Topology Simplification Method based on Switch Multiplexing Technique to Deliver DC-DC-AC Converters for Microgrids

Transcription

1 Renewable Energy and ehicular Technology Lab Topology Simplification Method based on Switch Multiplexing Technique to Deliver -- Converters for Microgrids Wen Cai, Shanxu Duan, Fan Yi & Babak Fahimi HUST & UTDallas September, 2015 Some pictures are from

2 List of contents Introduction Topology simplification with switch multiplexing Experimental results Conclusion 2015/11/12 2

3 1. Inclusion Background In microgrid, various sources and loads with different electrical characteristics are connected together, like solar panels, wind generators, batteries, fuel cells, utility grid and motors. Conventionally, several converters are used with the common bus. Common bus Fuel cell / / For energy generating devices, like fuel cell and solar panel, unidirectional - converters are necessary; / Utility grid For utility grid and motor, bi-directional - converters are required; Solar panel / For energy storage devices, like battery and super-capacitor, one needs bi-directional - converters. Battery / Wind turbine / motor 2015/11/12 3

4 1. Inclusion Research objective In order to integrate all the sources and loads and achieve high power conversion efficiency for microgrid application, a compact multiport power converter with fewer components can be used to replace all the converters with centralized control scheme which is easy to implement and protect. Common bus Utility grid / Fuel cell / Fuel cell Solar panel / / Utility grid Solar panel Multiport power converter fewer components Battery / Wind turbine Wind turbine / motor 2015/11/12 4 motor Centralized contol Battery

5 List of contents Introduction Topology simplification with switch multiplexing Experimental results Conclusion 2015/11/12 5

6 2. Topology simplification with switch multiplexing Basic units for bi-directional power transfer In order to analyze multiport converter, two-port converter are investigated firstly. Then it is desired to derive from two-port system to multi-port system. Here, non-isolated topologies are considered mainly. Basic unit for - power conversion Load bus bus bus Solar panel Fuel Cell Basic unit Buck Boost Bi-directional Basic unit for - power conversion bus Source bus load bus Grid Basic unit Rectifier Inverter Bi-directional 2015/11/12 6

7 2. Topology simplification with switch multiplexing Topology derivation based on switch multiplexing Basic idea: constitute three-port converter by combining two basic units. - Basic unit - Basic unit There are four cases as follows: /11/

8 2. Topology simplification with switch multiplexing Case 1: -- topologies / Unit Amp 1 2 1<2 Published 1 Note: The oltage drop of L is ignored - Unit 2015/11/ L o 3 1 2, 2 1 Amp 3 Amp L o 3

9 2. Topology simplification with switch multiplexing Case 1: -- topologies Amp G1 G1 G2 L 2 L L L 2 - Unit - Unit G2 G3 Examples 2015/11/12 9 T Equivalent mode

10 2. Topology simplification with switch multiplexing Case 1: -- topologies Amp erified L 2 L 2 - Unit - Unit i L1 i L2 Examples Equivalent mode 2015/11/12 10

11 2. Topology simplification with switch multiplexing Case 1: -- topologies Published 3 L 2 L 2 i L1 i L i L 2 1 i L2 - Unit - Unit Equivalent mode -- three-port converter can be constituted with 4-6 switches. 2015/11/12 11

12 2. Topology simplification with switch multiplexing Case 2: -- topologies )Switch multiplex - Unit - Unit 1 3 Examples 2015/11/12 12

13 2. Topology simplification with switch multiplexing Case 2: -- topologies Unit 3) Dual switch multiplex - Unit Examples 4) Bridge multiplex converter can be constituted with 6-8 switches. 2015/11/ Published

14 2. Topology simplification with switch multiplexing Case 3: isolated topology derivation Basic structure Examples L1 1 L L2 2 Published 2015/11/12 14

15 2. Topology simplification with switch multiplexing Previous topology Multi-level units Less harmonic Low switch frequency More switches Multiport units Flexible power flow Low switch power loss Complicated control Resonant units High efficiency High power density Frequency modulation L s 1 C out 1 C C L m 1 Isolated Non-isolated LLC-type LCC-type out L s NPC Flying cap MMC/CMC 1 C C 1 C /11/12 15

16 2. Topology simplification with switch multiplexing Extension Combination of multi-level technique and switch multiplexing technique Multi-level technique Topology Optimization Less harmonic Low switch frequency More switches Switch multiplexing New topology Flexible power flow Low switch frequency Complicated control To be analyzed L /11/

17 2. Topology simplification with switch multiplexing Extension Combination of resonant technique and switch multiplexing technique Resonant technique Topology Optimization High efficiency High power density Frequency modulation Switch multiplexing New topology Less switches High efficiency High voltage/current stress C 1 L s L s C s in 1 L 2 C 2 C L m 3 To be analyzed out 2015/11/12 17 C o

18 2. Topology simplification with switch multiplexing Extension Combination of multi-level unit and resonant unit with switch multiplexing technique Resonant technique Topology Optimization High efficiency High power density Frequency modulation Multi-level technique Switch multiplexing New topology Less harmonic Low switch frequency More switches C 1 To be analyzed 3 C 1 L s L s C s C s C 2 C 2 out out 2015/11/12 18 C o C o

19 List of contents Introduction Topology simplification with switch multiplexing Experimental results Conclusion 2015/11/12 19

20 3. Experimental results Prototype pictures 4-switch -- (500W) 5-switch -- (1kW) 6-switch -- (5kW) 2015/11/ switch -- (2kW)

21 3. Experimental results 4-switch converter Microgrid can achieve higher efficiency with modified topology; C L L switch converter 4-switch converter 2 switches are omitted which leads to efficiency improvement and power integration; oltage rating of link capacitors is decreased with better reliability; Power decoupling can be achieved with small capacitance; Power flow control is more complicated; v cap_ref + - v cap PI i L2_ref Sin(Ө) PLL + - i L2 PI K K + + d 1 -d 3 PWM distribution g1 g2 g3 Control strategy v g i bat_ref 2015/11/ i bat PI d 1 g4

22 3. Experimental results 4-switch converter Grid voltage Grid current Battery current(i 1 ) Battery voltage( 1 ) 95.0% 93.0% 91.0% 89.0% 4-switch -- (500W) Efficiency comparison 87.0% CH1:2A/div CH2:200/div CH3:200/div CH4:5A/div Experimental waveform Time:20ms/div 85.0% switch 6-switch Efficiency comparison W Experimental results demonstrate the feasibility of the 4-switch three-port -- converter and 2.0% power efficiency improvement in comparison with conventional topology. 2015/11/12 22

23 3. Experimental results 5-switch converter Reliability is improved with lower voltage requirement for battery; C L switch converter 5-switch converter One switch is omitted which leads to high power density; oltage range for battery is expanded with better reliability; Power decoupling can be achieved with small capacitance; Modulation method is complicated. 2015/11/12 23 CH1:2/div CH2:2/div CH3:5/div Time:40µs/div

24 3. Experimental results 5-switch converter Grid voltage Grid current 5-switch -- (250W) 90.0% Efficiency Battery current(i 2 ) Output voltage( 1 ) 86.0% 82.0% 78.0% CH1:2A/div CH2:200/div CH3:5A/div CH4:200/div Time:20ms/div 74.0% Experimental waveform 70.0% Experimental efficiency W Experimental results demonstrate the feasibility of the derived 5-switch three-port -- converter with capability to low-voltage batteries or super-capacitors. 2015/11/12 24

25 List of contents Introduction Topology simplification with switch multiplexing Experimental results Conclusion 2015/11/12 25

26 4. Conclusion What has been done 1. Proposed topology derivation method based on switch multiplexing; 2. Derived a series of three-port -- topologies and -- topologies; 3. erified the feasibility of the derived topologies and their superiority. Future work 1. To discuss topology selection method based on application requirements; 2. To optimize the derived topologies with multi-level technique and resonant technique; 3. To approach modular multi-level converter modeling and discuss its stability. 2015/11/12 26

27 Wen Cai PhD candidate & Research assistant University of Texas at Dallas / Phone: (469) /11/12 27