Research on harmonic analysis and Simulation of grid connected synchronous motor Jian Huang1,a, Bingyang Luo2,b

Transcription

1 5t nternational Conference on Environment, Materials, Cemistry and Power Electronics (EMCPE 06) Researc on armonic analysis and Simulation of grid connected syncronous motor Jian Huang,a, Bingyang Luo,b Scool of Jian Huang, Wuan University of Tecnology, Wuan , Cina; Scool of Bingyang Luo, Wuan University of Tecnology, Wuan , Cina. a @qq.com, b @qq.com Keywords: armonic, power distribution system, syncronous motor power generation, THD. Abstract. Harmonics in power system bring many adverse effects to te distribution system. Based on te analysis of te reason of armonic generation, tis paper puts forward te calculation metod of armonic analysis in te simplified circuit model, establises a syncronous motor power grid model, simulates in Simulink and gives te main armonic and total armonic current distortion rate in te syncronous motor power grid.. ntroduction deally, te power supply sould provide standard sinusoidal voltage signal for eac client, yet te so-called waveform distortion always exists in te actual voltage and current waveform, wic means te armonic distortion. Te armonic distortion of te power system is getting more serious wit te increasing of non-linear loads in te industry, te waveform distortion of voltage or current signal in te grid will create a lot of problems, for instance, transformer overeating, neutral line overload, fuse and electronic relay malfunction and telepone interference. Wit te development of power electronics tecnology and HDC transmission tecnology, te arm of armonics caused by te various power electronic equipment as become more and more serious. Wereupon, armonic researc plays a more and more important role in ensuring te reliable operation of te power grid and equipment and predicting te potential problems. Wit te rapid development of power electronic tecnology and computer tecnology, armonic generation will not only reduce te power quality, sorten te service life of te equipment, may also cause te maloperation of relay protection device, and as become an obstacle to te development of power electronic tecnology itself. Meanwile, people now pay more attention to te green power system. Tus te researc on te reason of armonic generation and te arm of te armonic generation is of great significance.. Harmonic sources Many industrial, commercial, and residential facilities will cause waveform distortion. Different nonlinear loads will produce different but discernible armonic spectrum, wic makes te task of identifying armonic distortion of te initiator becomes feasible. We must give proper consideration to te peak value of parallel resonance in te process of evaluating waveform distortion, oterwise, if we use a single tuned filter to eliminate a caracteristic armonic in some position, te sunt peaking (pole) of te filter will just be consistent wit a low order caracteristic armonic of a load, ten te filter will not eliminate filter, but amplify waveform distortion. On te oter and, te power quality of te public power supply will be reduced by te eavy armonic load on te weak feeder.. Traditional armonic sources ariable electronic stations wic work in saturated zone and user transformer act as te main armonic sources before te popularization of power electronic switc equipment. Nowadays, many cases would lead to armonic distortion, transformer saturation wen peak demand state and load 06. Te autors - Publised by Atlantis Press

2 state of te small step-up process are just two kinds of situations. Power converter and electric arc furnace are te main armonic sources in te industrial application of ig power, if armonic frequency generated by te arc device is lower tan te fundamental frequency, so called subarmonic; if armonic frequencies are not integer times tan te fundamental frequency, so called interarmonics.. Prospective armonic sources Harmonic sources of electrical system in te future will be more diverse, and sensitive electronic devices are constantly used, as a result of wic, te new system designed in te future sould be able to run in te environment in wic te armonic level is increasing. 3. nfluences of armonic on power distribution system Residential users lack of awareness of armonics caused by ouseold appliances, even te industrial and commercial users don t know te armonic filter very well, wic led to many power users suffering from adverse effects caused by armonic distortion to various loads. n a broad sense, tese adverse effects will be discussed in te following capter. 3. Termal effect of transformer Modern industrial and commercial networks are deeply influenced by te large number of armonic currents generated by various nonlinear loads, suc as variable speed drives, arc furnaces and fluorescent lamps. All of te devices described above need to be supplied wit power troug te transformer. Transformer wit delta-star connection or delta-delta connection sould ave a zero-sequence current, oterwise it will lead to overeating of te neutral line. Te circulation in te triangular connection causes te current to become larger and generates additional eat. We sould pay attention to tis problem. Te zero-sequence current can not be reflected by te current in te ig voltage side of te transformer wit triangular connection, but te eat loss caused by tem can not be ignored. 3. Abnormal action of electronic relays n practical applications, it is often encountered tat te frequency conversion driving equipment action leads to sutdown, and te armonic distortion sould be assessed. Altoug te unexpected overload is te main reason for te abnormal action of te relay protection, te serious armonic distortion caused by te increase of te nonlinear load can also cause te abnormal action of te relay protection. On te oter and, in te application of te frequency conversion device, te 3rd armonic currents caused by te serious imbalance of te line current may also cause te fault trip of relay protection. Terefore, it is necessary to evaluate te abnormal action of te relay protection in te device wit nonlinear load. Te specific metod is to detect te armonic distortion level, and ceck weter te relay needs to be fine tuned. f tere is an abnormal action of relay protection in industrial facilities, we sould begin to consider te filtering of armonics. 3.3 Ligting equipment Te armonic wose frequency is not an integer multiple of te fundamental frequency is called inter-armonic, inter-armonic can make te voltage oscillation, wic led to te ligts flasing. Te inter-armonics are mainly produced by cycloconverters wic are widely used in iron and steel, cement, mining and oter industrial and arc welding macine and arc furnace. According to te TF EEE and WG CGRE/CRED joint standard of te inter-armonic, te caracteristic frequency of cycloconverter is f i ( p m ± ) f ± p n f0 () n te formula, fi is te frequency of inter-armonic; f is te frequency of fundamental frequency; p and p are pulse numbers of ballast and output area respectively; m and n are integers like 0,,,3 and so on, but tey cannot be 0 at te same time; f 0 is output frequency of te cycloconverter. Superposition between te constant-frequency multi armonic voltage and te fundamental wave

3 voltage causes te ligts flicker, wic becomes te main adverse effects of inter-armonics. 3.4 Problems to consider in te operation of cables and equipment in armonic environment Wit te increasing degree of armonic distortion in power system, we need to re consider te selection criteria of power equipment in industrial facilities. For example, wen te distributed generator works in a nonlinear load dominated environment, te traditional generator designed wit iger order instantaneous reactance usually can cause serious termal effects and eventually make te equipment failure. Terefore, we must limit te operating parameters of te devices, so tat tese devices can witstand te adverse effects brougt by te armonic in te worst case. Of course, te situation is muc more complex tan tat of te device and network components tat are considered in te original state. 4. Harmonic analysis 4. Simplified calculation Wen te system is sown alike in Fig. circuit description, it can use te simplified manual algoritm. n some important results of te circuit, we can get te resonant frequency of te system by using te following expression: Sc c f s Qc l () n te formula, f s is te resonant frequency of te system, and is usually te integer multiples S c of te fundamental frequency; is Sort Circuit MA power of te system on considered resonant point; Qc is capacitors rated MA power of system voltage; c is capacitors reactance l of fundamental frequency; is te sort-circuit reactance of power supply substation. f calculated resonant frequency and te armonic source loads (nonlinear) of a caracteristic armonic frequencies are close to eac oter, ten te resulting great armonic voltage will cause serious distortion. Tis requires more accurate analysis and in-dept study. After simplification, te system impedance in te frequency domain can be approximately expressed as: ( R + jωl) Z( ω) [ ω ( LC) + jωrc] (3) n te formula, te system impedance Z(ω) is a function of frequency ( ω πf). Fig. Simplified circuit Tus, te armonic voltage of some armonic frequency can be obtained as follows: Z (4) Taking all orders of armonics into account, te effective value of voltage can be obtained as: n RMS + (5) 3

4 We can estimate total armonic distortion rate THD and telepone interference factor TF: THD (6) THD (7) ω TF RMS (8) n te formula, te definition of te index is defined by te concept of te total armonic distortion rate wit appropriate weigt coefficients ω, te weigt coefficient ω reflects te sensitivity of te uman ear to te noise of different frequencies. More accurate results can be obtained if te single armonic voltage and current are used. 4. Analysis example f te rotor speed n of te tree-pase AC motor and te frequency of te stator current f 60 f n meet te equation of te relationsip p, te motor is known as te syncronous motor. Wen syncronous generators are connected into parallel or grid, in order to avoid te large impact current wit power grid, syncronous generators connected into grid sould meet tree conditions, namely same pase and frequency wit grid, and te excitation EMF and grid voltage are equal in size and direction. To acieve grid-connected, te first condition must be met, te oter two may allow a sligt discrepancy. According to te specific requirements of grid-connected: n order to ensure safety, te system voltage deviation is not more tan 0% of te rated voltage, te pase deviation is not more tan 0 degrees, te frequency deviation is not more tan %. Tis paper gives te model of syncronous motor power generation and power generation, as sown in Fig.. Fig. Model of grid-connected syncronous motor Te power supply of te syncronous motor is supplied via te transformer. After te B position is connected to te ground fault, te current waveform and armonic spectrum of te simulation are sown in Fig.3 and Fig.4. 4

5 Fig.3 Tree pase current waveform during B position grounding fault Fig.4 Te current armonic spectrum of B position after te coincidence gate t can be seen tat tere are mainly nd, 3rd and 5t armonic currents in te 60Hz current, and te total armonic distortion rate of te B position is 6.0%. 5. Summary Tis paper analyzes te arm and te main armonic sources, and te armonics of power generation and grid-connected are analyzed in view of te problem tat te distributed generator can generate large armonics in te environment wit nonlinear load. A simulation model of syncronous generator is establised in MATLAB, and te main armonic and current total armonic distortion rate are acieved troug te analysis of te current armonic spectrum and te FFT analysis window, wic provide te teoretical data for armonic suppression in te future. References []. Jia Wen. Harmonic detection and analysis of tree pase bridge circuit [J]. Sanxi Electronic Tecnology, 04,04:8-0. []. Yongpei Cen. Application and development of power armonic in electric power measurement [J]. Heilongjiang Science and Tecnology nformation, 04,0:37. [3]. San Ci. Harm and suppression of armonics in electrical system design of civil buildings [J]. Electrical applications, 03,06:66-7. [4]. Dajun Tao, Baojun Ge. Te armonic caracteristics of te starting low frequency operation stage of te static frequency converter of te power generation motor [J]. Cinese Journal of Electrical Engineering, 04,36: [5]. Qing Zong. Design of syncronous generator in parallel connection training [J]. Modern enterprise education, 0,: [6]. Hong Liu. Distributed grid connected resonant suppression strategy based on grid connected voltage control [J]. Power grid tecnology, 05,0: [7]. Zibin Ye. Te arm and control of current armonic to electrical equipment [J]. Tecnology and enterprise, 0,6:8. [8]. iyang Song, Zong Zang. Harm and control of power system armonics [J]. Electrical tecnology of intelligent buildings, 009,05: