光伏发电的MPPT.pdf

Electric Power Components and Systems 36 1208 1217 2008 Copyright 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 tw 1208 Maximum Power Point Tracking for Wind Power1209 algorithm 5 20 Nevertheless the perturbation and observation method is the most popular The conventional perturbation and observation methods can track the maximum output power of the grid connected wind power generation system by calculating the power in the DC side or AC side However the conventional perturbationand observation methods require at least two signals detected voltage and detected current to calculate the generated power For simplifying the structure of a conventional perturbation and observation MPPT method there is a need for improvingthisperturbationand observation method This article proposes a novel MPPT method for the grid connected wind power generation system usinga permanent magnet synchronouswindgenerator PMSWG The salient feature of the proposed method is that no practical calculation for the generated power of a PMSWG is required as compared with the conventional perturbation and observation MPPT methods To verify the performance of the proposed MPPT method a prototypeof the grid connected wind power generation system based on 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 Confi guration and Operation Principle The wind speed S will affect the speed of a PMSWG in the wind power application The output power of a PMSWG is variant due to the different speed of a PMSWG under same wind speed The frequency of the output voltage of a PMSWG is proportional to the speed of a PMSWG Figure 1 shows the typical characteristic of the output power to wind speed of a PMSWG As seen in Figure 1 the operating frequency speed of a PMSWG for the maximum output power of a PMSWG is different under different wind speed Figure 2 shows the system confi guration of a small grid connected wind power generation system using a PMSWG where the grid connected wind power generation system includes a wind blade a PMSWG an AC DC power converter a DC DC power converter and a DC AC inverter The small PMSWG used in this article is the AIR X 400W 24V the AC DC power converter is a three phase bridge diode rectifi er the DC DC power 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 1210H L Jou et al Figure 2 System confi guration of the small grid connected wind power generation system The basic principles of the proposed MPPT method for the PMSWG are described as follows Assuming the utility voltage is vs t D Vpsin t 1 where Vpis the amplitude of the utility voltage Since the output current of the DC AC inverter 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 as iinv t D Iinvsin t 2 where Iinvis the amplitude of the DC AC inverter s output current Thus the output real power of the DC AC inverter can be expressed as pinv t D 1 2VpIinv 3 The output voltage of the PMSWG can be represented as EGD K 4 where K is a constant and and are the magnetic fl ux and the speed of the PMSWG As seen in Eq 4 because the magnetic fl ux is almost constant for the PMSWG the output voltage of the PMSWG is proportional to its speed Since the output of the PMSWG is connected with a diode rectifi er the DC voltage of the diode rectifi er is proportional to the output voltage of the PMSWG This means that the DC voltage of the diode rectifi er is also proportional to the speed of the PMSWG The amplitude of the utility voltage Vp can be regarded to be a constant value at a short time and could not be controlled thus Vpcan be regarded as a constant value in a certain time period As seen in Eq 3 the output real power of the grid connected wind power generation system is almost completely and directly proportional to the amplitude of the DC AC inverter s output current Iinv Besides the DC voltage of the diode rectifi er is proportional to the speed of the PMSWG Hence the y axis and x axis of Figure 1 can be replaced by the DC AC inverter s output current Iinv and the DC voltage of the diode rectifi er respectively The basic concept of the proposed MPPT method for the grid connected wind power generation system is to adjust the amplitude of the DC AC inverter s output current Iinv and then observe the variation of the DC voltage of the diode rectifi er to trace the maximum power point shown in Figure 1 for a specifi ed wind speed The proposed MPPT includes the following steps through adjusting the amplitude of the DC AC inverter s output current Iinv sensing the direction of the variation of the output voltage of the diode rectifi er and correcting the amplitude Maximum Power Point Tracking for Wind Power1211 increment and the direction of the DC AC inverter s output current Iinv the next round is then repeated For example if the amplitude of the DC AC inverter s output current Iinv is adjusted to be larger and the output voltage of the diode rectifi er connected with the PMSWG is increased the amplitude of the DC AC inverter s output current Iinv can be increased continuously Otherwise if the amplitude of the DC AC inverter s output current Iinv is adjusted to be larger and the output voltage of diode rectifi er connected with the PMSWG is decreased the amplitude of the DC AC inverter s output current Iinv should be decreased in the opposite direction Finally the output voltage of the diode rectifi 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 in the proposed MPPT method and it can simplify the control of the grid connected wind power generation system 3 Circuit and Control Block Diagram Figure 3 shows the developed power converter interface for a small grid connected PMSWG system Figure 3 a is the circuit confi guration The power converter interface includes a three phase diode rectifi er a push pull DC DC power converter and a DC AC inverter The control block diagrams for the push pull DC DC power converter and the DC AC inverter are shown in Figures 3 b and 3 c Because the output voltage of this PMSWG is 24 V and the expected input DC voltage of the DC AC inverter is 180 V the turn ratio of the transformer for the push pull DC DC power converter is 2 49 As seen in Figure 3 b the output voltage of the push pull DC DC power converter is detected by a voltage detector and compared with a setting voltage then the compared result is sent to a proportional integral P I controller The output of the P I controller is sent to a pulse width modulation PWM circuit The output of the PWM circuit is sent to a driver circuit to generate the driver signals for the power electronic devices of the push pull DC 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 phase lock loop PLL circuit to generate a reference sinusoidal signal whose phase is in phase with the utility voltage The output of the PLL circuit and an amplitude signal are sent to a multiplier to obtain a reference signal S1 The amplitude signal of the reference signal S1is determined by the MPPT control The output current of the DC AC inverter is detected by the current detector The reference signal S1 and the detected output current of the DC AC inverter are 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 circuit is sent to a driver circuit to generate the driver signals for the power electronic devices of DC AC inverter 4 Flowchart of MPPT Figure 4 is the fl owchart of the proposed MPPT method for the PMSWG As seen in Figure 4 the initial amplitude value of the DC AC inverter s output current is set as 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 diode rectifi er is detected The time interval must be long enough to wait the response of the PMSWG system The amplitude of the DC AC inverter s output current is increased and 1212H L Jou et al Figure 3 Developedpower conversionsystem for small PMSWG system a circuit confi guration b control block diagram of the push pull DC DC power converter and c control block diagram of the DC AC inverter sent to act as the amplitude signal in the controller of the DC AC inverter which means to increase the value of K The PMSWG system is operated under this new value of K for a time interval and then the new DC output voltage Vwind n of the diode rectifi er is sensed again The result of comparing Vwind n 1with Vwind nwill be employed to decide the 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 is decided Vwind n 1is replaced by Vwind n Subsequently a new series of steps is repeated continuously as the previous steps until a maximum power point of the PMSWG s output power is tracked Once an operation point of the maximum power point is detected the MPPT circuit controls the output power of the small grid connected PMSWG system s continuous perturbation around the operation point of the maximum power point Maximum Power Point Tracking for Wind Power1213 Figure 4 Flowchart of the proposed MPPT method 5 Experimental Results To 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 is addressing the MPPT method for a PMSWG system and the characteristic of output power of the PMSWG is similar to the characteristic of output power driven by the wind Figure 5 Experimental system used in this article 1214H 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 induction motor to drive the PMSWG The induction motor is driven by a motor driver The controllers of the DC DC power converter and the DC AC inverter shown in Figures 3 b and 3 c and the fl owchart of the proposed MPPT method shown in Figure 4 are implemented by a DSP TMS320C2407 controller Figure 6 shows the experimental results of the output power voltage P V curves of the PMSWG under the motor driver setting as 45 Hz 50 Hz 55 Hz and 60 Hz The above 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 that each different wind speed has a different maximum power point and the DC output voltage of the AC DC rectifi er for the different maximum power points is different under the different wind speeds This means that the MPPT method must be incorporated in Figure 7 Experimental output power of the PMSWG using the proposed MPPT under the motor driver setting at 60 Hz Maximum Power Point Tracking for Wind Power1215 Figure 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 7 shows the experimental result of the PMSWG system using the proposed MPPT method while the motor driver setting is 60 Hz This is used to simulate the wind speed of 11 12 m sec As seen in Figure 7 the output power is around 300 W after using the proposed MPPT method and this output power coincides with the maximum power under the wind speed of 11 12 m sec shown in Figure 6 Hence it can verify that the proposed MPPT 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 seen in Figure 8 the output current of the DC AC inverter is sinusoidal and in phase with the utility voltage This verifi es that the proposed power conversion system can convert the wind power generated from the PMSWG to a high quality AC power and this AC power injects into the utility Figures 9 and 10 show the experimental results of the Figure 9 Experimental output power of the PMSWG under the setting frequency of motor driver changed from 60 Hz 50 Hz 60 Hz 1216H L Jou et al Figure 10 Experimental result of the grid connected DC AC inverter under the setting frequency of motor driver changed from 60 Hz 50 Hz 60 Hz a DC output voltage of the AC DC rectifi er and b DC output current of the AC DC rectifi er MPPT method under the setting frequency of the motor driver changed from 60 Hz 50 Hz 60 Hz Figure 9 shows the output power variation of the PMSWG As seen in Fig 9 the proposed MPPT method can effectively track the maximum output power of the PMSWG while the wind speed is varied This verifi es that the tracking performance of the proposed MPPT method is very good Figure 10 shows the DC output voltage and current of the AC DC rectifi er while the wind speed is varied As seen in Figure 10 the DC output voltage and current of the AC DC rectifi er is varied as the wind speed is varied 6 Conclusions The MPPT algorithm is one of the key technologies of the power conversion system for effectively using the wind energy of the wind power generation system This article proposes a MPPT method for the PMSWG based wind power generation system The proposed method only adjusts the amplitude of the DC AC inverter s output current and observes the output DC voltage of the AC DC power converter In other words the proposed MPPT method does not need to calculate practical wind power value Then the MPPT method of the wind power generation system is simplifi ed A prototype is developed and tested to verify the performance of the proposed method The experimental results show that the performance of the proposed MPPT method can effectively trace the maximum power point of the wind power generation system References 1 Lyons J P and Vlatkovic V Power electronics and alternative energy generation IEEE Power Electron Spec Conf Vol 1 pp 16 21 June 2004 2 Halliday J A Wind energy anoption for the UK IEE Proc A Vol 140 No 1 pp 53 62 January 1993 Maximum Power Point Tracking for Wind Power1217 3 Richardson R D and McNerney G M Wind energy systems Proc IEEE Vol 81 No 3 pp 378 389 March 1993 4 Swisher R and De Azua C R Strong winds on the horizon Wind power comes of 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