Diagnosis And Fault-Tolerant Control Strategies Of Inverters In Three-Phase Motor Drive Systems

In modern aeronautic and astronautic fields, motor systems are used as actuators and their reliability has been a key technology for safe operation of aircraft and spacecraft systems. Therefore, highly fault-tolerant motor drive systems are recently proposed and concerned by researchers. Highly fault-tolerant motor drive systems can diagnose and analyze faults in real time, and then actively reconfigure hardwear and software structures so that the whole systems can operate safely with non-losing or partly derated performance. As research indicated, power semiconductors and their drives in power converters especially inverters are fragile parts of motor drive systems. By using on-line and real-time fault detection and tolerant control strategies, reliability of motor drive systems can be improved. Therefore, research on fault diagnostics and fault-tolerant control strategies of inverters in motor drive systems has great significance in theory and application.Fault diagnosis is the precondition of implementing fault-tolerant control strategies, and reliability as well as immediacy of fault diagnosis is directly related to effects of the fault-tolerant strategies. Analytic model-based diagnostics is a fast and effective fault diagnostic method, but conventional modeling methods of motor drive systems cannot be used for analyzing and detecting faults inside inverters. It is because these models are incapable of unifying both the motor and inverter into one model and revealing state characteristic of the systems. Motor drive systems are a typical hybrid system including continuous state variables and discrete switching events. In this thesis, hybrid system theory will be adopted to analyze motor drive systems and build their mixed logical dynamic(MLD) models. The behavior and characteristic of motor drive systems with some faults are analyzed based on the proposed model, which is the fundamental of fault diagnostic methods.Based on the presented MLD model of motor drive systems, system state residual functions are built to detect and locate inverter switch faults by means of residual evaluation in the static two-phase coordinate system. The MLD model-based inverter fault diagnostic method can get rid of effects on the diagnostic performance of close-loop control algorithms, and reduce the detection time to a quarter of fundamental-wave period. In this method, a threshold value is set in order to restrain effects of parameter errors, measurement errors, disturbances and noises. To reduce detection time further and eliminate effects on the diagnostic algorithm of loads, the MLD model of inverters is considered, and hereby error voltage based and leg neutral-point potential supervising based fault diagnostic methods are proposed, separately. Error voltage based diagnostic method uses errors between measured leg neutral-point-to-ground voltages and estimated ones to detect open-switch fault. In this method, amplitude and time width are adopted as dual criteria to evaluate error voltages in order to improve reliability and robustness by eliminating effects of swiching delay and dead time. Detection time of error voltage based method is reduced within a couple of switching periods. Photocouplers are used to supervise leg neutral-point potentials and transfer them to logical signals in leg neutral-point potential based fault diagnostic method. Then, these logical signals are used for Boolean calculation with switching signals to detect open-switch fault during one switching period. This method can get rid of effects of measurement errors and noises because it eliminates voltage sense and comparison. Meanwhile, this method uses rising edge delay of switching signals to eliminate effect of switch turn-on delay so as to obtain high reliability. These proposed methods are validated by simulations and experiments.Fault-tolerant control strategies of inverters can ensure post-fault systems have such derated operation capability by reconfiguring software and hardware structures. Switch-redundant inverters and cascaded two-level inverters as well as their post-fault configurations and control strategies are studied in this thesis. Switch-redundant inverters have simple configuration, and can operate as four-switch three-phase inverters after single switch fault or single leg fault. Four-switch three-phase inverters retain the same current output capability. Then, control strategies of four-switch three-phase inverters are studied, and compensated voltage-based over-modulation four-switch space vector PWM is proposed in order to improve DC-link voltage utility. Four-switch inverters are applied in permanent magnet synchronous motor(PMSM) and brushless DC motor(BLDCM) drive systems, and vector control scheme of four-switch three-phase PMSMs and flux linkage tracking control strategy of four-switch three-phase BLDCMs are researched, separately. In order to improve voltage output capability of post-fault systems and achieve motor speed index, cascaded two-level inverters(CTLIs) with good fault-tolerant performance are applied in open-end winding motor drive systems. Fault-tolerant strategies of single-source CTLIs have two reconfigured topologies: faulty phase short-circuit connected and open-circuit connected two-phase full-bridge inverters, which have the same voltage output capability with three-phase self-bridge inverters. They are used in PMSM and BLDCM drive systems, and two-phase vector control and quasi-vector control schemes of PMSMs as well as two-phase direct current control scheme of BLDCMs are proposed to maintain operation of motor drive systems.