Research On The Key Technologies Of Cascaded Multilevel Inverter High-Performance Control Method And Fault Diagnosis

Cascaded H-bridge multilevel inverter is mainly used in high voltage high power variable frequency speed regulation system. Because of the advantages such as simple topology, smaller harmonic distortion, lower device voltage stress, easy modularity, it has attracted wide attention and become the research focus in the field of high-voltage high-power AC drive applications in recent years.Based on the structural features of multi-level cascaded H-bridge inverter, combined with the actual demand of high power AC drive system, this dissertation focus on the research control technology, fault diagnosis and energy feedback control strategy of the multi-level cascaded H-bridge inverter. On the one hand, the modulation method, optimal control algorithm is improved and the fault diagnosis method is proposed to obtain better output performance and improve system reliability and fault tolerance based on the existing structure; On the other hand, the structure and control strategy is improved to develop multi-level cascade H-bridge inverter applications. The main work is as follows:The basic principles of the space vector modulation technique is described, the shortcoming of space vector modulation technique in multi-level cascaded H-bridge inverter applications is analyzed, the asynchronous motor direct torque control technique is studied; based on the characteristics of multi-level carrier phase shift modulation techniques, a suitable method of multi-level cascaded H-bridge inverter time staggered superposition space vector modulation direct torque control is proposed, this method simplify the complex calculations of switching table in traditional multi-level space vector modulation, and based on it the direct torque control of high-power induction motor is realized, the system output current ripple and electromagnetic noise is reduced.The common abnormal situation of power system is introduced, the affect of the power system instantaneous loss to the cascaded multilevel H-bridge inverter is described; the existing high-voltage inverter "flying restart" speed recognition technology is studied; a double closed-loop self-tuning PID fuzzy logic speed tracking method is proposed for the unpredictability and uncertainty of the abnormalities, a specific tuning rules is given to improve the system robustness of parameter variety to improve the dynamic and steady-state performance of the system.The high-voltage variable frequency control system fault diagnosis method is summarized, for the features of cascaded H-bridge multilevel inverter carrier phase modulation, a low cost single sensor and multi-voltage detection method is proposed to achieve fault diagnosis of the power cell rapidly and simply; under the condition of inverter output voltage frequency known, a variable sample number N synchronous sampling is proposed to solve the spectrum leakage of traditional non-synchronous sampling FFT calculation; with the calculated harmonic and single-sensor and multi-voltage characteristics of the detection results to improve the training of adaptive resonance theory neural network, and a intelligent fault diagnosis system is established to locate the fault switching devices of power cell.The shortage that the traditional multi-level cascaded H-bridge inverter can not operate under four-quadrant is analyzed, the circuit topology and mathematic model of the multi-level cascaded H-bridge inverter power cell with active front end is elaborated; based on the mathematical model of PWM rectifier in stationary αβ-coordinate system, combined with the instantaneous power theory and the characteristics of PWM rectifier direct power control, based on fuzzy logic, an instantaneous power prediction is derived and a novel direct power control strategy is proposed to solve the contradiction between the width and control accuracy of traditional PWM rectifier direct power control caused by hysteresis comparator, the proposed control strategy has good stability and fast dynamic response.In this dissertation, a lot of theoretical analysis and simulation is developed for the proposed method, and a multi-level cascaded H-bridge inverter experimental apparatus and a cascaded H-bridge multilevel inverter power cell with active front end experimental apparatus is built. Simulation and experimental results verify the correctness of these theories.