| Compared with a three-phase system, a multi-phase drive system has manyadvantages that include good fault-tolerant performance, better system stability,increased degree of freedom control and uses low-voltage switching devices to achievehigh-power drive systems. There are many similarities between multi-phase drivesystem and three-phase system’s control strategy. However, due to an increase in thenumber of phases, there is a big difference between a multi-phase system and athree-phase system’s mathematical model and control strategy. Therefore, there aremany aspects worthy of studying and improving the control of the multi-phase drivesystem. In this paper, the nine-phase induction motor drive control system is taken asthe research object, the realization of the vector control strategy for the nine-phaseinduction motor drive system which is based on the rotor flux orientation is studied.Presently, the SPWM (sinusoidal pulse width modulation) and SVPWM (spacevector pulse width modulation) are the most widely used PWM modulation methods inthree-phase transmission systems. but these two methods can not be directly applied tomulti-phase transmission systems by just extending the PWM method of thethree-phase system. the trigonometric formulas computing and coordinatetransformation, determining which sector the effective vector is fall in and calculatingthe corresponding space vector function-time are necessary processes of traditionalSVPWM. The more number of phases, the more complex the realization process, andworsens the real-time performance of the system. In order to achieve the control of thenine-phase inverter, carrier-based nine-phase SVPWM algorithm is put forward. Thealgorithm is that a unified mathematical form is used to represent the nine-phaseSPWM and SVPWM algorithm, according to the zero vector distribution in theswitching cycle, to achieve different nine-phase PWM modulations, The algorithm’sreal-time performance is high and it can be used in the drive control system which hasmore phases. The improvement of the traditional vector control strategy puts forwardthe method of decoupling the harmonic current plane. After decoupling, every currenton the DQ-axis is a closed-loop control, reduces the motor output torque ripple, andimproves the nine-phase drive system stability.When the transmission system is running, in the frequency inverter may appear asingle-phase or multi-phase bridge failure (a single-phase or multi-phase motor failure), resulting in system output torque fluctuating, the system stability being reduced, andthe transmission system running in a phase-fault state.To carry out an analysis for the9-phase induction motor’s phase-fault(phase-deficient) operation state, proposed that when operating the motor in a state ofphase-fault, then for each phase current carry out compensation control so that thepre-fault (under normal) and post-fault (fault conditions) space MMF generated by thestator winding is the same, the9-phase induction motor output torque is constant, andmaintain the normal operation of the9-phase transmission system.By using MATLAB software’s SIMULINK toolbox, A complete9-phaseinduction motor vector control system is built, simulated and analyzed, and an excellentspeed governing performance is obtained. Compared with traditional vector control, theimproved9-phase induction motor vector control strategy in this paper has bettertorque stability. Based on the SIMULINK model of the vector control system, thecurrent compensation control strategy is added in, the dynamic phase-fault stateperformance of the9-phase induction motor is simulated. The simulation results showsthat the lack of phase current compensation control strategy is feasible, and it proves thevalidity of the phase-fault control strategy. |
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