Improvement in DC-Link Utilization With Reduced Current and Torque Deterioration for Five-Phase Drives by Combination of Circulating-Current Filters and Simple Carrier-Based PWM Based on Closed-Form Expressions

Multiphase drives offer important advantages over three-phase ones. With pulsewidth modulation (PWM), zero-sequence and x-y signals can be injected to enhance dc-link utilization (DLU). For example, in five-phase drives, for given dc-link voltage, the fundamental is raised by 23.1%. For sinusoidally distributed windings, although x-y currents increase losses, torque is unaffected. However, no simple carrier-based PWM methods based on closed-form expressions have been presented for this purpose so far. Most importantly, x-y currents may be unacceptably large, due to the small x-y impedance. This is particularly troublesome when high fundamental voltage is needed continuously. Applying square waveform instead of PWM raises the fundamental from 23.1 to 27.3%. Given the square-voltage distortion, filters with large x-y impedance were devised for this approach. However, some square-waveform harmonics map into the torque-producing plane without attenuation, generating torque ripple. This article proposes to use a simple carrier-based PWM method in five-phase drives combined with a circulating-current filter. The x-y voltages, which see large filter impedance, are exploited to achieve a high DLU similar to previous solutions, but without torque ripple or excessive x-y currents. Guidelines are given for designing the filter when used with the presented PWM strategy. Experimental results verify the proposal.

Automated summary

Multiphase drives offer advantages over three-phase drives, but x-y currents may be too large. Using square waveform and filters are proposed to achieve high dc-link utilization. Experimental results verify the proposal.