Inter national J our nal of Electrical and Computer Engineering (IJECE) V ol. 4, No. 3, June 2014, pp. 322 328 ISSN: 2088-8708 322 A Comparati v e Study between DPC and DPC-SVM Contr oller s Using dSP A CE (DS1104) Adel Mehdi * , Salah-eddine Rezgui * , Houssam Medouce * , and Hocine Benalla * * F acult ´ e des Sciences de la T echnologie, Uni v ersit ´ e de Constantine 1 * D ´ epartement de l’ ´ electrotechnique, Rue Ain el-Be y 25000, Alg ´ erie * Laboratoire de l’ ´ electrotechnique de Constantine LEC Article Inf o Article history: Recei v ed Feb 9, 2014 Re vised Apr 8, 2014 Accepted Apr 25, 2014 K eyw ord: Direct po wer control space v ector modulation switching table po wer quality con v erter control harmonics, po wer f actor ABSTRA CT The aim of this paper is to compare tw o dif ferent control structures. The Simple Direct Po wer Control (DPC) and the Direct Po wer Control with Space V ector Modulation (DPC- SVM) for tw o le v el con v erter applications. The first strate gy (DPC) has been de v eloped to control the instantaneous acti v e and reacti v e po wer directly by selecting the optimum switching state of the con v erter . Applied to the Pulse W idth Modulation (PWM) con v erter its main feature is to impro v e the total po wer f actor and ef ficienc y , e v en harmonics compo- nents e xistence. In the second structure, the acti v e and reacti v e po wers are used as (PWM) control v ariables instead of the three-phase line currents usually used in other techniques. It is sho wn that DPC-SVM e xhibits se v eral properties; good dynamic response, constant switching frequenc y , and in particular it pro vides a sinusoidal line currents. Sim ulation and e xperimental results has sho wn that both control structures achie v e good performances. Copyright c 2014 Institute of Advanced Engineering and Science . All rights r eserved. Corresponding A uthor: Adel Mehdi Uni v ersit ´ e de Constantine 1 Rue Ain el-Be y 25000, Campus Ahmed Hammani, Constantine. (+213)776178524 Email: adel hdm@yahoo.com 1. INTR ODUCTION As DC po wer supplies are e xtensi v ely used, not only in industrial fields, b ut also in consumer products, se v eral problems with re g ard to their diode rectifiers ha v e been observ ed in recent years, lik e the lo w input po wer f actor , and the presence of harmonics in the input currents. Consequently , the pulse width modulation (PWM) con v erters are adopted in applications that require less distortion in the current w a v eforms, thus the unity po wer f actor operation can be easily performed by re gulating the currents in phase with the po wer -source v oltages [1]. De v elopment of control methods for PWM rectifiers w as possible thanks to adv ances in po wer semicon- ductor de vices and digital signal processors, which allo w f ast operation and cost reduction. It of fers possibilities for implementation of sophisticated control algorithms. Appropriate control can pro vide both the rectifier performance impro v ements and reduction of passi v e components. V arious control strate gies ha v e been proposed in recent w orks for this type of PWM rectifier [2]. A well-kno wn method of indirect acti v e and reacti v e po wer control which is based on current v ector orientation with respect to the line v oltage v ector (v oltage oriented control V OC ) [3]. V OC guarantees high static performance via internal current control loops. Ho we v er , the final configuration and performance of the V OC system lar gely depends on the quality of the applied current control strate gy [4]. Another less kno wn method based on instantaneous direct acti v e and reacti v e po wer control is called direct po wer control (DPC) [1][5]. But both strate gies mentioned do not perform sinusoidal current when the line v oltage is distorted. Only DPC based on virtual flux [6] instead of the line v oltage v ector orientation [7], called VF-DPC, pro vides sinusoidal line current and lo wer harmonic distortion [6]. Ho we v er , it contains a se v eral disadv antages as: V ariable switching frequenc y (dif ficulties of LC input filter design) Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 323 High sampling frequenc y needed for digital implementation of h ysteresis comparators F ast microprocessor and A/D con v erters requirements Therefore, it w as dif ficult to implement VF-DPC in industry . But all of the abo v e dra wbacks can be eliminated when instead of the switching table a PWM v oltage modulator is applied [8]. 2. DIRECT PO WER CONTR OL Direct po wer control is based on the same control principles as in the direct torque control technique (DTC). In DTC, it’ s the electromagnetic torque and the rotor flux which are directly controlled, while in DPC, it’ s the stator acti v e and reacti v e po wers that are directly controlled [9]. Also, in DPC no internal current control loops or PWM modulator block are required, because the con v erter switching states are selected by a switching table based on the instantaneous errors between the commanded and measured v alues of acti v e and reacti v e po wer . Therefore, the main feature of the DPC implementation is a correct and f ast e xtraction of the acti v e and reacti v e po wer [1]. Figure 1. Configuration of DPC Controller for PWM con v erter [6] 2.1. Instantaneous P o wer Sour ce Calculation the acti v e and reacti v e po wers are obtained by the follo wing equations P = v a i a + v b i b + v c i c (1) Q = 1 p 3 [ v a ( i c i b ) + v b ( i a i c ) + v c ( i b i a )] (2) 2.2. Line V oltage V ector P osition The phase of the po wer -s ource v oltage v ector is con v erted to the sector signal i . F or t h i s purpose, the stationary coordinates are di vided into 12 sectors, as sho wn i n T able I, and the angle can be deduced from equation (3) [5]. = arctan v v (3) 2.3. Switching T able the selection of the adequate v ector is determined by the follo wing table according to the v ariation in the acti v e and reacti v e po wer with the position of v oltage v ector . A Compar ative Study between DPC and DPC-SVM Contr oller s Using dSP A CE DS1104 (Adel Mehdi) Evaluation Warning : The document was created with Spire.PDF for Python.
324 ISSN: 2088-8708 T able 1. Switching T able dq qp 1 2 3 4 5 6 7 8 9 10 11 12 0 0 6 1 1 2 2 3 3 4 4 5 5 6 0 1 6 7 1 0 2 7 3 0 4 7 5 0 1 0 1 2 2 3 3 4 4 5 5 6 6 1 1 1 7 7 0 0 7 7 0 0 7 7 0 0 3. DIRECT PO WER CONTR OL WITH PWM The DPC-SVM with constant switching frequenc y uses closed-loop po wer control, as sho wn in Figure 2. The commanded reacti v e po wer Q r ef set to zero for unity po wer f actor operation and deli v ered from the out er PI dc v oltage controller . The reference acti v e po wer P r ef and reacti v e po wer Q r ef which are in the DC frame and flo wing between the supply and the dc link are compared with the calculated P mes and Q mes respecti v ely . The errors are deli v ered to a PI controller to eliminate steady-state error , and the output signals are transformed to the fix ed frame and used for switching signals generation by the space-v ector modulator (SVM)[10]. Figure 2. Configuration of DPC-SVM Controller for PWM con v erter 3.1. Synthesis of Acti v e and Reacti v e P o wer Contr ollers The synthesis of acti v e and reacti v e po wer control lers can be done analytically using a simplified model. In this model the switching w a v eforms created by the PWM con v erter are replaced by its a v erage v alue within the switching period [3].The acti v e and reacti v e po wer in (dq) coordinates has the form after orientation the frame. Figure 3. Simplified block diagram[8] IJECE V ol. 4, No. 3, June 2014: 322 328 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 325 P = U I q s (4) Q = U I ds (5) 4. SIMULA TION RESUL TS 4.1. Dir ect P o wer Contr ol 4.2. Dir ect P o wer Contr ol with Modulation (a) (b) (c) (d) (e) (f) (g) (h) Figure 4. Simula ted basic signal w a v eforms and line cur - rent harmonic spectrum under purely sinusoidal line v olt- age for DPC. From the top: instantaneous acti v e and re- acti v e po wer , DC link v oltage, line current, and harmonic spectrum of the line current (THD = 4.87%). Figure 5. Simul ated basic signal w a v eforms and line cur - rent harmonic spectrum under purely sinusoidal line v olt- age for DPC-SVM. From the top: instantaneous acti v e and reacti v e po wer , DC link v oltage, line current, and harmonic spectrum of the line current (THD = 3.87%). A Compar ative Study between DPC and DPC-SVM Contr oller s Using dSP A CE DS1104 (Adel Mehdi) Evaluation Warning : The document was created with Spire.PDF for Python.
326 ISSN: 2088-8708 5. EXPERIMENT AL RESUL TS 5.1. Dir ect P o wer Contr ol 5.2. Dir ect P o wer Contr ol with Modulation (a) (b) (c) (d) (e) (f) (g) (h) Figure 6. Experimental results for DPC. From the top: instantaneous acti v e and reacti v e po wer , DC link v oltage, line current, and a focused part of the line current. Figure 7. Experimental results for DPC-SVM. From the top: instantaneous acti v e and reacti v e po wer , DC link v oltage, line current, and a focused part of the line cur - rent. 6. EXPERIMENT AL SYSTEM CONFIGURA TION An e xperimental study has been de v eloped to e xamine operating characteristics of both techniques DPC and DPC-SVM. The po wer circuit of the PWM con v erter is constituted by an insulated g ate bipolar transistor (IGBT)- IJECE V ol. 4, No. 3, June 2014: 322 328 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 327 based full-bridge (SEMIKR ON) circuit. The electrical parameters are sho wn in T able II. Hall-ef fect current and v oltage sensors (LEM LA 25-NP) and (LEM L V 25-P) are emplo yed to detect the line currents and v oltages and the dc-b us v oltage. The estimation of the instantaneous po wer and the v oltages is proceeded by a dSP A CE card (DS1104), it is essential to mak e the control period as short as possible, because the estimating equations ha v e to be changed e v ery time of the switching state of the con v erter is changed. The interf ace circuits whi ch deal with detection of the line currents are specially desi gned to attain a f ast data acquisition corresponding to the control period of t he DSP [4]. F or this purpose, high-sampling-rate and high-resolution analog-to-digital con v erters (ADC’ s-12bit) are emplo yed in the system. All symbols that ha v e not been mentioned in the equation should be e xplained in the follo wing te xt. T able 2. P arameters Used In Simulation Po wer 7(kW) Grid side inductor 2e-3(H) Grid v oltage 250(V) Grid side resistor 3.87e-3( ) DC link v oltage 720(V) DC link capacitor 1e-3(F) Current 24(A) Load resistor(DC link) 68.8( ) Switching frequenc y 10(kHz) Simple time (DPC) 1e-6(S) Grid frequenc y 50(Hz) Simple time (DPC-SVM) 2e-6(S) T able 3. P arameters Used In Experiment Po wer 800(W) Grid side inductor 25e-3(H) Grid v oltage 104(V) Grid side resistor 0.7( ) DC link v oltage 190(V) DC link capacitor 1.1e-3(F) Current 4(A) Load resistor(DC link) 68.8( ) Switching frequenc y 10(kHz) Simple time (DPC) 8e-5(S) Grid frequenc y 50(Hz) Simple time (DPC-SVM) 8e-5(S) 6.1. Simulation Results and Analysis Fig.4-A and Fig.5-A sho w the beha viours of the instantaneous acti v e and reacti v e po wer under step v ariation, between 5 and 7 kW we can see that the responses of both structure pro vides an e xcellent performances, the quick v ariation of the acti v e po wer don’ t af fect the react i v e po wer which is k eeping at his references (v alue 0 V AR ), thus, decoupled control between acti v e and reacti v e po wer is achie v ed. Fig.4-B and Fig.5-B sho w the DC link capacitor v oltage, when a step v oltage is applied at t=0.6s, one can see, that the DPC-SVM structure need 0.1s to attend the references v alue. The phase current i a w a v eform is depicted on the Fig.4-C and Fig.5-C, the FFT analysis displays the fre- quenc y spectrum of the current grid. As e xpected, The T otal Harmonic Distortion (THD) is displayed abo v e the spectrum (THD=4.87% for DPC and THD=3.87% for DPC-SVM). 6.2. Experimental Results and Analysis Se v eral e xperimental tests ha v e been done to v erify feasibility of the proposed techniques. Fig.6 and Fig.7 presents the e xperimental results under the unity po wer f actor operation in the steady state. The po wer dissipated in the load resistance w as 750 (W) in DPC and 450 (W) in DPC-SVM, it can be seen that the po wer -source v oltage is successfully estimated. The line current i a sho wn on Fig.6(C-D) and Fig.7(C-D) is in phase with the actual po wer - source v oltage because the reacti v e po wer is controlled to be zero. The current w a v eform slightly contains lo wer order harmonic distortion. Fig. 6-A; Fig. 7-A; presents results of a step response a g ai nst the disturbance load po wer under the unity po wer f actor operation. The load po wer w as changed stepwise from 750 to 850 (W) in DPC and from 450 to 550 (W). It can be observ ed that the estimation of the po wer and v oltages can be performed and that the unity po wer f actor operation is successfully achie v ed, e v en in transient state, it can be observ ed that the acti v e po wer control and the reacti v e po wer control are independent of each other . A Compar ative Study between DPC and DPC-SVM Contr oller s Using dSP A CE DS1104 (Adel Mehdi) Evaluation Warning : The document was created with Spire.PDF for Python.
328 ISSN: 2088-8708 7. CONCLUSION This paper has described tw o concepts to impro v e the total po wer f actor and ef ficienc y of the PWM con v erter . The first method is direct instantaneous acti v e and reacti v e po wer control of the con v erter , in this method the acti v e and reacti v e po wer can be re gulated directly by relay control of the po wer , which is implemented by h ysteresis comparators and a switching table. In this configuration, the errors between the po wer commands and the feedback signals are compared by the h ysteresis el ements, and the specific switching state of the con v erter is appropriately selected by the switching table, so that the errors can be restricted within the h ysteresis bands. Also it is sho wn that DPC-SVM has pro v en e xcellent performance and v erifies the v alidity of the proposed control system. The DPC-SVM system constitutes a viable alternati v e to the con v entional control strate gies and it has the follo wing features and adv antages: Lo wer sampling frequenc y (than a con v entional DPC) Good dynamic response Of fers sinusoidal line currents (lo w THD), for ideal and distorted line v oltage Constant switching frequenc y A CKNO WLEDGEMENT we w ould lik e to thanks all members of (Laboratoire de l’ ´ electrotechnique de Constantine LEC) for your helps to complete this w ork . REFERENCES [1] Noguchi et al. ”direct po wer control of PWM con v erter without po wer -source v oltage s ensors”. Industry Appli- cations, IEEE T r ansactions on , 34(3):473–479, 1998. [2] Kazmierk o wski. ”control strate gies for PWM rectifier/in v erter -fed induction motors”. In Industrial Electr onics, 2000. ISIE 2000. Pr oceedings of the 2000 IEEE International Symposium on , v olume 1, page TU15–TU23. IEEE, 2000. [3] Lechat. ”v oltage oriented control of three-phase boost PWM con v erters”. 2010. [4] Malino wski et al. ”a comparati v e study of control techniques for PWM rectifiers in A C adjustable speed dri v es”. P ower Electr onics, IEEE T r ansactions on , 18(6):1390–1396, 2003. [5] Serpa et al. ”a modified direct po wer control strate gy allo wing the connection of three-phase in v erters to the grid through LCL filters”. Industry Applications, IEEE T r ansactions on , 43(5):1388–1400, 2007. [6] Serpa et al. ”virtual-flux direct po wer control for mains connected three-le v el npc in v erter systems”. In P ower Con ver sion Confer ence-Na goya, 2007. PCC’07 , page 130–136. IEEE, 2007. [7] Hu et al. ”direct acti v e and reacti v e po wer re gulation of grid-connected DC/A C con v erters using sliding mode control approach”. P ower Electr onics, IEEE T r ansactions on , 26(1):210–222, 2011. [8] Malino wski et al. ”simple direct po wer control of three-phase PWM rectifier using space-v ector modulation (DPC-SVM)”. Industrial Electr onics, IEEE T r ansactions on , 51(2):447–454, 2004. [9] T remblay et al. ”direct po wer control of a DFIG-based WECS with acti v e filter capabilities”. In Electrical P ower & Ener gy Confer ence (EPEC), 2009 IEEE , page 1–6. IEEE, 2009. [10] Restrepo et al. ”a simple switch selection state for SVM direct po wer control”. In Industrial Electr onics, 2006 IEEE International Symposium on , v olume 2, page 1112–1116. IEEE, 2006. BIOGRAPHY OF A UTHOR Adel Mehdi is a Ph.D. student and member at the electro-technique laboratory of Constantine LEC with Master of management and transformation of Electrical Ener gy from Uni v ersity of Constan- tine 1 Algeria (2011). He obtained Licence De gree in Ele ctrical Engineering from Institute the sciences of T echnology in 2009. His researc hes are in fields of control systems , digital signal pro- cessing,direct po wer control, microprocessors, rene w able ener gy , and micro-grids. He is af filiated with IEEE as student member from 2012.and at uni v ersity agenc y of francophone A UF from 2011. IJECE V ol. 4, No. 3, June 2014: 322 328 Evaluation Warning : The document was created with Spire.PDF for Python.