Multifunctional Cascade Control of Voltage-Source Converters Equipped With an LC Filter

this paper proposes a multifunctional cascade controller structure for voltage-source converters. The proposed structure contains a decoupling loop between the outer voltage control loop and the inner current control loop, and operation in either voltage or current control mode is possible. 

In voltage control mode, the current controller can be made completely transparent. In the case of faults, the proposed structure enables inherent overcurrent protection by a seamless transition from voltage to current control mode, wherein the current controller is fully operational. Seamless transitions between the control modes can also be triggered with an external signal to adapt the converter to different operating conditions. 

The proposed structure allows for integration of simple, accurate, and flexible overcurrent protection to state-of-the-art single loop voltage controllers without affecting voltage control properties under normal operation. The properties of the proposed controller structure are validated experimentally on a 10-kVA converter system.

Index Terms—Ac-voltage control, cascade control, current control, overcurrent protection, voltage-source converters.