Fig 10 - uploaded by Mahesh Swamy
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Schematic of test set up to study performance during brown out condition. A. With proposed circuit, and B. With standard circuit that has magnetic-contactor and soft-charge resistor unit.
Source publication
Variable-frequency drives (VFDs) with diode front-end rectifiers are typically equipped with a resistor-contactor arrangement to limit the inrush current into the dc-bus capacitors, thereby providing a means for soft charging the dc-bus capacitors. Because of the mechanical nature of the magnetic contactor typically used in VFDs, there exists a con...
Citations
... Transient overvoltage and inrush current during start-up of these high-power fast chargers have a negative impact on the performance in both the converter and the distribution system [9]. Additionally, such voltage and current spikes caused by the start-up process can reduce the life cycle of the capacitors and switches, stress the distribution system and deteriorate power quality [10][11][12]. ...
... In case of the resistor insertion, usually, a resistor in parallel with a magnetic switch is utilised for soft charging of the converters, but the mechanical parts of the magnetic switch are prone to fatigue due to the high peaks of energising current and transient over-voltages. Magneto resistance element (MRE), whose resistance depends on the surrounding external magnetic field, can limit the inrush current of the DC link [10]. However, MRE concepts are typically limited to low-power applications. ...
... In [10], a soft charging circuit combined with an active clamping circuit for a variable-frequency drive is proposed. In the proposed structure, a DC link inductor combined with an autotriggered thyristor-based path form the soft charging circuit and a second thyristor is utilised to clamp the DC link voltage below the maximum permissible limit. ...
With the increase in power rating of electric vehicle chargers, concerns regarding their integration to the grid have likewise grown. This paper investigates a novel technique for start‐up of high‐power fast electric vehicle (EV) charger using a solid‐state inrush current limiter (SSICL). The circuit consists of three similar sets of bidirectional switch and limiting resistor that utilizes a control strategy based on a simple Kalman filter (KF) to suppress the converter start‐up current and transient over‐voltages. In fact, the built‐up profile of the inrush current is dictated in accordance with the estimated current by the slow dynamic KF. Compared to alternatives, such as start‐up resistors, the presented SSICL achieves faster start‐up with comparable peak current, tends to provide lower distortion, and provides a good balance between speed and efficiency. Simulation and experimental results confirm that the proposed method can considerably suppress inrush currents, while improving the total harmonic distortion. Comparing the behaviour of the SSICL to other relevant techniques underlines the advantages of the proposed solution. Furthermore, although the focus of this paper is start‐up of the fast EV chargers, the proposed circuit can act as an inrush‐current limiter in most AC to DC converter structures.
... The resistor-contactor arrangement provides a soft charging to the DC-link capacitors (Fig. 1a). Because of the mechanical nature of the contactor, the reliability of the VFDs gets adversely affected [3,4]. Moreover, in high power applications, high power resistor banks and high current contactors are required which increase the total cost and size drastically. ...
... In this topology, similar to the previous method, the resistor banks are used to limit the current that charges the capacitors. After charging capacitor banks, the thyristor is turned on using a control logic circuit and resistors are bypassed [3,4]. However, the need for high power resistor banks and a high-power thyristor are the shortcomings of this method. ...
... It could be used to soft charge capacitors after the occurrence of a brownout condition or startup. Since the load current has to pass through the MR element and presently materials for MR elements are not capable of operating in high power applications, this topology may not be employed in medium/high power applications [3,4]. ...
One of the important issues in designing of AC
drives is soft charging of DC-link capacitors. With the increase
of electric drive power, the DC-link soft charge challenge
becomes even more serious. In this case, other common methods
of controlling the inrush current such as resistive pre-charge
circuits are not suitable for charging DC-link capacitors. This
paper presents the design and experimental evaluation of a
semi-controlled soft charging rectifier for the DC-link of AC
drives. The STM32F103C8 ARM microcontroller is employed
for digital implementation of the control system and generation
of thyristors' firing pulses. The employed method is robust
against noises and correctly diagnoses the sequence of phase
voltages. The simulation and experimental results confirm the
validity and effectiveness of the employed method. The
advantages of this circuit are its lifespan, lower size, and lower
cost compared to alternative topologies.
... The third-harmonic injection two-stage matrix converter (3TSMC) adopts hybrid front-end rectifier. Therefore, it combines the advantages of passive and active front end rectification, such as high efficiency, low electromagnetic interference noise, and good quality of input currents [1][2].In order to realize bidirectional energy flow, the 3TSMC uses active switches for the hybrid front-end rectifier. Those switches are mainly used for changing phase which just like the three phase diodes. ...
... And, as to the first-order nature of injection and output currents, the discrete-time models are ( 1) ( 1) ...
... The circuit shown in Fig. 1a depicts a soft charging circuit using mechanical contactor in parallel with a resistor bank connected in between DC link capacitor and diode bridge rectifier (Swamy et al., 2010). During initial switch on of the rectifier circuit the mechanical contactor is kept open, the capacitor is charged through the resistor bank connector in parallel to the contactor. ...
... • Huge resistor banks required • Not possible to charge the capacitor during brownout condition and fault conditions • High current DC/AC contactors • More power dissipation and cost • Welding of mechanical contactor Thyristor based soft charging circuits: The circuit shown in Fig. 1b is a conventional thyristor based soft charging circuit which consist of conventional diode bridge rectifier at is input and thyristor bank connected between DC link capacitor and diode bridge rectifier (Swamy et al., 2010). A resistor bank is connected across the thyristor for initial soft charging. ...
... One of the topologies studied here includes the use of an MR device that shows high resistance under the influence of large magnetic field and low resistance when the magnetic field resets to a lower level (Swamy et al., 2010). The MR element could be connected in series with the dc-bus capacitor to soft charge it at startup or during the recovery time after a brownout condition. ...
This study presents about various soft charging techniques used in variable frequency drives to limit the in-rush current into the dc-bus capacitors during pre-charging condition. The main objective of a pre-charging circuit is to charge the capacitor within possible allowed time and maximum converter current without any voltage overshoot. A capacitor pre-charging circuit needs to be robust and simple in control by limiting the dc link inductor and input ac current to any desired magnitude. In this study we will discuss about various soft charging topologies, techniques and their performance during different operating conditions such as partially pre-charged capacitors, input line voltage variation, ground faults and bus faults. In the final this study discusses also about a novel pre-charging circuit, technique and provides a comparison of proposed technique with the existing techniques.
This paper proposes a sample model predictive current control strategy for the third-harmonic injection two-stage matrix converter (3TSMC). The discrete-time model of 3TSMC is used to predict the future behavior for every feasible switching state. The control method chooses the optimal switching state that minimizes the cost functions, for rectifier and inverter. The model predictive current control consists of two parts. One is to produce sinusoidal three-phase input currents, and the other is to obtain high quality output currents. Besides, this control strategy guaranty good dynamic performance. Compared with the conventional PI current control method, the current quality has significantly improved by applying proposed approach. The feasibility of the proposed method is verified through simulation.
