Operation Of Uninterruptible Power Supply Research Articles

Battery autonomy estimation method applied to lead–acid batteries in uninterruptible power supplies

Uninterruptible power supplies (UPSs) provide energy to critical loads in the event of a power outage. During this event, batteries supply the load for a determinate amount of time, which can vary from a few minutes to several hours, depending on the load and battery capacity. The knowledge of this time period is useful to anticipate a system shutdown and to turn on backup generators, if present. With this in mind, this work contributes with a method for predicting battery autonomy time during the operation of UPSs in backup mode. The proposed method is implemented as an algorithm that predicts autonomy. A Thévenin equivalent circuit with variable resistance is used to model the battery. The circuit is employed in learning and predicting battery terminal voltage behavior during discharge. To achieve this, successive curve fittings are made using a Levenberg–Marquardt algorithm. In this way, the predictions of the behavior of terminal voltage and remaining battery autonomy are continuously adjusted. Due to the used strategy, the method has high adaptability, working even with variations in temperature, load steps, and battery aging. The method is developed based on a commercial 1 kW Single-Office/Home Office UPS, that uses a pair of series-connected 12 V/7 Ah lead–acid batteries. The compatibility with different battery banks is demonstrated, as well as the possibility of operation without measuring temperature and current at the batteries, two advantages in economic terms. Experimental results demonstrate the predictions of autonomy over time.

Characteristics of lead-acid and nickel metal hydride batteries in uninterruptible power supply operation

<span>Batteries are one of the main elements in Uninterruptable Power Supply (UPSs). To maintain good operation during power failure, UPSs must have adequate energy for their operation. It depends on the reliability and performance of batteries. Owing to low capital cost and wide availability, lead-acid batteries have been used extensively as the main energy source in UPSs. Nevertheless, as batteries technology grown, Nickel Metal Hydride (NiMH) batteries have offered more promising performance than lead-acid batteries; they are installed in various portable electronic devices. This paper provides an overview of the performance of lead-acid and NiMH batteries during the operation of a single-phase UPS. Their performances are studied based on 2 characteristics which are discharge curve and State of Charge (SOC). Based on those characteristics, both batteries have shown different performances. Simulation results have shown that the NiMH battery exhibits better discharge curve with higher voltage capacity and constant discharge current, and it is more reliable to obtain 12V at minimum percentage of SOC than the lead-acid battery.</span>

Analysis of Parallel Operation of Uninterruptible Power Supplies Loaded Through Long Wiring Cables

This paper discusses and analyses the parallel operation of uninterruptible power supplies (UPS) when loaded through long wiring cables having non-negligible inductance and resistance. This scenario is often encountered in practice, as the UPS power supplies are often located far from each other and from the load they are actually powering. The analysis demonstrates how long cable connections between the power supply system and the load deeply modify the behavior of the single UPS unit. It is shown how the cable inductance interacts with the UPS closed-loop output impedance modifying the control loop gain, ultimately generating resonance phenomena, which deteriorate or even compromise system stability and performances, if suitable provisions are not taken at the design stage. Experimental results carried out on two paralleled three phase, 40 kVA UPS units based on voltage-source inverters topologies confirm the validity of the theoretical discussion and the practical relevance of the phenomenon.

Fuzzy Controllers with Reduced Rulebases and Real-Time Capability for Power Systems Supervision

Multi-input/multi-output fuzzy logic-based controllers allow the inclusion of different types of knowledge about the controlled process. The application of multivariable fuzzy controllers in a real process is diffi cult due to practical limitations. This paper describes an approach to the implementation of a MIMO fuzzy hierarchical controller in a real process. Introducing a loop structure for the fuzzy controller, the approach is based on a mixed decomposition method and a hierarchical structure. The approach allows an important reduction in a global fuzzy relation needed to control the process under consideration−the parallel operation of uninterruptible power supplies. The process multivariable and nonlinear characteristics make it an appropriate one to test the presented method. Generalized simulation results are presented based on the proposed approach. The comparative experimental results presented show the validity of the method.