Luo Yao-hua

The zero sequence circulating current suppression based on virtual impedance

There are zero sequence circuits, when inverters work in parallel directly, and zero sequence circulating current would flow, when zero sequence voltage of the inverter is different with that of the gird. The mechanism of the zero sequence circulating current is analyzed. By the analysis of the influence of the power switch tube voltage-drop, the dead time of PWM and the most common two PWM methods on the zero sequence voltage, the zero sequence voltage is a periodic signal the frequency of which is triple of the fundamental frequency. A novel zero sequence circulating current suppression method based on virtual impedance is proposed by the analysis of the zero sequence output impedance of the inverter, and the zero sequence voltage harmonic impedance is increased to improve the performance. The results of simulations and experiments show that the circulating current is suppressed effectively.

GIMC based two-degree-of-freedom robust control of induction motor

The problems about guaranteeing robustness of decoupling control of induction motor and shortage of conventional robust control approaches in considering nominal and robustness performance synchronously are introduced. In order to solve these problems, principle and structure of generalized internal model control (GIMC) based two-degree-of-freedom (2DOF) is studied, the design methods of robust control compensator and nominal controller of the proposed method are investigated respectively. The proposed design is applied to design controllers for the nonlinear differential geometry based decoupling linear subsystems of induction motor, simulation results demonstrated that the proposed method has high robust performance to the influence of model uncertainty and external disturbance, and it can improved decoupling performance effectively.

Active damping control of PMSG with LCL filter in tidal generation system

This paper has researched on the control strategy of PMSG direct-drive tidal generation system with LCL filter. Firstly, the model of PMSG (permanent magnet synchronous generator) with LCL filter is established in dq-frame, and then according to the analysis of the model, the equivalent circuit and admittance seen from the converter side in dq-frame is obtained. The bode figure shows that the LCL filter may resonance the harmonic current and even break the stability of whole system. One way to restrain the resonance is in parallel or in series a resistance with the capacitor in AC filters which is called passive damping. However, the physical resistance in passive damping will cause the energy loss. So an active damping strategy using a virtual resistance parallel with capacitor in LCL filter is proposed to restrain the resonance and reduce the stator current THD. Based on the active damping, the control system of PMSG is designed, in which the rotor speed is controlled and the unity power factor is realized. Finally, the simulation results have verified the effectiveness of the proposed control strategy.

Interaction analyse and attenuation in cascade power converters system

In order to improve the performance of power converters based interconnected system, input and output impedance of power converter are employed to investigate the cause leads to interaction in a typical cascade system, detail theoretical analyse is presented in this paper, then some practical design guide lines are induced to attenuate the interaction among power converters, by applying these rules, the dynamic performance and stability of interconnected system can be improved. Simulation results demonstrate the correctness and effectiveness of the theoretical analysis and the proposed method.

Integrated control system for first tidal flow electricity generating ship of China

This paper introduces the composition, control method and testing results of the integrated control system for the first tidal flow electricity generating (TFEG) ship of China. The control method, control algorithm and the specific circuits for the hydraulics system are also introduced. Our research works are emphasized on the control algorithm of stabilizing frequency and some special problems of the controller. The related protection measures for hydraulic system and TFEG system have been taken. A brief explanation of the water turbine control is given.