A space vector modulation (SVM) technique of a dual-inverter system for an open-end winding motor drive is described in this paper, where one inverter has a battery power source and the other has an only capacitor across the dc bus. The SVM must be achieved to operate the motor with field-oriented control and simultaneously to control the capacitor voltage at a constant value by using redundant switching states of the dual-inverter system. The control of the capacitor voltage is carried out by selecting a charging or a discharging mode in each redundant switching state, taking the instantaneous motor power factor into account. In addition, it is also required to reduce the error voltage pulses, which are generated in output multilevel voltage waveforms during the dead time. The compensation method of the existing dead-time scheme and the improved SVM sequence to reduce the error voltage vectors are proposed in this paper. The proposed methods are examined through several experimental tests and are confirmed to generate superior output voltage waveforms from the viewpoint of the measured total harmonic distortion and dv/dt.
The dual inverter drive system feeding an open-end winding permanent magnet (PM) motor has been studied for developing autopilot technologies of hybrid vehicles. Autopilot systems require fault-tolerant functions, which enable it to continue to drive the motor even if some failure occurs in the motor drive system. The fault-tolerant function of a dual inverter drive system, which assumes that the DC-bus battery power source of the dual inverter drive system has failed, is discussed in this paper. In the dual inverter drive system that is considered, both the inverters have a capacitor in parallel with a battery across each DC-bus. The capacitor drives the motor continuously even if the DC-bus battery has failed. The inverter, in which the DC-bus battery has failed, is operated with the capacitor instead of the failed battery. It is required to both control the capacitor voltage at a constant value and simultaneously generate multilevel voltage waveforms across the motor windings with the space vector modulation (SVM). In this paper, the fault-tolerant function of the DC-bus battery in a dual inverter drive system is proposed, and its operation characteristics are examined through several experiments and compared with those of a normal system.
Recently, a dual inverter motor drive feeding an open-end winding permanent magnet (PM) motor has been studied, aiming for the improvement of total efficiency and a fault tolerant function of hybrid and electric vehicles. The authors have studied the fault tolerant operation of the DC-bus battery, where the failed inverter is operated only with a capacitor across the DC-bus and a space vector modulation (SVM) is employed to regulate the capacitor voltage. In our previous research, the SVM techniques for the fault tolerant operation in a low-modulation-index have been proposed. However, it was difficult to have fault tolerance in a high-modulation-index case. The voltage margin in the fault situation is limited because the failed inverter is operated with the capacitor. In this paper, the SVM technique to achieve the fault tolerant operation in the high-modulation-index state is investigated. The novel point of this paper is that the proposed technique introduces a field-weakening control in order to reduce the command voltage vector within the controllable voltage region. The proposed technique was verified through experimental tests and its operational characteristics were compared with the normal operation, from the viewpoints of the total harmonic distortion (THD) and the efficiencies of the inverters and the motor.
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