Influence of Single-Phase Voltage Loss and Load Carrying Mode on Mine Drainage Pump Motor in Vietnam

Mine drainage pump is the most important load in mining which requires high reliabilitywhen operating. Currently, the power supply of a mine drainage pump is connected to the same powerline with many nonlinear loads, and is equipped with power electronic converters, which makes thepower supply nonsinusoidal. During the working process of a mine drainage pump, the load-carryingfactor often changes, and many types of failures occur, among which single-phase voltage loss is themost common problem. In the case of a nonsinusoidal power supply, if a single-phase voltage lossoccurs in different load modes, it will greatly affect the working mode of the mine drainage pumpleading to influences on the working efficiency, the life of the pump, and sometimes it is necessary torecalculate the protection parameters. This paper studies the influence of single-phase voltage loss andload carrying mode on the working mode of mine drainage pump motor in case the of nonsinusoidalpower supply. Research results show that, in the case of nonsinusoidal power supplied with single-phasevoltage loss, copper losses in the rotor and stator circuits increase with increases in voltage totalharmonic distortion (THD) and load-carrying factor, 5th order reverse harmonic increases copper loss inasynchronous motor the most, and higher harmonic components have less effect on copper loss in themotor. At the same time, the speed ripple decreases with the increase of the motor load factor anddecreases in the presence of the 5th order negative sequence harmonic, and increases significantly in thepresence of the 7th order positive sequence harmonic. 5th order negative sequence harmonic increases,the torque ripple increases, while the 7th order positive sequence harmonic reduces the torque ripple inthe case of single-phase voltage loss. The results of the paper will help improve the operationalefficiency of the mine drainage pump in Vietnam's mines.

Double Synchronous Unified Virtual Oscillator Control for Asymmetrical Fault Ride-Through in Grid-Forming Voltage Source Converters

A double synchronous unified virtual oscillator controller (dsUVOC) is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced or distorted grids. The proposed controller leverages a positive- and a negative-sequence virtual oscillator, a double-sequence current reference generator, and a double-sequence vector limiter. Under fault conditions, the controller enables to clamp the converter output current below the maximum value limited by the converter hardware while retaining synchronization without a phase-locked-loop (PLL) regardless of the balanced or unbalanced nature of grid faults. Consequently, balanced and unbalanced fault ride-through can be achieved without the need for switching to a back-up controller. The paper presents the systematic development of the double-synchronous structure along with detail design and implementation guidelines. Validation of the proposed controller is provided through extensive control-hardware-in-the-loop (CHIL) and laboratory hardware experiments.

Base-Frequency Negative Sequence Impedance Modeling and Sensitivity Analysis of DFIG

The phenomenon of three phase voltage imbalance frequently occurs in large-scale new energy grid connected areas in China; in severe cases, a large number of wind turbines will be disconnected from the grid. To solve the problem of the voltage imbalance at the point of common coupling (PCC), analyze the influence of generator parameters change on negative sequence voltage under the background of unbalanced power grid, a modeling method of base-frequency negative sequence impedance of doubly fed induction generator (DFIG) which including phase locked loop (PLL), rotor side converter (RSC) and grid side converter (GSC) is proposed. By establishing the negative sequence equivalent circuit of grid-connected system of DFIG, the relationship between the negative sequence voltage of PCC and the negative sequence impedance of DFIG is listed, and analyzing the sensitivity of control parameters link to base-frequency impedance, the parameter that has great influence on base-frequency negative sequence impedance of PCC is found out. Finally, the accuracy of impedance modeling and sensitivity analysis is verified by simulation studies.

Research on Life Loss of Generator Retainer Caused by Negative Sequence Current

With a large number of wind and solar power sources connected to the power grid, higher requirements are put forward for the power generation equipment to respond to the power grid imbalance. The safety research of generator rotor retaining ring under the impact of negative sequence current is of great significance. For 300MW turbogenerator, the two-dimensional and three-dimensional eddy current, temperature rise, stress and life of generator rotor under the impact of negative sequence current are analyzed and studied. The two-dimensional calculation models of stator and rotor are established, and the distribution of negative sequence eddy current field in rotor section is analyzed; considering the contact resistance between rotor and retaining ring and the end effect of magnetic field, a three-dimensional analysis model is established, and the calculation results of three-dimensional eddy current field, temperature field and stress field are obtained. The analysis shows that after considering the contact resistance between rotor and retaining ring and end effect, the current density at the contact between retaining ring and rotor big tooth edge is 17.6 times of the two-dimensional calculation result of rotor section, and the maximum temperature of rotor retaining ring reaches 170.36°C.