Abstract
Pulse-width modulation (PWM) inverter drive systems are widely applied in industry for their great speed-control characteristics and performance. However, the common-mode voltage of the inverter induces motor bearing voltage and bearing current, which result in premature bearing failure. In this paper, the influence of stator and rotor grounding impedances on the bearing voltage of the motor is investigated. A comprehensive bearing-current equivalent model circuit is proposed. Based on circuit analysis, the relationship between bearing voltage ratio (BVR) and grounding impedances is derived, showing that bearing voltage varies with the stator grounding impedance on a V-shaped surface. The minimum BVR appears at some specific combinations of the stator and rotor grounding impedance. Based on this, a method of suppression of rotor-grounding bearing currents based on matching the stator and rotor grounding impedances is proposed. The analytical results are verified by experimental results and show that the bearing voltage can be mitigated by matching the grounding impedances in a proper range.
Highlights
With the development of modern drive technology, Pulse-width modulation (PWM) variable-frequency technology is widely used in AC motor drive systems
Bearing currents can be divided into four types, according to [5], which are the dv/dt bearing currents, electricdischarge-machining (EDM) currents, rotor-grounding bearing currents and circulating bearing currents. dv/dt currents and the EDM currents are related to the common-mode voltage of the inverter
+ Zrgrg+1/jωCwrwr fg Comparing (7) with (1), we find that the relationship between the common-mode voltage and the bearing voltage in Case 4 is more complex than that in Case 1
Summary
With the development of modern drive technology, PWM variable-frequency technology is widely used in AC motor drive systems. Common-mode voltage from the inverter is one of the main causes of high-frequency bearing currents [3]. Common-mode voltageminimization techniques using semiconductor-based inverters is an important method to reduce bearing voltage and bearing current [7]. To research the rotor-grounding bearing current, the relationship between bearing voltage and grounding impedance needs to be quantitatively studied, but the current research is limited to qualitative analysis. This paper will quantitatively analyze the relationship among the stator grounding impedance, rotor grounding impedance and bearing voltage, and search for a method to suppress the rotor-grounding bearing current. A method to suppress the rotor-grounding bearing current is put forward by adjusting the grounding impedance. The designed experiment is performed to verify the proposed method
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