Ken-ichiro Yamashita

Steady-state performance analysis of an integrated wind turbine generating system in a DC transmission system with thyristor inverter

Steady-state performances of an integrated wind turbine generating system connected to a DC transmission system with an externally commutated thyristor inverter are discussed. The relationships between the DC transmission line voltage and the powers at the connecting points for the grids are revealed. It is shown that the operating range of the DC transmission line voltage, which is varied with fluctuations in the wind velocities, is determined by the power at the receiving-end grid. Then, we discuss DC power control methods to obtain maximum utilization from wind power and to compensate the fluctuation in the power at the receiving-end grid in the above-stated operating range. A comparative study of the DC power control by either the firing angle for the sending-end rectifier or the leading angle of the inverter is investigated. Finally, a combined DC power control method with the firing angle and the leading angle is explored.

A simulation model of a self-excited three-phase synchronous generator for wind turbine generators

A high-voltage direct-current (HVDC) transmission system with a current-source thyristor inverter for wind farms has been proposed. In the system, synchronous generators are used such as a permanent magnet synchronous generator (PMSG) or a wound rotor synchronous generator (WRSG). In this paper, a simulation model of self-excited synchronous generator for wind turbine generators is derived, and based on the model steady-state characteristics of the wind turbine generator system containing the generator are discussed. The model is introduced based on the dq transformation for salient-pole type machines. The instantaneous voltage and current waveforms of the generator are simulated with this model. Then, the simulation is executed for the case that the generator output terminal is connected to the HVDC transmission system through a thyristor rectifier. The effects of short-circuit ratio of the generator on the system characteristics are also studied. Finally, experimental investigations are carried out to confirm the validity of the simulation model. It is shown that the proposed simulation model is useful for developing wind farms with self-excited synchronous generators.

Considerations of kVA capacity of power compensation systems for DC transmission system including wind turbine generating systems

An integrated wind turbine generating system in a DC transmission system with power compensation systems has been proposed and its steady-state performances have been analyzed. In this paper, the kVA capacity of the power compensation systems connected to the sending-end and the receiving-end grids and wind turbine generators is discussed. A set of system equations is first derived. The effects of the sending-end grid conditions on the kVA capacity of the power compensation systems are explored. It is shown that, although the effect of the sending-end grid power factor on the kVA capacity of the sending-end compensation system is small, the effect of the power factor on the kVA capacity of the receiving-end compensation system is large. The appropriate turns ratios of the transformers are also studied. Finally, the kVA capacity of the wind turbine generators is discussed.

A harmonics elimination method using a novel three-winding transformer for HVDC transmission systems

A high-voltage direct current (HVDC) transmission system including wind turbine generating systems has been proposed. In the system, the thyristor converter and inverter are used in the same way as in traditional HVDC transmission systems. Hence, the system is suitable for large-scale wind farms and it has high reliability. However, the traditional HVDC transmission systems cause a large number of harmonics in the sending-end grid current and the receiving-end grid current. In this paper, a novel harmonics elimination method using a three-winding transformer with negative leakage inductance for the HVDC transmission systems is proposed. The theory of the proposed method is discussed and the simulation model of the proposed system is developed first. The proposed method is confirmed to be effective when a resistance load is connected to the output terminal of the system. It is shown that the proposed method is useful to eliminate harmonic distortions generated at the inverter. Also, to obtain an accurate simulated result, the simulation model is modified to take in the effects of the excitation circuit of the transformer and its magnetic hysteresis loop. Finally, current waveforms and voltage waveforms of the transformer when receiving-end grid is connected to the output terminal of the system are discussed.

Steady-state characteristics of self-excited synchronous generators with damper windings for current-source type wind farm

Steady-state characteristics of self-excited synchronous generators with damper windings used for current-source type wind farm composed of series-connected wind generators are studied. A simulation model of the generators with damper windings is first derived based on dq transformation for salient-pole type machines. Experimental investigations were carried out to confirm the validity of the simulation model. The instantaneous voltage and current waveforms of the wind turbine generators are simulated with typical values of salient-pole synchronous generator constants, and the effects of the damper windings on the operating range of the wind generator are discussed. It is shown that the operating range for the generator with damper windings is extended in comparison to the case without damper windings. Finally, the steady-state characteristics for the case of 50 wind turbine generators are connected to the system are discussed.

Studies on a hybrid wind turbine generator system considering surplus power

A hybrid wind turbine generator system supplying constant output power has been proposed. In this paper, steady-state characteristics of the hybrid wind turbine generator system considering surplus electric power are investigated by simulation and experiments taking the sizes of the wind turbine into account. The experimental results showed close agreements with the simulation ones.

Dynamic performance analysis of control systems for a DC transmission system including wind turbine generating systems

A DC transmission system including wind turbine generating systems has been proposed and its steady-state performances have been revealed. The proposed system can be used as an offshore wind farm. In this system, each voltage on the DC transmission line should be controlled properly for utilizing wind power to the maximum. In this paper, the control systems are developed first, and their dynamic performances are discussed. It is shown that the dynamic responses of the system become oscillatory. These oscillations can be diminished by applying current minor loops to the control system. Furthermore, two types of the maximum power tracking control systems for the wind turbine generating systems are compared. It is clarified that the turbine torque control is appropriate for the proposed wind turbine generating systems. Finally, a method of improving the maximum power tracking control system is suggested and its dynamic responses are analyzed.