Experimental Verification of Variable Speed Wind Power Generation System Using Permanent Magnet Synchronous Generator by Boost Converter Circuit Sirichai Tammaruckwattana*
Kazuhiro Ohyama
Fukuoka Institute of Technology, 3-30-1 Wajirohigashi, Higashi-ku, Fukuoka (Japan)
[email protected]
Fukuoka Institute of Technology, 3-30-1 Wajirohigashi, Higashi-ku, Fukuoka (Japan)
[email protected]
Abstract - This paper presents the experimental results of variable-speed wind power generation system using permanent magnet synchronous generator. The boost converters are utilized as converters for the variable speed wind power generation system. The experimental results are obtained by the test bench using the wind turbine emulator. The wind turbine emulator are reproduced the behaviors of windmill by the servo motor drives. The mechanical torque reference to derive the servo motor is calculated from windmill wing profile, the wind velocity and windmill rotational speed. The boost chopper system has three speed control modes for the wind velocity. The control mode of low wind velocity regulates armature current of the generator with the boost chopper circuit to control the speed of wind turbine. The control mode of middle wind velocity regulates the DC link voltage with vector controlled inverter to control the speed of wind turbine. The control mode of high wind velocity regulates the pitch angle of the wind turbine with the pitch angle control system to control the speed of wind turbine. The hybrid of three control modes extends the variable-speed range. The boost chopper system simplifies the maintenance system. Keywords - Variable-speed wind power generation system; boost converter; Permanent magnet synchronous generator. I. INTRODUCTION At present, the practical application of variable-speed wind power generation systems using the PWM converter advances [1-4]. The cost is high because the PWM converter needs large number of switching devices and its control is complicated. However, the PWM converter is used for variable-speed largecapacity wind generator systems which require the control of windmill speed, because it can apply the vector control, and realizes the high-speed and high-precise generator torque control. The wind power generator system does not need to supply the excitation energy from the converter side, when the permanent magnet synchronous generator (PMSG) is used as a generator. Therefore, the wind generator systems using PMSG and diode bridge rectifier for the purpose of charging battery are mainly driven at the rated wind velocity of which induced voltage becomes high enough [5]. The wind generator system using PMSG and diode bridge rectifier can constitute the lowcost converter. However, the windmill speed control is difficult, since the torque control of PMSG cannot be carried 978-1-4799-0224-8/13/$31.00 ©2013 IEEE
out by using the converter. And, the induced voltage necessary for the system interconnection is not obtained in low wind speed. At present, the system using PMSG and diode rectifier which realized the windmill speed control and system interconnection is not reported. This paper proposes the variable-speed wind power generation system using the boost converters. The whole system including the wind turbine emulator, power system, main circuit and controllers are tested to verify the proposed system. In the experimental results, it is shown that the proposed system has the sufficient performances as variable speed wind power generation systems. VARIABLE-SPEED WIND POWER GENERATION SYSTEM Fig. 1 shows the variable-speed wind power generation system using the boost converter. It is not possible to operate the PMSG in the motoring mode, because the diode bridge rectifier limits the direction of DC link current. However, it is not a problem, because the motoring mode is not carried out in the wind generator systems. In the meantime, the value of DC link current depends on the relationship between the induced voltage of PMSG and the DC link voltage. Therefore, it is not possible for the diode bridge rectifier to control the generator torque. Then, the boost chopper circuit is added to improve the variable-speed range. The boost converter can control the DC link current regardless of the induced voltage value. In the low wind speed range in which the diode bridge rectifier cannot control the generator torque, the boost converter can control the generator torque by controlling the DC link current.
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II.
Ldc
D
Tr
θ set
ωg
Duty
Cdc
Rdc
Vdc
Vsref
v s , is
V0
Fig. 1. Variable-speed wind power generation system using boost converter.
III. CONTROL SYSTEM A. Wind Turbine Emulator[6] Fig. 2 shows the basic structure of wind turbine emulator. The wind turbine model is based on the blade element momentum theory [7]. The wind turbine model consists of the three dimensional table data of wind turbine characteristics and the mechanical model considering the difference between real wind turbine and induction motor. The wind velocity V0 is given as a condition of emulation. The windmill rotational speed ωr is detected with the rotary encoder (RE). The V0 and ωr are used as inputs of the three dimensional table.
link current which corresponds to the generator torque necessary for controlling the windmill speed, by controlling the boost converter. The DC link voltage is maintained at voltage 100V necessary for the system interconnection by the inverter, when the duty control system is on. Duty becomes 0, because the DC link voltage is maintained at 100V by the inverter, when the windmill speed rises, and when the line voltage of PMSG becomes over 100V. The operating range is correspondent to middle wind velocity, and only the rectification using the reactor and diode bridge rectifier is carried out.
(
K ⎞ ⎛ Duty = ⎜ K PS + IS ⎟ ω gref − ω g s ⎠ ⎝
)
(1)
Fig. 4. Duty ratio control system. Fig. 2. Wind turbine emulator. The three dimensional table data are composed of the torque Q for V0 and ωr. The three dimensional data are calculated by applying the wind turbine parameters of fig. 3 to the blade element momentum theory in advance. c[m]
r[m] code number A B C D E F G H I r [m]：diatance rom center of rotor 0.08 0.10 0.12 0.14 0.16 0.21 0.26 0.31 0.36 0.096 0.094 0.093 0.092 0.090 0.085 0.080 0.076 0.071 c [m]：width of code 2.4 4.4 5.6 5.6 5.6 5.6 － － － β [deg]：angle of twist NACA4415 － profile of NACA J K L M N O P Q 0.41 0.46 0.51 0.56 0.61 0.66 0.71 0.76 0.066 0.062 0.058 0.053 0.048 0.044 0.040 0.035 5.8 5.8 5.8 5.8 5.9 5.9 6.0 6.0 NACA4415
C. Inverter Control System Inverter control system for boost converter Fig. 5 shows the inverter control system for boost converter. The windmill speed control is carried out using the duty control system, when the induced voltage of PMSG is under 100V. Then the inverter control system maintains the DC link voltage at 100V. The duty control system cannot control the windmill speed, when the DC link voltage exceeds 100V. This operating range corresponds to the ranges of middle wind velocity, and high wind velocity. In middle wind velocity under the rated wind velocity, the windmill speed control is carried out with the inverter control system. Concretely, the inverter control system adjusts the electric torque of PMSG by adjusting the DC link voltage, and it controls the windmill speed. In high wind velocity, in which the wind velocity exceeds the rated wind velocity, the windmill speed control is carried out with the pitch angle control system, and the inverter control system carries out the electric power control. The inverter control system is configured by the following equations of PI speed controller.
(
K ⎞ ⎛ Vdcref_ ω = ⎜ K PS + IS ⎟ ω gref − ω g s ⎠ ⎝
)
(2)
Over the rated wind velocity, the rotational speed is controlled by regulating the wind turbine torque. The wind turbine torque is regulated by the pitch angle control system as follows.
Fig. 3. Wind turbine blade shape.
⎛ ⎝
θ ref = ⎜ K p +
B. Converter Control System Duty control system for boost converter Fig. 4 shows the duty control system for boost converter. The change of wind velocity includes the ranges of low wind velocity, middle wind velocity, and high wind velocity. For the low wind velocity, the duty control system adjusts the DC
(
K I ⎞ ref ⎟ ωr − ωr s ⎠
)
(3)
When the pitch angle control is activated, the DC link voltage reference is calculated by the following equation of PI power controller.
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(
K ⎞ ⎛ Vdcref_ P = ⎜ K PP + IP ⎟ Psref − Ps s ⎠ ⎝
)
(4)
The voltage control system is configured by the equation (5). The DC link voltage is controlled by regulating the active current. The DC link voltage reference is calculated by subtracting outputs of PI speed and power controllers from constant DC link voltage reference.
{
(
)}
K ⎞ ⎛ ref i sd = ⎜ K PV + IV ⎟ V dcref − V dcref_ ω + V dcref_ P − V dc s ⎠ ⎝
(5)
the windmill rotational speed for the Maximum Power Point Tracking. Over the rated wind velocity, The grid side converter (INV) controls the active and reactive power of grid. The Duty and PWM signals for controlling the Duty and INV are sent from DSP to the Short-circuit prevention circuit (FPGA) through the digital I/O board (DS4002). The Duty and PWM signals are sent to the Duty and INV through the optical circuit.
The reactive current reference is constant of zero to keep the power factor at 1. The output voltage references are calculated by the following equations.
V
ref sd
(
)
K ⎞ ⎛ = ⎜ K Psd + Isd ⎟ i sdref − i sd + e sd − ω s L s i sq s ⎠ ⎝
(
)
K Isq ⎞ ref ⎛ ⎟ isq − isq + ω s Ls isd Vsqref = ⎜⎜ K Psq + s ⎟⎠ ⎝
750[W ]
300[W ]
3φ 200V
(6)
ωg ref im
T
Vdc
vsu , ius
Vsref
Duty
vsw , isw
(7) Timref
vsu , ius vsw , isw
ωg Q
Vdc Duty
Vsref
V0
Fig. 6. Experimental system. IV. EXPERIMENTAL RESULT Fig.7 shows the change of the wind velocity V0 [m/s]. The change of wind velocity includes the ranges of low wind velocity, middle wind velocity, and high wind velocity. The high wind velocity means the wind velocity that exceeds the rated value All ranges include the change of wind velocity and frequency for natural wind.
Fig. 5. Inverter control system for boost converter. D. Experimental System Fig. 6 shows the experimental system. The digital signal processing (DSP) unit calculates the wind turbine torque reference from the wind velocity data and rotational speed of the induction motor (IM). The wind velocity data is given by the stored data in PC. The rotational speed of IM is estimated in the DSP by using the signals from the rotary encoder (RE). The torque of IM is controlled by the off-the-shelf inverter. The IM is operated based on the wind turbine torque reference sent from DSP through the D/A board (DS2102). The boost converter can control the generator torque by controlling the DC link current. The inverter controls the permanent magnet synchronous generator (PMSG). Under the rated wind velocity, after the wind turbine emulator is activated, the PMSG starts to rotate, and the boost converter control system starts to control
Fig. 7. Wind velocity. Table I shows the generator and power system parameters. The parameters of the PMSG, the mechanical model, the DC link model, the power system, and windmill model etc. are common. Table II shows the control parameters for boost converter. The control parameters of boost converter and duty control system are designed with the simulations using the implemented Simulink models. The control parameters of vector control system applied in the inverter side are designed with the conventional method considering the arrangement of pole and zero based on the control theory.
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TABLE. I
TABLE. II
Generator and Power System Parameters.
even when variations of wind velocity causes. The generated power is controlled by the inverter. V. CONCLUSIONS This paper described the control strategy of variable-speed wind power generation system using boost converters. for natural wind. The steady state and transient responses for wind velocity changes were tested by using the real machine. The simulation models of the variable-speed wind power generation system using the boost converters are implemented by using MATLAB/Simulink. The experimental results of the variable-speed wind power generation system using boost converters are compared with the experimental results of the variable-speed wind power generation system using PWM converter. The fundamental performance of the variable speed wind power generation system using boost converters were verified by discussing the experimental results.
Control Parameters for Boost converter.
Fig. 8 shows the experimental results for boost converter. The windmill rotational speed reaches the windmill rotational speed reference, and the power generation starts after 8 seconds when the wind velocity is 5[m/s]. In this region of low wind velocity, that windmill rotational speed can be controlled to keep the tip speed ratio at optimized value. In the region of middle wind velocity, the speed control is carried out by duty and inverter control systems even when variations of wind velocity causes. In the region of high wind velocity, the windmill rotational speed is controlled by the inverter. Figs. 9 shows the experimental results for PWM converter. The windmill rotational speed reaches the windmill rotational speed reference, and the power generation starts after 8 seconds when the wind velocity is 5[m/s]. In this region of low wind velocity, that windmill rotational speed can be controlled to keep the tip speed ratio at optimized value. The speed control is carried out by converter control and inverter control systems
REFERENCES [1] H. Chikaraishi, Y. Hayashi, and N. Sato: “A Variable Speed Control of the Induction Generator without Speed Sensor for Wind Generation”, T. IEE Japan, Vol. 110-D, No.6, pp.664 - 672 (1990-6) (in Japanese) [2] R. Pena, J. C. Clare, G. M. Asher: “Doubly fed induction generator using back-to-buck PWM converters and its application to variable speed wind-energy generation”, IEE Proc.-Electric. Power Appl., Vol. 143, No.3, pp.231 - 241 (1996-3) [3] G. Poddar, A. Joseph, and A. K. Unnikrishnan: “Sensorless Variable-Speed Controller for Existing Fixed-Speed Wind Generator With Unity-Power-Factor Operation”, T.IEEE, Vol.50, No.5, pp.1007-1015 (2003-10) [4] S. Tammaruckwattana, K. Ohyama: “Experimental Verification for Natural Wind of Permanent Magnet Synchronous Generator Wind Generation System”, Semiconductor Power converter and Motor Drive, IEEJ, MD pp.71-76 (2012) (in Japanese) [5] L. Latkovskis, K. Rashevits, L. Rutmanis, J. Stabulnieks: “Maximum Power Transfer in small Wind Energy Converter with Permanent Magnet Generator for Heating Purposes”, Proc. of EPE’99, CD-ROM, Lausanne, Switzerland (1999-9) [6] K. Ohyama, T. Nakashima: “Wind Turbine Emulator Using Wind Turbine Model Based on Blade Element Momentum Theory”, International Symposium on Power Electronics, Electrical Drives, Automation and Motion T. SPEEDAM pp.762 - 765 (2010) [7] D. M. Eggleston, and F. S. Stoddard: “Wind Turbine Engineering Design”, Van nostrand Reinhold (New York), pp. 15 - 64 (1987-4)
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(a). Generated power
(e). Rotational speed Reference
(b). Wind turbine Torque
(f). Duty control
(c). Tip speed ratio
(g). Integrated power
(d). Rotational speed
(h). Power reference
Fig. 8 Experimental results for boost converter 7161
(a). Generated power
(e). Rotational speed
(b). Wind turbine Torque
(f). Rotational speed Reference
(c). Thrust
(g). Integrated power
(d). Tip speed ratio
(h). Power reference
Fig. 9 Experimental results for PWM converter 7162
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