Syed Sabir Hussain Bukhari

An inrush current reduction technique for the line-interactive uninterruptible power supply systems

Numerous sensitive loads of commercial, industrial and domestic use depend upon an uninterruptible power supply (UPS) system to ensure uninterrupted, reliable, and high quality power during outages as well as over voltage and under voltage conditions to maintain healthy operation. In case of a power failure or other disturbance, a UPS system generally takes over the load within a few milliseconds in order to supply continuous power to the load and avoid any interruption. However, due to the magnetic saturation of the load transformer, this transition of load can cause significant inrush current generation. The generation of inrush current can cause the reduced line voltage and activate the over current protection of a UPS system. This paper proposes an inrush current reduction technique by supplying the rated current to the load and energizing the secondary of the transformer to its rated magnetizing current through a current regulated voltage source inverter after connecting it to the secondary of transformer. The possibility of the generation of inrush current is almost completely eliminated during all possible loading and transient conditions. Simulations have been performed by using simulink to validate the proposed inrush current reduction technique.

An on-line UPS system that eliminates the inrush current phenomenon while feeding multiple load transformers

Numerous industrial facilities involve the installation of load transformers with their respective loads. As loads are turned on and off, these transformers are energized and de-energized, respectively, which can cause serious disturbances to sensitive loads. An inrush current, which typically occurs when a transformer is energized, can easily be observed using on-line uninterruptible power supply (UPS) systems feeding such loads. This paper proposes an on-line UPS system that eliminates the inrush current phenomenon caused by the energizing of load transformers. The UPS inverter specifically utilizes a fast acting current control scheme that enables it to regulate current for the load during all energizing conditions of load transformer connected to the UPS system.

Unsymmetrical fault correction for sensitive loads utilizing a current regulated inverter

Many industrial applications involve loads which are very sensitive to electrical disturbances in the supply. These instances involve both various types of voltage unbalance as well as more series disturbances such as symmetrical and asymmetrical faults. This paper proposes a voltage unbalance and an unsymmetrical fault correction technique for a three phase load utilizing an industry-standard current regulated voltage source inverter by connecting it in parallel to the associated three phase transformer. The inverter regulates the current for the load and never allows the current to exceed to a prescribed value under any type of unsymmetrical condition.

A Cost-Effective, Single-Phase Line-Interactive UPS System that Eliminates Inrush Current Phenomenon for Transformer-Coupled Loads

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

Line-interactive Uninterruptible Power Supply System Eliminating the Inrush Current Phenomenon

Abstract Numerous critical load applications rely upon a line-interactive uninterruptible power supply system to maintain power during outages as well as during under- and over-voltage utility conditions. When any disturbance occurs at the utility side, the line-interactive uninterruptible power supply system takes over the load within a few milliseconds to avoid interruption. However, during this transition of load, a significant inrush current occurs due to the magnetic saturation of the load transformer. The inrush current phenomenon causes reduced line voltages and sometimes activates the over-current protection of the uninterruptible power supply system. This article proposes a new line-interactive uninterruptible power supply system that eliminates the inrush current phenomenon by connecting a standard current-regulated voltage source inverter to the secondary of the load transformer. During any transient condition at the utility side, the load current is monitored and regulated to achieve a seamless compensation or transition of load. Experimental results are obtained for a prototype during a number of possible irregular utility power conditions to endorse the performance of the proposed uninterruptible power supply system.

An inrush current elimination technique for a voltage sag compensator while powering transformer-coupled loads

Sags are the foremost power quality problem encountered by industrial consumers since they frequently causes the interruption of manufacturing processes that can result in significant economic loss. To resolve such problems, a voltage sag compensator is often installed by industrial consumers within critical industrial applications. However, the operation of the compensator takes a few milliseconds when a sag occurs. Hence the transformer, which is usually mounted in front of the critical load, is likely to be exposed to the sag voltages during this time interval. As a result, when the compensator reinstates the load voltage, a serious magnitude of transient current starts flowing towards the sensitive load. This inrush current can either damage the equipment or activate the protective devices of the compensator. In either case, compensation will eventually fail. To eliminate the inrush current phenomenon and to obtain seamless compensation for sensitive loads, this paper proposes a sag compensator based upon a customary current regulated voltage source inverter (CRVSI). This compensator employs a current control scheme implemented in a stationary frame of reference to regulate the current for the load by connecting it to the secondary of the load transformer. The operation of the proposed system is validated through laboratory test results obtained during different possible sag types.

A new single-phase sag compensator intended for transformer-coupled loads

In this paper we propose a new single-phase sag compensator intended for transformer-coupled loads that integrates a current-controlled inverter in parallel with the secondary winding of an isolation transformer. Compared with conventional single-phase series-voltage sag compensators that produce a high inrush current during the starting of the compensation process, the proposed sag compensator eliminates the inrush current and achieves seamless compensation for the load current. The performance of the proposed sag compensator is validated by our experimental results for a small prototype.