Modeling and Simulation of Permanent Magnet ... - IEEE Xplore

Modeling and Simulation of Permanent Magnet Synchronous Generator Wind Power Generation System Using Boost Converter Circuit Sirichai Tammaruckwattana and Kazuhiro Ohyama FUKUOKA INSTITUTE OF TECHNOLOGY 3-30-1 Wajirohigashi, Higashi-ku Fukuoka, Japan Tel.: +81 / (92) – 606.46.82. Fax: +81 / (92) – 606.07.51. E-Mail: [email protected], [email protected] URL: http://www.fit.ac.jp/en/undergraduate/ele

Keywords «Variable-speed wind generator system», «Boost converter», «Permanent magnet synchronous generator»

Abstract This paper proposes variable-speed wind generator system using the Boost chopper system. 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 and improves the reliability and reduces the cost in compare with PWM converter system. extensive

1. Introduction At present, the practical application of variable-speed wind generator systems using the PWM converter advances [1-5]. 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 variablespeed large-capacity 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 [6]. 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 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. The variable-speed wind generator system using diode bridge rectifier and boost converter as a converter was proposed [6]. For a realization of the boost converter scheme, the whole system including the windmill model, power system, main circuit and controllers are simulated. And the possibility of a realization using the real machine is discussed. In this paper, the boost converter scheme is realized with experimental system using the wind emulator. Also the wind generator system using the PWM converter is tested with experimental system to compare with the boost converter scheme. In the simulation and experimental results, it is shown that the boost converter has the sufficient performance as the variable-speed wind generator system.

2. Variable-speed wind generator system Fig. 1 shows the variable-speed PMSG wind 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.

D

Ldc

Tr

θ set

ωg

Cdc

Rdc

Duty

Vdc

Vsref

v s , is

V0

Fig. 1: Variable-speed PMSG wind generation system using boost converter.

3. Control system A. Wind Turbine Emulator [7] Fig. 2 shows the basic structure of wind turbine emulator. The wind turbine model is based on the blade element momentum theory [8]. 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.

Inverter

IM 3φ 200V

RE ref im

T

Wind Turbine Model Fig. 2: Wind turbine emulator

ωr

B. Converter Control System Duty control system for boost converter Fig. 3 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 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)

Boost_ signal ω gref +

ωg

K PS + −

K IS s

Duty

Fig. 3: Duty ratio control system. C. Inverter Control System Inverter control system for boost converter Fig. 4 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)

The condition under which the inverter speed controller operates is as follows.

pitch _ angle

= 10

AND

Duty

= 0

AND

V dcref_ P = 0

(3)

When the pitch angle control is activated, the DC link voltage reference is calculated by the following equation of PI power controller.

(

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 isd = ⎜ K PV + IV ⎟ Vdcref − Vdcref_ ω + Vdcref_ P − Vdc s ⎠ ⎝

(5)

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.

(

)

K Isd ⎞ ref ⎛ V sdref = ⎜ K Psd + ⎟ i sd − i sd + e sd − ω s L s i sq s ⎠ ⎝

(

(6)

)

K Isq ⎞ ref ⎛ ⎟ isq − isq + ω s Ls isd Vsqref = ⎜⎜ K Psq + s ⎟⎠ ⎝

(7)

Vdcref Diode_ signal +

ω gref +

ωg

K PS + −

K IS s

Vdcref_ ω −

−

K PV +

+

−

K IV s

ref i sd

Power_ signal

Psref +

Ps

K PP + −

K IP s

Vdcref_ P

Vdc

isu isv isw

+ −

e − jθ s

ref isq

+

−

+

Vsqref

Vsuref Vsvref e jθ s

ref Vsw

+

+

∫

Vsdref

+

θs

ωs

esd

Ls

Ls

−

+

Fig. 4: Inverter control system for boost converter.

4. Implementation process The implementation of boost converter is evaluated with the simulation study using Matlab/Simulink. The Simulink models for boost converter scheme are implemented. The Simulink models consider the windmill, the main circuits used in each scheme, the converter and inverter control systems, and the pitch angel control system. Only the models of converter side for the boost converter scheme consider the switching operation. The other models are fundamental wave models. This paper verifies the fundamental implementation of boost converter by comparing with the implementation of PWM converter.

4.1. Experimental System Fig. 5 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-theshelf 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 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.

Wind speed data

DS2001

DSP

Vdc, Isu, Isw, Vsu, Vsw

DS3001 DS2102

Branch Circuit RE

INV

Transformer

Diode

IM

PM SG

Ldc

Duty, PWM Signal

DS4002

Tr

Cdc

Duty Signal

FPGA

Rdc

GRID 60Hz. AC. 200V.

INV

Inverter PWM Signal

Optics Circuit

Fig. 5: Experimental system.

4.2. Gain design of the boost converter [4, 5, 9] 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. It is necessary to design the switching frequency and the reactor of boost chopper circuit by considering the PMSG as a power supply. In this paper, the size of the reactor is decided so that the current ripple may decrease sufficiently in the simulation after deciding the switching frequency in advance. The control parameters of boost converter and duty control system are designed with the simulations using the implemented Simulink models of [9]. The control parameters for 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. Table II shows the control parameters for boost converter. The current regulator PI gains of inverter side were already designed for the wind power generation system using the PWM converter in [4, 5]. The same gains are used for the wind power

generation system using the boost converter. The design procedures are explained in [9]. Fig. 6 shows the current control system of inverter side. The plants of d axis and q axis are equalized, and they are described by the first-order lag systems, since the decoupling circuits are built in. The PI gains are designed based on Fig. 6 to have the band width of 500 rad/s and the damping factor ζ of 0.8 by using the “sisotool” in Control System Toolbox of MATLAB. It is impossible to configure the plant like single input and single output system of the PWM converter method when the PI gains of speed regulator using the boost converter are designed. Therefore, the PI gains of speed regulator using the boost converter were designed by evaluating the simulation results. The design procedures are explained in [9]. The integrated output powers for the wind velocity including the sine wave fluctuation were evaluated to determine the PI gains.

Table. I Generator and Power System Parameters.

Table. II Control Parameters for Boost converter.

isref

+ −

PI

vs'

Power system 1 Rs + sLs

is

Fig. 6: Current control system of inverter.

5. Experimental Results 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 sinusoidal change of amplitude 0.5 [m/s] and 0.2 [Hz].

Fig. 7: Wind velocity Fig. 8 and 10 show the experimental results. The windmill rotational speed reaches the windmill rotational speed reference, and 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. Figs. 9 and 11 show the simulation results. The simulation models for the permanent magnet synchronous generator wind generation system using the boost converters are implemented by using MATLAB/Simulink. The simulation models consider the wind velocity, the main circuits, the duty control and inverter control systems, and the pitch angel control system. The sinusoidal fluctuations are superimposed at each wind velocity. The both schemes were simulated for the same change of wind velocity. The simulation results verify the fundamental performance of the wind generator system using boost converter scheme because the boost converter model shows the response of windmill speed which is equivalent to PWM converter model.

(a). Generated power


(b). Wind turbine Torque


(c). Tip speed ratio


(d). Rotational speed Reference


(e). Rotational speed

(e). Rotational speed

(f). Power reference


Fig.8: Experimental results for boost converter

Fig.9: Simulation results for boost converter









(e). Rotational speed Reference and Rotational speed

(e). Rotational speed Reference and Rotational speed



Fig.10:Experimental results for PWM converter

Fig.11: Simulation results for PWM converter

Conclusion This paper described the control strategy of variable-speed wind power generation system using boost converters. The simulation models of the variable-speed wind power generation system using boost converters are implemented by using MATLAB/Simulink. Also the steady state and transient responses for wind velocity changes were tested with the real machine. The simulation and experimental results of the variable-speed wind power generation system using boost converters are compared with the simulation and 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 simulation and experimental results.

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