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In order to reduce influence of peak voltage of motor terminal pulse on the ground insulation of motor and ensure safe and stable operation of frequency-conversion winch, a peak voltage absorption device of frequency-conversion speed-regulation for winch was designed based on the principle of uniform transmission line model and absorption circuit. The device adopts principle of capacitor charging and discharging, and can effectively reduce peak voltage of motor terminal, prevent the motor insulation breakdown. The test results show that the device reduces output voltage change rate of inverter, reduces instantaneous peak of motor terminal, the peak is reduced from 2 820 V to 2 330 V, so the output peak voltage is controlled effectively.

Two three-level inverters driving an open-end winding induction motor can generate equivalent voltage waveforms as a single five-level inverter-based drive. In addition, it can bring in benefits such as reduced dc-link voltage, less number of devices, and fault-tolerant capability, which is favored in high-power motor drive applications. The main challenge with this type of configuration is the appearance of large zero-sequence current circulating between the two inverters, which generates extra losses in the switching devices and the motor as well as affects the normal operation of the machine. Another challenge is to balance the dc-link neutral point voltage of the two three-level inverters. This paper has proposed a simplified decoupled space-vector pulsewidth-modulation (PWM) strategy to eliminate the averaged zero-sequence voltage in each switching cycle by the placement of redundant vectors of each individual inverter using a time shift. Neutral point voltage balance is further achieved by adjusting the time duration of the redundant vectors. In this paper, it is shown that it is possible to operate this kind of drive configuration with a single dc power supply and achieve averaged zero-sequence voltage elimination and neutral-point voltage balancing at the same time. Experimental results of a 5.5-kW dual three-level inverter drive using the proposed PWM strategy are presented, which validates the control method and drive configuration. [ABSTRACT FROM PUBLISHER]