A high voltage and high power adjustable speed drive system using the integrated LC and step-up transforming filter

A filter device is indispensable in most ac adjustable speed drive systems to eliminate the high-frequency components in the output voltage of an inverter, which could protect the insulation of the ac motor and reduce electromagnetic interference. Additionally, due to the restraints of power electronic devices, especially in the high voltage and high power systems with neutral point clamped (NPC) three-level structure, the step-up transformer is usually applied to ascend the output voltage. Thus, the system would be bulky when both of the components, filter and transformer, are adopted simultaneously. This paper efficiently utilizes the leakage inductance of the transformer and effectively integrates the filter and step-up transformer to achieve boosting and filtering simultaneously, and economizes on cost and volume. Besides, some relevant dynamic processes, like de pre-excitation at the starting process, the self-excitation in the pulse-blocking process, and the response to load variation are discussed, respectively. This integrated configuration is validated by corresponding simulations and experiments, and has also been successfully applied in the three-level NPC 6000 V/1 MVA system. The other relevant factors in this device are discussed in detail.