Continuously motor-synchronized ride-through capability for matrix-converter adjustable-speed drives

The ride-through capability of adjustable-speed drives has become an important issue due to its direct impact on production and revenue losses. Moreover, different industrial surveys have shown that voltage sags are the main cause of converter tripping. Disturbances such as swells, distortion, and impulses were found far less common and did not cause any tripping nor production losses. Matrix-converter (MC) drives are also prone to voltage sags, furthermore the lack of the dc-link capacitor renders them somehow more vulnerable. This paper presents a ride-through strategy for MC adjustable-speed drives. The strategy is based on the reduced speed/load approach for conventional drives and is capable of enforcing constant volts/hertz operation regardless of the supply voltage conditions by first regulating the modulation index of the matrix converter, which counteracts the supply voltage drop, and second by reducing the speed reference if required. This reduction seeks to maintain the maximum torque capability of the drive and not to reduce the motor load as in conventional drives. Hence, the proposed strategy is suitable for both variable and constant torque loads. Moreover, the converter never loses synchronization with the motor, so it is capable of immediate acceleration to its former speed after the disturbance disappears. The proposed strategy was experimentally verified under typical industry disturbances using a TMS320C32 DSP based system. Particularly, three-phase and single-phase sags varying from 10% to 60% were tested. Results obtained showed the effectiveness of the proposed strategy for MC adjustable-speed drives.