Research On Steady-state Performance Of Nine-phase Induction Motor Active Cutting Sleeve Operation

Due to its advantages of simple structure,high power density,and small torque ripple,multi-phase induction motors have become the preferred propulsion motor for the first-generation ship’s integrated power system.In order to improve the efficiency and reliability of the propulsion system,multi-phase induction propulsion motors often adopt multiple sets of multi-phase winding structures.When a certain phase winding fails,the entire set of windings where the faulty phase is located can be cut out to ensure that the other healthy phases of the motor continue to run.In addition,when the ship is cruising and operating,the system can choose to actively cut out one or several sets of windings making the propulsion motor system work in the cut-out operation state to improve operating efficiency.Therefore,for multiple sets of multi-phase induction propulsion motors,the cutting operation is a unique and indispensable operating condition,and it is necessary to conduct an in-depth study on the cutting operation performance.This article takes the nine-phase induction propulsion motor composed of three sets of three-phase windings as the research object,analyzing the change of the air gap magnetic field when the motor is cut-out,calculating the stator and rotor parameters after the phase number changes,and considering the ferromagnetic saturation factor.Based on the nonlinear magnetic circuit,the T-type equivalent circuit of multiple sets of multi-phase induction motors with variable parameters is established,and the steady-state performance of nine-phase induction motors with different sets of windings is further studied.O n this basis,based on the principle of minimum loss,the principle of active switching of the operating phase number of the nine-phase induction motor in the full torque range was proposed,and the test verification was completed on the 8 k W nine-phase induction motor test platform.First,the traditional magnetic potential analysis method is used to analyze the air gap magnetic potential of the nine-phase induction motor in the cut-out operation.The one-phase pulsating magnetic potential is decomposed into two rotating magnetic potentials,one positive and one negative,and then the multi-phase magnetic potentials are synthesized.From the perspective of space harmonics and time harmonics,the combined magnetic potential generated by the fundamental wave and harmonic current during normal operation of the motor,and the combined magnetic potential generated by the fundamental wave and harmonic current during the cut-out operation are sequentially calculated.The general expression of the co mposite magnetic potential when the multiphase induction motor is cut-out operation is presented.The results show that when the nine-phase induction motor is running with sets of winding out of service the fundamental magnetic field is still a circular ro tating magnetic field,and only the number of harmonic magnetic potentials increases.Secondly,recalculate the stator and rotor parameters and the nonlinear magnetic circuit of the motor cut-out operation.The corresponding element reflects the change of the phase number,and the calculation process is clear and simple.The distributed magnetic circuit opproach is further used to calculate the nonlinear magnetic circuit after the phase number of the motor changes,the nonlinear relationship between the exc itation current and the excitation inductance in the working range is obtained,and the excitation corresponding to any number of phases and excitation current can be obtained by interpolation.Inductance reduces repetitive calculations and avoids the disadvantage of finite element calculations that consume too much time.On this basis,a T-type equivalent circuit of the nine-phase induction motor cut-out operation with variable parameters is established,and combined with the propeller load characteristics,the steady-state performance index of the torque,power factor,and overload capacity of the propulsion motor cut-out derating operation is calculated.Finally,comprehensively considering the losses of the nine-phase induction propulsion motor and its drive inverter,the principle of active switching operation phase number switching in the full torque range is proposed.By separately calculating the core loss and copper losse of the moter during normal operation and operation with sets of winding out of service,as well as the switching loss and on-state loss of the inverter,the phase number switching criterion for the minimum system loss is proposed.That provides a theoretical basis for the propulsion motor system to always maintain hign effciency.