Influence of three-level active rectifier on energy quality in power supply systems in mines

Large-scale application of variable frequency electric drives in power supply systems in mines is accompanied with the worsening of energy quality. One of the methods to improve energy quality in power networks with low voltages to 1 kV and wattage to 1 MW can be the addition of frequency converters with active voltage rectifiers. Two-level rectifiers improve power quality; on the other hand, in case of low-power networks, the total harmonic content and voltage fluctuations may exceed standard values. This will require additional power quality control. In this case, it is expedient to change the two-level to three-level active rectifiers with the clamped neutral point. This study analyzes influence exerted on the voltage waveform and value in a power supply system by a frequency converter with a three-level active rectifier. The results on the influence of the three-level active rectifier on the power quality with and without a harmonic filter in the rectifier are described. For the maintenance of a preset voltage irrespective of the supply main and the motor load, it is proposed to use automatic voltage adjustment with the help of the negative voltage feedback. The test data on operation of the two-level and three-level rectifiers in case of the low-power supply are compared. It is shown that the three-level active rectifier is an effective tool to improve voltage waveform and ensure allowable voltage fluctuations in case of the low-power supply of the variable frequency electric drives.