Research Of Harmonic Suppression Of Soft Starting Based On Compound Control Of Double Closed-loop

Thyristor soft starter relied on its smooth starting characteristics, which could effectively reduce the current shock of Squirrel-cage three-phase asynchronous motor in the starting process. Thyristor soft starter getted more and more widely attention at home and abroad.However, thyristor soft starter as an application of the power electronic technology product,which consumed a large amount of reactive power and produced higher harmonic signal in working process. The harmonic caused serious harm to electrical equipment and power supply system. In this thesis, harmonics are generated by thyristor soft starter installated on air compressor in the starting process. The harmonic and compensate reactive current are suppressed by the shunt active power filter in dynamic process. Thesis uses adaptive harmonic test and double closed-loop compound control method, and mades a discussion in depth.The main contents on the following aspects:(1) Three-phase asynchronous motor of air compressor is builded an equivalent model.The starting characteristics are analysed, and the thyristor three-phase ac voltage regulation circuit and harmonic problems are analyzed. The comparative simulation of direct starting and current limiting soft starting demonstrates that the direct starting current is a few times of the rated current. The direct starting seriously affected the life of motor. The soft starting started smoothly, which can change starting characteristics accordding to the requirements. But at the same time, the thyristor starter occured current distortion phenomenon on the load side in working process.(2) Active power filter harmonic current detection uses adaptive harmonic test. The traditional fixed step least mean square(LMS) algorithm and the subsequent improved adaptive variable step LMS algorithm are researched. An adaptive variable step LMS algorithm is proposed, which dynamic factor and momentum factor are put forward unification. The factors changed as a minimalist style function of witch of agnesi. Through the comparative simulation shows that improved algorithm has good tracking features.(3) Active power filter tracking control method uses the double closed-loop compound control. According to waveform characteristics, active power filter uses different control strategies for internal and external closed-loop. For outer voltage loop, fuzzy PI control method is used to ensure the stability of the dc side capacitor voltage. For inner current loop,the control strategy that is designed to compensate periodical variational harmonic current signal. Single neuron PI control and series-parallel repetitive control are combined. By comparative simulation, it shows that the collocation of internal and external loop control is reasonable, and the effect is well.Both theoretical analysis and simulation study effectively proves that the thesis uses adaptive harmonic test and double closed-loop control for shunt active power filter to suppress harmonic current generated by thyristor soft starter of the three phase voltage regulation circuit, which can obviously suppress harmonic and improve application effect of active power filter.