DC Insulation Parameter Characteristics of XLPE in the Course of Its Aging

This paper deals with the experimental study on the correlation betweeninsulation resistance (R) and direct current (DC) component (i_(de)) and corresponding aging degreeof insulation in the course of the aging within cross linked polyethylene (XLPE) insulation. Theaging tests were performed on a section of 10 kV transmission XLPE cable by means of water needlemethod, and _R was measured by DC voltage superimposed method, R and i_(de) were found to besignificantly dependent on the correspondingaging degree of insulation in the course of aging ofXLPE, and different kind of aging stage has different characteristics. Beside, there are generallysimilar regularity but different amplitude in the course of aging of XLPE insulation in differentelectrolyte, and the various electrochemical tree were found on the surface of aging XLPE cableimmersed in CuSO_4, solution. Therefore, according to the changing regularity of the DCcharacteristic parameters i. e. R and i_(de) within XLPE insulation judging the aging degree of XLPEinsulation will be an effective method.

Grid-Connected Control Strategy of VSG under Complex Grid Voltage Conditions

Under complex grid conditions,the grid voltage usually has an imbalance,low order harmonics,and a small of DC bias.When the grid voltage contains low order harmonics and a small amount of DC bias component,the inverter’s output current cannot meet the grid connection requirements,and there is a three-phase current imbalance in the control strategy of common VSG under unbalanced voltage.A theoretical analysis of non-ideal power grids is carried out,and a VSG control strategy under complex operating conditions is proposed.Firstly,the third-order generalized integrator(TOGI)is used to eliminate the influence of the DC component of grid voltage.An improved delay signal cancellation(DSC)method is proposed to control the balance current and power fluctuation under unbalanced voltage based on the method of common VSG positive and negative sequence separation,It also eliminates the harmonic of command current.Then,the improved quasi proportional resonant controller(QPR)cascaded PI is used to suppress the harmonic current further so that the harmonic content of grid-connected current can meet the grid-connected requirements and achieve the three-phase current balance.Finally,the proposed strategy is verified by simulation under the control objectives of the current balance,active power,and reactive power constant.