# Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation
## 3 Solid-State Marx PGs
### Hybrid PGs  
Despite MMC advantages, the need for an HV input source is vital in order for normal operation to reach the required voltage levels. Topologies presented in the literature utilize the basic submodules to build a hybrid converter and mitigate the need for HV input. The generator comprises a voltage-boosting converter in the input stage. Other topologies may incorporate boosting and pulse generation in the same submodule as a single-stage PG. In [107], a three-stage pulse generator was presented that is fed from an LV DC source with two boosting stages. The first stage is a boost converter fed from an LV DC sources supplying a second stage comprised of two CDVM modules, which are utilized to boost  
Figure 22: Synergetic pulse generator based on resonant charged voltage adder: (**a**) converter composed of many modulesc and (**b**) circuit composed of a single module. the input voltage to a higher DC voltage level. The third stage is an HB-based MMC that is responsible for shaping the pulse waveform. As the CDVM modules are centrally fed, a virtual midpoint is available which allows the load to be connected between the midpoint of the leg and the midpoint of the two CDVM modules. This converter has the ability to generate both unipolar and bipolar pulses thanks to the way the load is connected. This configuration mitigates the need for a second MMC leg or two capacitor banks to establish a midpoint. In addition, utilizing two front-end boosting stages provides a higher gain ratio with the minimum number of controlled switches, and sensors. Furthermore, the components are of an LV rating and there is no need for series-connected switches or snubber circuits. All of these features lead to reduced weight, size, and cost. The drawbacks of this converter are that, as with any single-leg MMC-operated PG, it can only provide half the DC-link voltage for bipolar pulses, and that the charging energy is not equally distributed over the diodes and capacitors, i.e., the charging currents passing through the CDVM capacitors and diodes are not of the same value. The configuration presented in [93] employs a series connected HB submodule to build a mimic of an MMC arm in which submodules are charged sequentially from an LV DC source. The converter has two additional unidirectional switch banks; one in series with a DC supply to charge the submodules and the reverse voltage blocking capability equals to the pulse peak voltage \(nV_{C}\); the second bank is in parallel with the converter and DC source, this bank operates to deliver the pulse to the load. The author presented two charging schemes: one utilizing external current-limiting impedance in parallel with the load, and one utilizing the load impedance as a current limiter. The second scheme theoretically seems economical and reduces system size. However, it is not practically suitable for most applications, and may work only for water treatment, as an electroporation-based application must limit the thermal effect on the treated medium below a certain limit [7]. This configuration has two challenges: first, a long charging time, which means a lower pulse repetition rate, and second, that it generates only unipolar pulses, which can be mitigated by a second-stage HV H-bridge converter, though at increased cost and size. The authors mitigated the monopolar pulse limitation and introduced [108], in which they utilized a full-bridge instead of an HB submodule. An HV thyristor with pulse peak voltage blocking capability was used to bypass the load during the charging time. The authors claimed that the using a single thyristor is better, as it provides HV blocking capability; nonetheless, it is slow and reduces the repetition rate, much the same as the sequential charging method. Another configuration presented in [29] (shown in Figure 23) mimics a Marx generator with regard to charging and pulse generation. This configuration utilizes an HB submodule to initiate two identical arms.