Advantages and Circuit Configuration of a DC Microgrid

Transcription

1 PE&EE Since 2002 Advantages and Circuit Configuration of a Microgrid Toshifumi ISE (Osaka University, JAPAN) ise@eei.eng.osaka-u.ac.jp

2 Problems on Microgrids 1)Synchronization of distributed generators 2)Inrush current (transformers, Induction motors, Induction generators) 3) Three-Phase Unbalance (single-phase loads, single-phase generators such as photovoltaic) 2

3 Recent Trends 1) Introduction of many Inverter loads (/ and / conversions are included) 2) Introduction of distributed generations with output (photovoltaic, fuel cell, variable speed type wind turbine, micro turbine, gas engine) 3) Needs for higher quality power 3

4 Loop Type Configuration Bi-directional Rectifier 22kV/1.2kV 22kV/1.5kV Diode Rectifier PFC PV Cell High Quality Loop PV Cell Load SMES SFCL + Hybrid Switch G Wind Turbine MT Micro Turbine FC Fuel Cell 22kV/1.5kV 22kV/1.2kV PFC Normal Quality Loop 2kV Secondary Battery Load Load 2kV 4kV 4

5 Circuits for Loss Comparison 2kV 1km Load1 20MW 0.5km Loop System 1km Load2 20MW 0.5km 6.6kV 1km 1km Load3 Load1 20MW 20MW 0.5km Radial System Load2 20MW 0.5km Load3 20MW 5

6 Reduction of Rectifier Losses 12 Type Distribution System D C L oop T ype D istribution System 10 Loss [MW] Rectifier E fficiency of D C L oop T ype D istribution System 6

7 Distance of Cable and Losses Type Distribution System 16 D C Loop Type D istribution System Loss [MW] Distance of C able [km ] 7

8 Loss Reduction due to Loop System Loss [MW] Losses of Inverters and R ectifier Losses of C able 0 Loop Type Distribution System Type Distribution System (W ithout Loop) 8

9 Loss Reduction by Feeding from Two Systems O ne A C System Two System s Loss [MW] P ow er of L oad1 [M W ] 9

10 Control Method of Rectifiers Using Gain-Scheduling Method P Controlled Characteristics with Proportional Controller K 1 K > K 1 2 system Bi-directional Rectifier Voltage Control P K 2 i * i K V dc * V dc P * V + dc K * i V K Gain Scheduling P LPF V dc 10

11 Effect of Gain Scheduling P K1 K > K 1 2 Power sharing K 2 Large Gain K Small Gain K Gain Scheduling Voltage regulation Voltage Regulation Excellent Fair Good V Power Sharing Fair Excellent Good 11

12 Control of Multiple Rectifiers system system 1 1 Bi-directional Rectifier Voltage Control P 1 i 1 i * K V dc 1 * V dc P 1 Gain Scheduling K P LPF system system 2 2 i 2 i * K Communication line * V dc V dc 2 P 2 P 2 12

13 Voltage %Load 50%Load 100%Load voltage variation 2% voltage variation 6% Gain K versus Voltage Characteristics Gain K Gain K Gain K for Various Load Power with 2% Voltage Variation Montreal Symposium 0.4 on Microgrids Load power 13

14 Simulation Circuit 0.5km 0.5km system1 Ls Rs Bidirectional rectifier Cd + - R R dc 1 dc3 V dc1 22 kv /1.2kV 400kW(Max) 300kW(Max) Rectifier power1 1km 1km system2 Rectifier power2 R dc2 + - V dc2 1km 300kW(Max) 14

15 Simulation Results of Power Sharing system1 system2 Load1 Load2 Load3 Gain-scheduling Load Power Load Power Load Power 10% 50% Power Sharing (MW) % Voltage (kv) +2 2% Gain +20 Common Gain Load Power (MW) Time(s) Power Ratio Constant Gain 54:46 K=2 Constant Gain K=30 Load Power Load Power Load Power 10% Power 50% Ratio Power Sharing (MVA) +0.6 % : Voltage (kv) % Power Ratio Load Power (MW) Power Sharing (MVA) 57: Time(s) 1% +1.9 Voltage (kv) Load Power (MW) Time(s)

16 Simulation Circuit for Protecting Operation 22kV/1.5kV Battery 二次電池 1 交流システム System 1 Ls Rs PFC Cd Ldci IS1L1 IS1S2 1km 1km SFCL HS km Cd1 Load1 負荷 Load1 負荷 1 Solar 太陽光発電 Battery SFCL HS11 Hybrid ハイブリッド Switch スイッチ 1 IL1L2 Fault 短絡事故 Point 0.25km 22kV/1.5kV Battery 二次電池 2 交流システム System 2 Ls Rs Ldci PFC Cd IS2L3 HS22 1km SFCL 0.5km SFCL Cd2 HS21 IL2L3 Cd3 Load3 Hybrid ハイブリッド Switch スイッチ 2 LCフィルタ Filter Load2 負荷 Load 負荷 2 負荷 Load 負荷 3 16

17 Simulation of Protecting Operation 1ms 1ms Current Through the Mechanical Switch Current Through the Semiconductor Switch 17

18 Low Voltage Type Microgrid Photovoltaic Cell 200 V Bulk Power system Secondary Battery G Electric Double Layer Capacitor Co-generator Bi-directional Rectifier Islanding Protector Rectifier 170 V 170 V Communication Line 100V 3φ 200 V 1φ 100 V Power Exchange 100V 1φ 100 V 100 V Power Exchange 100V 1φ 100 V Center Building Fuel Cell 18

19 Features of Low Voltage Type Microgrid Distributed scheme of load side converters contributes to provide a super high quality power supplying. Various forms of electric power like single phase 100V, three phase 200V, 100V can be obtained without using transformers. If power consumption become more than a power production during a long term isolation, micro-grid can stop supplying power for some loads intentionally by load side converters in order to continue supplying power for more important loads. When a temporary overload occurs at one load, electric power can be shared by using additional electric power lines between load side converters. 19

20 Features of Microgrid Synchronization of distributed generators are not necessary. Fluctuation of generated power of distributed generators and load power can be compensated in the dc line by using energy storage devices. Loads are not affected by voltage sag, voltage swell, three-phase voltage unbalance, and voltage harmonics. Power quality is not affected by Inrush current, singlephase loads and single-phase generators. Higher efficiency than microgrid is expected. 20