A bidirectional multi-port DC-DC converter with reduced filter requirements

TLDR: In this paper, the authors proposed a converter that not only can perform fast battery voltage balancing and limit ground leakage current, but also features low switching ripple and component count, providing significant cost savings from reduced filter requirements and improved efficiency.

Abstract: Practical challenges in distributed generation and electric vehicles have motivated the rapid development of bidirectional multi-port dc-dc converters. This paper proposes a converter that not only can perform fast battery voltage balancing and limit ground leakage current, it also features low switching ripple and component count, providing significant cost savings from reduced filter requirements and improved efficiency. Experimental testing of a 3.3 kW prototype confirms the bidirectional power transfer capability and demonstrates above 99% converter efficiency over a wide range of input power.

Figures

Figure 3.2: Switching state 1 of variant 1 of the proposed converter.

Figure 4.5: Anti-windup method used for the current control loop.

Figure A.3: Magnetic losses and load current plot for various duty cycle ratios.

Table A.2: Magnetic losses for various duty cycles.

Figure 1.1: Classical cascaded buck converter.

Figure 5.7: Current and delta controller saturation graph where a value of "1" indicates saturation.

Full text

A Bidirectional Multi-Port DC-DC Converter with Reduced
Filter Requirements
by
Yuanzheng Han
A thesis submitted in conformity with the requirements
for the degree of Master of Applied Science
Graduate Department of Electrical and Computer Engineering
University of Toronto
©
Copyright 2016 by Yuanzheng Han

Abstract
A Bidirectional Multi-Port DC-DC Converter with Reduced Filter Requirements
Yuanzheng Han
Master of Applied Science
Graduate Department of Electrical and Computer Engineering
University of Toronto
2016
Practical challenges in distributed generation and electric vehicles have motivated the
rapid development of bidirectional multi-port dc-dc converters. This paper proposes a
converter that not only can perform fast battery voltage balancing and limit ground
leakage current, it also features low switching ripple and component count, providing
signicant cost savings from reduced lter requirements and improved eciency. Experimental
testing of a 3.3 kW prototype conrms the bidirectional power transfer capability and
demonstrates above 99% converter eciency over a wide range of input power.
ii

Contents
1 Introduction 1
1.1 Research Challenge in DC-DC Converter . . . . . . . . . . . . . . . . . . 1
1.2 Existing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Proposed Converter Topology 7
2.1 Design Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Proposed Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Variants and Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Principle of Operation 12
3.1 Input Output Relationship . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2 Interleaved Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3 IVSB Analysis of the Proposed Conguration . . . . . . . . . . . . . . . 17
4 Control Strategy 20
4.1 Theoretical Control Design . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 Practical Control Challenge . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.1 Predict-Reset Control . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.2 Integrator Anti-Windup . . . . . . . . . . . . . . . . . . . . . . . 26
5 Case Studies 28
5.1 Simulation Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.1 Switching Performance . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.2 Bidirectional Power Transfer . . . . . . . . . . . . . . . . . . . . . 31
5.1.3 Voltage Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.4 Controller Saturation . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.2.1 Switching Performance . . . . . . . . . . . . . . . . . . . . . . . . 37
iii

5.2.2 Bidirectional Power Transfer . . . . . . . . . . . . . . . . . . . . . 39
5.2.3 Voltage Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.2.4 Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6 Cascaded Conguration 43
6.1 Topology and Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.2 Control Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7 Conclusion 53
7.1 Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Bibliography 55
A Eciency Analysis 58
A.0.1 MOSFET Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
A.0.2 Inductor Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
A.0.3 Circuit Conduction Losses . . . . . . . . . . . . . . . . . . . . . . 62
A.0.4 Evaluation of the Loss Model . . . . . . . . . . . . . . . . . . . . 63
iv

List of Tables
2.1 Comparison of various capacitor congurations. . . . . . . . . . . . . . . 11
5.1 Components used in the simulation and experiment. . . . . . . . . . . . . 28
5.2 Simulation comparison between the proposed converter and the double-
input single-output classical cascaded buck converter. . . . . . . . . . . . 30
5.3 Comparison of the experimental and simulated switching ripple of the
proposed converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
6.1 Initial input voltage for each port for the cascaded converter. . . . . . . . 51
A.1 Variables used in loss calculation. . . . . . . . . . . . . . . . . . . . . . . 60
A.2 Magnetic losses for various duty cycles. . . . . . . . . . . . . . . . . . . . 62
A.3 Comparison of key parameters used in the theoretical loss model and the
same parameters calculated from the trendline coecients. . . . . . . . . 65
v

Frequently asked questions

Q1. What are the contributions in this paper?

This paper proposes a converter that not only can perform fast battery voltage balancing and limit ground leakage current, it also features low switching ripple and component count, providing signi cant cost savings from reduced lter requirements and improved e ciency. 

Q2. What are the future works in this paper?

Further testing on the prototype to quantify and categorize power losses in addition to the e ciency analysis shown in Appendix A in order to better understand the di erence between measured losses and calculated losses ; and Further testing on the prototype with actual battery packs instead of super capacitors to verify the control for bidirectional power transfer and voltage balancing.