Regenerative Braking

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Mitsubishi Electric Corporation has developed a new technology that reduces total railway energy consumption by up to five percent. The technology enables full use of regenerative power in trains through real-time control of voltages at nearby substations. The five-percent reduction of total railway energy consumption was achieved in numerical simulations using a high-density urban railway model. 

As an important transportation infrastructure, railway systems are facing the need to save energy given their high volume of electricity consumption. Currently, electricity generated when trains decelerate using regenerative brakes is reused by other trains that need to accelerate. Current regenerative systems, however, limit the amount of reused power when there is excess regenerative electricity or when there are few accelerating trains, because voltage distributed from substations is maintained at a high, fixed level to provide enough power to all trains even if they accelerate at the same time. As a result, a large amount of regenerative power is not utilized and is wasted as heat. 

The new system controls the voltage distributed from substations based on train locations and acceleration/deceleration data collected from the train integrated management system (TIMS) of each train. The company's simulation shows that the new system reduces regenerative power wasted as heat in current systems by as much as 80%, and prevents voltage in feeding lines from becoming too high. Even if the amount of regenerative power becomes excessive, it can be fully utilized with power storage systems, such as batteries or regenerative inverters installed at stations.

Since electricity for railways in many countries has a substantial share of power coming from fossil fuels the technology can help in reducing CO2 emissions. In fact Delhi Metro in India used this technology and has also developed a project under Clean Development Mechanism to claim carbon credits.

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