A Study On Double-fed Control Strategy And System Of100MVA Pulse Generator Unit

J-TEXT device is a pulsed medium-sized tokamak device in HUST. Its predecessor is the TEXT-U device in the University of Texas in USA. The main power of J-TEXT supply is a100MVA pulse generator unit, which is consisted of a1500kW triple-phase asynchronous motor and a100MVA pulse generator. Its rated speed is713rpm, and the maximum stored energy is185MJ. The generator unit was designed in USA, which grid is12kV/60Hz, but in China the grid10kV/50Hz. Due to the difference of grid frequency, the rotational speed can only reach5/6of the rated value, and the stored energy can only reach70%of the rated value. As a result, J-TEXT has to operate under low parameter, and a double-fed speed control system is designed to raise the speed of the generator unit.This paper investigated in the double-fed control system of the pulsed generator unit, and studied on the vector control strategy of three phase motor, the two level voltage source AC-DC-AC converter, and the sensorless rotor angle observer. A double-fed speed control system is designed for the100MVA pulse generator unit. The simulation and experimental results verified the control strategy and system design.Under the MT coordinate system, a double-fed control strategy is designed to control the speed and rotor current of motor. With the double closed loop feedback control method, the M axis and T axis component of rotor current could be controlled independently and stable. The structure and algorithm of stator flux observer have been analyzed, as well as the influence of the calculation step. In rotor current feedback control, the value of M axis component of rotor current is been calculated in the situation of minimum rotor current and zero reactive power in rotor side.In order to measure the angle between rotor winding and stator flux vector, a rotor current based sensorless rotor angle observer is introduced in this paper. To improve the dynamic performance of observer, the control parameter range have been discussed. A parameter variable PI controller is designed to reduce the effect of rotor current harmonic.The simulations and experiments are made to verify the observer model.In double-fed system, the two level voltage source AC-DC-AC converter is selected as the power supply in rotor side. Based on the voltage vector oriented coordinate system, the rectifier control strategy is designed. With this strategy, the DC voltage and the rectifier current could be controlled. In the case of motor drive, the design method of low pass RLC filter in converter output side have been analyzed,Based on the former researches, this paper designs the double-fed speed control system of the100MVA pulse generator unit. The power scale of the system, the parameters of the main components, the structure of the AC-DC-AC converter and its drive circuit have been analyzed. According to the operation characteristic of the pulse generator, the action sequence of the breaks in the double-fed system have been designed. The software structure of double-fed control system is divided into three layers. The software system of double-fed control system is integrated into J-TEXT COD AC system. Under QNX operating system, the rotor angle and speed measurement method based on PCI-1784U and the feedback control algorithm of rotor currents have been analyzed. The simulations and prototype experiments are made to verify the hardware and software design of the double-fed system. The appliance of double-fed system could raise the stored energy of the100MVA pulse generator unit, and provide a solid foundation for the high parameter discharge experiment in J-TEXT.