Commissioning of 30 kva variable-speed direct drive wind power plant
30 kva gücünde değişken hızlı ve doğrudan tahrikli rüzgar enerji santralının incelenmesi
- Tez No: 840499
- Danışmanlar: PROF. EWALD F. FUCHS
- Tez Türü: Doktora
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1999
- Dil: İngilizce
- Üniversite: University of Colorado at Boulder
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Elektrik ve Bilgisayar Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Elektrik Makinaları ve Güç Elektroniği Bilim Dalı
- Sayfa Sayısı: 236
Özet
Most wind turbines in service today employ induction generators together with a step-up mechanical gear so that the operational speed is close to the synchronous speed of two or four-pole generators. Because of the torque-speed characteristic of induction generators, the range of speed change is rather small; therefore, the operational speed can be considered to be nearly constant. Mechanical gears are subject to wear and tear, reduce reliability of the drive train and add to its weight. The maximum power that can be extracted from wind varies with its speed. Therefore, a direct-drive system, where a wind turbine is directly coupled to the generator shaft, is desirable along with a variable-speed operation. The variable-speed, direct-drive train described in this thesis consists of a low-speed, permanent-magnet generator (60 to 120rpm), a resonant rectifier and a pulse-width-modulated inverter. It supplies 30kVA/20kW apparent/real power to the utility system at leading and unity power factors for a given DC link voltage. The amplitude and phase (leading, unity) of the AC current delivered to the utility system are controllable and the voltage/current wave forms at the point of common coupling satisfy standard IEEE-519. The overall efficiency of the drive train is about 83% (excluding the generator), whereby the rectifier has an efficiency of 86% and the inverter efficiency is around 95%. Using two different approaches (computer-aided and three-voltmeter methods), the losses of inductors are measured for the frequency range of 0 to 6kHz. Measurement errors of both methods are less than 10% when measuring a few watts. The AC resistance increase of a Litz-wire inductor without a core is smallest among all of the inductors being tested. Stranding of individual (uninsulated) wires to obtain a flexible cable results in more losses than using a solid cable having the same cross-sectional area as that of a stranded cable. Nonsinusoidal voltages and currents in a power system can produce an additional power, called distortion power, generated from the cross products of voltage and current harmonics of different frequencies. This additional power increases system losses that cannot be easily compensated. Existing definitions of distortion power are not quite correct either from a numerical or a physical point of view because they involve voltage and current harmonics of the same frequency; therefore, a correct formulation is given which agrees well with experimental results. When a transformer is operating under nonsinusoidal voltages and currents, its apparent power output must be reduced (derating) in order not to exceed the rated temperature. Comparison of measured derating values with ones obtained from K- and F_HL-factor approaches reveals that the K-factor approach yields somewhat greater derating values than the F_HL-factor approach. The losses of conductive materials in the presence of magnetic fluxes are also investigated and it has been found that the maximum losses in these components occur at a specific (material-dependent) frequency. The losses are proportional to the power of 0.8 below this frequency and are inversely proportional to the power of 0.9 above this frequency.
Özet (Çeviri)
Most wind turbines in service today employ induction generators together with a step-up mechanical gear so that the operational speed is close to the synchronous speed of two or four-pole generators. Because of the torque-speed characteristic of induction generators, the range of speed change is rather small; therefore, the operational speed can be considered to be nearly constant. Mechanical gears are subject to wear and tear, reduce reliability of the drive train and add to its weight. The maximum power that can be extracted from wind varies with its speed. Therefore, a direct-drive system, where a wind turbine is directly coupled to the generator shaft, is desirable along with a variable-speed operation. The variable-speed, direct-drive train described in this thesis consists of a low-speed, permanent-magnet generator (60 to 120rpm), a resonant rectifier and a pulse-width-modulated inverter. It supplies 30kVA/20kW apparent/real power to the utility system at leading and unity power factors for a given DC link voltage. The amplitude and phase (leading, unity) of the AC current delivered to the utility system are controllable and the voltage/current wave forms at the point of common coupling satisfy standard IEEE-519. The overall efficiency of the drive train is about 83% (excluding the generator), whereby the rectifier has an efficiency of 86% and the inverter efficiency is around 95%. Using two different approaches (computer-aided and three-voltmeter methods), the losses of inductors are measured for the frequency range of 0 to 6kHz. Measurement errors of both methods are less than 10% when measuring a few watts. The AC resistance increase of a Litz-wire inductor without a core is smallest among all of the inductors being tested. Stranding of individual (uninsulated) wires to obtain a flexible cable results in more losses than using a solid cable having the same cross-sectional area as that of a stranded cable. Nonsinusoidal voltages and currents in a power system can produce an additional power, called distortion power, generated from the cross products of voltage and current harmonics of different frequencies. This additional power increases system losses that cannot be easily compensated. Existing definitions of distortion power are not quite correct either from a numerical or a physical point of view because they involve voltage and current harmonics of the same frequency; therefore, a correct formulation is given which agrees well with experimental results. When a transformer is operating under nonsinusoidal voltages and currents, its apparent power output must be reduced (derating) in order not to exceed the rated temperature. Comparison of measured derating values with ones obtained from K- and F_HL-factor approaches reveals that the K-factor approach yields somewhat greater derating values than the F_HL-factor approach. The losses of conductive materials in the presence of magnetic fluxes are also investigated and it has been found that the maximum losses in these components occur at a specific (material-dependent) frequency. The losses are proportional to the power of 0.8 below this frequency and are inversely proportional to the power of 0.9 above this frequency.
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