Modular battery pack: let the battery assembled like building blocks

At the Frankfurt Motor Show, the Karlsruhe Institute of Technology (KIT) demonstrated through its electric bus a new concept of modular battery technology that can improve the battery energy of electric buses usage efficiency. The electric bus for display is the result of a research project Competence E, funded by the German Federal Ministry of Economics and Technology.

The core of the show is a set of drive mechanisms consisting of a large torque motor, high voltage circuit, battery management system and modular Lithium Battery system. During the demonstration, the electric bus for road tests provided several different designs of electric drivetrain.

Modular battery system

Modular battery system is the most important part of the drive mechanism, but also the basis of this technology. Modular battery system consists of battery cells composed of flat-panel battery components, according to the needs of people can be combined into different sizes and performance. Battery modular technology, or more precisely, flat-panel battery components can have different battery capacity, voltage and size as needed. The number of battery cells and the length of each battery pack can be different.

This flexible customization has the advantage of being self-contained as long as the final total output voltage does not exceed 60 volts (14 cells), and components over 60 volts must be maintained by specially trained people. In addition, due to the controllable number of cells in the module, small-sized flat-panel battery modules can be used in devices where the internal space is small.

As long as the same size of flat-panel battery components, you can continue to integrate into the battery pack. Benefit from the adaptive connection technology, in a battery pack, the connection of the flat battery components can be series, parallel, can also be mixed in series and parallel. If you want to build large-scale decentralized battery system, such as fixed Energy Storage System, you can connect multiple such battery pack.

Due to the easy access of the conductors in the battery cell, automatic joint processing technology can be applied, but also plug-in and clip-on two ways to charge, the two charging mode is the current mainstream mode. Coolant flows through the cooling pipe adjacent to the conductor to cool the current conductor. Electrical conductors and cooling ducts are mounted inside the battery pack at a distance from the battery pack housing away from areas of the battery pack that may be impacted to ensure that the battery cells within the battery pack can absorb most of the impact energy in the event of an impact, Thereby minimizing the damage to the current conductor and the cooling pipe and avoiding a safety accident.

The battery pack can also heat the battery cells through a layer of heating pad covered by the outer surface of the battery cells. When the temperature is below 5 ℃, the battery unit will not be able to charge, then the heating pad comes in handy. During the battery charging and discharging process, the volume of the battery cell changes. Therefore, a uniform compressible foam layer is installed in the battery pack to compensate for the size adjustment, thereby ensuring the safety of the battery pack. Filling the foam layer between adjacent battery cells of the two modules can increase the friction, prevent the battery cells from slipping, reduce the mechanical stress on the conductors, and evenly distribute the stress between the battery cells.

By adjusting the size and number of flat-panel battery components, modular battery pack to adapt to a variety of models of different sizes of installation space. The battery management system and drive control system used on the show's electric buses are able to adjust the bus's driving conditions based on the performance limits of the installed battery packs and other accessories.

Electric bus show in kind

The electric bus is driven by a synchronous motor, and the torque generated by the synchronous motor is transmitted to the rear wheels through the differential to propel the car. With a DC output of 650V for the modular battery pack, the maximum output power of this drive system can reach 160 kW, allowing electric buses to travel at speeds of up to 107 km / h on flat roads.

The continuous high torque output at low speeds allows a 9-ton electric bus to climb a 15% slope at a maximum speed of 25 km / h. Although the researchers designed the final version of the modular battery pack output DC voltage can reach 750V, but in the first stage, the modular battery pack output DC voltage is set to 450V, limiting the battery pack operating current, thus affecting the Synchronous motor maximum output power.

In order to drive the synchronous motor, the constant current of the modular battery pack is converted to three-phase alternating current by an inverter. In addition to powering the powertrain, the modular battery pack can be connected to high-voltage auxiliary equipment via power distribution units and a high-voltage / low-voltage DC-to-DC converter converts high-voltage DC to low-voltage DC for braking on electric buses Equipment, cooling pumps, fans and control equipment to provide electricity.

The car's vehicle control system can exchange data with other control systems (such as the battery management system, motor control system) and convert the driver's operation (throttle and brake pedal position changes) into torque requirements for the electric drive. The size of the torque demand is determined by the battery pack's performance.

KIT hopes to validate the innovative potential of the modular battery pack through this demonstration and analyze the interaction between the modular battery pack and other components on the electric bus through experiments in a simulated operating environment.

Competence E.

The Competence E project covers all relevant research from the manufacture of battery materials to electric drives. With the open Battery Electric vehicle drive technology platform and fixed energy storage system have been developed, the project's research shifted to the modular battery pack industrial applications and production processes.

It is estimated that by 2018, thanks to the integration of upstream and downstream industry chains, the production cost of a battery system with an energy density of 250 Wh / kg is estimated to be about 2,100 yuan / kWh.