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A new medium voltage drive has been developed based on the active neutral-point clamped 5-level (ANPC-5L) topology with the option of transformerless network connection. In the last decade three-level neutral-point clamped (NPC) converters have become the industry standard in MV Drives. Although the three-level NPC converter has proven itself in the toughest applications in industry, the call for more efficient use of energy has raised the demand for converters to be used with standard catalogue motors, both for retrofit and new installations. The option to avoid the additional cost of the input transformer in such applications is also a great advantage. The structure of the converter will be described with an explanation of the multiple levels of redundancy available. The necessary conditions for regulating the neutral-point and phase (or floating) capacitor voltages will be illustrated. The direct torque control (DTC) method is used in the inverter control. The synchronous frame current regulator used for rectifier control allows for full four-quadrant operation on the network side. The modular mechanical design philosophy will be displayed along with the salient technical features: rectifier and inverter operating waveforms, protection concept, and ride through behavior. Finally, experience in pilot installations will be described.
Kieferndorf et al. (Tue,) studied this question.