Isolated Power Generation System Using Permanent Magnet Synchronous Generator with Improved Power Quality

Abstract

This paper deals wind energy based power generation system using Permanent Magnet Synchronous Generator (PMSG). It is controlled using advanced enhanced phase-lock loop for power quality features using distribution static compensator to eliminate the harmonics and to provide KVAR compensation as well as load balancing. It also manages rated potential at the point of common interface under linear and non-linear loads. In order to have better efficiency and reliable operation of PMSG driven by wind turbine, it is necessary to analyze the governing equation of wind based turbine and PMSG under fixed and variable wind speed. For handling power quality problems, power electronics based shunt connected custom power device is used in three wire system. The simulations in MATLAB/Simulink environment have been carried out in order to demonstrate this model and control approach used for the power quality enhancement. The performance results show the adequate performance of PMSG based power generation system and control algorithm.

Appendix

KW Wind Turbine Parameters

Rotor diameter: 10 m, rotor rated speed: 300 r.p.m, cut-in wind speed: 3 m/s, rated wind speed: 15 m/s, inertia: 18 kg m².

The $f_{p} (\lambda )$ curve of the wind turbine can be expressed approximately using the following polynomial equation [1]:

$$ f_{p} \left( {\lambda ,\beta } \right) = f_{1} \left[ {\frac{{f_{2} }}{{\lambda_{i} }} - f_{3} \beta - f_{4} } \right]e^{{\frac{{f_{5} }}{{\lambda_{i} }}}} + f_{6} \lambda $$

(11)

where, f₁ = 0.5176, f₂ = 116, f₃ = 0.4, f₄ = 5, f₅ = 21, f₆ = 0.0068, tip speed ratio (λ) = 0.54, pitch angle (β), internal coefficient (λ_i) and optimum value of power coefficient (f _pmax ) = 0.495.

KW PMSG Parameters

Rated phase voltage: 240 V, line current (rated): 16.86 A, rated frequency: 50 Hz, rated speed: 300 r.p.m, L ¹ _d  = L ¹ _q  = 15 mH, magnetic flux: 0.80 Wb, R_s = 1.8 O, pole pairs: 10, inertia: 0.140 kg m².

DSTATCOM Parameters

Supply: 3-phase, 415 V (L–L), 50 Hz; load: (1) linear: series connected resistive and inductive load operated at 7.5 kVA with p.f. 0.8 (lagging); (2) non-linear: Three phase thyristorised rectifier load with firing angle (α = 20°) connected to RL load with value R = 29 Ω, L = 70 mH; battery voltage (V _B ): 700 V; interfacing inductor $(L_{f} )$ = 3 mH, sampling time $(t_{s} )$ = 100 μs, cut off frequency of low pass filter used in frequency loop = 2nd order, 14 Hz, ripple filter: $R_{f}$ = 4.5$\varOmega$, $C_{f}$ = 10 μF, cut off frequency of low filter used in amplitude of terminal voltage: 2nd order, 11 Hz, gains of PI controller for frequency controlled loop: $k_{pd} = 1.968$, $k_{id} = 2.85$; gains of ac voltage PI controller: $k_{pq} = 4.5$, $k_{iq} = 0.5$.

The Relation between Wind Speed, Power and Mechanical Torque

The wind power acting on the swept area, A, of the blade is a function of the air density $\rho$ and the wind speed $V_{w}$. The transmitted power $P_{m}$ is generally deduced from the wind power using the power coefficient $F_{p}$, as:

$$ P_{m} = \left( {1/2} \right)F_{p} (\lambda )A\rho V_{w}^{3} $$

(12)

The power coefficient is a non-linear function of the tip speed ratio λ which depends on the wind velocity and the rotation speed of the shaft ω.

$$ \lambda = \left( {R\omega /V_{w} } \right) $$

(13)

where, R represents the blade radius. As the wind turbine and generator shafts are directly coupled, there is only one state variable. So, that relation between wind speed, electromagnetic torque, and mechanical torques are related as:

$$ \left( {d\omega /dt} \right) = \left( {1/j} \right)\left( {T_{m} - T_{e} - f\omega_{m} } \right) $$

(14)

where, T_m is the mechanical torque, T_e is the electromagnetic torque, ω is the mechanical speed of the rotor, j is the moment of inertia and f is the coefficient of viscous friction.