Conversion Topology for Reducing Failure Rate and Life-Cycle Costs of High-Power Wind Turbines

The paper presents a Current-Source Inverter (CSI) topology tailored for large multi-megawatt wind turbine applications. The cable distance between the generator and the mains enables the realization of a significant portion of the DC-link inductance. In order to improve the efficiency and to allow the possible utilization of rugged inexpensive Thyristors, PWM modulation is not used in the main conversion chain. Unity fundamental power factor at the mains is guaranteed at any load condition while the 5th and 7th harmonics of the mains line currents are greatly reduced by choosing a proper nominal operating point for the turbine. Further harmonic reduction is achieved through an active filter controlled via a newly proposed methodology suitable for Digital Signal Processor (DSP) implementation. Such a controller relies on the real-time minimization of a proper functional and is capable of implementing true-feedback current regulation. A part of design simulation results, aimed at building a 10 kW prototype are presented together with the description of its experimental setup currently in construction. Nomenclature α Iγ (n) = n-th bilateral Fourier spectral component of the actual line current to be synthesized in the phase γ α Iγ_ref (n) = n-th bilateral Fourier spectral component of the reference line current in the phase γ C_Im(n) = Complex Fourier coefficient of the n-th spectral component of the mains line current in phase a f c = Sampling frequency of the controller ϕ = Phase-control angle for the Thyristor bridge γ = Index identifying the mains phase a, or b, or c (γ ={a,b,c}) Idc = DC-link current i a_sin (t) = Reference sinusoidal mains line current in phase a delivering the desired mains average power i b_sin (t) = Reference sinusoidal mains line current in phase b delivering the desired mains average power i c_sin (t) = Reference sinusoidal mains line current in phase c delivering the desired mains average power i γ (t) = Actual line current in the phase γ (γ ={a,b,c}) i γ _ref (t) = Reference line current in the phase γ (γ ={a,b,c}) j = Imaginary unit K_thyr = Transformation ratio between the secondary phase voltage at the Thyristor bridge and the primary ine-to-line voltage K_fc = Transformation ratio between the secondary phase voltage at the fully controllable bridge and the primary line-to-line voltage n = Integer representing the harmonic order t = Actual time t c = Specific sampling instant T c = …