Effect of Inductor Placement on DC Bus Capacitor of Adjustable Speed Drives
16 Dec 2020-
TL;DR: In this paper, the difference in the DC bus capacitor ripple current values between the two topologies for a given grid disturbance condition was identified, and it was found that the DC choke topology is better in terms of the stress on DC bus capacitance under balanced, unbalanced, and distorted grid conditions, considering the practical field data.
Abstract: Commonly available adjustable speed drives with diode bridge front end usually employ an inductor either in the AC side (line choke) or in the DC side (DC choke). While both the topologies are commercially popular, the difference between their performances under grid disturbances is of interest. It is identified that there exists a difference in the DC bus capacitor ripple current values between these topologies, for a given grid disturbance condition. However, both the topologies result, approximately, in the same amount of ripple in the torque for most of the cases, irrespective of the grid disturbances (up to the level of disturbance considered). It is found that the DC choke topology is better in terms of the stress on the DC bus capacitor under balanced, unbalanced, and distorted grid conditions, considering the practical field data.
Citations
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TL;DR: In this article , the authors compared the performance of different types of DC bus capacitors with DC and AC choke capacitors under balanced, unbalanced, and distorted grid voltage conditions, for the same value of the equivalent inductance in the AC and DC side.
Abstract: Abstract Diode bridge front-end Adjustable Speed Drives (ASDs) generally have an inductor either in the DC side (DC choke) or in the AC side (AC choke). Since both the types of ASDs are commercially widely used, a comparison of their behavior under normal and abnormal grid conditions is of interest. It is identified in this work that there exists a difference in the ripple current through the DC bus capacitor between the two variants. Further, the difference in the ripple current varies depending on the type of the disturbance and its level. As an outcome of the study, it is identified that the stress levels arising in the DC choke variant on the DC bus capacitor are lesser compared to the corresponding AC choke variant under balanced, unbalanced, and distorted grid voltage conditions, for the same value of the equivalent inductance in the AC and DC side. In order to match the stress levels arising in the DC bus capacitor between the ASDs with DC and AC choke, it is found that a 50% higher value of inductance is required in an AC choke variant. The effects are analyzed by simulations and validated using an experimental setup.
References
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14 Mar 1999
TL;DR: In this article, an evaluation of DC-link capacitor heating in adjustable speed drive systems with different utility interface options is presented based on the level of ripple currents DClink capacitors can endure that lead to self-heating and reduction of capacitors' operating life.
Abstract: In this paper, an evaluation of DC-link capacitor heating in adjustable speed drive systems with different utility interface options is presented. The evaluation is based on the level of ripple currents DC-link capacitors can endure that lead to self-heating and reduction of capacitors' operating life. Three popular utility interface options for ASD systems are considered for evaluation. First, a standard six-pulse diode rectifier with and without DC-link inductor is examined. Second, an active PWM rectifier, which draws nearly sinusoidal current from the utility, is studied. Third, an auto-connected 12-pulse rectifier system for utility interface is analyzed. A new term capacitor heating factor (CHF) based on the dependence of ESR on frequency is introduced and is computed for various utility interface options and the results are compared. A mathematical procedure is outlined to analytically compute the capacitor ripple current and hence heating. Simulation and experimental results are presented to verify analytical calculation. Finally, a relative comparison of capacitor heating as a function of utility interface options is presented.
36 citations
TL;DR: In this paper, the impact of the inductor placement in the adjustable-speed drive (ASD) topology on the drive's performance under voltage unbalance or sag conditions was investigated.
Abstract: Voltage unbalance or sag conditions generated by the line excitation can cause the input rectifier stage of an adjustable-speed drive (ASD) to enter a single-phase rectifier operation. This degradation of the input power quality can have a significant negative impact on the induction machine performance characteristics, but the presence of an LC filter in the drive's input rectifier stage can be used to attenuate these undesired effects. The purpose of this paper is to investigate the impact of the inductor placement in the ASD topology on the drive's performance under voltage unbalance or sag conditions. More specifically, the relative advantages of choosing either a dc-link choke inductor or three ac line inductors are discussed using a combination of closed-form analysis and simulations. The results of first-order sizing calculations show that a dc-link choke inductor may offer some volume and mass advantages over three separate ac line inductors for the same ASD performance under unbalanced voltage conditions. Experimental results using a 5-hp ASD confirm the key analytical performance predictions
24 citations
TL;DR: In this paper, a simulation is conducted to investigate the influence of the loading of the drives and the system source impedance on the performance of variable frequency drives (VFDs) in a power distribution system with VFDs as dominant loads in the oil field.
Abstract: AC line reactors and dc link reactors are widely used in variable frequency drives (VFDs) to improve the drive performance such as reducing input harmonics, improving the input power factor, and protecting the drives from surges, etc. The effectiveness of both types of reactors in reducing input harmonics is affected by many factors, including the loading of the drives and the system source impedance. In this paper, a simulation is conducted to investigate the influence of such factors. Two power distribution systems with VFDs as the dominant loads in the oil field are used as the case studies. The rules to evaluate the needs and effectiveness using ac line or dc link reactors are proposed for practical applications.
22 citations
01 Jan 2017
TL;DR: In this paper, the impact of grid voltage amplitude and phase unbalances on the lifetime of DC-link capacitors used in a standard three-phase motor drive was investigated.
Abstract: DC-link capacitor is one of the reliability-critical components in motor drive applications, which contributes to a considerable cost, size and failure. Its reliability performance depends on both inherent physical strength and external loading. The grid unbalances could alter the electro-thermal stresses of key components in a motor drive. Therefore, this paper investigates the impact of grid voltage amplitude and phase unbalances on the lifetime of DC-link capacitors used in a standard three-phase motor drive. The theoretical stress models and experimental measurements of the capacitor voltages and ripple currents are presented. The relationship between the DC-link capacitor lifetime and the level of unbalances and loads are discussed based on a 7.5 kW motor drive system. The results serve as a guideline to size the DC-link capacitors to be robust enough at the presence of grid unbalance conditions.
22 citations
TL;DR: The article proposes the derating of load required to keep the capacitor current within the safe value irrespective of the level of abnormalities and grid impedance.
Abstract: Among the various supply voltage abnormalities, unbalance and distortion are some of the major threats to the dc bus capacitor of adjustable speed drives. The effect of supply voltage unbalance on the dc bus capacitor changes in the presence of supply voltage harmonics. Further, the value of grid impedance and the load on the drive influences the response of these supply voltage abnormalities on the dc bus capacitor. This article analyzes the impact of unbalance, distortion, and simultaneous presence of unbalance and distortion in the supply voltage, on the dc bus capacitor, along with the effect of grid impedance and the load on the drive. As a result of the analysis, the article proposes the derating of load required to keep the capacitor current within the safe value irrespective of the level of abnormalities and grid impedance. The effects are analyzed by simulations and validated by the hardware test setup.
13 citations