# DC-DC Multistage Fibonacci Converter (MFC) Configuration

The power circuit of the DC-DC three-stage Fibonacci converter configuration is shown in Figure 5.3. The configuration derived by using switches and capacitors circuitry and the Fibonacci series is shown by the voltage conversion ratio [49.229-231].

At the output side we achieve high voltage; this configuration required a large number of capacitors and switches. However, a DC-DC MFC configuration has the following drawbacks:

• • It requires 3Ns + 1 number of diodes and switches to design an Ns stage Fibonacci converter configuration. Thus, it required many diodes and switches.
• • The converter configuration is unidirectional.
• • The voltage conversion ratio of converters follows Fibonacci series and hence

it is impossible to attain a conversion ratio, which is not in a Fibonacci series like 2, 4.....................

# DC-DC Multistage Magnetic-Free Converter (MMC) Configuration

The power circuit of the DC-DC three-stage magnetic-free converter configuration is shown in Figure 5.4. The converter configuration is designed by connecting a modular block in a mesh pattern [49,232]. The modular block of the converter is formed by using one capacitor and two transistors. This converter configuration is bidirectional and operates in a buck and boost mode. In buck mode operation, Ns-stage magnetic-free converter configuration provides output voltage 1 /Ns times

FIGURE 5.3 Power Circuit of DC-DC Three-Stage Fibonacci Converter Configuration.

FIGURE 5.4 Power Circuit of the DC-DC Three-Stage Magnetic-Free Converter Configuration.

compared to the input voltage. In boost mode operation. tVs-stage magnetic-free converter configuration provides output voltage Ns times compared to the input voltage.

The voltage across each transistor is identical and equal to input supply; thus, it is independent of the voltage conversion ratio and duty cycle. The DC-DC MMC configuration has the following drawbacks:

• • To design the DC-DC MMC configuration for the Ns number of stages, Ns x (Ns + 1) number of control switches, 0.5 x (Ns x 2 + Ns) number of capacitors, and Ns (Ns + 1) number of diodes are required. Hence, many switching devices and capacitor are required, which increases the size of the converter.
• • It is challenging to manage the power flow direction of the converter because many switches are available for the conducting path. Hence, the configuration also required complex circuitry.
• • The direction of the power flow of the converter depends on the terminal voltage at DC-Bus. Thus, this converter is not suitable for the application where input source voltage is varying in characteristics.

# DC-DC Step-Up Modified Switched-Mode Converter Configuration or DC-DC Switched-Mode Converter Configuration

The power circuit of the DC-DC step-up modified switched-mode converter configuration or DC-DC switched-mode converter configuration is shown in Figure 5.5. The converter configuration is simple in control, capable of offering continuous input current, and the voltage conversion ratio is adjusted by changing the ON time switches [49,233].

FIGURE 5.5 Power Circuit of DC-DC Step-Up Modified Switched-Mode Converter Configuration or DC-DC Switched-Mode Converter Configuration.

In Table 5.1, the detailed study about the working modes of converter and capacitor states are provided. The Electro Magnetic Interference (EMI) problem is reduced because of continuous current from the low-voltage source at the input side. The DC-DC switched-mode converter configuration has the following drawback:

• • It requires more switches.
• • Efficiency is low' because switching losses are high.
• • They do not increase the voltage conversion ratio further because a similar extension is not possible for this configuration.
• • The configuration does not provide a good agreement for a high-voltage high- power application due to a low-voltage conversion ratio.

TABLE 5.1

State of Capacitor and Working Mode of Operation of DC-DC Switched- Mode Converter Configuration [49,233]

 Working Modes Switches State Capacitors of Left Part (Section-1) Capacitors of Right Part (Section-2) S1 S2 S3 S4 S5 S6 S7 S8 I # \$ # \$ \$ # \$ # C D II # # # # \$ # \$ # NA D III \$ # \$ # # \$ # \$ D C IV \$ # \$ # # # # # D NA

C: Charging. NA: No Action. D: Discharging. #: OFF state. S: ON state.

# DC-DC Switched-Capacitor Converter Configuration

The power circuit of the DC-DC switched-capacitor converter configuration is shown in Figure 5.6. The input current ripple of this configuration is low. The EMI effect is reduced because of continuous input current with low ripples [49,234]. However, there is no provision to increase the voltage conversion ratio.

# DC-DC Capacitor Clamped Modular Multilevel Converter (CCMMC) Configuration

The power circuit of the DC-DC capacitor clamped modular five-level converter configuration is shown in Figure 5.7. This capacitor is designed only by using

FIGURE 5.6 Power Circuit of the DC-DC Switched-Capacitor Converter Configuration.

switches and capacitors [49,235]. The following are the major drawbacks of a CCMMC configuration:

• • High voltage is achieved at the output. However, many capacitors and switches are used to design CCMCC configurations.
• • It requires high-voltage rating switches due to high voltage stress across the switches. For /Vv-level configuration, the voltage stress across N-2 switching devices is double the input voltage, and the remaining switches have voltage stress equal to the input voltage.