Module Library for Rapid Prototyping and Hardware Implementation of Vector Control Systems

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1 Module Library for Rapid Prototypin and Hardware Implementation of Vector Control Systems József Vásárhelyi Mária Imecs Department of Automation Department of Electric Drives and Robots University of Miskolc Technical University of Cluj H355 Miskolc Eyetemváros 34 ClujNapoca, PO., Box 99 Hunary Romania János J. Incze Csaba Szabó Department of Electric Drives and Robots Department of Electric Drives and Robots Technical University of Cluj Technical University of Cluj 34 ClujNapoca, PO., Box ClujNapoca, PO., Box 99 Romania Romania Abstract The paper focuses on the implementation of a module library for vector control systems of AC drive. The rapid prototypin and fast implementation of vector control systems becomes possible with the created module library. The control system structures are implemented in confiurable loic cells usin Field Prorammable Gate Array (FPGA). The performances of the created control structures were compared with other simulation results. I. INTRODUCTION Most motor control applications concern with vector control for AC drives. Vector control systems for induction motors ive the best dynamic behaviour. Analysin these systems some modularity can be observed, which help fast implementation of motor control applications in reconfiurable structures [3], []. Reconfiurable hardware was used in vector control in the last years for control system implementations. We speak about dynamic reconfiuration of vector control systems for AC drives when the realtime application (software) chanes the computin platform structure (hardware). In vector control systems, the reconfiurability was introduced by Imecs et all. in []. In this concept, each confiuration is considered as a state of a loic state machine. When reconfiuration condition occurs, the system will start reconfiuration process in which it switches the current confiuration to the next correspondin one. This type of confiuration is the context switchin and was developed by Sanders in [6]. While context switchin is a reconfiuration technoloy for Field Prorammable Gate Arrays (FPGA), the loic state machine with different control system structure in each state is a reconfiuration method for vector control systems presented in the followin fiure: Poweron Init STATE Confiuration STATEn Confiuration n STATE Confiuration Fi.. State machine with different vector control structures in each state. In order to make the reconfiuration possible, there is a need a close analysis of the known control structures. Kelemen and Imecs in [5] presented most of the known control structures for AC drive. A part of the analysis is presented in the next section. II. VECTOR CONTROL SCHEME ANALYSIS The dynamic behaviour of the AC machines is improved by vector control procedures based on the fieldorientation principle. The necessity of reconfiuration is based on the observation that the performance of the drive is dependin on the vector control structure correlated with the type of the supply power frequency converter [9], []. The analysis of the control schemes was performed based on the followin criteria: Given two vector control structures when common modules exist: o Which are the common modules in the same position with the same function? o Which are the common modules with different o functionality? Which are the particular modules of each reconfiurable structure? When reconfiuration condition occurs, is it possible the parameter transfer for the modules on the same position or no parameter transfer allowed? Is the parameter transfer of the PI controllers of the different schemes possible? Is it possible to ive a eneral mathematical form of all the modules? Resultin from the analyses, the module library should be universal for rapid prototypin of any vector control system and from the prototype the implementation should directly result Let us analyse such a reconfiurable vector control structure for AC drives with two confiurable states. This vector control structure presents the eneralities of the most common control schemes and in the meantime contains some particular modules. The reconfiurable state machine presented in Fi. for the vector control structure presented in Fi. is workin in state as a tandem converter [7], [8], [9]. The tandem converter is workin with two inverters. The two inverters are: Current Source Inverter (CSI), which is controlled in current, and the other the Voltae Source Inverter (VSI) is controlled in voltae.

2 Ψ r ω r ω r Flux Controller Speed Controller isd λ r i λr i λr Speed Controller u sdλr u λr Current Controllers Identified Field Mechanical Anular Speed ω V s C Zp isdλ r i λ r v sd v Ψ r i sdλr i λr cosλ r CooT [D(λr)] VA sinλ r Rotorflux Computation sd x x CooT [D(λr)] ψ rd ψ rq isd i i sd i ψ r Co Airapflux Compensation ψ md ψ mq i s π 3 sd v v VA ψ m Co CSI Current ψ sd ψ Statorflux Compensation i DC ε s v sd v ψ s C Statorflux Computation DClink current controller Synchronisation Fi.. Reconfiurable vector control structure with two confiuration states. VA 3 V s γs PhT i sd i i DC SVM α f s ε CSI PhT PWM loic Phase Transformation Phase Controlled Rectifier [u s] [i s ] Induction motor PAMCSI [u s ] AC line L d UsC Diode Rectifier 3xC C d PWM VSI In this way the VSI controlled by PulseWidth Modulation (PWM) supplies the reactive power required to improve the quality of the motor currents in order to compensate them into sine wave form. For the case of the loic state machine in state, only the current source inverter is workin, the inverter currents are synchronized with respect to the control variables of the statorcurrent dq components. The Transition from state to state is made when the Voltae Source Inverter fails and the control structure need to be reconfiured in order to be able to control the AC drive with the Current Source Inverter. State 3 (represented in Fi. ) could be another confiuration of the vector control system when the CSI fails and only the Voltae Source Inverter has to control the motor. A possible representation of the transition from one state to the other, in fact, may be a demultiplexer and a multiplexer, but one should note that, these components miht be carried out in reality, while they are intended to be abstract entities, which did not need any implementation at all [3]. One may observe in the module analysis, that the flux computation modules are common in both control schemes and so they will be one of the most used modules in the module library. As the three fluxcomputation modules can be computed in a sinle equation, they will represent a sinle module, with the followin equation: rd ( σ r ) ( u sd R s i sd ) dt [( σ r ) Lσ s Lσ r ] i sd Ψ = (.a) rq ( ) ( u R i ) dt ( σ ) r s [ r Lσ s Lσ r ] i Ψ = σ (.b) In this way in the module library for the flux computation we will have one module, but when it is needed can easily be created all the modules needed for the flux computation (Ψ sd,q, Ψ md.q, Ψ rd,q ) separatin the stator field computation (Ψ sd,q ) and the flux compensation modules (Ψ md,q, Ψ rd,q ). In addition, the library can handle both flux oriented control schemes, such as rotor flux oriented and stator flux oriented vector control system for any converter fed AC drive. One of the most common modules (oftenused modules) is the Vector Analyser (VA), and as is illustrated in Fi.. It is used to compute different modulus of different parameters. Its equations iven in the eneral forms as follows: q d = d q ; sin λ = ; cos λ = (.) The other two modules, which are common in many control structures, are the Coordinate transformation modules (CooT[D(λ)], CooT[D(λ)]) with the eneral equation: = cos λ sin λ ; (3.a) sdλ r sd r ± λr = cos λr m sd sin λr ; (3.b) One should mention also the other common modules such as the Phase Transformation module (PhT and PhT for current and voltae). These modules aain are eneral computation modules. For all the mentioned modules when reconfiuration occurs there is no need for parameter transfer as they do all the computation for the actual sampled values. The modules where one have to consider the parameter transfer is for example the so called control stratey block, represented in this case by the PI controllers of speed, current and torque. These modules are called toether control stratey block, as they can be realised in many ways. The control stratey can be implemented usin fuzzy r

3 loic, neural networks, or other intellient control methods. The most critical part of the reconfiuration is the parameter transfer of the PI controllers. In the case when (as in Fi. ) the output variables of the controllers are different in each state (in one case this is the current reference i, and on the other case is the voltae sd,qλr reference vsd,qλ r ), the parameter transfer cannot be solved. This explains why the reconfiuration method applied here is context switchin. From the analysis, results, that a module library can be created for fast modellin. The modularity is important when the implementation taret is reconfiurable hardware such as Field Prorammable Gate Arrays (FPGAs) or Confiurable System on a Chip (CSoC) []. III. MODULE LIBRARY CHARACTERISTICS The creation of a module library was motivated by the fact that the simulation of the reconfiuration process it is not possible or it is difficult while no tools exist for this kind of simulation. On the other hand recently it has become possible to implement diital sinal processin alorithms on FPGAs directly from Matlab Simulink environment. This possibility ave the idea to implement the mentioned module library, which is completely parametrisable and any chane on the vector control system s structure can be applied very fast and easy in the implementation hardware. The elements of the library are the most common modules of vector control systems (as described in the previous pararaph), and each present a standalone unit in the library. As result of this independency, the vector control system can be synthesised module by module or as a whole. Most of vector control system implementations use 6 bit two s complement fixedpoint data format. Here this format was also adopted for the input variables of each module. Inside the module for constant representation it was adopted the same data format, but the binary point has variable position, dependin on the motor parameters. The major advantae of usin the module library (when implementation is tareted) is: the computation speed increase. This results from the parallel alorithm computation of both components (d, q) and the parallel computation of each module. This would be a sinificant advantae compared to the DSP sequential implementations. IV. SIMULATION AND RAPID PROTOTYPING WITH MODULE LIBRARY Theoretically with the created module library, any vector control system can be tested, simulated, and implemented. Usin the module library in this way a vector control system can be implemented in short time based on reconfiurable hardware. The motor data used for simulation are: 5.5 kw, 5 Hz, V r.m.s., 4 A r.m.s. and 4 polepairs. The simulation was performed for the presented vector control system structures as follows: First: The confiuration of State CSIVSI driven AC drive was simulated, then the confiuration of Sate CSI driven AC drive was simulated. Second: The simulation performed for the reconfiuration process. The motor started in State and after.5s was reconfiured to State. The results compared with simulation results produced by the simulation model done with Simulink models. One can conclude that some parameters are workin better with the module library (for example the PI implementation), but in some cases, the quantisation errors were not satisfactory aainst our expectancies. The followin diarams show the simulation results for the runnin motor and reconfiuration applied after start at time.5s. Fi. 3 shows the stator current waveform resultant as the sum of the output current of the CSI inverter and the output current of the VSI inverter. Also the fiure shows that after reconfiuration the stator current results as the sum of CSI output currents and the capacitor currents. Fi. 4 to Fi. 6 represents several spacephasors of the output currents, CSI and VSI spacephasors. Fi. 7 and Fi. 8 represents the computed rotorflux spacephasor and the resultant statorflux spacephasor. While the resultant stator flux and computed rotor flux is represented in Fi.. Fi. 9 shows the resultant statorterminalvoltae spacephasor. The reconfiuration of the control structure (i.e when the VSI fails and the CSI will work alone) it is observable in all the fiures. The reconfiuration effects are observable also in the motor parameters (speed and torque) as shown in Fi. and Fi.. Stator Current CSI Current VSIC Current A] time [s] Fi. 3. Current waveforms before and after reconfiuration. Stator curren d Stator current q 5..4 Fi. 4. Motor Statorcurrent spacephasor..6.8

4 6 5 Stator curren d 4 Stator terminalvoltae[v] 4 5 Stator current q Stator terminalvoltae q [V] Fi. 5. CurrentSource Inverter output current spacephasor. Fi. 9. Resultant Statorterminalvoltae spacephasor. VSI or Capacitor current d VSI or Capacitor current q Resultant Rotorflux Rotorflux Resultant Statorflux Fi. 6. VSI or Capacitor outputcurrent space phasor. Fi.. Resultant, rotorflux and resultant statorflux. rotorflux d rotorflux q Electric anular speed[rad/s] Electromanetique torque[nm] Fi. 7. rotorflux spacephasor. Fi.. Electric anular speed and electromanetic torque..5 8 Resultin statorflux d Resultin statorflux q Speed [rad/s] Torque [Nm] Fi. 8. Resultin statorflux spacephasor. Fi.. Resultant dynamic speedtorque mechanical diaram.

5 The method used for reconfiuration was the context switchin method previously named pinpon []. In this case, there is no need for parameter transfer at all, as both vector control systems are workin in parallel and all the modules also are workin in parallel. This allows us to exploit all the parallelism of the vector control alorithm and the implementation possibilities in FPGA. V. IMPLEMENTATION POSIBILITIES Comparin the performances of implemented modules, there one have to consider the followin: the evolution of the module computation compared to the model, the quantisation error produced by the module, the time delay introduced by the module, the hardware resources occupied when the module is implemented. On the followin we analyse some modules considerin the mentioned criteria. For a simplified analysis of the modules the simulation for the vector control scheme in Fi. was performed without reconfiuration and for the tandem converter structure, which corresponds for selection of the multiplexer inputs. The simulation performed for second and at,35s it is observable a speed inversion. Fi. 3, Hiba! A hivatkozási forrás nem található. and Fi. 4, represents the the dcomponent evolution of the Flux Controller and inverse coordinate transformation CooT[D(λ)] respectively. The output q component of the module CooT[D(λ)] is also presented in Fi. 5. As result from the fiures (Fi. 3 Fi. 4), there is no sinificant difference between the simulation and the output variable resultant from the library module computation. The quantisation error of the computed variables are minimal exceptin the module CooT[D(λ)], where the quantisation error of the reference voltae Usd is between 5 and 5. Even under these circumstances the results are promisin. The time delay and the hardware resource consumed by the analysed modules are presented in TABLE TABLE. HARDWARE RESOURCES CONSUMED AND TIME DELEY INTRODUCED BY THE MODULE FLUX CONTROLLER Release 4..3i Map E.33 Xilinx Mappin Report File for Desin Desin Information Command Line: map p xcv4cs446 cm area pr b k 4 c tx off Taret Device: xv4 Taret Packae: cs44 Taret Speed: 6 Mapped Date: Tue Mar 6 5:6:39 Desin Summary Number of Slices: 4 out of 56 9% Number of Slices containin unrelated loic: out of 4 % Total Number 4 input LUTs: 4 out of 5 4% Number used as Shift reisters: 4 IOB Flip Flops: 4 Number of GCLKs: out of 6 6% Total equivalent ate count for desin: 5,73 The Averae Connection Delay for this desin is:.83 ns The Maximum Pin Delay is: 4.6 ns The Averae Connection Delay on the Worst Nets is:.64 ns Listin Pin Delays by value: (ns) d <. < d <. < d < 3. < d < 4. < d < 5. d >= Simulated Output current of flux controller Output current of flux controller Quantisation error of the computed output current Fi. 3. Outputs of the modelled and implemented flux PI controller and the resultant quantisation error. Simulated Output Voltae d of the CooT[D(l)] Output Volate d of the CooT[D(l)] [V] Quantisation error of the computed otuput voltae x Fi. 4. Output Voltae erence d component of the module Inverse coordinate transformation CooT[D(λ)]. Simulated Output Voltae q of the CooT[D(l)] Output Voltae q of the CooT[D(l)] Quantisation error of the computed output voltae x Fi. 5. Output Voltae erence q component of the module Inverse coordinate transformation CooT[D(λ)]. Output Voltae V sd [V] Output Voltae V [V] 5..4 Fi. 6. Statorterminalreference voltae spacephasor of module CooT[D(λ)].6.8

6 TABLE. HARDWARE RESOURCES CONSUMED AND TIME DELEY INTRODUCED BY THE MODULE CooT[D(λ)] Release 4..3i Map E.33 Xilinx Mappin Report File for Desin Desin Information Number of Slices: 5 out of 3,7 % Number of Slices containin unrelated loic: out of 65 % Total Number 4 input LUTs:, out of 6,44 9% Number used as LUTs:,8 Number used as a routethru: 4 Total equivalent ate count for desin: 5,579 The Delay Summary Report The Score for this desin is: 534 The Averae Connection Delay for this desin is:.969 ns The Maximum Pin Delay is:.56 ns The Averae Connection Delay on the Worst Nets is: 7.36 ns Listin Pin Delays by value: (ns) d<.< d<4. < d<6. < d< 8. < d <. d >= As observed from the tables the hardware resources consumed by the modules flux controller and inverse coordinate transformation are sinificant, and this may be a disadvantae of the developed module library, while the time delay introduced by the module is a positive result, which have to be considered when computation speed is important. VI. CONCLUSIONS The created module library like other Matlab tools, helps the development of rapid model based vector control systems for AC drives. The module parameters are freely modifiable on demand. It allows the simulation of the reconfiuration process and effects on the AC drive. VII. AKNOWLEDGMENT A research project in the subject of the tandem inverter was realized at the Institute of Enery Technoloy, Aalbor University, Denmark. Special thanks to Prof. A. Trzynadlowski from Nevada University, Reno, USA for the collaboration in this theme, to Prof. F. Blaabjer from the Aalbor University and to the Danfoss Drive A/S, Denmark for their enerous support. The authors are rateful to Triscend Inc. and Xilinx Inc. for donations, which made possible the research on some aspects of reconfiurable vector control framework. VIII. REFERENCES [] Mária Imecs, P. Bikfalvi, S. Nedevschi, J. Vásárhelyi Implementation of a Confiurable Controller for an AC Drive Control a Case Study, Proceedins of IEEE Symposium on FPGAs for Custom Computin Machines FCCM, Napa, California, USA,, pp [] Mária Imecs, J. J. Incze, J. Vásárhelyi, Cs. Szabó Vector Control Of Tandem Converter Fed Induction Motor Drive Usin Confiurable System On A Chip, INES IEEE International Conference on Intellient Enineerin Systems, September 68,, HelsinkiStockholmHelsinki, Finland Sweden, pp [3] Mária Imecs, J. Vásárhelyi, J. J. Incze, Cs. Szabó, Tandem Converter Fed Induction Motor Drive Controlled With ReConfiurable Vector Control System, Power Electronics Intellient Motion Power Quality Conference PCIM, Nürnber, Germany, pp [4] Mária Imecs OpenLoop VoltaeControlled PWM Procedures, ELECTROMOTION 99, Patras, Greece, Vol. I, pp. 859 [5] Á. Kelemen., Mária Imecs Vector control of AC Drives, OMIKK publisher Budapest, ISBN , Budapest, 99, pp.34. [6] A. Sanders The Desin and Implementation of Context Switchin FPGA, IEEE Symposium on FPGAs for Custom Computin Machines FCCM 998, Los Alamitos California, USA, April 57, 998, pp [7] A. M. Trzynadlowski, F. Blaabjer, J. K. Pedersen, Niculina Patriciu The Tandem Inverter: Combinin the Advantaes of VoltaeSource and Current Source Inverters, Applied Power Electronics Conference, APEC 98, Anaheim, USA, pp.353. [8] A. M. Trzynadlowski, Mária Imecs, Niculina Patriciu Modellin and Simulation of inverter Topoloies Used in AC Drives: Comparison and Validation of Models, ELECTRIMACS 99, Volume I/3, Lisboa, Portual, 999, pp [9] J. Vásárhelyi, Mária Imecs, J.J. Incze Runtime Reconfiuration of Tandem Inverter used in Induction Motor Drives, Proceedins of Symposium on Intellient Systems in Control and Measurement, Veszprém, Hunary,, pp [] J. Vásárhelyi RunTime Reconfiuration of AC Drive Controllers, Dastuhl Seminar 6 on Dynamically Reconfiurable Architectures, June,, Germany,

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