Improving Efficiency of Multi-phase Cascaded DC-DC Boost Converters in Discontinuous Conduction Mode

Arwindra Rizqiawan
Sekolah Teknik Elektro dan Informatika

Abstract

• This study presents an improvement on the efficiency of of a proposed multiphase cascaded DC-DC boost converter by employing Discontinuous Conduction Mode
(DCM) for its operation.
• The proposed multiphase cascaded DCDC boost converter is characterized by high voltage gain and low input current ripple, this converter consists of two stages and is designed to connect a photovoltaic (PV) system to a DC microgrid bus.
• First, the loss equations for the converter is analyzed, then discontinuous conduction mode is applied to the first stage of the proposed converter.
• Further, comparison with two operation modes, Continuous Conduction Mode
(CCM) and Boundary Conduction Mode (BCM), is provided.
• To verify the proposed analysis dan calculation, experiments are conducted by implementing the circuitry in a lab scale prototype.
• The results show that the operation of DCM has demonstrated a substantial reduction in switching losses, leading to a notable increase in efficiency.

Keyword: boost converter, multiphase, cascaded, CCM, BCM, DCM, loss, efficiency..

Introduction

• The needs of high voltage gain low ripple converter for renewable energy application.
• In accordance with the specified needs, the multiphase cascaded DC-DC boost converter emerges as a viable solution due to its capacity to deliver a substantial voltage increase while minimizing input current ripple.
• This topology features a two-stage configuration, a multiphase setup in the first stage, subsequently interconnected in a series or cascaded manner with a boost converter in the second stage, as shown in Fig. 1.
• However, it should be noted that the efficiency of the multiphase cascaded DC-DC boost converter has not reached.

Discussion & Result

• Simulation depicts the input voltage of 36 V represents the output voltage of a photovoltaic system. The simulation control utilized pulse width modulation (PWM) signals to regulate the switches with specific duty cycles. A duty cycle value of 0.67 for the first stage of the converter. The duty cycle for the second stage was set to 0.75 to achieve high voltage amplification. The switching frequency was set to 20 kHz.
• For the predetermined parameters, an output current of 0.32A operates the converter in boundary mode. At this boundary point, the converter operates at a power of 150W. The shape of the inductor current can be observed in the three operating modes as depicted in Fig. 2.
• It can be observed that efficiency decreases as the converter’s power increases. In other words, in CCM, the efficiency decreases. This is because at higher power levels, the losses in the converter’s components also increase. These losses are proportional to the increase in converter power.
• Additionally, in DCM, soft switching occurs, resulting in a significant reduction in switch losses. This is what leads to a notable increase in efficiency between BCM and DCM, despite being at similar output power levels.
• The loss characteristics of BCM and CCM are similar, hence the similarity in their loss calculations.
• The efficiency trend for different output currents and power values is depicted in Fig. 3.

Experimental Results

• At a lower output current of 0.285 A, the converter operates in DCM condition. The highest efficiency is achieved in this DCM condition, reaching 92.35% at an output power of 120.7 W.
• On the other hand, in the CCM condition, the efficiency only reaches a peak value of 91.61% at an output power of 131 W, which is close to the boundary mode.
• The lowest tested efficiency occurs at an output current of 0.605 A and an out-put power of 215.5 W, at 90.17% in CCM operation.
• The efficiency trend observed is the highest in DCM, followed by BCM, and the lowest in CCM.
• The experimental results are shown in the graph in Fig. 8.
• In DCM, the losses are dominated by the inductor core.
• In BCM and CCM, the fraction of losses can be said to be similar, with inductor losses dominating the overall losses.
• Fraction of losses are shown in Fig. 5.

Conclusion

• The results show that by implementing DCM operation, the proposed converter achieves the highest efficiency.
• In the proposed converter, the dominant source of losses is attributed to the inductor, accounting for approximately 62% of the total losses in DCM.
• The operation of DCM has demonstrated a substantial reduction in switching losses, leading to a notable increase in efficiency.

Improving Efficiency of Multi-phase Cascaded DC-DC Boost Converters in Discontinuous Conduction Mode Suitable for Renewable Energy Application,
Muhammad Farras Muzakki, Arwindra Rizqiawan, Jihad Furqani International Journal of Power Electronics and Drive System (IJPEDS) (Under review, 1st round revision stage)