Analysis On Advers Eeffects Of High Voltage Inverter Drive System With Long Cable And The Associated Countermeasures

The widespread use of electrical energy, promoted the rapid development of industrialization and information technology of modern society. The efficiency of motor system is importance for energy saving, which has brought significant economic benefits. Motormainly relies on inverter technology to improve efficiency, and achieve energy saving. Inverter has high power factor, stable starting, wide speed range and ease of use in industrial production.In practical application, theinverter can not ignore the existence of negative effects, mainly including common-mode voltage generated by the inverter and the overvoltage on the motor terminal. At present, the main high-power switching device-IGBT, which typical rise time is 100ns, during such a short rise time, pulse voltage instantaneously from zero to maximum voltage or falling from the highest voltage to zero, when the high frequency and rapid change dv/dteffects on the motor side, due to the presence of high-frequency parasitic capacitances inside the motor, inducted shaft voltage on the motor bearing. When shaft voltage increases to a certain extent, it will make the bearing oil film breakdown, produce a discharge current, resulting in the motor bearing temperature rise in a short time recess, eventually damage the whole system. On the other hand, the high-frequency common-mode voltage of the entire system work on the stray capacitance and parasitic coupling capacitance, formedcommon mode current paththrough the motor housing, land and inverter, which resulting in conductive electromagnetic interference EMI. In addition, the leakage current may cause the malfunction of earth current relayforprotection. In some special field, like oildrilling, paper, mining, etc., because the motor and drive are far away, the inevitable need to use a long cable between them, PWM signal transport to the motor through the cable, due to the high voltage conversion rates, and when the cable reaches a certain length, PWM signal can be seen as a traveling wave in the cable transmission, since the impedance of the motor and the cable impedance mismatch, PWM wavewill reflecton the motor terminal, the forward and reverse traveling wave superimposedeach other and over-voltage occur at the motor end. The overvoltage includes both differential mode voltage and common-mode voltage doubling. The doublecommon mode voltage will aggravate its negative effects, the double differential mode voltage will increases the insulationstress of the motor, causes serious damage to the motor insulation.Therefore, the study of negative effects and countermeasures of the variable frequency speed regulation system in the long cable transmission is particularly important. This paper studies the theory, topology of high voltage variable frequency drive system, includes a rectifier, DC link, inverter, emphaticallyanalyzes the pulse wave rectifier and the principle of phase-shifting transformers in the high-voltage inverter. Secondly, studied the mechanism of common-mode voltage produced by the inverter, it is concluded that the common mode voltage related to the inverter’s switching state, based on this,researched the modulation strategy of the three-level inverter to the suppressionof common mode voltage, studied traditional SPWM of three-level inverter, SPWM for reducing the common mode voltage and SPWM for eliminate common mode voltage, studied the effect oftraditional SVPWM on common-mode voltage, proposedimproved policy for the elimination of the common mode voltage, and verify its correctness by simulation. Again, using the theory of transmission line analysisthe characteristics of PWM pulse wave on long cable transmission and the causes of overvoltage phenomena on the motor terminal, and analyzes the distribution parameters of the cable effect on the motor terminal voltage, that is distributed inductance, distributed capacitance, characteristic impedance, cable length influence on the motor terminal over-voltage. Finally, the motor terminal overvoltage suppression measures, the research of passive filter design method. Proposed SHEPWM modulation technique and the combination of the LC filter on the motor side of the overvoltage suppression. Studied the principle, the selection of initial value, the calculation of the angle. Based on this and then used mathematical software MATLAB to study the feasibility suppression strategy.