GeoPlex experimental setup: generator and converter

GeoPlex experimental setup: Generator and converter Arnau Dòria Cerezo, Carles Batlle Arnau, Enric Fossas Colet ACES: Control Avançat de Sistemes d’Energia IST_2001_34166 IOC-DT-P-2006-1 Gener 2006 GeoPlex experimental setup: Generator and converter. Arnau D`oria-Cerezo, Carles Batlle and Enric Fossas Universitat Polit`ecnica de Catalunya September, 2005 Abstract The experimental setup of the Flywheel Energy Storage System is presented. The system is made of a doubly-fed induction machine coupled to a flywheel and a back-to-back converter. 1 Introduction The system studied in this workpackage is an autonomous energy–switching system that regulates the energy flow between a local prime mover (a flywheel) and the electrical power network, in order to satisfy the demand of a time–varying electrical load. This system, used in the CERN (Centre Europ´een pour la Recherche Nucl´eaire) to store electrical energy for the particle accelerator or at the Okinawa Electric Power Company [1], has been also studied in [1]. The main goal of the system is, basically, to store kinetic energy into a flywheel and deliver it when an external load requires a high energy flow. Power Network Local Load B2B DFIM Flywheel Control Inputs Local Source Single-phase Source vs inil is vr irωr Figure 1: Doubly fed induction machine coupled to a flywheel, controlled by a back-to-back converter and connected to a power network and a load. The system (see Figure 1) is composed by a doubly–fed induction machine (DFIM) coupled to a flywheel and controlled through the rotor windings by a back-to-back converter (B2B). This is the most common control architecture of the DFIM [1][6][8][9][10][11][14][15] , typically achieved 1 by means of a B2B. In a case that the AC source of the B2B is connected to the 3-phase power grid, this architecture is also known as Scherbius Drive [8], i.e. the power converter is in a closed–loop with the DFIM. In practice, due to the fact that the power flowing through the power converter is smaller than the power flowing to the DFIM stator side, it is common to neglect this feedback connection. The DFIM is controlled through the rotor windings port (vr, ir∈R3, where vand iare a three-phase voltage and current variables, and subindex rrefers to the rotor). It is coupled to an energy–storing flywheel with port variables (τeelectrical torque, ωmechanical speed). An electrical network modelled by an ideal AC voltage source with port variables (vn, in∈R3subindex nrefers to the network variables), and a generic electrical three-phase load, represented by its impedance Zl, is connected to the stator port variables (vs, is∈R3). As mentioned above, the main objective of the system is to supply the required power to the load with a high network power factor. Depending on the load demands, the DFIM acts as an energy–switching device between the flywheel and the electrical power network. The control problem is to optimally regulate the power flow. These goals, assuming a maximal active power of the network PM AX n, can be summarized as follows: •To supply the extra energy required by the load. Notice that this objective concerns the active power, and considering a constant grid voltage, Vn=ct, this requirement is achieved by the stator currents. •To store kinetic energy in the flywheel when the load does not require all the grid power. •To compensate the power factor (cos φ), i.e., the whole system (load and local source acts as a pure resistor). That is cos φ∼0, or, in other words assuming, sinusoidal waveform and an equilibrated system, this objective can be written as Qn∼0. This control problem can be achieved by commuting between different steady–state regimes. The switching strategy was studied in [2]. 2 The doubly-fed induction machine Doubly–fed induction machines (DFIM) form a class of induction machines which have become very popular for renewable energy applications. They have been proposed in the literature, among other applications, for wind-turbine generators [8][13], hybrid engines [3] or high performance storage systems [1][2]. The attractiveness of the DFIM stems primarily from its ability to handle large speed variations around the synchronous speed (see [11] for an extended literature survey and discussion). Another advantage is that the power electronic equipment to control the machine only has to handle a fraction (maximum 20 −30%) of the total power [12]. Therefore, the losses in the power electronic converter can be reduced, compared to a system where the converter has to handle the total power. In addition, the cost of the converter becomes lower. Figure 2 shows the DFIM coupled to a flywheel. In order to increase the performance of the experimental setup the flywheel is split into two different inertias. The DFIM is a 1.1kW machine De Lorenzo DL 1022K, with the following parameters: number of poles n= 2, voltage fed 220/380V(∆/Y), nominal current 4.8/2.8A(∆/Y), stator resistance Rs= 4.92Ω, rotor resistance Rr= 4.42Ω, mutual inductance Lsr = 0.71H, stator inductance Ls= 0.725H, rotor inductance Lr= 0.715H, mechanical damping Br= 0.005Kgm2s−1and inertia Jm= 0.00512Kgm2. The flywheel is a De Lorenzo DL-10410 with J= 0.055Kgm2each inertia. 3 The back-to-back converter Electronic power converters [4] are devices able to deliver electrical energy in a suitable way for the applications, i.e., with prescribed frequency, voltage amplitude or any other specification. They 2 DFIM Flywheel Figure 2: The DFIM coupled to a flywheel. ++ + + + vi L r C va vb vc i ia ib ic s1s2 t1t2 s4s5 t4t5 s6 t6 iDC vDC Figure 3: Back-to-back converter. do the trick by periodically storing the energy in inductors and capacitors before releasing it in the desired form; in a given period the converter goes through a series of topological circuit changes by means of controlled switches (for instance IGBT switches). The back-to-back converter consists of two converters, namely, machine-side converter and grid-side converter, that are connected ”back-to-back”. Between the two converters a dc-link capacitor is placed, as energy storage, in order to keep the voltage variations (or ripple) in the dc-link voltage small. With the machine-side converter it is possible to control the torque or the speed of the DFIM and also the power factor at the stator terminals, while the main objective for the grid-side converter is to keep the dc-link voltage constant. Figure 3 shows the back-to-back converter selected for this system. It differs from the typical topology in the grid-side converter; in this case the dc-link voltage is controlled by a single-phase boost rectifier instead of a three-phase rectifier. The machine-side converter is a three-phase dc/ac inverter. The whole converter has an ac single input and its outputs are three-phase PWM (pulse width modulation) voltages which feed the rotor windings of the electrical machine. This system can be split int two parts: a dynamical subsystem (the full bridge rectifier, containing the storage elements) and an static subsystem (the inverter, which from the energy point of view, acts like a 3 transformer). A single-phase ac voltage source viprovides the energy in the direct operation mode, Lis the inductance, Cis the capacitor of the dc-link, rtakes into account all the resistance losses (inductor, source and switches), skand tk(k= 1,2,3,5,6). Switch states take values in {−1,1} and t-switches are complementary to s-switches: tk= ¯sk=−sk. Additionally, s2= ¯s1=−s1. One of the principal requirements is that the B2B converter has to allow a bidirectional power flow, since, dpending on the operational specifications, the DFIM can extract energy through the rotor. This feature is achieved using IGBT switches instead of diodes and thyristors, which have a low cost and an easiest implementation in the experimental setup [7]. The back-to-back converter is depicted in Figure 4 and has the following parts: •A full-bridge boost converter (depicted in Figure 4) with IGBT switches (Siemens BSM 25GD 100D) and parameters: r= 0.1Ω, L= 1mH, C= 4500µF. The switching frequency of the converter is 20 KHz and a synchronous centered-pulse single-update pulse-width modulation strategy is used to map the controller’s output to the IGBT gate signals. •A 3-phase DC/AC inverter with a set of IGBT switches (1200 V, 100 A). The switching frequency of the inverter is 20 KHz and a synchronous centered-pulse single-update pulsewidth modulation strategy is used to map the controller’s output to the IGBT gate signals. •The analog circuitry for the sensors: the AC main source, PMW and DC bus voltages and currents are sensed with isolation amplifiers. All the signals from the sensors pass through the corresponding gain conditioning stages to adapt their values to A/D converters. •Control hardware and DSP implementation: the control algorithm can be implemented using the Analog Devices DSP-21116 and DSP-21992 processors. The processing core of this device runs at 100MHz and has a 32bit floating-point unit. The sampling rate of the A/D channels has been selected at 20KHz, the same as the switching frequency of the full-bridge system. •The nominal RMS AC mains voltage is Vs= 48.9V RMS and its nominal frequency is 50 Hz. 4 Interconnection and Control The control algorithm is coded into a computer running with RTLinux (Real Time Linux), using RTiC-Lab (Real Time Controls Laboratory) [5]. The control hardware setup consists of: •PC computer: Pentium IV, 1.8 GHz, 512MB RAM. •A/D card: 3 PCI-DAS 4020/12 modules. Ultra High-Speed PCI-bus Compatible, 4-Channel, 12-Bit Analog Input Board with two Analog Output Channels and 24 Digital I/O Channels. •PWM card: NuDAQ PCI-8133. 3-Channel quadrature encoder counters for a PCI PnP-bus and a 12-Bit PWM waveform generators. Figure 5 shows the signal connection scheme between the system and the control hardware 1. References [1] H. Akagi and H. Sato. Control and performance of a doubly-fed induction machine intended for a flywheel energy storage system. IEEE Trans. Power Electron., 17(1):109–116, 2002. 1The processing hardware of another plant [3], called Joint System (JS), which shares some elements with ours (FW), is also displayed 4 Inductor Capacitor IGBT full-bridge Input (AC source) Output (Load) Figure 4: Experimental setup: full-bridge rectifier, DSP card, sensors, data acquisition. [2] C. Batlle, A. D`oria-Cerezo, and R. Ortega. Power Flow Control of a Doubly–Fed Induction Machine Coupled to a Flywheel. European Journal of Control, 11(3):209–221, 2005. [3] P. Caratozzolo. Nonlinear control strategies of an isolated motion system with a double-fed induction generator. PhD thesis, Universitat Polit`ecnica de Catalunya, 2003. [4] R. Erickson. Fundamentals of Power Electronics. Kluwer, 1997. [5] E. Hilton. Manual for the Real Time Controls Laboratory, RTiC-Lab, 2000. [6] B. Hopfensperger, D. Atkinson, and R. Lakin. Stator-flux-oriented control of a doubly-fed induction machine with and without position encoder. In IEE Proc. Electric Power Applications, volume 147-4, pages 241–250, 2000. [7] S. Hui, H. Chung, and S. Yip. A bidirectional ac-dc power converter with power factor correction. IEEE Transactions on Power Electronics, 15(5):942–949, September 2000. [8] R. Pe˜na, J. C. Clare, and G. M. Asher. Doubly fed induction generator using back-to-back pwm converters and its application to variable speed wind-energy generation. In IEEE Proc. Electric Power Applications, volume 143-5, pages 231–241, 1996. [9] R. Pe˜na, J. C. Clare, and G. M. Asher. A doubly fed induction generator using back-to-back pwm converters supplying an isolated load from a variable speed wind turbine. In IEEE Proc. Electric Power Applications, volume 143-5, pages 380–387, 1996. [10] S. Peresada, A. Tilli, and A. Tonelli. Indirect Stator Flux-Oriented Output Feedback Control of a Doubly Fed Induction Machine. IEEE Trans. Control Systems Technology, 11(6):875–888, 2003. 5 F/V sw 1:1 SERVO AMPLIFIER Advanced Motion Control Three Phase Inverter C B A 3 3 3 3 #SD Promax 1 Promax 2 AD215BY Isolation Amplifier Promax 2 PCI DAS 4020/12 PCI8133 1:13 Protection System (Salicrú) Vbus + Vbus - 6N137 Optocouplers Pentium 4; 1,8 GHz; 512 MB RAM 74HC244 Buffer Non-Inverting AD215BY Isolation Amplifier Brake DFIM Generator Rotor Stator Induction Motor 3ph 1:13,4 AD215BY Isolation Amplifier 2 2 2 2 2 2 3 1A-250mV 1000rpm 1V DL10050 1000rpm 1V DL10050 Jeulin 188 019 Jeulin 188 016 12 Hall Sensor EH050 Hall Sensor EH050 1A-250mV ADC - 12BNCs DAC Board Channel Signal 0 0 0 0 1 1 1 1 2 2 2 2 0 1 2 3 0 1 2 3 0 1 2 3 I6 I5 I4 I3 I2 I1 DFIM speed 3ph speed V4 V3 V2 V1 DIO Encoder 360 pulses/revol. Encoder 100 pulses/revol. data1 data2 data3 data4 data5 data6 data7 data8 data9 data10 data11 data12 #PWME A , B 74HC14 Inverter notA notB A , B 2 2 A , B 74HC14 Inverter notA notB A , B 2 2 22 2 80% de 46V 75% de 42V DC Motor PWMs U+ (16) V+ (17) W+(18) U- (34) V- (35) W-(36) nB2(24) nA2(23) A2(5) B2(6) 2 nB1(21) nA1(20) A1(2) B1(3) Bridge Off + 5V PCIDAS4020 Ramp Braking DC Motor V5 I1 I3 I2 W1I6 V1 V2 K1 V3 V4 I4 I6 I5 K2 Select 12 DAQs A , B 74HC14 Inverter notA notB A , B 2 2 22 nB3( ) nA3( ) A3( ) B3( ) Stator Encoder 360 pulses/revol. 1A-250mV 2 2 Hall Sensor EH050 DFIM FW 1 FW 2 Rotor Stator JS FW Breaker POWERBOX 100V-10A FW JS Transformer 1v / 6,75v LOADS 1:120 AD215BY Isolation Amplifier 2 Open=FW Close=JS FW JS JS & FW FW JS JS & FW Earth leak 1:?? V5 F/V Conversor 0-10V F/V 0-10V to -5V+5V Vfrec Frequency measurement Idc JS FW JS Idc JS Pinza o Salida Servo FW JS FW JS W,A,V 1V à 100mV 1A à 250mV 1W à 10mV YOKOGAWA WT-1600 3-Phase Digital Power Meter Phase R Phase S Phase T Phase R Phase S Phase T Trafo 220V (50Hz) 220V (50Hz) PB-read-0,1,2 PA-write1 3 3 3 3 Promax OENA (34) GND (15) + 5V Promax 3 Promax 3 3 SD Vin+A Vin-A Vin+B Vin-B Reset Fault A Fault B GND SD Vin+A Vin-A Vin+B Vin-B Reset Fault A Fault B GND SD Vin+A Vin-A Vin+B Vin-B Reset Fault A Fault B GND 1 2 3 4 5 6 +5V GND +15V GND -15V +12V GND U V W 330 Ohm 330 Ohm 330 Ohm Uc +5V +12V 6 IGBT In: 3x400V Out: 3x0 a 440V 3xSw 220VAC 24Vdc Breaker Earth leak VARIAC Figure 5: Experimental setup: Interconnection scheme. 6 [11] S. Peresada, A. Tilli, and A. Tonelli. Power control of a doubly fed induction machine via output feedback. Control Engineering Practice, 12:41–57, 2004. [12] A. Petersson. Analisys, modeling and control of doubly-fed induction generators for wind turbines. PhD thesis, Chalmers University of Technology, Sweden, 2005. [13] J. Slootweg, H. Polinder, and W. Kling. Dynamic modelling of a wind turbine with doubly fed induction generator. In IEEE Power Engineering Society Summer Meeting 2001, pages 644–649, 2001. [14] A. Tapia, G. Tapia, J. X. Ostolaza, and J. R. S´aenz. Modeling and control of a wind turbine driven doubly fed induction generator. IEEE Trans. Energy Conversion, 18:194–204, 2003. [15] L. Xu and W. Cheng. Torque and reactive power control of a doubly fed induction machine by position sensorless scheme. IEEE Trans. Industry Applications, 31(3):636–642, 1995. 7