Abstract
Aiming at the problems emerging in a pulse width modulation (PWM) drive system with long cables, the accurate modeling of power cables is the premise for predicting and analyzing these relevant phenomena, and a proper filter design is the key solution to these problems. This paper proposes high-frequency cable models to represent these frequency-dependent characteristics, especially for the high-frequency resistance of cables, which is an easily overlooked factor that determines the damping of overvoltage. The proposed models can be used for accurately representing the cable characteristics in a wide frequency range, and correctly simulating the differential mode (DM) overvoltage and common mode (CM) current, including the peak value, oscillation frequency, and damping of the transient waveform. In addition, improved filter networks are proposed to suppress the DM voltage and CM current, with the merit of low losses, small volume, and excellent abilities for suppressing overvoltage. The proposed cable models and the filter design were validated in a 750 W PWM drive system with 200 m power cables.
Highlights
The high-frequency problems will be more serious if long power cables are required to be connected between the inverter and motor, like the adjustable speed drive (ASD) in offshore or land-based wells [2], mining plants [3], and wind farms [4], because the voltage reflection owing to cable–motor impedance mismatch occurs along the cable and twice or higher dc-bus voltage appears at the motor terminal, which may destroy the insulation of the cables and motors
The cable model is the most important and complex part of the long cable system, and the model of the inverter and motor could be simplified owing to their rather minor influence on most occasions, especially for a cable as long as, or more than, a hundred meters, where the cable model plays the main role in the aspects of differential mode (DM) overvoltage and common mode (CM) current, which will be verified in the following content
The filter design can be divided into two parts, the DM filter to suppress the overvoltage at the motor terminal and the spike current at the inverter side, and the CM filter to mitigate the CM current
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The passive filter is an effective method to solve the high-frequency problems in the long-cable drive system, and is easier to realize compared with insulation enhancement of motors or modulation improvement of the inverter control. Two high-frequency cable models were proposed to improve the frequencydependent characteristics of a power cable, and both models were compared, showing that the proposed ladder circuit has similar and even better performance, but takes more time to calculate and simulate. In order to check the simulation results of DM overvoltage and CM current based on the model of the drive system, including long cables, inverter, and motor model, an experiment was carried out on a 750 W test platform. The advantages of the proposed filter network, including volume, efficiency, and suppression ability for overvoltage, were confirmed by an experiment on the same test platform
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