Inter national J our nal of P o wer Electr onics and Dri v e Systems (IJPEDS) V ol. 6, No. 4, December 2015, pp. 683 692 ISSN: 2088-8694 683 De v elopment of Pr edicti v e Curr ent Contr oller f or Multi-P ort DC/DC Con v erter Santhosh T K and Go vindaraju C Department of Electrical and Electronics Engineering,Go v ernment Colle ge of Engineering, Salem,India Article Inf o Article history: Recei v ed Jul 03, 2015 Re vised Aug 14, 2015 Accepted Aug 29, 2015 K eyw ord: Multiple Input Con v erter Predicti v e Current Control Hybrid Electric V ehicle Ultracapacitor Digital Signal Processor ABSTRA CT This paper in v estig ates the utilization of a predicti v e current control for a four port DC/DC po wer electronic con v erter with an input port, tw o storage ports and a load port suitable for a Hybrid Electric V ehicle. Being a po wer con v erter with mult iple ports, it has dif fer - ent operating modes. While the Stateflo w controller is emplo yed to handle mode selection, the predicti v e current controller is us ed to control the inductor current . The control la ws go v erning each operating mode is deri v ed out for v a lle y current control. By making the inductor current in the upcoming switching c ycle equi v alent to the reference, the duty c y- cle is predicted. Simulation and e xperime ntal results sho w impro v ements in current ripple minimization, f aster dynamic performance and comparable to traditional PI control method. Copyright c 2015 Institute of Advanced Engineering and Science . All rights r eserved. Corresponding A uthor: T .K. Santhosh Department of Electrical and Electronics Engineering Go v ernment Colle ge of Engineering, Salem,India Email: tksanthosh.kct@gmail.com 1. INTR ODUCTION The recent de v elopments in the po wer processing and storage technology are promoting electric propulsion. Dif ferent po wer con v erter topol ogies suitable for automoti v e applications ha v e found rene wed interest in the recent past. During the course of its e v olution, man y sources and storage units ha v e found its place in a Hybrid Electric V ehicle. Dif ferent topologies incorporating multiple input and output ports ha v e been de v eloped in the past. These po wer con v erters emplo y dif ferent control techniques to achie v e control objecti v es [1]. The control objecti v e could be tar get current [2, 3] or v oltage [4], the limit on a ripple [5], f aster or slo wer response [6] and quick reco v ery from a disturbance or a stability cr iterion [7]. T raditional control techniques in both analog and digital domain ha v e been in use for an e xtended period. W ith the adv ent of digital control, the traditional analog ha v e transformed into the digital domain, and ne w controllers are being introduced to control a specific or set of system paramet ers. Inductor current control is one of the control method that helps to e xtract constant po wer from input sources. Inductor current control is usually done by making the inductor current to follo w a particular reference to minimize error . The idea of predicti v e control is to predict the duty c ycle of the succeeding switching c ycles based on the measured system parameters. The predicti v e current could be of three types: v alle y , peak or a v erage current. Out of these three, v alle y current control is in v estig ated in this w ork for trailing edge modulation. The Predicti v e Current Control(PCC) is applied to a F our Port Con v erter proposed in [8]. Control la ws are deri v ed for each operating mode, and the performance is analyzed both through simulation and e xperimental results. The concept of predicti v e control [9, 10, 11, 12] is to predict the duty c ycle command for the upcoming switching periods based on the pres ent and past status of system parameters. The topology selected in this w ork necessitates a strict constraint on the inductor current that shall be fulfilled by the predicti v e current control technique. Each mode necessitates a separate control la w . Ho we v er , from the analysis, it has been found that the first four operating modes utilize a similar control la w with dif ferent parameters for duty c ycle c o m putation. So the same control la w could be implemented for the modes I-IV , by switching the parameters used for computation. Mode V and VI utilize a separate control la w for duty c ycle command computation. By making the predicted current equal to the Evaluation Warning : The document was created with Spire.PDF for Python.
684 ISSN: 2088-8694 Figure 1. F our Port Con v erter for Hybrid Electric V ehicle reference current in the computation of duty c ycle, the reference current could be easily achie v ed. The originality of the w ork lies in the utilization of predicti v e controller for the inductor current inductor current and its implementation to the F our Port Con v erter . The rest of the paper is or g anized as follo ws: section II presents the details of the po wer con v erter topology , section III deals with dif ferent operating modes and the deri v ation of control la ws, section IV e xplains the control la w implementation, section V presents the results and section VI concludes the paper . 2. T OPOLOGY A F our Port Con v erter with an input port( V i ), tw o storage ports( V b ; V uc ) and a load port( V 0 ) suitable for Hybrid Electric V ehicle applications is considered for the implementation of predicti v e current control. The po wer circuit of the con v erter is sho wn in Figure 1. Being a multi-port topology , it has six dif ferent operating modes. Each operating mode has tw o dif ferent switching states. A summary of all the operating modes with the first switching state denoted by the dark ened lines and the second switching state represented by discontinuous red line is sho wn in Figure 2 and Figure 3. The detailed synthesis and analysis of the four port con v erter is handled in [8]. This con v erter requires tw o dif ferent controllers: one for mode selection and other for inductor curr ent re gulation. A Stateflo w controller is used for mode selection and the predicti v e control is used for current re gulation. The Predicti v e Current Controller has to respond to sudden v ariations in modes and system parameters. Our in v estig ation is limited to the utilization of predicti v e current control for inductor current re gulation. 3. PREDICTIVE CURRENT CONTR OL FOR FPC This section presents the control la w deri v ation for each operating mode. T o be gin with, the inductor current w a v eform is considered and a duty c ycle is deri v ed using the char ge-second balance. The duty c ycle calculation is then e xtended to the another switching period to find the final e xpression. 3.1. Mode I In the first operating mode (refer Figure 2(a)), ener gy is transferred from the primary source port ( V i ) to the load ( V 0 ). In the first state(denoted by dark ened lines) S 3 , D 1 , and D 3 are ON and during the second switching state(denoted by discontinuous red line), switching de vices D 1 and D 2 are turned ON. The char ging slope is gi v en by V i =L 1 and the dischar ging slope is gi v en by ( V i V 0 ) =L 1 as sho wn in Figure 4. Assuming the con v erter operates in Continuous Conduction Mode(CCM), the ne xt switching c ycle als o repeats the same beha vior . The inductor current i ( n ) in n th switching c ycle is gi v en by , i ( n ) = i ( n 1) + V i d 3 [ n ] T s L 1 + ( V i V 0 ) d 0 3 [ n ] T s L 1 (1) Where T s is the switching period and d 3 is the duty c ycle of switch S 3 . Extending the same ar gument to the ( n + 1) th switching c ycle, i ( n + 1) = i ( n 1) + V i d 3 [ n ] T s L 1 + ( V i V 0 ) d 0 3 [ n ] T s L 1 + V i d 3 [ n + 1] T s L 1 + ( V i V 0 ) d 0 3 [ n + 1] T s L 1 (2) IJPEDS V ol. 6, No. 4, December 2015: 683 692 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 685 (a) Mode I (b) Mode II (c) Mode III (d) Mode IV Figure 2. Switching States in Operating Modes I-IV Grouping v ariables, i ( n + 1) = i ( n 1) + 2 V i T s L 1 V 0 T s ( d 0 3 [ n ] + d 0 3 [ n + 1]) L 1 (3) Using the relation d+d’=1 and rearranging, the duty c ycle for ( n + 1) th is gi v en by d 3 [ n + 1] = 2 d 3 [ n ] + L 1 V 0 T s [ i ( n + 1) i ( n 1)] 2 V i V 0 (4) De velopment of Pr edictive Curr ent Contr oller (Santhosh T K) Evaluation Warning : The document was created with Spire.PDF for Python.
686 ISSN: 2088-8694 (a) Mode V (b) Mode VI Figure 3. Switching states in Operating Modes V -VI Figure 4. Inductor Current W a v eform 3.2. Mode II In this mode, ener gy is transferred from the primary storage de vice( V b ) to the load(refer Figure 2(b)). This mode is initialized when V i drops belo w a prefix ed threshold le v el. So the diode D 1 will block the primary source( V i ). In the first state, the switching de vices S 1 ; S 3 and D 3 are turned ON and the switching de vices S 1 ; D 2 are turned ON IJPEDS V ol. 6, No. 4, December 2015: 683 692 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 687 during the second switching state. The char ging and dischar ging slope could be found in T able 1. Inductor current for ( n + 1) th switching c ycle in Mode II is gi v en by , i ( n + 1) = i ( n 1) + V b d 3 [ n ] T s L 1 + ( V b V 0 ) d 0 3 [ n ] T s L 1 + V b d 3 [ n + 1] T s L 1 + ( V b V 0 ) d 0 3 [ n + 1] T s L 1 (5) Simplifying for duty c ycle in ( n + 1) th switching period, d 3 [ n + 1] = 2 d 3 [ n ] + L 1 [ i ( n + 1) i ( n 1)] V 0 T s 2 V b V 0 (6) Mode Source Port Load Port Description Char ging slope Dischar ging slope I V i V 0 Input source supplying load V i L 1 V i V 0 L 1 II V b V 0 Primary storage supplying load V b L 1 V b V 0 L 1 III V i , V uc V 0 Secondary storage aids Input source to supply load V i + V uc L 1 V i V 0 L 1 IV V b ; V uc V 0 Secondary storage aids primary storage to supply load V b + V uc L 1 V b V 0 L 1 V V i V b Input source supplying primary storage V i L 1 V i V b L 1 VI V 0 V uc Re generation V 0 L 2 V uc L 2 T able 1. Summary of Dif ferent Operating Modes 3.3. Mode III This is a h ybrid mode which utilizes po wer from the primary source ( V i ) and secondary storage port( V uc ) to the load. This mode(Figure 2(c)) is initialized when the v oltage le v el of the primary source f alls belo w a threshold v alue. The polarity of the secondary storage is re v ersed to ensure v oltage addition. switching de vices S 3 ; S 4 and D 1 are turned on in state I and during switching state II D 1 and D 2 are ON. The inductor current in ( n + 1) th c ycle is gi v en by , i ( n + 1) = i ( n 1) + ( V i + V uc ) d 4 [ n ] T s L 1 + ( V i V 0 ) d 0 4 [ n ] T s L 1 + ( V i + V uc ) d 4 [ n + 1] T s L 1 + ( V i V 0 ) d 0 4 [ n + 1] T s L 1 (7) Re grouping v ariables and solving for the predicted duty c ycle yields, d 4 [ n + 1] = L 1 ( V uc + V 0 ) T s [ i ( n + 1) i ( n 1)] + 2 V 0 V i V uc + V 0 d 4 [ n ] (8) 3.4. Mode IV This is another h ybrid mode in which secondary storage ( V uc ) assists primary storage port ( V b ) and deli v ers po wer to the load port. This mode(Figure2(d)) is initiated when both the primary source port( V i )and primary storage port( V b ) are belo w the threshold le v el. Inductor char ges when switching de vices S 1 ; S 3 and S 4 are ON in state I and dischar ges to the load when switching de vices S 1 and D 2 are ON in state II. The predicted duty c ycle for ( n + 1) th c ycle could be predicted by , d 4 [ n + 1] = L 1 ( V uc + V 0 ) T s [ i ( n + 1) i ( n 1)] d 4 [ n ] + 2 V 0 V b V uc + V 0 (9) 3.5. Mode V This is an unique mode which transfers po wer from primary source port ( V i ) to primary storage port ( V b ). Excess ener gy produced when the load is of f could be stored for future use. The acti v e switching de vices are S 3 ; D 1 and D 3 are during the state1 and S 2 and D 1 during state II(refer Figure3(a)). The v alue for the predicted duty c ycle could be computed using, d 4 [ n + 1] = 2 d 4 [ n ] + L 1 V b T s [ i ( n + 1) i ( n 1)] + 2 V i V b (10) De velopment of Pr edictive Curr ent Contr oller (Santhosh T K) Evaluation Warning : The document was created with Spire.PDF for Python.
688 ISSN: 2088-8694 3.6. Mode VI This mode f acilitates re v erse po wer flo w . The re generated ener gy from the load port is fed back to the secondary storage port V uc . This mode replicates the operation of a b uck-boost con v erter as it pro vides v oltage reduction and in v ersion. The first s witching state in this mode as in (Figure 3(b)) sho ws the switches S 5 is ON. During the second switching state, ener gy stored in inductor L 2 will be transferred to the secondary storage port. The duty c ycle prediction could be done using the follo wing relation, d 5 [ n + 1] = L 2 ( V 0 V uc ) T s [ i ( n + 1) i ( n 1)] d 5 [ n ] 2 V uc V 0 V uc (11) (a) Mode I (b) Mode III Figure 5. Controller Structure 4. PREDICTIVE CURRENT CONTR OLLER LA WS This section describes the controller for the F our Port Con v erter . This con v erter has dif ferent operating modes. The control objecti v e is to re gulate the inductor current based on a fix ed reference v alue. So the con v erter requires tw o controllers: one for mode selection and other for inductor current control. An MA TLAB based Stateflo w controller is used to select a particular mode based on the measured system parameters. While this w ork focuses on the utilization of predicti v e current control for FPC, the Stateflo w controller is discussed in [8]. Control la ws for dif ferent operating modes are deri v ed out in the pre vious section. By making the inductor current i ( n + 1) in the ( n + 1) th switching c ycle equal to the reference current i r ef , the inductor current could be made to follo w the reference e xactly . IJPEDS V ol. 6, No. 4, December 2015: 683 692 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 689 (a) Inductor current with PI Controller and Predicti v e Current controller (b) Simulink Model for Code Generation Figure 6. Dynamic w a v eform and related simulink control model By substituting, i ( n + 1) = i r ef i ( n 1) = i s (12) where i s is the sampled current. By substituting Eq.12 in final equation corresponding to Mode I (Eq.4), it becomes d 3 [ n + 1] = 2 d 3 [ n ] + L 1 V 0 T s [ i r ef i s ] 2 V i V 0 ( M odeI ) (13) Doing the similar substitutions in Eqns.6,8,9,10&11, the final equations for duty c ycle computation becomes, d 3 [ n + 1] = 2 d 3 [ n ] + L 1 V 0 T s [ i r ef i s ] 2 V b V 0 ( M odeI I ) (14) d 4 [ n + 1] = L 1 ( V uc + V 0 ) T s [ i r ef i s ] d 4 [ n ] + 2 V 0 V i V uc + V 0 ( M odeI I I ) (15) d 4 [ n + 1] = L 1 ( V uc + V 0 ) T s [ i r ef i s ] d 4 [ n ] + 2 V 0 V b V uc + V 0 ( M odeI V ) (16) d 4 [ n + 1] = 2 d 4 [ n ] + L 1 V b T s [ i r ef i s ] + 2 V i V b ( M odeV ) (17) d 5 [ n + 1] = L 2 ( V 0 V u c ) T s [ i r ef i s ] d 5 [ n ] 2 V uc V 0 V uc ( M odeV I ) (18) The proposed predicti v e current controller for FPC is simulated using PSIM. The measured parameters are commu- nicated to the Stateflo w controller through an Outlink node. As described before, a Stateflo w controller decides the operating mode and communicate to PSIM through an Inlink node. Based on the command recei v ed, a specific oper - ating mode is acti v ated and the corresponding current control is acti v ated. A schem atic diagram of Mode I is sho wn in Figure 5a. The final equations of Mode I, II and V(Eq.13,14,17) has a similar structure and could be implemented just by switching v ariables used for the computation of the predicted duty c ycle. In the same w ay , Mode III(Figure 5b) and IV has a similar structure so that these could use the same b uilding block. De velopment of Pr edictive Curr ent Contr oller (Santhosh T K) Evaluation Warning : The document was created with Spire.PDF for Python.
690 ISSN: 2088-8694 (a) Inductor Current with PI controller (b) Inductor Current with Predicti v e Current controller Figure 7. Steady state w a v eforms 5. RESUL T AND AN AL YSIS This section presents the steady-state and dynamic results of the proposed predicti v e current control method- ology . Simulation is done using the co-simulation tool of PSIM utilizing MA TLAB. Simulation results of Mode I using PI controller and the proposed Predicti v e Current Controller in steady state is sho wn in Figure 7. The steady- state w a v eforms sho w a reduced current ripple in using PCC compared to the PI controller . The controller is subjected to a step v ariation in load and the results are sho wn in Figure 6a. The PI controller goes for a spik e and settles while the PCC controller results sho w that the inductor current e xactly follo ws the refer ence irrespecti v e of a v ariation in load. The Predicti v e Current Controller is impl emented using a Piccolo DSP controller . The controller is programmed using the Embedded Coder toolbox of MA TLAB/Simulink with support from Code Composer Studio V3.3. The Simulink model used for code generation is sho wn in Figure 6b . F or e xperimental v eri fication, a Photo V oltaic(PV) panel(12V ,200Wp) is connected to the primary source port. A 14V , 5Ah battery is deplo yed in primary storage port and tw o ultracapacitors each of 2.7V , 50F rating, are connected in series and utilized as the secondary storage unit. A step v ariation in load is applied to the FPC through mechanical arrangement and its results in PI controller( K p =0.104117, K i =0.0334486) is sho wn in Figure 8a. The response to the step v ariation in load for PCC is presented in Figure 8b. The Predicti v e Current Controller responds quickly to a step v ariation and k eeps the inductor current e xactly equal to the reference v alue. 6. CONCLUSION This paper proposes a predicti v e current control technique for a F our Port DC/DC con v erter . As the con v erter has six dif ferent operating modes, a Stateflo w controller is used for mode selection and PCC is utilized for inductor current control. The control la ws to predict the duty c ycle for each operating mode is deri v ed out. The feasibility of the proposed control methodology v erified using simulation and hardw are. The proposed controller pro vides the adv an- tage of lo w current ripple and dra w constant current from the sources (PV and Battery) which impro v es the life span of both. The results are compared to a traditional PI controller and sho w impro v ements in current ripple minimization, f aster dynamic performance and is more suitable for current sensiti v e Hybrid Electric V ehicle applications. REFERENCES [1] C. Larouci, K. Ejjabraoui, P . Lefranc, and C. Marchand, “Impact of Control Constraint on A Multi-Objecti v e Buck Con v erter Design, International J ournal of P ower Electr onics and Drive Systems , v ol. 2, no. 3, pp. 257– 266, 2012. IJPEDS V ol. 6, No. 4, December 2015: 683 692 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 691 (a) Response with PI Controller (b) Response with Predicti v e Current Controller Figure 8. Dynamic response to step v ariation in load [2] J. Shieh, “Closed-form oriented loop compensator design for peak current-mode controlled DCDC re gulators, IEE Pr oceedings - Electric P ower Applications , v ol. 150, no. 3, p. 351, 2003. [3] R. Ask our and B. B. Idrissi, “DSP-Based Sensorless Speed Control of a Permanent Magnet Synchronous Motor using Sliding Mode Current Observ er, International J ournal of P ower Electr onics and Drive Systems , v ol. 4, no. 3, pp. 281–289, 2014. [4] W . M. Utomo, S. S. Y i, Y . M. Y . Buswig, Z. a. Haron, a. a. Bakar , and M. Z. Ahmad, “V oltage T racking of a DC-DC Flyback Con v erter Using Neural Netw ork Control, International J ournal of P ower Electr onics and Drive Systems , v ol. 2, no. 1, pp. 35–42, 2012. [5] A. K ouzou, H. A. Rub, M. O. Mahmoudi, M. S. B o uc h e rit, and R. K ennel, “Current/v oltage ripple minimization of DC/DC interf ace system for rene w able ener gies, in International Ae g ean Confer ence on Elect rical Mac hines and P ower Electr onics and Electr omotion, J oint Confer ence . IEEE, Sep. 2011, pp. 758–763. [6] S. Changchien, T . Liang, J. Chen, and L. Y ang, “F ast Response DC/DC Con v erter with T ransient Suppression Circuit, in 37th IEEE P ower Electr onics Specialists Confer ence . IEEE, 2006, pp. 1–5. [7] S. V esti, J. Oli v er , R. Prieto, J. Cobos, and T . Suntio, “Stability and transient performance assessment in a CO TS-module-based distrib uted DC/DC system, in 2011 IEEE 33r d International T elecommunications Ener gy Confer ence (INTELEC) . IEEE, Oct. 2011, pp. 1–7. [8] T . K. Santhosh, K. Natarajan, and C. Go vindaraju, “Synthesis and Implementation of Multi-Port DC/DC Con- v erter for Hybrid Electric V ehicle, J ournal of P ower Electr onics , v ol. 15, no. 5, pp. 1178–1189, 2015. De velopment of Pr edictive Curr ent Contr oller (Santhosh T K) Evaluation Warning : The document was created with Spire.PDF for Python.
692 ISSN: 2088-8694 [9] A. Prodic, R. R. W . Erickson, D. Maksimo vic, J. Chen, A. Prodi ´ c, R. R. W . Erickson, and D. Maksimo vi ´ c, “Predicti v e digital current programmed control, IEEE T r ansactions on P ower Electr onics , v o l . 18, no. 1 II, pp. 411–419, Jan. 2003. [10] W . F ang, X.-D. Liu, S.-C. Liu, and Y .-F . Liu, “A Digital P arallel Current-Mode Control Algorithm for DCDC Con v erters, IEEE T r ansactions on Industrial Informatics , v ol. 10, no. 4, pp. 2146–2153, No v . 2014. [11] M. Hall w orth and S. A. Shirsa v ar , “Microcontroller -Based Peak Current Mode Control Using Digital Slope Compensation, IEEE T r ansactions on P ower Electr onics , v ol. 27, no. 7, pp. 3340–3351, Jul. 2012. [12] Z. Shen, X. Chang, W . W ang, X. T an, N. Y an, and H. Min, “Predicti v e Digital Current Control of Single-Inductor Multiple-Output Con v erters in CCM W ith Lo w Cross Re gulation, IEEE T r ans- actions on P ower Electr onics , v ol. 27, no. 4, pp. 1917–1925, Apr . 2012. [Onli n e ]. A v ailable: http://ieee xplore.ieee.or g/lpdocs/epic03/wrapper .htm?arnumber=6020807 BIOGRAPHY OF A UTHORS Santhosh T K recei v ed his B.E de gree in Electrical and Electronics Engineering from K umaraguru Colle ge of T echnology , Coimbatore, India in 2009 and M.E de gree in Po wer Electronics and Dri v es from K.S.R.Colle ge of Engineering, T iruchengode, India in 2011. He is currently w orking to w ards Ph.D in Electrical Engineering at Go v ernment Colle ge of Engineering, Salem under Anna Uni v er - sity , Chennai. His research interest includes multiple input con v erters for electric v ehicle, digital control of po wer electronic systems and rene w able ener gy . Go vindaraju C recei v ed his B.E de gree in Electrical and Electronics Engineering from Go v ern- ment Colle ge of Engineering, Salem, in 1999 and M.E de gree in Po wer Electronics and Dri v es from Colle ge of Engineering, Anna Uni v ersity , Chennai, in 2003. He recei v ed Ph.D in the field of ener gy ef ficient multile v el in v erters from Anna Uni v ersity , Chennai in 2011. He is an Assistant Professor in department of Electrical and El ectronics Engineering, Go v ernment Colle ge of Engineering, Salem, T amilnadu, India. His research interest includes multile v el in v erters, po wer electronics interf ace for rene w able ener gy systems, and Smart grids. IJPEDS V ol. 6, No. 4, December 2015: 683 692 Evaluation Warning : The document was created with Spire.PDF for Python.