A SIMPLIFIED CONTROL SCHEME FOR THREE-PHASE THREE-LEVEL (NPC) SERIES ACTIVE FILTER TO COMPENSATE ALL VOLTAGE PERTURBATIONS

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1 52 Acta Electrotechnica et Informatica, Vol. 11, No. 4, 211, 52 59, DOI: / A SIMPLIFIED CONTROL SCHEME FOR THREE-PHASE THREE-LEVEL (NPC) SERIES ACTIVE FILTER TO COMPENSATE ALL VOLTAGE PERTURBATIONS Salim CHENNAI *, Mohamed Toufik BENCHOUIA ** * Electrical Engineering Department, Nuclear Research Center of Birine, Algeria, chenaisalimo@yahoo.fr ** Electrical Engineering Department, L.G.E.B, Uniersity of Biskra, Algeria ABSTRACT This paper presents a simplified control scheme for three-phase three-leel series actie power filter to compensate all load oltage perturbations such us harmonic unbalances, sags and swells. The standard configuration of three-phase series actie power filter uses the two-leel three-phase oltage source inerter with hysteresis controller. This configuration presents some drawbacks and is limited to low power systems. Today three-leel (NPC) inerter is one of the most successfully employed topology in arious industrial applications. In this paper a new scheme to increase the capability of series Actie Power Filter (APF) oltage controller based on three-leel inerter using simplified Pulse Width Modulation (PWM), is proposed. The control strategy adopted use instantaneous reactie power theory, easy to implement and gies good performance for all load oltage perturbations. The numerical simulation results carried with MATLAB-Simulink and SimPowerSystem Toolbox show the effectieness of the proposed control scheme. Keywords: Logic oltage controller, Three-leel (NPC) inerter, Series actie power filter, Voltage perturbation compensation, Matlab-Simulink and SimPowerSystem Toolbox 1. INTRODUCTION With proliferation of nonlinear loads, harmonic pollution is being considered as one of the major problems that degrade the power quality [1]. So far, shunt actie power filters hae been proposed as an interesting and high performance solution to improe the power quality, the shunt actie power filter is used for reactie power and load current compensation by injecting equal but opposite harmonics current [2]. To protect sensible loads and improe the power quality in the distribution system, some solutions hae been proposed by seeral authors. Among them the series actie power filters hae proen as an important and flexible alternatie to compensate most important oltage perturbations []. The series actie filter is especially used for compensation of oltage: unbalances, sags, swells and harmonics. The series actie filter injects a oltage component in series with the supply oltage and can be regarded as a controlled oltage source [4]. The standard configuration is based on PWM-Voltage Source Inerter inserted in series between the load and the source oltage. Three single phase transformers are used to perform the series connection. This structure is limited to low power applications, for medium or high oltage three-leel inerter is recommended. The performance of any Series AF is based on three essentials design criteria: inerter topology, method used to determining the reference oltage compensation and lastly the controller capable to generate the inerter switching pulses. Today three-leel inerter is one of the most widely employed multileel topology and is applied in medium and high power applications [5]-[6]. The principally control techniques used to determining the compensation reference oltage are the instantaneous power theory [7] and the synchronous reference frame detection method [8]. The controller is the main part of any actie power filter operation and has been a subject of many researches in recent years [9], pwm controller is a ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM one of most commonly used controller with good performance compared to conentional hysteresis controller. This paper presents a new pwm oltage controller for three-leel neutral point clamped (NPC) series actie filter for protecting sensible and critical oltage loads under all oltage perturbations. Simulation results are presented in order to emphasize the good performance of the proposed series power filter topology. The systems performance is ealuated using Matlab-Simulink and SimPowerSystem Toolbox under different oltage perturbations in terms of source oltage Total Harmonic Distortion (THD) and robustness compensation under different source perturbations. The obtained results show the effectieness of the proposed control scheme. The organization of this paper begins with series actie filter configuration based on three-leel inerter, followed by control strategy adopted to calculate compensation oltages, before coming to the results simulation and discussion, and ended with conclusions. 2. SERIES ACTIVE FILTER CONFIGURATION The circuit configuration of the series actie filter is shown in figure 1. The Series AF is inserted between the perturbed oltage source and a protected load. It is composed of three phase oltage source conerter, LfCf filter to suppress switching ripples and series transformers which inject the compensating oltage to the line [1]. Fig. 1 Three-leel (NPC) series actie filter ISSN (online)

2 Acta Electrotechnica et Informatica, Vol. 11, No. 4, THREE-LEVEL (NPC) INVERTER Multileel inerters are being inestigated and recently used for actie filter topologies. Three-leel inerters are becoming ery popular today for most inerter applications, such as machine dries and power factor compensators. The adantages of these conerters are reduction of the harmonic content generated by the actie filter and decreasing the oltage or current ratings of the semiconductors. Figure 2 shows the three-leel inerter based on the six main switches (T11, T21, T1, T14, T24, T 4) of the traditional two-leel inerter, adding two auxiliary switches (T12, T1, T22, T2, T2, T) and two neutral clamped diodes on each bridge arm respectiely, the diodes are used to make the connection with the point of reference to obtain Midpoint oltages. For this structure, three kinds of output oltage leel can obtain Udc/2, and Udc/2 corresponding to three kinds of switching states P,, N. As a result, there exist 27 kinds of switching output from the three-phase three-leel inerter [11], [12]. top two switches Tk1 and Tk2 are turned on, the switching state is P. When the medium switches Tk2 and Tk are turned on switching state is O. When the lower switches Tk and Tk4 are turned on, the switching state is N [1]. Table 1 Switching states of three-leel inerter Switching Voltage Tk1 Tk2 Tk Tk4 States output P Ud/2 ON ON OFF OFF OFF ON ON OFF N Ud/2 OFF OFF ON ON 4. REFERENCE VOLTAGE IDENTIFICATION The proposed series actie filter adopted the power reactie theory to compensate all oltage perturbations. To extract the reference oltages a p-q theory described in [7], [8] is used. When the three-phase load instantaneous oltages Ulu, Ul, Ulw and currents Ilu, Il, Ilw, are transformed into two-phase (α β) coordinates, two phase oltages u, u and currents i, i are respectiely gien by: u u i i Ulu Ulu Ul C U 2 l (4) U lw U lw ilu ilu il C i 2 l (5) i lw i lw 2 2 Fig. 2 Three-leel NPC inerter The switch connection function FKS indicates the opened or closed state of the switch TKS [12]: 1 If T close ks FKS (1) If T open ks For a leg K of the three phases three-leel NPC VSI, seeral complementary control laws are possible. The optimal control law of this inerter is: FK 41FK 1 FK 1FK 2 Half leg connection function b K 4 K1 K 2 b FK FK 4 K F F F F b F is defined as: km With m=1 for the lower half leg and m= for the upper half leg. As indicated in Table 1, each leg of the inerter can hae three possible switching states, P, O, or N. When the (2) () On the (α β) plane, u can be considered to be composed of u and u and i of i and i : u u u (6) i i i Assume that of i and u q ofi ; u u p q u u p q u p and uq u p is the projection of u in the direction the projection of u in the ertical direction can be represented by: U lu sint cost U l cost sint U lw 2 2 U lu C C pq 2 Ul U lw Where C pq is the pq transformation matrix, which executes the calculation to conert the two-phase oltages u and u into u p and u q. (7) ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM ISSN (online)

3 54 A Simplified Control Scheme for Three-Phase Three-Leel (NPC) Series Actie Filter to Compensate When Ulu, Ul and Ulw are the three-phase oltage source, the respectie components u p and uq in u p and uq are corresponding to the positie sequence fundamental actie and reactie components in three-phase oltages. The fundamental components Uluf, Ulf and Ulwf in load oltages can be obtained by an inerse transformation of (7): 1 1 Uluf sint cost u p Ulf cost sint U uq lwf 2 2 U luf 1 u p Ulf C C 2 pq u U q lwf 1 Where C is the inerse matrix of C pq pq, which executes the calculation to conert u p and u q back into (α β) coordinates. Hence the oltage compensation can be calculated out as: Uluc Ulu Uluf Ulc Ul Ulf U lwc U lw U lwf (8) (9) Fig. 4 PWM logic control The control of inerter is summarized in the two following stages: Determination of the intermediate signals Vi1 and Vi2: If error Ec carrying 1 Then Vi1= 1, If error Ec carrying 1 Then Vi1=, If error Ec carrying 2 Then Vi2=, If error Ec carrying 2 Then Vi2=-1. Determination of control signals of the switches Tij (i=1,2,; j=1,2,,4): If (Vi1+Vi2)=1 Then Ti1=1, Ti2=1, Ti=, Ti4=, If (Vi1+Vi2)= Then Ti1=, Ti2=1, Ti=1, Ti4=, If (Vi1+Vi2)=-1 Then Ti1=, Ti2=, Ti=1, Ti4=1. 6. SIMULATION RESULTS AND DISSCUSSION The Matlab-Simulink simulation block diagram of the proposed three-leel series actie filter based on pwm oltage controller is shown in figure 5. The model parameters used for simulation are: Voltage source Vs=22V, Frequency Fs=5Hz, Resistor Rs=.1mΩ, Inductance Ls=.2mH, Resistor Rl =48.6Ω, Inductance Ll=4mH, Capacitance C1= C2=μF, Resistor Rc=.27m Ω, Inductance Lc=.8mH. Fig. Reference compensation oltage calculation 5. SERIES ACTIVE FILTER LOGIC CONTROL The PWM logic controller for three-leel (NPC) inerter proposed to replace conentional hysteresis controller is shown in figure 4. The difference between the injected oltage and the reference oltage determines the reference oltage (e), this output oltage is compared with two carrying triangular identical waes shifted one from other by a half period of chopping and generate switching pulses[14]. Fig. 5 Three-leel series actie filter using pwm oltage controller based on p-q theory ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM ISSN (online)

4 Acta Electrotechnica et Informatica, Vol. 11, No. 4, The proposed series actie power filter is simulated under MATLAB-Simulink and SimPower System enironment to estimate its' performance. It is tested for seeral different operating conditions such as steady-state, transient condition for oltage sag, swell, unbalance and under balanced distorted utility oltages, intending to alidate the Series APF system performance. The simulation results obtained for all oltage perturbations are shown in figures 6 to 12 and discussed in the following subsections Voltage harmonics compensation compensation oltages (V) (c) Compensation oltages When the three-phase oltages are balanced-distorted, the mains oltages contain the fundamental component and harmonic components. The expression of the balanced-distorted oltages source used is expressed bellow: 11sin( t) 141sin(2 t) 5 sin(4 t) 14 sin(5 t) sa sin( t ) 141sin(2 t ) sb (1) sin(4 t ) 14 sin(5 t ) sin( t ) 141sin(2 t ) 5 sin(4 t ) sc 4 14 sin(5 t ) At time t1=.1s to t2=.2s, harmonic oltage perturbation is introduced oluntarily in the utility. The series APF is put into the operation; it starts immediately the process of compensation. The load oltage before series actie filter operation, three-phase fundamental oltages, injected oltages by series APF and the threephase compensated oltages deliered to critical load are shown in figure 7. After compensation the THD of the load oltage is reduced from 46.9% to.52% in conformity with IEEE-519 standard Norms (d) Load oltages after compensation Fig. 6 Simulation results with harmonics oltage compensation Magnitude compared to fundamental Harmonic order Fig. 7 Load oltage harmonic spectrum without Series AF (Fundamental (5Hz) = 1.1, THD=46.9%) (a) Load oltages before compensation Magnitude compared to fundamental Harmonic order (b) Reference oltages Fig. 8 Load oltage harmonic spectrum with Series AF (Fundamental (5Hz) = 8.2, THD=.52%) ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM ISSN (online)

5 56 A Simplified Control Scheme for Three-Phase Three-Leel (NPC) Series Actie Filter to Compensate 6.2. Voltage unbalances compensation In this case, the three phase oltages sources are unbalanced, but do not contain harmonic components, their expressions are gien in (11): 11sin( t) 1sin( t) sa sin( t ) 1sin( t ) (11) sb sin( t ) 1sin( t ) sc Figure 9 shows the three-phase oltage load, threephase fundamental oltages, three-phase oltage compensation and the three-phase compensated load oltage with unbalance oltage perturbation introduced oluntary between t1=.1s and t2=.2s. 6.. Voltage sags compensation To study the performance of series actie filter during oltage sag conditions, we suppose that the load oltage is sinusoidal and the sag (5%) is introduced oluntary between instants t1=.1s and t2=.2s. The expression of the sag oltage is gien by equation (12): sa sb sc 2 sin( t) 4 2 sin( t ) (12) 2 2 sin( t ) The series APF is put into operation instantly to compensate this perturbation. After instant t2=.2s, the system is again at normal working condition. The load (a) Load oltages before compensation (a) Load oltages before compensation (b) Reference oltages (b) Reference oltages compensation oltages (V) compensation oltages (V) (c) Compensation oltages (c) Compensation oltages (d) Load oltages after compensation Fig. 9 Simulation results with unbalances oltage compensation ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM (d) Load oltages after compensation Fig. 1 Simulation results with sags oltage compensation ISSN (online)

6 Acta Electrotechnica et Informatica, Vol. 11, No. 4, oltages, three-phase fundamental oltages, compensating oltages and the load oltages after compensation obtained by simulation are shown in figure Voltage swells compensation A swell (5%) is now introduced on the system during the time t1=.1 sec to t2=.2 sec. Under this condition the series APF injects an out of phase compensating oltage ( %) in the line through series transformers, equal to the difference between the reference load oltage and oltage without compensation. As shown in figure 11 the load oltage profile before compensation, three-phase fundamental oltages, the compensating oltages in and the load oltages after compensation using the proposed series actie filter. The expression of the swell oltage is gien by equation (1): sa sb sc 4 sin( t) 4 4 sin( t ) (1) 2 4 sin( t ) 6.5. All oltage perturbation compensation The performance of the proposed Series actie power filter system is also tested under all oltage perturbations simultaneously. The simulation results are shown in figure 1. The oltage swell is introduced oluntarily in the utility oltage (5%) between t1=.1s and t2=.16s. And after that, a oltage sags (%) is introduced between t2=.16s and t=.22s. The oltage harmonics is introduced between t=.22s and t4=.28s. The oltage (a) Load oltages before compensation (a) Load oltages before compensation (b) Reference oltages (b) Reference oltages compensation oltages (V) compensation oltages (V) (c) Compensation oltages (c) Compensation oltages (d) Load oltages after compensation Fig. 11 Simulation results with swells oltage compensation ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM (d) Load oltages after compensation Fig. 12 Simulation results with all oltage compensation ISSN (online)

7 58 A Simplified Control Scheme for Three-Phase Three-Leel (NPC) Series Actie Filter to Compensate unbalances is introduced between t4=.28s and t5=.4s. After t5=.4s the system is again at normal working condition. The load oltages, three-phase fundamental oltages, compensating oltages and the load oltages after compensation obtained by simulation are shown in figure 12. It is illustrate that the proposed system does not show any significant effect of distortion present in the utility oltages on its compensation capability and the load oltage under all oltage perturbations is maintained constant and sinusoidal. The performance of the proposed series AF system is tested under all oltage perturbations separately and simultaneously: harmonics, swells, sags and unbalances. Figures 7 and 8 show respectiely the harmonic spectrum of the oltage deliered to sensible loads before and after application of the series actie filter. It is obsered that the load oltage harmonics is widely reduced from 46.9% to.52% in conformity with standard Norms. In cases of oltage swell (5%), oltage sag (%) and unbalances introduced oluntarily in the supply oltage between t1=.1s and t2=.2s, the load oltage is instantly compensated. The effectieness of the proposed series actie filter has been demonstrated in maintaining the three-phase load oltages balanced and sinusoidal, moreoer the proposed system does not show any significant effect of perturbation type present in the utility oltages on its compensation capability and the load oltage under all oltage perturbations is maintained constant and sinusoidal. 7. CONCLUSIONS To enhance the power quality and improe the oltage deliered to sensible and critical loads, a new series actie power filter configuration using pwm oltage controller based on three-leel (NPC) inerter topology has been proposed in this paper. The oltage perturbations studied in this paper concern oltage: harmonics, sags, swells and unbalances, all these perturbations are successfully compensated using the proposed system. The load oltage harmonic leels are maintained below IEEE-519 standard Norms when the source oltage is distorted, the THD of the load oltage is significantly reduced from 46.9% to.52%. The simulation results show that the new system is efficacies and compensates all type of oltage perturbations. Howeer, the current source is highly distorted and rich on harmonics. To eliminate this drawback, the future research work will be focused on current source compensation using hybrid series actie filter configuration or Unified Power Quality Conditioner system. REFERENCES [1] HONGHAO ZHONG PINGPING CHEN ZHENGYU LU ZHAOMING QIAN: Noel Control Scheme Based on Per-phase Reference Current Calculation for Hybrid Series Actie Power Filter with Fundamental Current Bypass Channel in Unbalanced Conditions, IEEE, 5th Annual Power Electronics Specialists Conference, pp , 24. [2] AB. HAMADI S. RAHMANI K. AL-HADDAD: Series Actie Filter to mitigate power quality for medium size industrial loads (multi-pulses transformer and modern AC drie, IEEE, ISIE, pp , 26. [] AB. HAMADI S. RAHMANI K. AL-HADDAD: A new hybrid series Actie Filter configuration to compensate oltage sag, swell, oltage and current harmonics and reactie power, IEEE, International Symposium on Industrial Electronics, pp , 29. [4] F. Z. PENG H. AKAGI A. NABAE: A new approach to harmonic compensation in power systems a combined system of shunt passie and series actie filters, IEEE Trans. Ind. Applicat., ol. 26, n 6, pp , 199. [5] O. VODYAKHO D. HACKSTEIN A. STEIMEL T. KIM: Noel direct current-space ector control for shunt actie power filters based on three-leel inerters, IEEE, pp , 28. [6] O. VODYAKHO T. KIM S. KWAK: Comparison of the space ector current controls for shunt actie power filters, IEEE, pp , 28. [7] REYES H. HERRERA PATRICIO SALEMERON HOYOSUNG KIM: Instantaneous Reactie Power Theory Applied to Actie Power Filter Compensation: Different Approaches, Assessment, and Experimental Results," IEEE, Trans. on Industrial Electronics, pp , 28. [8] S.BHATTACHRYA D. DIVAN: Synchronous frame based controller implementation for a hybrid series actie filter systems, IEEE, pp , [9] GUIYING LIU SHIPING SU PENG PENG: Intelligent Control and Application of All-function Actie Power Filter, IEEE, International Conference on Intelligent Computation Technology and Automation, pp , 28. [1] FATIHA MEKRI MOHAMED MACHMOUM NADIA AIT AHMED BENYOUNES MAZARI: A comparatie studies of oltage controllers of series actie power filter, Elseier, Electric power systems research, Article in press, pp. 1 12, 29. [11] A. MUNDUATE E. FIGURERES G. GARCERA: Robust model-following control of a three-leel neutral point clamped shunt actie filter in the medium oltage range, Elseier, Electrical Power and Energy Systems 1, pp , [12] YUN WAN JIANGUO JIANG.: The study of FPGA-based three-leel SVM NPC inerter, IEEE, pp , 29. [1] T. ABDELKRIM K. BEAMRANE E. M. BERKOUK T. BENSLIMANE: Neutral Point potential balancing algorithm for sliding mode controlled three-leel power filter, Electrical Engineering Journal, EEJ, 21. ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM ISSN (online)

8 Acta Electrotechnica et Informatica, Vol. 11, No. 4, [14] CHENNAI S. BENCHOUIA, M. T. GOLÉA, A. ZOUZOU, S. E.: Fuzzy logic current controller for shunt actie filter to compensate harmonic currents based on ANN dc oltage regulator, International Conference on Electrical Engineering, Electronics and Automatics, ICEEA 1, 21. Receied June 12, 211, accepted Noember 18, 211 BIOGRAPHIES Chennai Salim was born in Biskra, Algeria, on February, He obtained his engineering degree in Electrotechnics from Biskra Uniersity in He was recruited in 199 as senior engineer in power electronics in the Nuclear Research Center of Birine, Algeria. Since 2, he has been working as researcher in the Electrical Engineering Department. He obtained his M.Sc degree in electrical engineering in 29 from Medea Uniersity. He is currently working towards his PhD degree in Electrical Engineering from Biskra Uniersity, Algeria. His research interests are electrical dries, power electronics, energy quality, power systems, and intelligent control. Benchouia Mohamed Toufik He receied his engineering degree in Electrotechnics and M.Sc degree in electrical engineering from Biskra Uniersity in 1991 and 1998, respectiely. He obtained his Ph.D. in electrical engineering from Biskra Uniersity in 26. Since 21, he has held teaching and research positions in the Electrical Engineering Department of Biskra Uniersity, Algeria. His research interests include electrical dries, power electronics, energy quality and power systems. ISSN (print) 211 FEI TUKE Unauthenticated Download Date 1/15/14 :21 AM ISSN (online)