| Wind power is an emerging clean energy source that can be relied on for the long-term future. The power capacity of wind turbines grow rapidly in recent years in order to cut the cost of per kWh down. The soaring growth in capacity of wind turbines brings new problems and challenges, too. New solutions provided in article are trying to solve some problems, especially focus on rectification side.Multi-generator with single-stage gearbox substitutes the single PM generator, achieving high power density with low mechanical stress. A converter suitable for this new type power system is proposed. Based on series and parallel connection between several electrical isolated rectifier modules with different phase angle, the multi-pulse rectifier achieves smooth power output with high voltage and low current.A novel flexible thyristor rectifier with wide input voltage range is presented based on flexible topology converter theory. The rectifier consists of two 3-phase thyristor bridges and an auxiliary circuit containing diodes and a switch. By changing the state of the switch, the relationship of the two rectifiers jumps dynamically between series and parallel mode. When the turbine speed is low, the switch is turned on; the two bridges work in series mode to increase the input voltage. When the turbine speed is approaching to the rated speed, the switch is off; the two bridges work in parallel to enlarge power capacity. The switchable thyristor rectifier substitutes traditional 3-phase PWM rectifier or diode plus dc-dc boost rectifier as front end, the generator design is free from voltage and power level limited by IGBTs.The process of dynamic topology switching is an important issue and a great challenge for control. Traditional PI control methods are not satisfactory when applied to flexible topology converter, because the current overshoot during topology switching can not be compensated. Quick current tracking responses, robust operations under polluted voltage, especially the elimination of current overshoot are achieved when a novel peak current predictive controller is applied to the novel flexible thyristor rectifier.The AC voltage integration on inductor is periodical according to the novel peak current predictive control. Therefore, the maximum peak current on inductor can be predicted according to the trend of voltage integration in last cycle when triggering. As a result, prediction model is established only on the relationship of voltage integration and current of the inductor. It simplifies the calculation process greatly, because it has nothing to do with the load, thus avoiding solving transcendental functions based on load model. Triggering of thyristor is no longer depending on the voltage phase information, and the robustness of performance is improved. The novel control method is verified by both simulation and experiment. Two predictive controllers calculate the parallel and the series mode separately, achieving a smooth transition during topology switching. Reasonable control strategy can eliminates the adverse effects brought by topology switching. The theory of flexible topology converter is further verified in the AC-DC power conversion.The generator cannot operate in unity power factor using the flexible topology thyristor rectifier. But, the 6-phase double-Y PM machine has the advantage of low 5th and 7th harmonics in space flux when connected with rectification load. When it is adopted with the new flexible thyristor rectifier, the degraded usage of generator is alleviated greatly compared with 3-phase PM machines.The heavy nacelle half sky is supported by a slim tower. The system is an under damped system, and it oscillating for a long run under the push of wind. The disturbance accommodating controller derives disturbances of wind speed from state space variables, and then compensates it by adjusting pitch. Results show that the damping ratio is improved greatly, and the mechanical fatigue drops accordingly.
|
PDF Full Text Request