Control of parallel-connected grid-side converters of a wind turbine with real-time ethernet

As power level grows, the power converter of wind turbines tends to use parallel-connected smaller converters. The main reason for parallel is that modular design of those smaller converters is relatively mature and cost-effective. However, the parallel of GSCs (Grid-Side Converters) is notorious for its difficulty in control. Bulky and costly filtering capacitor bank is common and LCL resonance problem often occurs in wind farm. Due to communication speed, synchronization and engineering limitation, conventional methods cannot obtain a good balance between the control performance and the system reliability. This paper first proposes to utilize the real-time Ethernet technology for the control of parallel-connected GSCs of a wind turbine. With the proposed technology, the conventional control deficiencies of parallel-connected GSCs can be satisfactorily overcome. The reliable real-time Ethernet single line connection greatly simplifies the system interconnection and provides a unified information interface for all control devices. The high-speed communication and real-time response capability make it possible to perform fast closed-loop control in one master controller. Moreover, as all control information is collected in the master controller, the best coordination strategy can be applied to improve the system performance. The high accuracy of synchronization enables slave controllers to synchronize at carrier frequency level so that they can use phase-shifted carrier to cancel the switching ripple of branch currents. The HIL (Hardware-in-The-Loop) experimental results verify the feasibility and high performance of the proposed control system. The application of real-time Ethernet is promising to become a new trend in wind power converter design.