# Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation
## 3 Solid-State Marx PGs
### Hybrid PGs
The capacitors are charged simultaneously through directing/blocking diodes while at the same time keeping the capacitor charge balance without the need for a sorting algorithm or voltage sensors. An LV DC source voltage is increased through dual boost converters that feed submodules through diodes. Both arm capacitors are charged at the same time, which leads to a reduced charging time and higher repetition capability. However, while the directing/blocking diodes are of the same voltage, they have different currents. The boosting switches have rated voltages equal to the input source voltage. The upper arm generates the positive pulse and the lower arm generates the negative voltage. Only one arm operates at any instant in time, while the other arm is bypassed to provide a closed path for the pulse. For a unipolar pulse operation, the authors suggested replacing one of the arms with a single IGBT switch that can be used to provide a closed path during pulse generation and block reverse conduction during charging. This switch should be capable of blocking input voltage and withstanding the pulse current. To reduce the number of capacitors, the HB submodule is replaced by a full-bridge configuration and a switch is inserted in series with each directing/blocking diode. This modification may reduce the capacitor number; however, it leads to increased switch count and system control complexity. In [109], a two-stage isolated PG system fed from a single LV source was presented. The first stage is an isolated DC-DC converter comprising a full bridge that produces an AC rectangular wave to transmit energy through nanocrystalline-based transformers. The secondary side of the transformer feeds the full-bridge diode rectifier to provide a smooth DC voltage to the cascaded full-bridge modules, which form the second stage and the pulse generator. The load is connected between the terminal at the top full bridge and the terminal at the lowest full bridge. This configuration can provide both unipolar and bipolar pulses, and can generate any shape by inserting and bypassing the cascaded bridges. Another PG topology based on an isolated front-end boosting DC-DC converter fed by a single-leg MMC was presented in [110]. This paper presented a two-stage PG, shown in Figure 24, with parallel-input series-output isolated DC-DC followed by a single-leg MMC converter to shape HV pulses. The isolating transformer utilizes a nanocrystalline core that exhibits low leakage and magnetizing inductances and is suitable for high-frequency operation. The isolated converter comprises an inductor, a switch, a nanocrystalline transformer, two capacitors, and a diode. While the upper arm submodules utilize a two-switch HB configuration, the lower arm uses a switch and diode for the upper and lower devices. The load is connected between the leg midpoint and the leg LV point; therefore, the PG is of a unipolar capability. This generator utilizes a higher number of components by using the diodes and capacitors at secondary sides in addition to the capacitors for the MMC. Based on the capacitance value and the rated voltage, this system would be large and occupy the same volume as the traditional two-stage system (i.e., a cascaded DC-DC boost followed by a cascaded H-Bridge PG). Utilization of MMC presents added value for the work, and a better solution than series-connected switches, although it requires double the number of devices and capacitors. In addition, the submodules of the two arms do not have the same ratings. The operating frequency of the boosting modules and the repetition frequency of the pulse seems to be the same, with the coupling presenting a massive drawback; especially for low repetition frequency, the boosting action would not work properly. However, the author claims that it can be decoupled by setting two different frequencies for the pulse repetition and boosting action. This can be achieved by skipping the boost carrier for many cycles before delivering one pulse. Figure 23: LV half-bridge MMC mimic-based PG topology.