composed of submodules, with certain arms responsible for generating the uni/bipolar pulses and other switch-diode arms providing the charging current path. The switches should be able to withstand the source voltage \(V_{dc}\), while the diodes need to block \(V_{dc}(n-1)\), where \(n\) is the number of submodules per arm. As in the previous modification, this converter maintains zero current and voltage switching and does not utilize voltage sensors. Despite the introduced LV charging feature, the minimum pulse duration is increased, and depends on the number of modules and capacitor charging time constant. Figure 19: Different submodule configurations: half-bridge and full-bridge. Figure 20: Sequentially charged MMC submodule-based PG. II. Cascaded H-Bridge PGs  
H-Bridge modules present a complicated version of the HB submodule with twice the number of semiconductor devices, control signals, and gate drivers. However, the H-bridge can provide bipolar pulses and can block any fault current by generating opposite polarity. In [73], the H-bridge circuit was used as the basic building cell for a versatile multilevel converter intended for use in electroporation-based cancer treatment. Instead of supplying the whole converter using a single HV source, as in MMC, the cascaded H-bridge converter requires many isolated DC sources equal to the number of modules. This can increase the size and cost of the converter if isolation is achieved with a low-frequency transformer. To mitigate these cons, the authors utilized a high-frequency resonant inverter supplying high-frequency transformers, with the series connection of primary sides and each secondary side isolated to deliver the energy to a single H-bridge module capacitor. III. Voltage Adder PGs  
A voltage adder generator is presented in Figure 21. Such a generator is formed by cascaded connected modules, with each module utilizing an isolating transformer to supply power to the module to charge the capacitor [104; 105]. The module consists of an AC-DC rectifier, a capacitor \(C_{x}\), a diode \(D_{x}\), and a switch \(S_{x}\). Capacitors are charged independently through the module transformer and diode and discharged through switches that provide the series connection of capacitors to form the pulse and deliver it to the load. This topology utilizes the same module power rating, which mitigates the drawbacks of Marx generators. In addition, different pulse waveforms can be generated by switching modules on and off to shape the pulse. The use of an isolating transformer makes it easier to provide a floating power supply to drive the switch by embedding auxiliary winding into the transformer. Synergetic pulses (HV short pulses and LV long pulses) can enlarge the tissue ablation area and enhance the overall electroporation process; therefore, in [106], a voltage adder-based PG was presented (shown in Figure 22) with the ability to generate synergetic pulses without the need for any changes to the system hardware. This PG comprises a single-input LV source and a high-frequency resonant inverter to transmit the energy to the modules. Voltage adder modules comprise a pair of each of the following: magnetic rings, storage capacitor, diode rectifier, bypass diode, and switch. The number of secondary turns on the  
Figure 21: Solid-state voltage adder topology-based PG. magnetic rings is different for HV and LV capacitor charging circuits. These systems can generate long and short pulses in the same cycle.