光伏发电的MPPT

Electric Power Components and Systems, 36:1208 – 1217,2008Copyright ? Taylor accepted 10 March 2008.Address correspondence to Prof. Hurng-Liahng Jou, Department of Electrical Engineering,National Kaohsiung University of Applied Sciences, 415 Chien-Kung Road, Kaohsiung, 80782,Taiwan, R.O.C. E-mail: hljou@mail.ee.kuas.edu.tw1208Maximum Power Point Tracking for Wind Power 1209algorithm [5 – 20].Nevertheless, the perturbation and observation method is the mostpopular. The conventional perturbation and observation methods can track the maximumoutput power of the grid-connected wind power generation system by calculating thepower in the DC side or AC side. However, the conventional perturbation and observationmethods require at least two signals — detectedvoltage and detected current — tocalculatethe generated power. For simplifying the structure of a conventional perturbation andobservation MPPT method, there is a need for improving this perturbation and observationmethod.This article proposes a novel MPPT method for the grid-connected wind powergeneration system using a permanent magnet synchronous wind generator (PMSWG). Thesalient feature of the proposed method is that no practical calculation for the generatedpower of a PMSWG is required as compared with the conventional perturbation andobservation MPPT methods. To verify the performance of the proposed MPPT method, aprototype of the grid-connected wind power generation system, basedon a small PMSWG(AIR-X 400W; Southwest Wind Power, Inc., USA) and DSP controller (TMS320C2407;Texas Instruments, Inc., USA), is developed and tested.2. System Con?guration and Operation PrincipleThe wind speed(S) will affect the speed of a PMSWG in the wind power application. Theoutput power of a PMSWG is variant due to the different speed of a PMSWG undersame wind speed. The frequency of the output voltage of a PMSWG is proportional tothe speed of a PMSWG. Figure 1 shows the typical characteristic of the output powerto wind speed of a PMSWG. As seen in Figure 1, the operating frequency (speed) of aPMSWG for the maximum output power of a PMSWG is different under different windspeed.Figure 2 shows the system con?guration of a small grid-connected wind powergeneration system using a PMSWG, where the grid-connected wind power generationsystem includes a wind blade, a PMSWG, an AC/DC power converter, a DC/DC powerconverter, and a DC/AC inverter. The small PMSWG used in this article is the AIR-X400W-24V, the AC/DC power converter is a three-phase bridge diode recti?er, the DC/DCpower converter is a push-pull converter, and the DC/AC inverter is a single-phase full-bridge inverter.Figure 1. Characteristic of the output power to wind speed of PMSWG.1210 H.-L. Jou et al.Figure 2. System con?guration of the small grid-connected wind power generation system.The basic principles of the proposed MPPT method for the PMSWG are describedas follows.Assuming the utility voltage isvs .t/ D Vp sin.!t/; (1)where Vp is the amplitude of the utility voltage. Since the output current of the DC/ACinverter is expected to be a sinusoidal waveform and in phase with the utility voltage,the output current of the DC/AC inverter can be expressed asiinv.t/ D I inv sin.!t/; (2)where I inv is the amplitude of the DC/AC inverter ’soutput current. Thus, the output realpower of the DC/AC inverter can be expressed asp inv.t/ D 1Maximum Power Point Tracking for Wind Power 1211increment and the direction of the DC/AC inverter ’soutput current, I inv, the next roundis then repeated. For example, if the amplitude of the DC/AC inverter ’soutput current,I inv , is adjusted to be larger, and the output voltage of the diode recti?er connected withthe PMSWG is increased, the amplitude of the DC/AC inverter ’soutput current, I inv, canbe increased continuously. Otherwise, if the amplitude of the DC/AC inverter ’soutputcurrent, I inv, is adjusted to be larger and the output voltage of diode recti?er connectedwith the PMSWG is decreased, the amplitude of the DC/AC inverter ’soutput current,I inv , should be decreasedin the opposite direction. Finally, the output voltage of the dioderecti?er would be oscillated around the maximum power point of the PMSWG system.Hence, there is no need to really calculate the output real power of the PMSWG inthe proposed MPPT method, and it can simplify the control of the grid-connected windpower generation system.3. Circuit and Control Block DiagramFigure 3 shows the developed power converter interface for a small grid-connectedPMSWG system. Figure 3(a) is the circuit con?guration. The power converter interfaceincludes a three-phase diode recti?er, a push-pull DC/DC power converter, and a DC/ACinverter. The control block diagrams for the push-pull DC/DC power converter and theDC/AC inverter are shown in Figures 3(b) and 3(c). Because the output voltage of thisPMSWG is 24 V and the expected input DC voltage of the DC/AC inverter is 180 V, theturn ratio of the transformer for the push-pull DC/DC power converter is 2:49. As seenin Figure 3(b), the output voltage of the push-pull DC/DC power converter is detectedby a voltage detector and compared with a setting voltage; then, the compared result issent to a proportional-integral (P-I) controller. The output of the P-I controller is sent to apulse-width modulation (PWM) circuit. The output of the PWM circuit is sent to a drivercircuit to generate the driver signals for the power electronic devices of the push-pullDC/DC converter. Figure 3(c) shows the control block diagram of the DC/AC inverter.The DC/AC inverter is controlled by the current-mode control. As seen in Figure 3(c),the utility voltage is detected by the voltage detector and sent to a phaselock loop (PLL)circuit to generate a reference sinusoidal signal whose phase is in phase with the utilityvoltage. The output of the PLL circuit and an amplitude signal are sent to a multiplier toobtain a reference signal S1. The amplitude signal of the reference signal S1 is determinedby the MPPT control. The output current of the DC/AC inverter is detected by the currentdetector. The reference signal, S1, and the detected output current of the DC/AC inverterare sent to a subtractor; then, it is sent to a controller to form a current-mode control.The output of the controller is sent to a PWM circuit, and the output of the PWM circuitis sent to a driver circuit to generate the driver signals for the power electronic devicesof DC/AC inverter.4. Flowchart of MPPTFigure 4 is the ?owchart of the proposed MPPT method for the PMSWG. As seenin Figure 4, the initial amplitude value of the DC/AC inverter ’soutput current is setas K and sent to act as the amplitude signal in the controller of the DC/AC inverter.After a time interval, the initial value of the DC output voltage, Vwind _n 1, of the dioderecti?er is detected. The time interval must be long enough to wait the response of thePMSWG system. The amplitude of the DC/AC inverter ’soutput current is increased and1212 H.-L. Jou et al.Figure 3. Developed power conversion system for small PMSWG system: (a) circuit con?guration,(b) control block diagram of the push-pull DC/DC power converter, and (c) control block diagramof the DC/AC inverter.sent to act as the amplitude signal in the controller of the DC/AC inverter, which meansto increase the value of K . The PMSWG system is operated under this new value of Kfor a time interval, and then the new DC output voltage, Vwind _n, of the diode recti?er issensedagain. The result of comparing Vwind _n 1 with Vwind _n will be employed to decidethe adjusting direction of the K value. If Vwind _n > Vwind_n 1, the K value is increased.Otherwise, if Vwind _n < Vwind _n 1, the K value is decreased. After the new K value isdecided, Vwind _n 1 is replaced by Vwind _n. Subsequently, a new series of steps is repeatedcontinuously as the previous steps until a maximum power point of the PMSWG’s outputpower is tracked. Once an operation point of the maximum power point is detected, theMPPT circuit controls the output power of the small grid-connected PMSWG system ’scontinuous perturbation around the operation point of the maximum power point.Maximum Power Point Tracking for Wind Power 1213Figure 4. Flowchart of the proposedMPPT method.5. Experimental ResultsTo verify the performance of the proposed MPPT method, a prototype of the grid-connected wind power generation system based on a small PMSWG (AIR-X 400W)is developed. The experimental system is shown in Figure 5. Because this article isaddressing the MPPT method for a PMSWG system, and the characteristic of outputpower of the PMSWG is similar to the characteristic of output power driven by the windFigure 5. Experimental system used in this article.1214 H.-L. Jou et al.Figure 6. Experimental P-V curves of the PMSWG under the motor driver set at 45 Hz, 50 Hz,55 Hz, and 60 Hz.turbine and motor [10 – 20],the experimental system is set up by coupling an inductionmotor to drive the PMSWG. The induction motor is driven by a motor driver. Thecontrollers of the DC/DC power converter and the DC/AC inverter, shown in Figures 3(b)and 3(c), and the ?owchart of the proposed MPPT method shown in Figure 4, areimplemented by a DSP TMS320C2407 controller.Figure 6 shows the experimental results of the output power-voltage (P-V) curvesof the PMSWG under the motor driver setting as 45 Hz, 50 Hz, 55 Hz, and 60 Hz. Theabove frequencies can equivalently represent the wind speed as 9.84 m/sec, 10.15 m/sec,10.73 m/sec, and 11.12 m/sec, respectively. As seen in Figure 6, it can be found thateach different wind speed has a different maximum power point, and the DC outputvoltage of the AC/DC recti?er for the different maximum power points is different underthe different wind speeds. This means that the MPPT method must be incorporated inFigure 7. Experimental output power of the PMSWG using the proposed MPPT under the motordriver setting at 60 Hz.Maximum Power Point Tracking for Wind Power 1215Figure 8. Experimental result of the grid-connected DC/AC inverter: (a) utility voltage and(b) output current of DC/AC inverter.the control of the power conversion system to operate the PMSWG effectively. Figure 7shows the experimental result of the PMSWG system using the proposed MPPT methodwhile the motor driver setting is 60 Hz. This is used to simulate the wind speed of11.12 m/sec. As seen in Figure 7, the output power is around 300 W after using theproposed MPPT method, and this output power coincides with the maximum power underthe wind speed of 11.12 m/sec shown in Figure 6. Hence, it can verify that the proposedMPPT method can trace the maximum power point of the PMSWG system effectively.Figure 8 shows the experimental result of the grid-connected DC/AC inverter. As seenin Figure 8, the output current of the DC/AC inverter is sinusoidal and in phase withthe utility voltage. This veri?es that the proposed power conversion system can convertthe wind power generated from the PMSWG to a high-quality AC power, and this ACpower injects into the utility. Figures 9 and 10 show the experimental results of theFigure 9. Experimental output power of the PMSWG under the setting frequency of motor driverchanged from 60 Hz– 50Hz– 60Hz.1216 H.-L. Jou et al.Figure 10. Experimental result of the grid-connected DC/AC inverter under the setting frequencyof motor driver changed from 60 Hz– 50Hz– 60Hz: (a) DC output voltage of the AC/DC recti?erand (b) DC output current of the AC/DC recti?er.MPPT method under the setting frequency of the motor driver changed from 60 Hz–50 Hz– 60Hz. Figure 9 shows the output power variation of the PMSWG. As seen inFig 9, the proposed MPPT method can effectively track the maximum output power ofthe PMSWG while the wind speed is varied. This veri?es that the tracking performanceof the proposed MPPT method is very good. Figure 10 shows the DC output voltageand current of the AC/DC recti?er while the wind speed is varied. As seen in Figure 10,the DC output voltage and current of the AC/DC recti?er is varied as the wind speed isvaried.6. ConclusionsThe MPPT algorithm is one of the key technologies of the power conversion systemfor effectively using the wind energy of the wind power generation system. This articleproposes a MPPT method for the PMSWG-based wind power generation system. Theproposed method only adjusts the amplitude of the DC/AC inverter ’soutput current andobserves the output DC voltage of the AC/DC power converter. In other words, theproposed MPPT method does not need to calculate practical wind power value. Then,the MPPT method of the wind power generation system is simpli?ed. A prototype isdeveloped and tested to verify the performance of the proposed method. The experimentalresults show that the performance of the proposed MPPT method can effectively tracethe maximum power point of the wind power generation system.References1. Lyons, J. P., and Vlatkovic, V., “ Powerelectronics and alternative energy generation, ”IEEEPower Electron. Spec.Conf., Vol. 1, pp. 16– 21,June 2004.2. Halliday, J. A., “ Windenergy — anoption for the UK?” IEE Proc. A, Vol. 140, No. 1, pp. 53– 62,January 1993.Maximum Power Point Tracking for Wind Power 12173. Richardson, R. D., and McNerney, G. M., “ Windenergy systems, ”Proc. IEEE, Vol. 81, No. 3,pp. 378– 389,March 1993.4. Swisher, R., and De Azua, C. R., “ Strongwinds on the horizon: Wind power comes of age, ”Proc. IEEE , Vol. 89, No. 12, pp. 1757– 1764,December 2001.5. 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