Challenges of Low-Voltage Energy Storage for Lifts

Nowadays, the lift industry is moving towards finding new solutions for energy management. Examples of this are energy recovery systems based on local storage in ultracapacitors, battery-powered lifts for peak power consumption mitigation and improved UPS operation, solar and/or wind powered lifts, among others. Most of these new concepts include energy storage systems, so they require batteries and/or ultracapacitors, depending on the energy to be stored and the power cycling profile. As a matter of fact, both batteries and ultracapacitors are low voltage technologies, whereas lift traction systems are based on well-known three-phase industrial AC drives, operating at high voltage levels of around 600V at their DC bus. One of the possible solutions consists of the serialization of a large amount of basic cells until industrial voltage levels are reached. This solution, though apparently simple, is not practical because it is expensive and safety and reliability problems are multiplied. Thus, a practical energy storage system for lift applications should operate at around 48V, which is a safe, commercially standard and cost-effective voltage level. Some modifications are required if a 48V energy source must be integrated in a lift traction system. There are two possible options. First, (bidirectional) DC-DC converters can be used interconnecting low-voltage 48V to conventional lift traction systems at 600V. Second, the entire traction system can be redesigned so as to operate at 48 V. This work shows the technical challenges of the integration of low-voltage energy storage systems in lift traction systems. Issues related to efficiency, cost, availability of required parts for production, flexibility of use and others are analysed. This way it is possible to identify the key challenges and the best suited solutions in each case.