Compensation of Unbalanced Impedance of Asymmetric Wind Power PMSG Compensated by External Circuits in Series

The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator(PMSG)compensated by external circuits in series with the 3-phase windings is investigated in this paper.The asymmetric impedance includes the unbalanced resistances,unbalanced self-inductances,and unbalanced mutual inductances.From the perspective of the second harmonic inductances in dq-frame and from the perspective of the second harmonic power,it is theoretically demonstrated that the original asymmetric 3-phase system with asymmetric impedance can be modified to a balanced system by external circuits consisting of resistances and inductances.Therefore,the second harmonic power and DC bus voltage due to the asymmetries can be suppressed naturally without any software modifications.The feasibility of this compensation method is validated by elaborate experiments at different speeds and under different load condition,although the effectiveness might be slightly affected by the non-linearity of the compensation inductance in practice.

Power hardware in the loop validation of fault ride through of VSC HVDC connected offshore wind power plants

This paper presents the power hardware in the loop(PHIL)validation of a feed forward DC voltage control scheme for the fault ride through(FRT)of voltage source converter(VSC)high voltage DC(HVDC)connected offshore wind power plants(WPPs).In the proposed FRT scheme,the WPP collector network AC voltage is actively controlled by considering both the DC voltage error and the AC current from the WPP AC collector system which ensures fast and robust FRT of the VSC HVDC connected offshore WPPs.The PHIL tests were carried out in order to verify the efficacy of the proposed feed forward DC voltage control scheme for enhancing the FRT capability of the VSC HVDC connected WPPs.The PHIL test results have demonstrated the proper control coordination between the offshore WPP and the WPP side VSC and the efficient FRT of the VSC HVDC connected WPPs.

柔性直流输电并网风电厂的低电压穿越能力改进(英文)

To achieve active control of the AC voltage magnitude of wind power plant(WPP)collector network and improve the fault ride-through(FRT)capability,an FRT scheme based on feed forward DC voltage control is presented for voltage source converter-high voltage direct current(VSC-HVDC)connected offshore WPPs.During steady state operation,an open loop AC voltage control is implemented at the WPP-side VSC of the HVDC system so that any possible control interactions between WPP-side VSC and VSC of wind turbine are minimized.Whereas during any grid fault,a dynamic AC voltage reference is made according to both the DC voltage error and AC active current from the WPP collector system,thus ensuring fast and robust FRT of the VSC-HVDC-connected offshore WPPs.Under the unbalanced fault condition in the host power system,the resulting oscillatory DC voltage is directly used in the VSC AC voltage controller at the WPP side so that the WPP collector system voltage also reflects the unbalance in the main grid.Time domain simulations are performed to verify the efficacy of the FRT scheme based on the proposed feed forward DC voltage control.Simulation results show satisfactory FRT responses of the VSC-HVDC-connected offshore WPP under balanced and unbalanced faults in the host power system,as is shown under a serious fault in the WPP collector network.

Message from Editors

Due to high torque density and efficiency,permanent magnet machines have been used for many applications,ranging from domestic appliance,industrial automation,robot,electric vehicle,to wind power generation etc.Various novel permanent magnet machine topologies have been developed and many new topologies are still emerging,whilst many novel control strategies are being developed.On the other hand,magnetless machines,including induction,switched and synchronous reluctance,and wound-field synchronous machines,can eliminate the use of expensive rare-earth magnets and their design,analysis and control are currently under extensive investigation.

Fuzzy logic based coordinated control of battery energy storage system and dispatchable distributed generation for microgrid

Microgrid is a good option to integrate renewableenergy sources (RES) into power systems. Inorder to deal with the intermittent characteristics of therenewable energy based distributed generation (DG) units,a fuzzy-logic based coordinated control strategy of a batteryenergy storage system (BESS) and dispatchable DGunits is proposed for the microgrid management system(MMS). In the proposed coordinated control strategy, theBESS is used to minimize active power exchange at thepoint of common coupling of the microgrid for grid-connectedoperation, and is used for frequency control for islandoperation. The efficiency of the proposed controlstrategy was tested by case studies using DIgSILENT/PowerFactroy.