# State-of-the-Art DC-DC Converters for Satellite Applications: A Comprehensive Review
## 3 Review of DC-DC Converters for Satellites
### DC-DC Converters for Electric Propulsion  
The PPU of the EP unit uses a highly efficient, isolated converter for voltage conversion. The topology selection depends on the type of satellite and the thruster. For small satellites, the pulsed plasma thruster (PPT) is a preferable choice [116; 117; 118]. It stores and discharges energy in the form of short pulses through a pair of electrodes. The energy storage function in PPTs is achieved using capacitor banks, and a DC-DC converter is used to charge and discharge the capacitor. The small satellite's input voltage is minimal, but the PPT thruster needs a very high DC output voltage. Therefore, to attain such high gain, a high-voltage, low-power DC-DC converter is needed. Moreover, the instantaneous release of energy from the capacitor into the thruster creates large reverse voltages, which may damage the sensitive electronic components. Thus, isolated DC-DC converters are the preferred  
Figure 18: (**a**) Non-isolated PWM TPC. (**b**) Two-switch forward with integrated buck converter. \begin{table}
\begin{tabular}{l l l l l l l l l l l} \hline \hline
**Converter** & **References** & \begin{tabular}{l} **Switching** \\ **Frequency (kHz)** \\ \end{tabular} & \begin{tabular}{l} **Component** **Count** \\ **S** \\ \end{tabular} & \begin{tabular}{l} **Power (W)** \\ **L** \\ \end{tabular} & \
\begin{tabular}{l} **Isolated/Non-Isolated** \\ **C** \\ \end{tabular} &
\begin{tabular}{l} **Main Features** \\ \end{tabular} \\ \hline Three-port modified & & & & & & & & & & & & Soft switching duration/ \\ half-bridge converter & [38] & - & 5 & 1 & 2 & 3 & 200 & Isolated & & & & \\ [Figure 17b] & & & & & & & & & & & & & \\ Non-isolated PWM three-port & & & & & & & & & & & & Simple circuit, \\ converter [Figure 18a] & & & & & & & & & & & & & \\ Two-switch forward with & & & & & & & & & & & & Low mass and voltage/ \\ integrated buck converter & [18] & & & & & & & & & & & & & \\ Figure 18b] & & & & & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of various integrated DC-DC converters. choice. In [117], a flyback converter was proposed, and the results were demonstrated for a 20W CubeSat, achieving an efficiency of 88%. To overcome the low efficiencies of the flyback converter, [116] proposed a boost-flyback converter operating in DCM and critical conduction mode for a similar application. In [118], a full-bridge LLC resonant topology was used for EP for micro- and nano-satellites. A 10 W prototype of the converter was developed to validate the performance. For large satellites, the Hall-effect thruster and the gridded ion thruster are predominantly used. In [119], a 15 kW, 400 V discharge supply for the PPU of a Hall-effect thruster using SiC was proposed. The system uses two parallel full-bridge modules, each operating at 7.5 kW, 300 V nominal voltage. A 200 W prototype of the converter demonstrated an efficiency of around 92%. In [120], a resonant converter-based 4 kW discharge supply for a Hall-effect thruster was proposed. The converter demonstrated good performance over a broad spectrum of input and output conditions. A PPU for a 6 kW Hall-effect thruster with a wide output voltage range was proposed by JAXA in [121]. The output current and voltage ranges of the converter are 4 to 34 A and 175 to 800 V, respectively. The design is based on four 1.5 kW modules, which switch between series and parallel connections for multiple output connections. The modular structure significantly minimizes the thermal and mechanical design. An efficiency of 96% and a power density of 0.3 kW/kg were obtained. The control algorithm for the thruster was discussed in [122]. A forward converter-based heating power supply for a Hall-effect thruster was proposed in [123]. A 150 W experimental prototype of the system demonstrated an efficiency of 90%. A 5 kW PPU for a 40 cm gridded ion thruster was proposed in [124]. The design was based on a phase-shift-modulated/PWM DAB converter, which showed high power density and efficiency. Ref.