A SERIES-PARALLEL RESONANT CONVERTER FOR …

1 A SERIES parallel RESONANT CONVERTER FOR electrochemical wastewater treatment By KATHRYN M. KLEMENT A thesis submitted to the Department of Electrical and Computer Engineering in conformity with the requirements for the degree of Master of Applied Science University of Toronto Toronto, Ontario, Canada Copyright by Kathryn M. Klement (2009) ii Abstract A SERIES-PARALLEL RESONANT CONVERTER for electrochemical wastewater treatment Kathryn M. Klement Master of Applied Science Department of Electrical & Computer Engineering University of Toronto (2009) Advantages of electrochemical wastewater treatment over conventional wastewater treatment include its smaller footprint, modularity, and ability to meet increasingly stringent government regulations.

2 A power supply that can be packaged with an electrochemical stack could make electrochemical wastewater treatment more cost effective and scalable. For this application, the series and series parallel RESONANT converters are suitable power CONVERTER candidates. With an output current specification of 100A, the series parallel RESONANT CONVERTER (SPRC) is superior due to its simpler output stage. The thesis presents the design of a 500W SPRC for a wastewater treatment cell stack. A rudimentary cell model is derived experimentally. The closed loop analysis, controller design and simulation results are presented. The output voltage and current are estimated using sensed quantities extracted from the high voltage, low current primary side.

3 Low voltage experimental results verify the operation of the power stage and voltage estimation circuitry in open loop pulsed operation. iii Acknowledgements I would like to express my deepest gratitude to Professor Francis Dawson for his invaluable guidance, encouragement and support throughout this work. I would also like to thank my co supervisor Professor Steve Thorpe for his guidance on the electrochemical aspects of this work. I thank Xogen Technologies Inc. and in particular Angella Hughes for supporting this project. For their technical input, I would like to thank Professor Peter Lehn, Professor Don Kirk and Professor Aleksandar Prodic. For their technical guidance, administrative support, and help in general, I would like to thank Lorie Roberts, Ryan Gilliam, Amgad El Deib, Hamid Timorabadi, Jim Prall and Belinda Li.

4 Finally, I thank my family and friends for their support and encouragement. Funding for this project was generously provided by Xogen Technologies Inc., the Ontario Centres of Excellence and the Natural Sciences and Engineering Research Council of Canada. iv Table of Contents Abstract ..ii Table of Contents ..iv List of List of Figures ..viii List of Symbols ..xiii List of Chapter 1 1 Scope of Thesis ..4 Thesis Objectives ..5 Thesis Chapter 2 electrochemical Load Characterization .. 8 Overview of electrochemical Basic Cell Electrical Double Layer ..10 electrochemical Cell Pulsed versus Steady State electrochemical Experimental Voltage Regime Selection ..19 Model Pulse Cyclic v Model under Chapter 3 CONVERTER Selection and 28 RESONANT CONVERTER Options.

5 28 Steady state CONVERTER Series RESONANT CONVERTER Output Transformer Open Loop Transient Studies: Design of Q ..40 Design Small signal Series parallel RESONANT CONVERTER Design ..55 Output Transformer Open Loop Transient Studies: Design of Q ..56 Design Small signal Schottky versus synchronous Standard full wave rectifier versus current doubler Choice of CONVERTER Chapter 4 Closed Loop 78 Voltage and Current Estimation ..80 Gating signal generator ..84 vi Small Signal Current sensor and compensator ..86 Voltage sensor and compensator ..88 Chapter 5 Experimental Results .. 94 Prototype circuit Steady state circuit Gating waveforms.

6 95 RESONANT tank waveforms ..97 Output Pulsed circuit verification under open loop Voltage estimation Discussion ..105 Chapter 6 Conclusions, Contributions and Future 107 Future 110 Appendix A 114 Output Filter Inductors .. 114 Series RESONANT Inductor .. 117 Appendix B Prototype Circuit Parts List .. 123 Appendix C Prototype Circuit Schematics .. 124 vii List of Tables Table : Effect of voltage on removal of E. Coli, BOD and NH3 at , and Table : Curve fit data for the Butler Volmer and exponential models..23 Table : Summary of CV results at half cell voltages of interest, neglecting the electrolyte iR Table : Estimated actual half cell potentials and system efficiency.

7 25 Table : Comparison between SRC and SPRC topologies..30 Table : RESONANT tank parameters for the SRC and SPRC topologies..33 Table : Transformer parameter Table : SRC parameter and component Table : SPRC parameter and component values..62 Table : Comparison between SRC and SPRC device viii List of Figures Figure : Conventional wastewater treatment plant [1]..2 Figure : electrochemical wastewater treatment plant [1]..3 Figure : Power supply connected to a rudimentary model of the electrochemical load..5 Figure : Basic water electrolysis Figure : Basic schematic of the electrical double 11 Figure : Basic large signal circuit model for an electrochemical cell..12 Figure : Schematic of Faradaic current as a function of overpotential (the Butler Volmer equation).

8 13 Figure : Linearized equivalent cell circuit Figure : Experimental apparatus for electrochemical cell studies in Figure : Cell circuit model and control loop..18 Figure : wastewater temperature at 5 minute intervals during each voltage regime Figure : Half cell (anodic) voltage decay under open circuit conditions..23 Figure : Cyclic voltammetry curve for the 2 plate cell in wastewater , scan Figure : Series RESONANT CONVERTER with LC RESONANT tank..29 Figure : Series parallel RESONANT CONVERTER with LCC RESONANT tank..29 Figure : Gating of input switches Q1, Q2, Q3, and Q4, and the RESONANT tank input voltage Figure : Sample input voltage and RESONANT current waveforms for a CONVERTER above resonance (zero voltage switching).

9 32 Figure : Conversion ratio as a function of normalised switching frequency and Q factor for the ix (a) SRC and (b) Figure : EE core Figure : Equivalent circuit, neglecting the transient response of the output filter..41 Figure : Effect of Q on the SRC equivalent circuit transfer function Figure : SRC open loop transient response for Q = 4..43 Figure : SRC open loop transient response for Q = ..43 Figure : SRC open loop transient response for Q = ..46 Figure : Equivalent CONVERTER circuit for Figure : Response of output voltage to an input voltage step, for the generalized average model versus circuit Figure : SRC frequency to output current transfer function at full and half rated loading conditions.

10 54 Figure : Poles of the frequency to output current transfer Figure : Equivalent circuit, neglecting the transient response of the output filter..57 Figure : Effect of Q on the poles of the SPRC equivalent circuit transfer Figure : SPRC open loop transient response for Q = Figure : SPRC open loop transient response for Q = Figure : SPRC open loop transient response for Q = Figure : Conversion ratio curves for minimum and maximum Q, at Cp/Cs = Figure : SPRC open loop transient response for Q = 1 at N = Figure : Equivalent CONVERTER circuit for Figure : Response of output voltage to an input voltage step, for the generalized average model versus circuit x Figure : SPRC frequency to output current transfer function at full and half rated loading conditions.