Analysis And Suppression Of Motor Terminal Over-Voltage Phenomenon In PWM Drive System

PWM drive system is not only an important part of AC variable frequencyand speed system, but has also become one of the important ways of industrialproduction, with significant energy saving effect and economic benefits.However, PWM drive system will bring some notable adverse effects in thewide industrial applications. For example, in PWM drive system, the highdv dt isproduced when the inverter switching devices in a fast turn-on and off at themoment, due to too highdv dt, it will be very big impact to the PWM inverterdriving motor; sometimes, the inverter and the motor is installed often different,its distance is very far, so which requires long cable PWM pulse voltage to themotor side, causing the motor terminals over-voltage phenomenon and high fre-quency damped oscillation due to the presence the cable characteristic impedanceand motor characteristic impedance mismatch, in the situation severe, will causemotor or cable insulation breakdown, and even burn out the motor, burst cable.So, studying the generation of the motor terminals over-voltage phenomenon andsuppressing its negative effect have important theoretical and practical signifi-cance.First, this topic establishes the mathematical model of the PWM drive sys-tem by using the transmission line theory, through using this model, obtains themathematical description which the motor terminals line voltage is less than,equal to greater than the two times of the PWM voltage pulse amplitude, and bythe mathematical description analyses the influence of the pulse rise time, cablefeatures (length, inductance and capacitance), the motor characteristics imped-ance, switch frequency, and pulse occupies to the motor terminals over-voltage,and then simulation test through the Matlab/Simulink simulation software.Due to the existence of the motor terminals over-voltage phenomenon, in order to avoid the shorter motor service life, the subject first studied several con-ventional measures to inhibit the motor terminals over-voltage, are comparedthrough the simulation to take before and after suppression measures, but becauseof the conventional suppression methods are mostly heuristic or experimentalmethod to determine the filter parametes,did not give a clear set of parameters, sothis topic is based on the mathematical model of the PWM drive system, in con-sidering the reflection coefficient of the transmission line, the characteristic pa-rameters of cable and the characteristic impedance of motor for the filter toachieve the design specifications, research the design procedures of second orderRLC inverter output terminal filter parameters, the method can not only inhibitthe motor terminal conventional over-voltage phenomenon, at the same time, butalso has very significant inhibition effect for the motor producing overvoltagephenomenon of super2times amplitude and the high harmonic oscillation, thefeasibility and the effectiveness are verified by simulation.