Research On Drive And Fault-tolerant Control Technologies Of Five-phase Permanent Magnet Synchronous Motor

Nowadays, with the development of power electronic conversion technology, AC motor drive systems have got rid of the phase number constraint from traditional three-phase power supply network. Control freedom degree and design flexibility are improved due to the higher phase number. Attribute to small torque ripple, large power output, strong fault-tolerance capability and high reliability, multi-phase motor drive systems have attracted more and more attention in many application areas such as ship electric propulsion, urban mass transit, aerospace and weapon equipment, etc. This dissertation chooses five-phase permanent magnet synchronous motor(PMSM) as the research object, and focuses on analyzing magnetomotive force(MMF) harmonic, building accurate mathematical model, achieving high performance pulse width modulation(PWM) algorithm, fault diagnosis and fault-tolerant control of the five-phase PMSM drive system.Firstly, the MMF produced by five-phase concentrated and full-pitch winding is deduced based on winding function theory and Fourier analysis method. By summarizing the temporal and spatial distribution of MMF harmonics, their roles in the electromechanical energy conversion process are illustrated. By means of equivalent transformation between different coordinate system, the decoupling mathematical model of five-phase PMSM under normal condition and fault condition are established. According to the torque equation, it can be found that the average torque could be increased by injecting third harmonic current under normal condition, and the ripple torque could be eliminated under fault condition. Adopting the field-oriented control method, the fundamental and third harmonic current can be controlled independently.Secondly, the pulse width modulation algorithms for five-phase voltage source inverter(VSI) are researched thoroughly. If the conventional two-vector SVPWM algorithm is extended directly to the five-phase VSI, it can get a higher DC bus utilization, but there are a large number of harmonic components in the output voltage simultaneously, which is not conducive to long-term operation of the drive system. The four-vector SVPWM algorithm can produce standard sinusoidal phase voltage, so the modulation factor has been reduced and the calculation process is more complex. By reconstructing basic space voltage vector, the existing four-vector SVPWM algorithm is improved in this dissertation. The proposed method has the same linear modulation range as two-vector SVPWM algorithm, restrains the harmonic voltage as much as possible and the phase voltage could achieve smooth transition from standard sinusoidal to non-sinusoidal. Through comparing and analyzing the modulation function and harmonic spectrum, the equivalent relationship between carrier-based PWM algorithm with zero-sequence injection and various SVPWM algorithms.Thirdly, by diagnosing and isolating the fault circuit of five-phase PMSM drive system real-time and effectively, then taking the appropriate fault-tolerant control strategy, reliability of multi-phase motor drive system can be improved. The impact of different load torque on voltage and current variables before and after fault is analysed, it can be seen that current-based fault diagnostic method is susceptible to load disturbance and control strategy and the detection time requires at least one fundamental period. The generation principle and manifestations of error voltage is deduced, then the error voltage is standardized and transformed into logical signal. In this method, a threshold value is set to eliminate effect of measurement errors, and a minimum duration is set to avoid misdiagnosis caused by dead time and switching delay, so as to obtain high reliability and robustness. The proposed method is independent of load current and DC bus voltage, it is suitable for any control strategy.Lastly, fault-tolerant control strategies of five-phase PMSM with one open phase are researched. Based on the principle that MMFs remain unchanged before and after faults, by solving nonlinear equations, the amplitude and phase of current can be obtained. According to the mathematical model of five-phase PMSM under fault condition, combining torque equation with copper loss equation, based on the constraint of average torque remained unchanged and ripple torque remained at zero, the corresponding fault-tolerant current generation methods are proposed by optimizing design of current component in generalized zero-sequence subspace. Utilizing a second rotating coordinate transformation, the d-q axis current can be controlled independently; by means of feedforward compensation, the system performance under fault condition is improved significantly.