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Novel Three-Port DC-DC Converter for Sustainable Energy System

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Author/Institute

 

Introduction

Electric vehicles (EVs) have been quickly extended in their application over recent years and have been widely commercialized due to environmental concerns and energy resource diversity. It is essen- tial to develop a Three-Port Converter (TPC) with high step-down conversion for energy transference among the main battery, auxiliary battery, and accessories in the EV system, as shown in Fig. 1. A Three-Port High Step-Down DC-DC Converter is proposed by adopting the tapped-inductor technique with leakage inductance energy recycle for improving the conversion efficiency, as shown in Fig. 2. It is constructed with one tapped-inductor, one inductor, four power switches, and four diodes. Switch S1 is used to control energy from the main battery to the auxiliary battery, switch S2 is used to control energy from the auxiliary battery to the accessories, and switch S3 is used to control energy from the main battery to the accessories. Also, the energy stored in the leakage inductance is recycled by Cs to suppress the voltage spikes of the power switches and transfer to the load.

Fig. 1. TPC for EV dual battery system

Fig. 2. The proposed high step-down TPC

 

Methods

The proposed converter can be operated with five functional stages specified as below:

  1. Single Input Single Output-I (SISO-I): The main battery provides energy to the accessories.
  2. Single Input Single Output-II (SISO-II): The auxiliary battery provides energy to the accessories.
  3. Single Input Single Output-III (SISO-III): The main battery provides energy to the auxiliary battery.
  4. Single Input Dual Output (SIDO): The main battery provides energy to the accessories and the auxiliary battery
  5. Dual input single output (DISO): The main battery and auxiliary battery both provide energy to the accessories.

The operating principles of five functional stages are analyzed in detailed, voltage gain of each stage are derived. After that, the key parameters are calculated by Mathcad. Then, simulation is run by SIMPLIS to verify the theoretical analysis. Finally, a prototype of the proposed three-port converter is realized by digital signal processor TMS320F28335 and driver IC SI8271 is used to drive the main switches.

 

Results

The experimental prototype with a switching frequency of 50 kHz, 300 V for the main battery, 48 V for the auxiliary battery, 24 V output voltage, and 300 W rated power is implemented to verify the theoretical analyses. The maximum efficiencies of the proposed TPC are 94.3% under 150 W, 96.6% under 60 W, 94.4% under 75 W, 94.4 % under 90 W, and 95% under 140 W at SISO-I, SISO- II, SISO-III, DISO, and SIDO mode, respectively. The efficiency curves of SISO-I, SISO-II, SISO- III, DISO and DISO stages are shown in Fig. 3, Fig. 4, Fig. 5, Fig. 6, respectively.

Fig. 3. Measured efficiency under SISO-I   |   Fig. 4. Measured efficiency curve under SISO II

Fig. 5. Measured efficiency curve under SISO III   |   Fig. 6. Measured efficiency curve under DISO

(a) With different load power and Pb =50W   |   (b) With different auxiliary battery power and Po = 50W

Fig. 7. Measured efficiency curve under SIDO

 

Discussion

The proposed high step-down three-port DC-DC converter is suitable for a dual battery system in EV. By adopting the tapped-inductor technique with a clamping circuit, the voltage spike on the main switches is suppressed and the conversion efficiency is improved. Experimental results reveal that the main battery and auxiliary battery can provide energy to the accessory load with flexible PWM control.