## 3 Design Procedure of the HESS
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Rated voltage & 16.2 V \\ Surge voltage & 17.1 V \\ Nominal voltage & 13.5 V \\ Minimal voltage & 6.0 V \\ Nominal capacitance & 10 F \\ Continuous current at 40 \({}^{\circ}\)C rise & 33.6 A \\ Continuous current at 15 \({}^{\circ}\)C rise & 20.4 A \\ Maximum peak current & 60 A \\ Equivalent series resistance & 25 m\(\Omega\) \\ Number of cells & 36 \\ Weight & 150 g \\ Nominal voltage energy & 911.25 J \\ Minimal voltage energy & 180.00 J \\ \hline \hline \end{tabular}
\end{table} 
Table 2: SC module main parameters. Figure 3: 3D model of SC module. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Range** \\ \hline Buck mode voltage & 6–75 V \\ Boost mode voltage & 3–48 V \\ Max. current & 60 A \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Interleaved bidirectional DC/DC converter parameters. The SC module was connected to the boost side of the converter because the unregulated bus has voltages in the range of 20-34 V, and the SC module has a maximum working voltage of 13.5 V, so the voltage needs to be boosted. At the buck side, the load and unregulated bus were connected because if the load recuperates, the voltage needs to be stepped down to store energy in the SC module properly. Because the eval board is universally designed by the manufacturer, the interconnecting board was designed to provide a power path to the SC module, unregulated bus, and load. Also, the control signals need to be wired to the eval board from the custom control board based on the C2000 DSP from Texas Instruments, where the control algorithm is executed. Because of the control algorithm, additional measurements and sensors must be added to the board to monitor voltages and currents properly. The following values are observed in Table 4.  
The interconnecting board was designed as a four-layer board with final dimensions of 158 \(\times\) 153 mm. Figure 4 shows the final setup consisting of a DC/DC converter, an interconnecting board with an SC module, and a control board with a C2000 kit (Dallas, TX, USA). The system comprises three interconnected boards, which manage energy flow between an accumulator, an SC module, and a load. The primary role of this system is efficient energy management and monitoring system variables. The PCB Stack-up consists of:  
* Interconnect PCB;
* Bidirectional DC/DC converter PCB;
* Control PCB. The interconnect PCB is placed between the control and DC/DC converter PCBs. Circuits placed on the board monitor critical electrical parameters such as currents, voltages, and individual supercapacitor cell voltages. Subcircuits are:  
**Input port for an unregulated bus (accumulator)**--This port connects to the main power source, in this case, the accumulator, which provides a limited amount of current. This port also serves as a measuring point for the unregulated bus voltage and is shared with the buck side of the bidirectional DC/DC converter. **Port for the load**--This port connects the load to the system. Because the load can sink and source power, the current measurement is designed to be bidirectional. Voltage is also measured to calculate the load power. **Input port for the SC module**--This port connects the SC module with the boost side of the bidirectional DC/DC converter. This port also monitors the voltage and current of the SC module. Current measurement is also designed as bidirectional. **Measurement and auxiliary circuits**--This board is also populated with another measurement circuit for monitoring individual cell voltages to implement an overvoltage protection of the supercapacitor cell, which is susceptible to overvoltage conditions. The connector for the control board is also populated on this board, together with the auxiliary power supply, which provides the necessary voltages for the measurement and control circuits.