Research on Controller of Micro-hydro Power System Nan XIE 1,a, Dezhi QI 2,b,Weimin CHEN 2,c, Wei WANG 2,d

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1 Advanced Materals Research Submtted: ISSN: , Vols , pp Accepted: do: / Onlne: Trans Tech Publcatons, Swtzerland Research on Controller of Mcro-hydro Power System Nan XIE 1,a, Dezh QI 2,b,Wemn CHEN 2,c, We WANG 2,d 1 Dept. of Computer and Informaton Engneerng of Zhejang Conservancy and Hydropower College, Hangzhou, ,Chna 2 College of Mechancal and Electrcal Engneerng, Chna Jlang Unversty, Hangzhou, , Chna a emal:nkxexe@163.com, b emal: qdz_001@126.com, c emal:c9419@sna.com, d emal:wangwe@cjlu.edu.cn Keywords: Mcro-hydro Power;Self-excted Asynchronous Generator;Double Loop Control;Crcut Topology. Abstract. On the exstng ndependent operaton of mcro-hydro systems, a knd of crcut topology of mcro hydro power based on self-excted asynchronous generator are studed. Usng power electronc devces to meet power standard and reduce crcut losses. The double loop to control of nner current loop and outer voltage loop s studed, realzes the fast control of system and njected nto the grd n the form of current, t s safety and hgh effcency. Last,usng expermental platform to verfy the feasblty of the system. Introducton Wth ncreasng shortages for energy, people have a more deeply research on renewable energy power generaton technology such as wnd power, photovoltac, mcro- hydro,and dstrbuted generaton and grd technology has been known to the publc. Chna s rch n mcro- hydro resources, mcro-hydro [1]have the advantages whch power transmsson lne s smple, low cost, low mantenance costs, envronmental polluton-free.etc, as one of mportant mcro power s ncreasngly people's attenton. From the cost analyss, f mcro- hydro uses the tradtonal control of small and medum hydro electrc power, t wll have a hgh cost,therefore, mcro-hydro use the asynchronous generator whch does not control, the output power s constant. When users load changes, mcro- hydro systems need to mantan a constant power outp ut for the power balance [2][3], users load wll absorb excess power through certan controls to ensure that the termnal voltage s constant. At present, mcro- hydro power s used n remote mountanous areas n Chna, wth the popularty of the grd, the grd n remote mountanous areas have been covered, but they are bascally on the tp of the grd,and have poor power qualty, hgh electrcty costs. On the bass of new energy technology on the network [4][5][6], ths paper proposes a new mcro- hydro power topology and control strategy that based on the self-excted nducton generator whch s not control, t can be acheved a complementary between mcro-hydro and electrc power,and reduce electrcty cost of users. Mcro-hydro Systems Topology When turbne drves n asynchronous generators, through the exctaton and electromagnetc nducton, the stator current and stator voltage are generated n the sde of generator stator. The hydropower potental dfference n the nput sde and the output load s fxed, the turbne speed s constant, the nducton generator to mantan constant voltage and frequency values, so that the generator output voltage and frequency s constant, namely,power generaton devces have a constant power output. The topology structure of mcro-hydro power system as shown n Fg.1, the user load s drectly connected to the asynchronous generator, the generator supply power to the local user load.the dfference between the generator output power and load demand power wll be backed to the grd by control crcut, thus ensurng the stablty of the system. In order to avod ncreasng the All rghts reserved. No part of contents of ths paper may be reproduced or transmtted n any form or by any means wthout the wrtten permsson of Trans Tech Publcatons, (ID: , Pennsylvana State Unversty, Unversty Park, USA-06/03/16,05:54:17)

2 1122 Energy Research and Power Engneerng 2014 harmonc to generator by the control loop, the control crcut s dvded nto two parts, before part adopts controllable rectfer, after part uses grd nverter, and then access LC flter crcut. The advantage of ths desgn s the only dfference power through electronc crcuts, whch reduces the capacty requrements of power electronc devces and equpment costs. Fg.1. The grd-connected crcut topology of mcro-hydro power system The Grd-connected Control Strategy of Mcro-hydro Systems Analyss of the prevous secton, the no-controlled mrco-hydro output power s stablty, once the users load changes, the generator voltage wll also changes. In order to mantan the generator output voltage s stablty, correspondng control strategy s used to calculate the dfference power whch depends on the load sde voltage changes, then the dfference power s njected nto the grd n the current form, thus ensurng clents voltage s stablty. In ths paper, double-loop control strategy s used. Fgure 2 s a block dagram of double-loop control. Current loop control and voltage loop control can be analyzed separately. In the nner current loop, ncludng the current PI controller transfer functon, the transfer functon of the nverter, the flter transfer functon. Its grd-connected process: gven the reference current *L, compared wth the nverter sde of the nductor current L, the dfference s accommodated by PI current controller, and then get modulated sgnal Ur through the nverter part, whch wll be corrected by the grd voltage, the snusodal current wll be outputted wth same frequency and phase of the grd after fltered lnks, system acheves grd-connected. * Udc k k p + s * L k p + k s K 1 Ls+R L L D 1 Cs Udc Fg.2. The block dagram of double closed loop

3 Advanced Materals Research Vols The nner current loop transfer functon s: Kk p Kk G ( s) = L L (1) R L + Kk 2 p Kk L L In Fg.2, the voltage loop control s analyssed, whch gnores the voltage samplng delay lnk, t conssts of outer voltage transfer functon of the PI controller, the current nner loop transfer functon, the transfer functon of the DC bus sde. U*dc s reference voltage of DC bus, D s the DC current perturbaton, Udcs the actual DC lnk voltage. Its operaton process s: compared the actual DC voltage wth the reference voltage, the voltage dfference s processed by the PI controller, t wll generate reference value nner current, adjusted through the current nner loop, the actual current of the output nverter sde s dsturbed by dsturbance current and decouplng control,so that the DC bus voltage s stablty. The outer voltage loop transfer functon: k K p k K + G ( s) = C C (2) k p K 2 k K C C Experment Results In ths paper, the expermental platform s bulded to verfy the feasblty of systems. In the experment, usng frequency converter control 2.2kW three-phase asynchronous motors that smulates mcro-hydro turbne, 1.5kW three-phase squrrel cage nducton motor s choosed as self-excted generator, the output sde of generator connects to the varable resstve load. Fgure3(a) s the waveform of generator output voltage and output current wth the load sde changes, the curve 1 s output voltage of the generator, the curve 2 s load current n the user sde. Fgure3 (b) s the waveform of generator output current and nverter output current when the load sde changes, the curve 2 s load current n the user sde, the curve 3 s the output current of the nverter sde. Before the pont of m, when the generator s opened, as the local load power s 0W, load current n generator sde s 0A, the maxmum output voltage s 220V, the output maxmum current of the nverter s 2.3A. When the load power ncreases 400W at the pont of m, the load current s 1.2A, the output current of the nverter sde that grd current s automatcally reduced, the voltage s essentally unchanged. It llustrates that the system whch uses a self-excted nducton generator-controlled has a good operatng performance and feasble. U/(50V/dv) I/(5A/dv) (a) (b) Fg.3 The waveform of output voltage n generator sde and current of load and output current n nverter sde wth the load power changes Fg.4 s the waveform of output current n the nverter sde and the grd voltage, the curve 4 s the output current n nverter sde, curve 5 s the grd voltage. From the Fg.4,as the phase and frequency of the nverter output current and grd voltage, the grd current has a good trackng varaton wth the grd voltage, and the output current s stable, the power factor s close to 1.

4 1124 Energy Research and Power Engneerng 2014 Fg.4. The waveform of output current n nverter sde and grd voltage wth the load power changes Concluson Ths paper presents a novel mcro-hydro system crcut topology and the correspondng control strategy. Expermental results show that when the load changes, the output voltage of the generator-sde remans substantally constant, the generator-sde load current ncreases, the output current of the nverter sde decreases, that s n lne wth the theoretcal analyss. The output current of the nverter can mantan the same frequency and phase wth the grd voltage, power factor closes to 1, the system s relable. References [1] YUAN Ln-juan, ZHANG Xn, HE Xang-l, The Progress and Developng Trend of Rural Mcro-hydropower Statons, Chna Rural Water and Hydropower, 2011(7), [2] Youssef, K.H.Wahba, M.A.Yousef, Hasan A. A New Method for Voltage and Frequency Control of Stand-Alone Self-Excted Inducton Generator Usng PWM Converter wth Varable DC lnk Voltage,Amercan Control Conference, 2008 Dgtal Object Identfer,2008, [3] Ramrez, J.M. Torres, M.E.An Electronc Load Controller for Self-Excted Inducton Generators, Power Engneerng Socety General Meetng,2007,1-8. [4] LIU Yang-hua,WU Zheng-qu,TU You-qng, A Survey on Dstrbuted Generaton and Its Networkng Technology,Power System Technology, 2008,32(15), [5] YIN Gulang,ZHANG Shengmng, Modelng and Smulaton of Mcro-Hydropower Unt System,Power System Technology,2012,36(2), [6] WU Zhen-xng, ZOU Xu-dong, HUANG Qng-jun, Research on Grd Connecton Converter of Three-phase Power Electronc Load,Proceedngs of the CSEE,2012, 30(24),

5 Energy Research and Power Engneerng / Research on Controller of Mcro-Hydro Power System /