Design of 3-phase static modular double-conversion lithium-ion-based UPS system

Abstract

A challenge for industries nowadays is to optimize the functionality of their critical processes. Whether they be manufacturing, production, healthcare, banking, data, research, or shopping centres, they are becoming large and complex with several critical loads and processes whose availability is crucial to their overall effectiveness and market competitiveness. Based on their design specifications and accuracies expected, these processes often tend to have a low tolerance and are susceptible to power failures, spikes, brown-out, dip, or surges. They require a high integrity power supply to guarantee their correct functioning, increase their robustness against the damaging effect of power disturbances and operational availability. Eskom’s network instability, lower energy availability, and poor power quality, unfortunately, cannot guarantee the integrity of supply to these critical loads. An increase in load shedding in the past few years highlights this low energy availability factor. Based on these reasons, the facility opted to install 4 x 1100kVA online lead-acid-based rotary uninterruptible power supplies (UPSs) to sustain a sturdy power supply through periods of power disturbances. The sustainability of power will also allow orderly processes shutdown in case of prolonged power interruption and avoid any outage-related financial setbacks. Commissioned back in 1995, they have attained their end-of-life and suffer regular costly maintenances, higher losses, and higher spares cost due to unavailability. Although these are considered legitimate running costs, they occur on a capital scale after few years. Given the system’s age, running cost, and inefficiency, the facility would be efficiently and cost-effectively served by newer high-performance UPS systems. The process of choosing the right UPS system and energy storage solution for critical infrastructure has now become more challenging than ever. Today’s UPS technologies and their corresponding backup storage solution must maintain or even increase the availability and manageability of power on their respective facilities. In the effort to reduce the total cost of ownership, it is imperative to extend lifetime, decrease footprint, streamline maintenance, and lower cooling costs and other operating expenses, in addition to reducing the upfront capital investment. Lithium-ion-based static UPS systems are poised to enhance energy storage for secure power applications. They provide benefits in reducing the installation and maintenance costs and have low waste energy resources making them have high operational efficiency and weigh less than the rotary UPS system. The energy storage system used in these systems has since transformed from medium-lifetime, sprawling, and heavy lead-acid batteries to a long-life, compact, lightweight solution with predictable performance, simplified maintenance, and robust life cycle management. It is not just the UPS system that develops through the adoption of lithium-ion technology; critical power is also going through a period of rapid changes calling for UPS systems to increase their availability and manageability of power. Facilities are, therefore, required to revisit their complete concept of critical power and develop new supply methodologies. There is now a strong need to bring up innovative ways that dispatch the battery stored energy differently. Facilities must continually evaluate their time of energy use in relation to their tariff structures for better energy management and costs control. Time-of-use tariffs are structured to reward consumer who lowers their consumption during peak periods. The intervention strategy will present a comprehensive assessment that offers a site-specific solution. It will also provide a financial and performance analysis of the current rotary UPS system versus the new static UPS system with the desire to improve the facility’s power protection, secure its long-term availability, strengthen its energy efficiency capacity, and reduce maintenance costs and carbon footprint. It will evaluate the financial impact that tariff structures and various modelled energy dispatch have on the facility energy budget.